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MORPHOLOGICAL STUDY OF BASILAR ARTERY AND ITS VARIATIONS
Thesis submitted in Partial Fulfillment for the Award of degree of Doctor of Philosophy in Medical Anatomy
BY J.KALAIVANNAN
UNDER THE GUIDANCE OF
PROF. DR.M.L JAIN, M.S
VINAYAKA MISSIONS UNIVERSITY (Vinayaka Missions Research Foundation Deemed University)
SALEM, TAMIL NADU- INDIA PIN CODE – 636 308 NOVEMBER- 2016
TABLE OF CONTENTS
S.NO
TITLE
PAGE No
1 Declaration
i
2 Certificate By The Guide
ii
3 Acknowledgement
iii
4 Abstract vii
5 List of Figures
x
6 List of graphs xi
7 List of Tables
xii
8 List of Symbols and Abbreviations
xiii
9 Introduction
1
10 Review of Literature
25
S.NO
TITLE
PAGE No
11 Need for the study
72
12 Objectives
74
13 Methodology
75
14 Results and discussion 84
15 Conclusion 124
16
Bibliography 125
17 Annexure I - Ethical committee clearance certificate 149
18 Annexure II - List of publications 150
i
DECLARATION
I, J.Kalaivannan, declare that the thesis entitled
MORPHOLOGICAL STUDY OF BASILAR ARTERY AND ITS
VARIATIONS submitted by me for the degree of Doctor of
Philosophy in Medical anatomy is the record of research work
carried out by me during the period from January 2011 to
December -2016 under the guidance of Dr. M.L.Jain , M.S, Former
Professor and HOD, VMMC&H, and has not formed the basis for
the award of any degree, diploma, associate-ship, fellowship, titles
in this or any other university or other similar institutions of higher
learning.
Place: Signature of candidate
Date: (Mr.J.KALAIVANNAN)
ii
VINAYAKA MISSIONS UNIVERSITY
CERTIFICATE BY THE GUIDE
I, Dr. M.L.Jain, certify that the thesis entitled MORPHOLOGICAL
STUDY OF BASILAR ARTERY AND ITS VARIATIONS submitted
for the degree of Doctor of Philosophy in Medical anatomy by
Mr.J.Kalaivannan, is the record of research work carried out by
him during the period from January 2011 to December 2016 under
my guidance and supervision and that this work has not formed
the basis for the award of any degree, diploma, associate-ship,
fellowship, titles in this or any other university or other similar
institutions of higher learning.
Place: Signature of the Supervisor
Date:
(Dr .M .L. Jain)
Former Prof.&HOD of Anatomy
VMMC &H, Karaikal.
iii
ACKNOWLEDGEMENT
My sincere gratitude goes to our honorable Founder, Late
Dr.A.Shanmugasundaram, for allowing me to do this PhD
research work under our esteemed Vinayaka Missions University,
Salem.
I express my sincere obligations to THE HONORABLE
CHAIRMAN, Dr. A.S.Ganesan, the Vice President
Mr.Chandrasekar Sir,
Dr. R. Annabelle,M.D., Dean, Vinayaka Mission’s Medical
College, Karaikal, for their constant encouragement and help.
I sincerely thank Dr.C.L. Prabavathi, the controller of
examinations, Vinayaka missions University for her kind support
and permission.
I greatly express my thankfulness to the Former Dean Prof. Dr.K
Jayabal, the Present Dean Prof.Dr.P.S.Manoharan VMKV
medical college, Salem for providing with all necessary support to
carry out this PhD research work.
iv
It is my immense pleasure to express my heartfelt gratitude to my
teacher and guide. Prof. Dr. M.L.JAIN, M.S., for initiating and
supporting this work. It was his constant encouragement and
meticulous guidance that helped me in the successful completion
of my research work. I thank sir for giving me the privilege to work
under his guidance.
I wish to thank who heartedly PROF.G.CHANDRASEKARAN,
Chengalpet, for his strenuous efforts and precise advise without
which this work would not have been feasible.
I express my sincere obligations to Dr. Rajendran, PhD, Former
Dean (Research), Vinayaka Missions University, for the strict
guidance and motivation given by him and his enormous patience
with which he answered my repeated phone calls about the
research work.
I also thank Dr. K. Srinivasan, M.S., former Dean, Vinayaka
Mission’s Medical College and Hospital, Karaikal for helping me to
start my PhD research work.
I would like to thank Dr. K.Shanthini arulselvi, M.D., Professor
H.O.D, Department of anatomy for her encouraging comments on
this work.
v
I express my sincere obligations to Dr. Sankar Ph.D Professor
and Head, PGIBMS, university of madras for helping me on this
work.
I wish to thank Dr. T. Rajan, Professor and Head, Department of
Anatomy, AVMC for his support. And Dr. Krishnakumar M.D
radiologist for his immense helps in this work
I like to thank to Dr. Senthil Asst.professor Dept of community
medicine, Rajah Muthiah Medical College, Chidambaram for
helping me in stastitics.
I offer my heartfelt thanks to Dr.Abdul Majeed, Mrs. Udaya
sankari and Dr.Indu Department of anatomy, Vinayaka missions
Medical College and Hospital, karaikal, for their constant support,
valuable suggestions and help throughout my research work.
I feel special pleasure to thank Mr.Packirisamy and Mr.Raju
dissection hall attender, Mr.Manoj kumar, for his help in
photoimage work, Mr.Jayakumar Office attender, Mr.Srinivasan
Artist, Mr.kamaraj Lab technician, Mr. Lakshmikanthan and Mrs.
Sujatha and Mrs .Megala Ward aid, who always stood by my side
in need during this thesis work in my department.
vi
And I like to thank our librarian Mr. Madan for helping me to get
references for my work.
My dreams regarding this work would never have fulfilled but for
sincere prayers, moral support and constant encouragement of my
dear parents, dear wife Mrs. Logeswari and my dear children
Miss. Bhavana devi and Miss Shanmitha shree. A very big
THANK-YOU to them.
Above all I thank GOD for HIS constant showers of blessings and
guidance through HIS unseen presence in each and every work
I’ve done.
PLACE:
DATE: (J.KALAIVANNAN)
vii
ABSTRACT
Basilar artery is the chief artery which supplies the brain stem
including Pons, midbrain and medulla and also the cerebellum.
The basilar artery forms the main part of the posterior circulation of
the brain. Our aim of our study is to analyse the morphological
aspect of basilar artery in the cadaveric brain. And to record the
data observed in the study. The basilar artery is an important
factor in the various clinical conditions of the brain. The anatomical
components and variations of the vertebrobasilar system must be
well known for precise interpretation of the, diagnoses,
endovascular interventions, ischemic ranges and posterior cranial
fossa surgeries.
OBJECTIVES:
The aim is to study the length, diameter, formation and
termination of basilar artery, and angle of formation of basilar
artery. The course of the basilar artery is also analysed.
viii
METHODOLOGY:
TOOLS: Digital vernier calliper, Manual Goniometer, Scalpel,
Dissection forceps (pointed, tooth, and blunt), Scissors, Bone saw
and Magnifying Hand lens.
METHODS USED: Dissection method
SAMPLING METHOD USED: Sampling method used in the study
is cluster sampling. The study was conducted in 100 adult human
brain specimens preserved in the Department of Anatomy of
Vinayaka Mission’s Medical College, Karaikal, Aarupadai Veedu
Medical College, Puducherry and Dr.A.L.M. Post graduate Institute
of Basic Medical Sciences, Taramani.
STATISTICS USED: Stastistical significance was determined with
help of Chi-square test, one way Anova and Duncan Multiple
Range Test (DMRT) using SPSS version 18.0.
RESULTS: The Mean length and diameter of basilar artery is
30.98mm and 3.65mm, level of formation is at Ponto-medullary
(PM) junction is 77% above 10% and below is 13%, the level of
termination at MB-P(Midbrain-pontine junction is 82%, above 11%
and below is 7%, the angle of formation of basilar artery ranged
ix
between 55 to 75. The symmetrical diameter is seen in 50% and
larger left vertebral artery is seen 35%, larger right vertebral artery
is present in 11% and right hypoplastic vertebral artery is seen in
2% and left hypoplastic vertebral artery is seen in 1%. And in one
specimen there is complete absence of left vertebral artery, the
right alone continued as basilar artery. The variation in the course
of basilar artery is seen in 16% were the basilar artery has the
curvature on the right and 7% in the left side, and in 77% it was
normal and is having a straight course.
CONCLUSION: The current study is to add knowledge in the
morphological aspect of basilar artery
KEY WORDS: Basilar artery, vertebral artery, formation of basilar
artery, termination of basilar artery, length and diameter of basilar
artery, angle of formation.
x
LIST OF FIGURES
S.No FIGURE TITLE PAGE No
1 The branching of basilar artery 4 2 Arteries at the base of the brain 9 3 Branches of Basilar artery 15
4 Development of Vertebral artery 38
5 General plan of branches of Dorsal aorta 41
6 Embryo12.5mm - Frontal view 44
7 Embryo 14mm - Frontal view 46
8 Embryo12.5mm - Lateral view 48
9 Embryo 18mm – Development of Vertebral arteries. 49
10 Dissection Instruments 75
11 Manual Goniometer 76
12 Digital Vernier Caliper 77
13 Aplasia of Left vertebral artery 86
14 Left Vertebral artery dividing into PICA and vertebral artery 88
15 Level of formation – above PM junction 90
16 Level of formation – below PM junction 96
17 Curvature of basilar artery on the Right side 112
18 Curvature of basilar artery on the Left side 114
19 Straight course of basilar artery 116
20 Dolichoectasia 119
xi
LIST OF GRAPH
S.No GRAPH TITLE Page No
1 The Formation of Basilar artery 87
2 The level of Formation of Basilar artery 93
3 Length of Basilar artery 96
4 Diameter of Basilar artery 106
5 Basilar artery at Different Levels of Termination 108
6 Variation in the course of basilar artery 113
xii
LIST OF TABLES
S.No TABLE TITLE PAGE No
1 Variation in the Formation of basilar artery 85
2 Variation in the Level of formation of the basilar artery 89
3 Comparison of Level of formation 91
4 Length of basilar artery 94
5 Comparison of Length of basilar artery 97
6 One way Anova for significant difference among Level of formation with respect to the Length of basilar artery
99
7 One way Anova for significant difference among Level of formation with respect to Angle of formation of basilar artery
100
8 Comparison of Angle of formation of basilar artery 101
9 Diameter of basilar artery 102 10 Comparison of Diameter of basilar artery 104
11 Variation in the Level of termination of basilar artery 107
12 Comparison of Level of termination 109
13 DMRT for significance difference among the Level of formation with respect to the Diameter of basilar artery
110
14 Variation in the course of basilar artery 111
xiii
ABBREVIATIONS
BA Basilar artery
AICA Anterior inferior cerebellar artery
CT Computerized Tomographic
CTA Computerized Tomographic Angiography
DMRT Duncan Multiple Range Test
DSA Digital subtraction angiography
MB-P jn Midbrain-pontine junction
MRA Magnetic resonance angiography
MRI Magnetic resonance imaging
PCA Posterior cerebral artery
PICA Posterior inferior cerebellar artery
PM jn Ponto-medullary junction
SCA Superior cerebellar artery
SPSS Statistical package of social sciences
TCCS Transcranial color-coded sonography
TOF Time-of-flight
VA Vertebral artery
xiv
VBD Vertebro-basilar dolichoectascia
VBS Vertebro-basilar system
1
1. INTRODUCTION
Needless to say, it is of vital importance for workers in the
neurological field to know and understand the circulatory system of
the central nervous system. The basal vessels of the brain,
especially the circle of Willis and basilar artery are of particular
interest as they are main and only source of nutrition to many vital
structures as basal ganglia, hypothalamus, midbrain and pons.
The circle of Willis is the arterial anastomosis at the base of the
brain which is also known as Circulus arteriosus cerebri.
Circle of Willis was named after a popular British Anatomist-
Physician Thomas Willis (1621 -1673) who was the first to
describe it completely though called a circle; it is precisely a
nonagon or a nine sided polygon. It is located in the cistern
interpeduncularis, surrounding the optic chiasma, the neural
infundibular stem of the hypophysis cerebri and other neural
structures in the inter peduncular fossa. Anteriorly the anterior
cerebral arteries are joined by the anterior communicating artery
posteriorly the basilar artery divides and originates the two
posterior cerebral arteries and each artery is joined to the
ipsilateral internal carotid by a posterior communicating artery. The
vessels of the circle of Willis vary in calibre, and are often
2
maldeveloped or even absent. In about 60% of the cases the circle
shows some variation or anomaly. Cerebral and communicating
arteries, anterior and posterior, may be absent, hypoplastic, double
or triple. It is found, however in about 90% of the cases some form
of complete circular arterial channel between the internal carotid
arteries, the posterior cerebral arteries and anterior cerebral
arteries, but in most cases one vessel is sufficiently small or
narrowed to reduce the collateralization capability. The greatest
variation in length is found in the anterior communication artery
and in diameter in the posterior communicating artery.
The hemodynamic balance is usually disturbed by variation
in the calibre of the communicating arteries, often associated with
variations in size of the first segments of the anterior and posterior
cerebral arteries extending from their origins to their junctions with
the corresponding communicating arteries.
The function of circle of Willis is to equalise the blood flow to
the distinctive areas of the brain and under ordinary condition little
interchange of blood takes place across the anastomotic channel
due to quality of the blood pressure. The streams of blood
conveyed by the carotid and vertebral systems meet in the
posterior communicating artery at a dead point where the pressure
3
of the two is equal and no admixture of blood occurs. However, in
case of occlusion of one of the arterial systems, the blood crosses
the middle line through the communicating branches and
maintains nutrition of the opposite brain by contralateral flow.
Therefore, the circle of willis acts as principal collateral channel to
preserve the independent cerebral blood flow when normal, or
dependent blood flow in occlusion of one of the main arterial
feeders. Moreover, in obstruction of one internal carotid artery in
the neck, the collateral channels may be established with a
reverse flow through the external carotid circulation in the face and
scalp, and the ophthalmic artery.
Unlike the cerebrum, the anastomosis of the arteries of the
brain stem across the midline is poor. Hence in occlusion of the
brainstem arteries the lesion is limited to one side.
Physiological consideration of cerebral circulation
The ever active brain with little metabolic reserve requires a
copious constant blood flow and derives its energy almost
exclusively from glucose and oxygen. The brain forms about 2% of
the body weight, but requires about one-fifth of the cardiac output
and about 20% of the oxygen utilized by the body.
4
5
About 750ml blood circulates through the brain of average weight
per minute. The circulation time through the brain from the internal
carotid artery to the internal jugular vein is about 7 seconds. The
brain is extremely susceptible to oxygen lack, and occlusion of its
blood supply produces unconsciousness within a period of 10
seconds.
Under normal blood pressure the cerebral blood flow is
regulated mostly by the CO2 tension of blood which exerts
profound influence on the vascular tone of the cerebral blood
vessels. The cerebral vessels possess thin muscle coat and thick
internal elastic lamina. A rise in CO2 tension or fall of O2 tension
dilates the cerebral vessels, and vascular constriction takes place
in reverse condition. The role of autonomic nervous system in
cerebral vasodilatation is relatively minor in human brain.
BASILAR ARTERY:
The basilar artery are formed by the union of the right and
left vertebral arteries at the level of pontomedullary junction. It lies
in the median groove of the pons in the cistern pontis, on the
basilar part of the occipital bone and the dorsum sellae of the
sphenoid. It runs over the ventral surface of the pons in the
6
shallow groove and terminates in the upper border of the pons by
dividing into right and left posterior cerebral arteries. The basilar
artery forms an important part of the posterior circulation of the
brain and supplies its many vital parts. Its area of distribution
includes the internal auditory meatus, cerebellar hemisphere,
paramedian areas of the pons, choroidal plexus of the third
ventricle and crus cerebri. The areas supplied by its terminal
branches are the thalamic muclei, lateral geniculate body,
mesencephalon and primary visual cortex. It gives five types of
branches on either side,
Branches –
1. The anterior inferior cerebellar artery arises at the lower border of
the pons,
2. The artery of the labyrinth arises beside or from the anterior
inferior cerebellar artery.
3. Numerous, slender pontine branches pierce the pons, some in its
medial part, others further laterally.
4. The large superior cerebellar artery arises close to the superior
border o the pons.
5. The large posterior cerebral artery diverge at the superior border
of the pons.
7
Pontine branches: median and transverse branches
Median branches – small and numerous arteries that originate
from the posterior part of the basilar artery, entering the pons at
the median groove. These arteries penetrate the pons deeply,
reaching the floor of the fourth ventricle.
Transverse branches – there are usually four to six pairs of these
arteries. The transverse branches arise from the lateral aspect of
the basilar artery and encircle the anterior and lateral borders of
the brain stem. These arteries originate several small perforating
branches that penetrate the pons at right angle with the parent
vessel.
Anterior inferior cerebellar artery (AICA):
The AICA originates from the proximal or middle third of the
basilar artery. The artery is divided in main trunk, recurrent limb,
and is further divided in two major branches, the lateral branch and
medial branch. The internal auditory is in general a proximal
branch of the AICA. The size of the AICA is inversely proportional
to the size of the PICA. When one is absent or hypoplastic the
other ipsilateral artery is larger and replaces blood flow to the
normally nourished territory.
8
The main trunk of the AICA courses laterally land downward,
in contact with either the dorsal or the ventral aspects of the
abducens nerve. Within the cerebellopontine angle cistern the
proximal arterial trunk usually lies ventral and medial to the roots of
the facial, intermediate and acoustic nerves. These nerves are
very close together and may be considered as a unit regarding the
relation with the AICA. The main trunk of the AICA supplies small
branches to the pons, to the lateral aspect of the pons from the
middle third down to the upper part of the medulla.
The recurrent limb of the AICA arises from the area of the
internal acoustic meatus and courses medially to reach the
cerebellopontine angle and extends to reach the cerebellum
dorsally.
The lateral branch courses laterally and turns around the
flocculus running within the horizontal fissure between the superior
and inferior semilunar lobules of the cerebellum. The artery sends
hemispheric branches to the superior and inferior semilunar
lobules and the distal hemispheric branches anastomosis with
branches of the superior cerebellar artery and PICA.
9
FIG 2: ARTERIES AT THE BASE OF THE BRAIN
10
The medial of the AICA courses medially and downwards to the
medial and anterior border of the cerebellum, supplying the
biventral lobule. This branch also anastomosis with the PICA.
The internal auditory artery originates from the proximal
segment of the AICA in 95% of the cases or may arise from the
basilar artery above the origin of the AICA. This artery supplies the
structures within the meatus of the auditory canal including the
nerve roots and internal ear.
Superior cerebellar artery (SCA)
This artery originates from the basilar artery, proximal to the
origin of the posterior cerebral artery. It may also arise from the
posterior cerebral artery. The proximal trunks of the SCA runs
posteriorly in the perimesencephalic cisterns encircling the upper
pons and lower mesencephalon. It supplies portions of the
midbrain, the superior surface of the cerebellar hemisphere, the
superior vermis, and the cerebellar nucleus.
The proximal trunk or cisternal segment of the SCA is
divided in 3 segments. Anterior pontine, ambient, and
quadrigeminal segments. It has cortical and perforating branches.
11
Anterior pontine segment:
This is the proximal portion of the SCA, it courses laterally on
the anterior surface of the pons in an arcuate curve. It lies inferiorly
to the emerging roots of the oculomotor nerve, separating it from
the proximal segment of the posterior cerebral artery. This
segment may duplicate or triplicate and give of the marginal and
superior vermis branches.
Ambient segment:
This is the second portion of the SCA, beginning at the
lateral border of the pons and turning posteriorly over the
branchium pontis or middle cerebellar peduncle. It course
posteriorly in the infratentorial position of the ambient cistern. This
segment parallels the course of the trochlear nerve.
Quadrigeminal segment
This is the distal segment of the SCA which lies within the
lateral aspects of the quadrigeminal cistern. At this point the
arteries approach each other near the midline, giving of
anastomotic branches.
12
Cortical branches
Lateral marginal branch: The marginal branch is the first largest
branch of the SCA, originating at the second portion of the SCA
within the ambient cistern, or more rarely from the anterior pontine
segment. This artery reaches the anterolateral margin of the
cerebellum running posterolaterally in the region of the horizontal
fissure. It demarcates the superior and inferior cerebellar lobes.
The hemispheric branches originate from the marginal branch of
the SCA.
Hemispheric branches: there are two or three of these branches
arising distally to the origin of the marginal branch from ambient or
second segment of the SCA when the artery runs around the
posterior surface of the brain stem. These branches course
upwards reaching the superior surface of the cerebellum where
they distribute radially in direction of the horizontal fissure. They
supply the dentate nucleus, and at the cortical territory they supply
the medial portion of the quadrigeminal and superior semilunar
lobules and the superior half of the vermis.
Superior vermis branch: this is the terminal branch of the SCA
originated at the third or quadrigeminal segment. There are one or
two vermis branches on each side. Anastomosis may be found in
13
between these branches, when they get closer within the
quaadrigeminal cistern, and between these branches and the
inferior vermis branches from the PICA. They run over the vermis
close to the midline.
Perforating branches: many small branches originate from the
main trunk of the SCA perforating the brain stem. These branches
are more common in the interpeduncular and quadrigeminal
regions. The branches to the pons and mesencephalon originate
from the anterior pontine segment of the SCA. The few branches
arising from the ambient segment of the SCA are also perforating,
and supply the lateral portion of the brain stem. The inferior
colliculus are supplied by the small branches that arise from the
quadrigeminal region of the SCA. Several larger branches arising
from the distal ambient segment of the SCA supply the dentate
nucleus and course down the superior cerebellar peduncle.
Posterior cerebral artery
The posterior cerebral artery generally receives the blood
supply form the basilar artery. They are located above the
tentorium, and originally derive the blood supply from the internal
carotid artery. The posterior cerebral artery shifts its origin from the
carotid to the basilar system in the final stages of embryonic
14
development and the ultimate origin is form the basilar artery
bifurcation at the interpeduncular fossa. But this pattern is not and
in some cases the embryonic pattern persists. In 10.4% of the
case the fetal type persists on the right side, while 9.5% persists
on the left side, and it is bilateral 7.7% of the cases. In the fetal
type the posterior cerebral artery originates from the internal
carotid artery.
The posterior cerebral artery has a communication with the internal
carotid artery through the posterior communicating artery and with
the basilar artery through the communicating basilar segment or.
The calibres of these arteries are inversely proportional among
them, varying from agenesis and to a size equal to the posterior
cerebral artery. Both may have the same size and the same
importance in the flow into the posterior cerebral artery.
The posterior cerebral artery courses posteriorly in the
perimesencephalic cisterns to encircle the midbrain. Terminal
cortical branches supply the occipital poles, the medial and inferior
portions of the occipital lobes, and the medial portions of the
temporal lobes. The proximal trunk of the posterior cerebral artery
is divided into peduncular, ambient and quadrigeminal segments,
corresponding to the cisterns through which the vessel passes.
15
16
Peduncular segment
This is the proximal segment of the posterior cerebral artery, which
arises from the basilar artery and it is closely related to the
anteromedial portion of the peduncle of the midbrain. The posterior
communicating artery connects to the midportion of the peduncular
segment. The proximal portion of the peduncular segment is
closely related to the oculomotor nerve. The peduncular segment
is usually horizontal, but when the basilar artery is short with a low
birfurcation the peduncular segments are directed upwards in a V
like configuration. With elongation of the basilar artery, the
peduncular segments pass anteriorly and inferiorly to reach the
surface of the peduncles. Asymmetry is common.
Ambient segment
It is the second cisternal segment of the posterior cerebral
artery. It courses posteriorly in the hippocampal fissure between
the midbrain and hippocampal gyrus. It parallels the basal vein,
which lies superior, and to the trochlear nerve, at the free edge of
the tentorium. The superior cerebellar artery is inferior to the
ambient segment. The relationship of this segment with the free
17
margin of the tentorium varies. With low origin of the posterior
cerebral artery the ambient segment cross the line of the tentorial
margin from below. With high origin, the ambient segment courses
posteriorly in the hippocampal fissure above the tentorium.
Quadrigeminal segment
It is the continuation of the posterior cerebral artery within the
lateral aspect of the quadrigeminal cistern. At this level the
quadrigeminal segments approach each other and then continue
posteriorly beneath the splenium of the corpus callosum to
terminate in cortical branches.
Branches
1. Mesencephalic branches :-
a) Interpenduncular perforating branches
b) Tiny peduncular branches
c) Circumflex mesencephalic branches
2. Thalamic branches :-
a) Anterior thalamoperforating branches
b) Posterior thalamoperforating branches
c) Interpeduncular thalamoperforating branches
d) Thalamogeniculate perforating branches.
18
3. Posterior choroidal branches
a) Medial posterior choroidal artery
b) Lateral posterior choroidal artery
4. Hippocampal branches
5. Meningeal branches
6. Posterior pericallosal artery
7. Cortical branches
a) Anterior temporal artery
b) Posterior temporal artery
c) Parieto-occipital artery
d) Calcarine artery
Mesencephalic branches:
The interpeduncular perforating branches arise from intitial
posterior surface of the posterior cerebral artery. There are three
to six perforating branches which penetrate the rostral floor of the
interpeduncular fossas thrugh the posterior perforated substance.
Supply the oculomotor and trochlear nuclei, the paramedian
mesencephalic reticular formation, the pretectum, and the
rostroedian floor of the IV ventricle.
The tiny peduncular branches arise from the posterior
cerebral artery and penetrate the cerebral peduncle. They supply
19
the corticospinal and corticobulbar pathways as well as the
substantia nigra, red nuclei, and other structures of the
tegmentum.
The circumflex mesecephalic branches are a group of
several small vessels of variable length, arising from the
peduncular segment of the posterior cerebral artery that passes
around the midbrain. Supply small perforating branches to the
cerebral peduncle and substantia nigra, but also the posterior
tegmental structures.
Thalamic branches:
The so called thalmoperforating arteries are divided into an
anterior and a posterior group. The anterior thalmoperforating
arteries are a group of 7 to 10 arteries, arising from the lateral
aspect of the posterior communicating artery. They supply the
posterior chiasma, optic tract, posterior hypothalamus, and part of
the cerebral peduncle.
The posterior thalmoperforating arteries consist of two
groups of arteries. The interpeduncular thalmoperforating
branches originate from the proximal peduncular segment of the
posterior cerebral artery. Penetrate the thalamus via the
20
paramedian aspect of the posterior perforate substance. The
thalmogeniculate perforating branches arise from the ambient
segment of the posterior cerebral artery. Three to six small arteries
that penetrates the base of the thalamus and the geniculate
bodies.
Posterior choroidal branches
Posterior medial choroidal artery
It usually arises from the proximal segment of the posterior
cerebral artery. Runs parallel to the posterior cerebral artery and is
interposed between that artery and the midbrain to which gives
small branches. Enters the lateral portion of the quadrigeminal
cistern, supplying the quadrigeminal plate and the pineal gland.
Approaches the midline and courses forward in the roof of the III
ventricle adjacent to the internal cerebral vein. Multiple small
branches of this artery reach the level of the foramen of Monro and
supply choroid plexus of the III ventricle. Supplies also the dorsal
medial nucleus of the thalamus.
Posterior lateral choroidal artery
Originates from the ambient segment of the posterior
cerebral artery. Variations in origin are common. May be a single
21
trunk or multiple trunks. The anterior branch supplies the anterior
portion of the choroid plexus of the temportal horn of the ventricles,
while the posterior branch supplies the choroid plexus of the
trigone and lateral ventricle. The lateral choroidal artery also
supplies the crus cerebri, commissure, body and part of the
anterior columns of the fornix and thalamus. The size of this vessel
is usually inversely proportional to the size of the anterior choroidal
artery. There is anastomoses between branches of this artery with
branches of posterior-medial and anterior choroidal arteries.
Hippocampal branches
The arteries to the hippocampus originate from the trunk of
the posterior cerebral artery near the origin of the lateral choroidal
arteries. They are 1 to 4 in each side.
Meningeal branches
The meningeal branches are small and arise from the
peduncular segment of the posterior cerebral artery. They course
around the midbrain and supply the midline strip of the inferior
surface of the tentorium opposite to the junction of the falx cerebri
with the tentorium.
22
Posterior pericallosal artery
Usually arises at the level of the quadrigeminal cistern from
the parieto-occipital branch of the posterior cerebral artery. It may
also arise from the posterior cerebral artery or from the lateral
choroidal artery or from the posterior temporal artery. It is usually a
plexus of small arteries, rather than a single vessel. This artery
passes around the splenium running anteriorly within the
supracallosal cistern and anastomosing with the distal branches of
the anterior pericallosal artery.
Cortical branches
There are 4 main cortical branches of the posterior cerebral artery.
Anterior temporal artery
Arises as a single trunk or as multiple branches from the
proximal ambient segment of the posterior cerebral artery. Runs
lateral and anterior under the hippocampal gyrus supplying the
inferior aspect of the anterior portion of the temporal lobe. There
are anastomoses with the anterior temporal branches of the middle
cerebral artery.
23
Posterior temporal artery
Arises from the midambient segment of the posterior
cerebral artery as a single trunk. May give origin to an anterior
temporal branch. Courses posteriorly and laterally along the
hippocampal gyrus. Several small branches originate from this
artery along the inferior surface of the posterior temporal lobe and
adjacent occipital lobe. The distal vessels may anastomose with
branches of the calcarine artery in the posterior third of the
calcarine fissure. Supplies the primary visual cortex.
Parieto-occipital artery
May arise independently from the posterior cerebral artery at
the level of the ambient cistern. It may also originate with the
calcarine artery from the bifurcation of the posterior cerebral trunk
in the proximal third of the calcarine fissure. This artery originates
from the quadrigeminal segment. It arises as single trunk and the
branches include lateral posterior choroidal arteries, branches to
hippocampus, pulvinar and medial and lateral geniculate bodies.
The main trunk of the parieto-occipital artery usually divides into a
number of cortical branches that supply the medial portion of the
parieto-occipital lobe, precuneus and deep into the parieto-occiptal
fissure.
24
Calcarine artery
Arises at the bifurcation of the main posterior cerebral trunk
in the rostral third of the calcarine sulcus. At its origin, this artery
lies just lateral to the parieto-occipital branch. After this it follows a
winding posterior course deep in the calcarine fissure, supplies
part of visual cortex.
25
2. REVIEW OF LITERATURE
EMBRYOLOGY
Development of extra embryonic blood vascular system
In the early part of third week, the extra-embryonic blood vessels
and blood cells develop from the angioblasts which re
differentiated from the mesenchyme of three regions in the wall of
the yolk sac, the connecting stalk and the chorion. The angioblast
cells proliferate as the blood islands. Numerous cleft like spaces
appear within the blood islands, the peripheral cells persist as the
flattened endothelium and the central cells are detached from the
walls of the clefts to form the blood corpuscles. The clefts thus
formed intercommunicate with one another by sprouting and
establish a plexiform network of capillary vessels. The vessels
arising from the capillary plexus of the wall of the yolk sac form the
vitelline vessels, those developing in the chorion and the
connecting stalk constitute the umbilical vessels.
Development of intra-embryonic vessels and the primitive
heart
In the later part of third week, the intra-embryonic blood vessels
and blood cells differentiate in situ from the angioblast cells of the
26
intraembryonic mesoderm and establish secondary connections
with the extra-embryonic blood vessels. Prior to the formation of
the embryonic folds, two longitudinal vessels known as the dorsal
aortae appear in the flattened embryonic area on each side of the
notochord and along the dorsal wall of the yolk sac. At the cephalic
end dorsal aortae invade the cardiogenic plate as the lateral
endothelial heart tubes, which develop in the splanchnopleuric
mesoderm underlying endoderm. The cardiogenic plate intervenes
between the dorsal wall of the yolk sac and the floor of the
pericardial cavity. The two endothelial heart tubes are separated
from the floor of the pericardial sac by a thickened plate of
mesodermal tissue known as the myo-epicardial mantle. From the
caudal end of the embryonic area the two dorsal aortae extend into
the connecting stalk as the umbilical arteries which break up into
the capillaries of the chorionic villi. The returning venules from the
chorion join to form two umbilical veins in the connecting stalk, and
each vein runs headwards along the somatopleuric layer of the
intraembryonic coelom. Simultaneously, some blood vessels
sprout laterally from each dorsal aorta and form capillary plexus in
the wall of the yolk sac. The vitelline veins arise from this plexus,
and each extends, headwards along the splanchnopleuric layer of
the coelom. The vitelline and umbilical veins of the corresponding
27
side pass through the septum transversum which until now
occupies the most cephalic end of the embryonic area, and join
with cranial end of each endothelial tube of the primitive heart.
Meanwhile, the cardinal veins of the body wall supplement the
aforesaid veins and negotiate with cranial end of the primitive
heart.
With the formation of the head fold of the embryo the picture is
completely changed. The part of the yolk sac contained within the
head fold forms the tubular foregut. The pericardial sac lies in the
ventral wall of the foregut with reversal of its surfaces. The dorsal
wall or somatopleuric layer of the sac now becomes ventral and
the ventral wall or the splanchnopleuric layer of the sac occupies
dorsal position. Therefore, the two endothelial tubes of the
primitive heart now lie between the ventral wall of the foregut and
splanchnopleuric layer of the pericardial sac, from the latter the
primitive heart is separated by the myoepicardial mantle which
invests the front and sides of the endothelial tubes. Initially the
myo-epicardial mantle is separated from the endothelial tubes by
cardiac jelly, which is a acellular matrix secreted by the developing
myocardium, subsequently the jelly is replaced by the myocardium
which is derived from the mantle. The caudal end of each
28
endothelial heart tube now becomes cephalic and is continuous
with the corresponding dorsal aorta along the lateral wall of the
foregut through the first aortic arch. Due to the similar reason the
umbilical, vitelline and somatic veins now drain into the caudal end
of each primitive heart tube. Thus the cardiogenic area is bounded
ventrally by the pericardial sac, dorsally by the foregut, on the
cephalic side by the stomodeum and buccopharyngeal membrane,
and on the caudal side by the septum transversum.
Development of the definitive heart
With the development of the head fold of embryo, the two
paramedian endothelial tubes of the heart lie ventral to the foregut,
and they project into the dorsal wall of the pericardial sac covered
by the myoepicardial mantle. The cephalic and lateral folding of the
embryo bring two lateral endothelial tubes closer in the thoracic
region, where they meet and fuse in cranio-caudal direction to form
a single primitive heart tube. The cranial end of the single tube
may be called the arterial end of the heart, it bifurcates into two
branches known as the first aortic arches which pass by the side of
the pharynx and are continuous with the corresponding dorsal
aorta. Subsequently five core pairs of aortic arches appear and
connect the cranial end of the primitive heart with dorsal aorta. The
29
caudal venous end of the heart tube is at first embedded in the
mesenchyme of the septum transversum, and presents right and
left horns. Each horn receives the vitelline vein from the yolk sac,
the umbilical vein from the placental and the common cardinal vein
from the body wall. The myo-epicardial mantle forms the
pericardium and myocardium after replacement of the cadiac jelly,
the endothelial tube persists as the endocardium of the heart. The
primitive heart starts beating on the day 22, and by 24th day blood
begins to throughtout the embryo.
Development of vascular system:
In the early stages of development, the intraembryonic blood
vessels consist of networks of diffuse capillary plexuses which are
placed along the course of future definitive vessels. Under the
influence of the local haemodynamic factors and genetic factors,
some of the capillaries dilate and coalesce with the adjacent ones
to direct the blood flow, whereas the other capillaries regress and
they finally disappear. The preferred channels thus formed persist
as definite arteries or veins. In the beginning both arteries and
veins consist of simple endothelial tubes and histological
differentiations become clearly visible in the later stage of
30
development by the thickening of the muscular wall under the
influence of haemodynamic factors.
AORTIC ARCHES (BRACHIAL ARCH ARTERIES)
The primitive aortae with two longitudinal vessels first appear in
the flattened embryonic area prior to the formation of the
embryonic folds. The primitive aorta intervene between the
notochord and the dorsal wall of the yolk sac, and extend
headwards in the cardiogenic area to establish connections with
caudal ends of the endothelial tubes of the primitive heart. With the
formation of head fold of the embryo, the heart tube lies ventral to
the foregut and its caudal end becomes cephalic which forms the
bulbus cordis of the primitive heart. The primitive aorta bends
ventrally along the lateral walls of the foregut (pharynx) through the
mesodermal core of the first pair of branchial arches and
communicate with the bulbus cordis of the heart tube. Hence, the
aorta consist of three parts, ventral aorta lying ventral to the
foregut, first aortic arches passing through the first branchial
arches and dorsal aortae lying dorsal to the foregut.
Cephalic to the bulbus cordis the two ventral aorta fuse to form the
truncus arteriosus which dilates to form the aortic sac. Distally, the
aortic sac bifurcates into right and left limbs. Initially each limb of
31
the sac is connected to the corresponding dorsal aorta though the
first aortic arch which is in fact the continuation of the primitive
aorta. When five more pairs of the branchial arches appear in the
lateral wall of the pharynx caudal to the first pair in carnio-caudal
sequence, each limb of the aortic sac sends further connections to
the dorsal aorta through five aortic arches. Altogether six pairs of
aortic arches embrace the lateral wall of the pharynx and extend
from the ventral to the dorsal aorta.
In water breathing vertebrate’s fishes with gills each branchial arch
artery consists of an afferent part which conveys deoxygenated
blood from the heart and breaks up into capillary plexus of the gill
filaments and an efferent part which conveys the oxygenated blood
to the dorsal aorta for distribution to the entire body. With the
advent of pulmonary respiration in terrestrial vertebrates and with
the septation of the heart, the aortic arches are greatly modified for
the development of the arteries of the head, neck and thorax. The
distal part of the aorta-pulmonary septum divides the truncus
arteriosus into the ascending aorta ventrally and pulmonary trunk
dorsally the cephalic edge of the septum fuses with dorsal wall of
the aortic between fifth and sixth pairs of the aortic arches. As a
result, upper five pairs of the arches are connected with the
32
ascending aorta conveying oxygenated blood from the left
ventricle, and the sixth pair of arches is attached to the pulmonary
trunk carrying deoxygenated blood from the right ventricle.
Therefore, sixth pair of arches may be called the pulmonary
arches. The dorsal aortae present two characteristic features:
1. Each aorta extends headwards beyond the first aortic arch towards
the developing brain where it gives off an opthalmic branch to the
optic vesicle, anterior and middle cerebral branches to the brain. It
terminates as the posterior communicating artery and turns
caudally to join with the developing basilar artery.
2. The two dorsal aorta fuse caudo-cranially to form a single aorta
which extends from the 4th lumbar to the 4th thoracic segments.
In human embryos the aortic arch pattern may be considered in
two phases branchial and post branchial.
BRACHIAL PHASE
In this phase six pairs of aortic arches are not present all at a time.
Fifth arches are transitory and disappear early. When, the first pair
of arches disappears except a part for maxillary artery, the third
pair of visualised. The second pair disappears next except a part
for stapedial artery, and during that period the fourth pair
33
undergoes differentiation. The regression of the first two pairs of
aortic arches is probably due to caudal shift of the heart, so that
they lie at disadvantageous positions to direct the blood flow to the
dorsal aorta. Due to changes in the aortic arch patter., the blood
flows in succession though the first aortic arch, first and second
arches, second and third arches, third and fourth arches, and third,
fourth and sixth arches. Therefore, first, second and fifth aortic
arches lie in oblivion whereas third, fourth and sixth arches persist
in pavilion.
Associated with regression of the first and second aortic arches, a
new vessel- the external carotid artery sprouts headwards from the
aortic sac close to the origin of the third aortic arch and extends
along the ventral wall of the pharynx to establish secondary
connection with the united origin of the maxillary and mandibular
branches of stapedial artery. Thereafter, the origin of the external
carotid artery is incorporated with third aortic arch. The growth of
the upper limb bud demands nutrition, and this is maintained by
the development of the seventh intersegmental artery which
sprouts outwards from each dorsal aorta distal to the attachment of
the sixth aortic arch. Form the initial stage, each sixth arch artery
gives a branch which breaks up into capillary plexus to supply the
34
development lung beds. The branchial phase of the aortic pattern
persists upto 12 m CR length of the embryo.
POST- BRANCHIAL PHASE
Three changes are observed in this phase and these culminate in
the development of adult pattern of blood vessels.
1. Due to caudal displacement of the heart and gradual elongation of
the neck, the blood stream in the third aortic arch is directed
towards the cephalic end of the embryo, and the blood in the fourth
aortic arch flows caudalwards. As a result, the portion of the dorsal
aorta between the third and fourth arches ductus caroticus
disappears on each side. Thus the dorsal part of the third aortic
arch and the dorsal aorta cephalic to the ductus caroticus form
together the internal carotid artery. The ventral part of the third
aortic arch together with the elongation of the aortic sac persists as
the common carotid artery.
2. The ventral part of the right sixth aortic arch forms the right
pulmonary artery, whereas its dorsal part regresses and loses
connection from the dorsal aorta. Similarly, the ventral part of the
left sixth aortic arch forms the left pulmonary artery, but its dorsal
part persists in foetal life as the ductus arteriosus which conveys
the blood from the pulmonary trunk to the descending part of the
35
left dorsal aorta. After birth, the ductus arteriosus is fibrosed and
converted into the ligamentum arteriosum which connects the left
pulmonary artery to the underface of the arch of aorta.
3. The portion of the right dorsal aorta caudal to the origin of the right
seventh intersegmental artery disappears and the regression
extends upto the fusion of the two dorsal aorta. The cause of
preferential regression on the right side is not known.
The right fourth aortic arch, a part of the right dorsal aorta caudal
to the ductus caroticus, plus the right seventh intersegmental
artery forms together the right subclavian artery. Right limb of the
aortic sac, which is connected with the third and fourth aortic
arches, persists as the brachio-cephlalic trunk.
On the left side, the definitive arch of aorta is developed from three
sources which are mentioned from ventral to dorsal aspects.
1. Left limb of the aortic sac: it forms the part of the arch which
intervenes between the origins of the brachiocephalic trunk and left
common carotid artery.
2. Left fourth aortic arch: it forms that part of the arch which
extends between the left common carotid and left sublavian
arteries, the latter vessel develops only from the left seventh
intersegmental artery. This portion of the arch of aorta is
36
connected on its caudal surface with ductus arteriosus which is
derived from the dorsal part of the left sixth aortic arch. The origin
of the left subclavian artery gradually shifts more cranially due to
the descent of the heart, until it appears close to the origin of the
left common carotid artery cephalic to the attachment of the ductus
arteriosus.
3. Left dorsal aorta: it forms the distal part of the arch of aorta and
extends upto the 4th thoracic segment where the two dorsal aortae
fuse.
DORSAL AORTAE AND THEIR BRANCHES
Both dorsal aortas fuse caudo-cranially and the fusion extends
upto the fourth thoracic segment, above that level they persist as
individual aorta. The portion of the dorsal aorta cranial to the
ductus caroticus forms the main component of the internal carotid
artery. Part of the right dorsal aorta between the ductus caroticus
and the origin of the right seventh intersegmental artery
incorporates in the development of the right subclavian artery, left
dorsal aorta between the left seventh intersegmental artery and
the cranial end of the fused aorta persists as the distal part of the
arch of aorta. The remaining part of the fused aorta forms the
descending thoracic and abdominal aorta, opposite the sacral
37
segment it persists in rudimentary forms as the medial sacral
artery.
Each dorsal aorta, even before the stage of fusion, gives
segmentally numerous branches which arise at right angles to the
long axis of the aorta and are arranged in three different groups.
1. Ventral splanchnic branches which supply the gut and its
derivatives
2. Lateral splanchnic branches to the derivates of the intermediate
mesoderm
3. Somatic intersegmental branches to the body wall and the neural
tube.
SOMATIC INTERSEGMENTAL BRANCHES
The somatic arteries arise from the dorso-lateral aspect of the
dorsal aorta and run horizontally between the somites extending
from the occipital to the sacral regions. Opposite the heads of the
ribs each artery divides into dorsal and lateral rami. The dorsal
ramus passes between the ribs and the transverse processes of
the vertebra, and supplies the muscles and integument of the
back, in addition each dorsal ramus provides a spinal branch
which enters the vertebral canal and supplies the meninges and
38
the neural tube. The lateral ramus encircles the body wall
accompanied by the corresponding spinal nerve, provides a lateral
and close to the mid ventral line forms a longitudinal anastomotic
FIG 4: DEVELOPMENT OF VERTEBRAL ARTERY
channel by linking up with the adjacent intersegmental arteries.
The ventral somatic anastomosis persists in adults as the internal
thoracic, superior and inferior epigastric arteries.
In the thoracic and lumbar regions the intersegmental arteries form
the posterior intercostals, subcostal and upper four lumbar
39
arteries. The fifth lumbar intersegmental artery is represented by
the common iliac artery. Sacral intersegmental arteries are
withdrawn from the aorta and are incorporated with internal iliac
artery as the parietal branches of the latter vessel.
In the cervical region the intersegmental arteries link up with one
another and form the following longitudinal anastomotic channels.
1. Pre-costal anastomosis connects the intersegmental arteries distal
to the origin of the dorsal rami, it persists as the thyrocervical
trunk, superior intercostals, and ascending cervical arteries.
2. Post-costal anastomosis intervenes between the ribs and the
transverse processes of the vertebrae and connects the dorsal
rami, persists as the major part of the vertebral artery.
3. Post-transverse anastomosis lies dorsal to the transverse
anastomosis lies dorsal to the transverse processes and forms the
deep cervical artery.
4. Pre and post-neural anastomosis lie within the vertebral canal and
are formed by the spinal branches of the dorsal rami.
Except the seventh cervical intersegmental artery, rest of the
cervical arteries regress and are modified to form the vertebral
artery. The seventh intersegmental vessel forms the subclavian
artery and is continued as the axis artery of the upper limb. The
40
vertebral artery is a composite vessel and is developed from the
following sources.
1. First part of the artery, which extends from the subclavian artery to
the foramen transversarium of the sixth cervical vertebra, is
developed from the dorsal ramus of the seventh intersegmental
artery.
2. Second part of the artery extending through the foramina
transversaria from the sixth to the first cervical segments is
developed from the enlargement of the post-costal anastomosis,
with the consequent regression of the stems of the upper six
intersegmental arteries.
3. Third part of the artery, which rests on the posterior arch of the
atlas, is derived from the spinal branch of the first cervical
intersegmental artery.
41
FIG 5: GENERAL PLAN OF BRANCHES OF DORSAL AORTA
(PICTURE COURTESY: A.K.DATTA HUMAN EMBRYOLOGY)
4. Fourth part of the artery owes its development from the pre-neural
division of the spinal branch, which meets with the corresponding
branch of the opposite side at the caudal border of the pons to
form the basilar artery. The latter vessel bifurcates, and after
joining with the posterior communicating branch of the internal
carotid artery is continued on each side as the posterior cerebral
artery.(A.K.DATTA)
42
In 1954, Padget made an extensive study on the development of
the cranial arteries in the human embryo. In the primitive vascular
plexus at this stage, the course of all the major cranial arteries is
distinct but not their direction or their size. These are determined
by the subsequent growth of the brain, which requires
augmentation of certain channels and allows the disappearance of
others.
The internal carotid, the basilar and the vertebral arteries are
formed during the first three stages: Stage I – 30 days, 4-5mm in
length of the embryo, Stage II- 31 days, 5 to 6 mm, Stage III –
33 days, 7-12mm in length of the embryo.
At Padget stage I: the primitive internal carotid gives two major
divisions, a caudal branch which later forms the posterior
communicating artery after anastomosing with the bilateral or
longitudinal neural artery which precede the basilar artery. And the
cranial branch which curves canioventrally around the base of the
optic vesicle. Although this latter division has often been called the
anterior cerebral artery and only a small part of it is represented in
the adult vessel. From this primary division of the carotid several
collateral branches arise. During later stages, they are the anterior
43
choroidal, the middle cerebral and lastly the major part of the
anterior cerebral artery.
During the 20 mm stage when the anterior cerebral extends up
between the cerebral hemispheres, the primitive olfactory artery
dwindles and sends an offshoot to the anterior perforating
substance as well as to the formation of plexus in the region of
anterior communicating artery. The more constant medial striate,
recurrent artery of Heubner which arises from the anterior cerebral
at the level of the anterior communicating artery, is very
conspicuous in the embryo after 20 mm stage.
The posterior communicating artery which represents the original
caudal division of the primitive internal carotid, remains relatively
large throughout all the stages in this series. Until the completion
of the vertebral artery in the early post-branchial phase (12-
14mm), it is the channel through which the internal carotid supplies
all the arteries of the hindbrain. The posterior cerebral artery
emerges by means of an elaboration of one of the large
diencephalic or mesencephalic branches of the posterior
communicating artery in the stage of 40mm.
44
Of all the cerbellar arteries, the superior cerebellar artery is the first
identifiable at the 7 to 10mm stage. Then the stems for both the
45
inferior cerebellar arteries. Anterior and posterior becomes
recognizable.
In embryo between 20 to 40mm stage both arteries are
represented by vessels which terminate in the large choroid plexus
of the fourth ventricle which these arteries which these arteries
supply via small branches in the adult.
Before the 40mm stage, these arteries can usually be identified
only tentatively as those which are larger and longer than
numerous other associated basilar and vertebral branches which
arise to supply the hindbrain regions, lying between the 7th and 12th
cranial nerve roots massed in this area.
Since these transverse branches are so often connected by
longitudinal remnants of a prominent lateral channel (the primitive
lateral basilo-vertebral anastomosis) paralleling the basilar artery
and the cerebral part of the primitive vertebral artery, the arteries
of the embryonic medulla long present a somewhat plexiform
appearance.
46
47
The variable origin in the adult of the anterior and posterior
cerebellar arteies, in contrast with relative constancy of the
superior cerebellar artery is thus readily explained (Stopford 1916)
The conspicuous temporary artery contributes extensively toward
the formation of the bilateral longitudinal neural arteries which join
to form the basilar artery, and because of its position it has been
named the primitive trigeminal artery.
The cranial end of each neural artery is supplied by the trigeminal
artery, which, following the involution of the first two aortic arches
is now considered a branch of the primitive internal carotid artery.
Development of the diencephalic and mesencephalic regions at
this time is accompanied by an extension of the primary caudal
division of the internal carotid artery. Not until it has developed the
secondary anastomosis with the cranial end of the neural artery.
However, does the caudal division of the carotid become the
definitive posterior communicating artery. Until this time, the
trigeminal branch of the internal carotid is the major source of
blood to the longitudinal neural artery of the hind brain, the caudal
connections of which with transitory hypoglossal artery and the first
cervical segmental artery are typically small.
48
FIG 8: EMBRYO 12.5mm. LATERAL VIEW TO SHOW THE CERVICAL SEGMENTAL ARTERIES FUSE TO FORM THE
VERTEBRAL ARTERIES
Subsequently, the bilateral neural arteries consolidate to form the
basilar artery. Concomitantly or soon thereafter, the posterior
communicating artery takes over from trigeminal artery the role of
supply to the arteries of the hind brain during the reminder of the
branchial period.
The formation of the vertebral arteries relieves the internal carotid
of its earlier role of supply to all the arteries in the hindbrain.
49
A longitudinal neural artery appears on each side which is
cranially supplied by the terminal and descending branch of the
trigeminal artery and caudally supplied by the ascending branch of
the first segmental artery ( Proatlantal artery). Laterally each
longitudinal neural artery receives the otic and hypoglossal
arteries.
At Padget stage II: the two longitudinal neural arteries partially
merge to form the basilar artery. Meanwhile the posterior
communicating artery takes over from the trigeminal artery, the
role to supply the hind brain during the remaining branchial period.
FIG 9: EMBRYO 18mm. DEVELOPMENT OF VERTEBRAL ARTERIES: (FROM PADGET EMBRYOLOGY)
50
At Padget stage III: one of the caudal and cranial longitudinal
collateral branches pairs, arising from the first six segmental
arteries, fully anastomoses in the caudo-cranial direction. The first
segmental artery or Proatlantal artery is linked to the basilar artery
by its cranial branch. Its caudal branch is considered as being
starting of the cervical formation of vertebral artery in the cranio-
caudal direction. When the collateral caudal branch of the 6th
segmental artery, anastomoses with the cranial branch of the 7th
segmental artery or the future subclavian artery, the blood flow
backwards in the caudo-cranial direction. The ventral trunks of the
first six segmental arteries slowly disappear to form the complete
vertebro-basilar system.
51
REVIEW OF LITERATURE:
EARLIER WORKS ON BASILAR ARTERY:
Fawcett And Blachford 1905 studied on the circle of willis in 700
specimens. In this there was no mention of basilar artery in the
studies.
J.S.B.Stoppard 1916 studied the arteries of the pons and medulla
oblongata in 150 cadaveric brain specimen, in his work he
mentioned about the formation of basilar artery at the lower border
of pons is seen in 73% and above the lower border is 8% and
below the lower border of pons it is seen in 19%.
Buntaro adachi 1928 studied the entire vascular system of
human body in Japanese population over a period of years. In this
he has given the average basilar artery length extends from 25-
30mm.
Lang and Kollmannsbeger 1961 found the length of basilar
artery is between 23-28mm.
Gunter Seydel, H et al 1964 studied on the diameter of the
cerebral arteries of the 98 human fetal specimens where he
studied the diameter of the posterior cerebral artery.
52
Vare.A.M and Bansal 1970 studied the arterial pattern at the base
of the human brain from 175 dissection hall specimens in which he
mentioned about the level of formation of basilar artery – below the
lower border of pons the formation of basilar artery is present in
16%, above the lower border of pons in 4.5% and at the lower
border of pons it is present in 79.4% of specimens.
Naokatsu Saeki, Albert L Rhoton 1977 studied on the
microsurgical anatomy of the upper basilar artery and the posterior
circle of Willis, work was done in 50 cadaveric brain, and the mean
length of basilar artery is 32mm and range between 15-40mm.
Sylvia Kamath 1979 studied on the dimensions of the basilar
artery in 97 south Indian subjects. The length of basilar artery
ranged between 22 to 45.2mm and the greatest percentage
(44.2%) lies between 25 to 30mm. the external diameter ranged
between 1.9 to 6.0mm and the greatest percentage (43.35%) lies
between 3.0 to 3.5mm. And he was trying to correlate the
reciprocal relationship between the diameter of internal carotid
arteries and basilar arteries.
53
Akimoto. H. 1979 studied the roentogenological aspect of the
basilar artery and its significance in clinical diagnosis –
angiographical study of basilar arteries was done in 130 normal
vertebral angiograms. The length of basilar artery was 25.5±
6.6mm in frontal aspect and 32.8±5.8mm in lateral view. The
course of basilar artery is straight type was common in young age
and 'curved type' in old age.
Orlandini GE et al 1985 studied on the blood vessel size of
circulus arteriosus on 100 fresh cadavers of Italian subjects, the
following arteries was measure basilar artery, internal carotid
arteries, anterior and posterior cerebral arteries and anterior and
posterior communicating artery.
Richer H Lye et al 1985 found the basilar artery ectasia – an
unusual cause of trigeminal neuralgia.
Smoker WR et al 1986 studied the basilar artery in high
resolution computed tomography in 20 unfixed brain specimens
are injected with silicone rubber solution. The length of basilar
artery was 28.1±1.35mm and the course of basilar artery is straight
in 45% and curved in35% and tortuous in 20%. And in another
work he studied the normal size and position of basilar artery in
high resolution computed tomography was done 126 patients. The
54
mean normal diameter of basilar artery is 3.17mm. In 92% of
normal cases the basilar bifurcation is located in the
interpeduncular cistern adjacent to the dorsum sellae or in the
suprasellar cistern below the level of the floor of the third ventricle.
In 98% of normal individuals the basilar artery courses in the
midline, medial to the lateral margins of the clivus and dorsum
sellae.
Wojtowicz.Z et al 1989 studied the basilar artery in humans, in his
studies he worked on the formation of basilar artery – the normal
formation at the level of inferior margin of pons was seen in 44.6%,
below the inferior margin of pons the formation is seen in 40.4%
and above the inferior margin of pons in 15.1% cases ,diameter of
the basilar artery in the new born at the level of formation is 1.9mm
and at the level of termination of basilar it is 1.8mm and in the
adult it exceeded 4mm. The length of basilar artery in new born
ranged 17.2mm and in adult of 20 years it is above 33mm.
Jablonski R et al 1989 studied the basilar arteries of the brain in
wild boar. He studied it in 34 brains of wild boar and the basilar
artery showed variation in the site of origin and its course.
Bohutova J et al 1990 studied on the anomalies of the basilar and
vertebral arteries that are of practical importance. In his work he
55
studies the anomalies of vertebrobasilar system which arise due to
embryonic developmental deteriorations.
Eicchorn M et al 1990 worked on the causes of variations in the
pathway of the basilar and vertebral arteries in 60 corpses and
observed the variations in the positions of vertebral and basilar
arteries and correlated them with respective age at the time of
death.
Torche. M et al 1992 studied in 20 unfixed brain specimens the
length of basilar artery is 28.1±1.35mm and the course of basilar
was studied.
Nishijima. Y 1994 studied on the anatomical analysis of the
basilar artery and its branches in 52 brains, the max diameter is
3.93±0.76mm and minimum diameter is 3.14±0.58mm and the
average length of basilar artery is 35.0±5.1mm.
Akar et al 1994 studied the microsurgical anatomy of the
intracranial part of the vertebral artery in 11cadaveric brain, in their
work the formation of basilar artery at the ponto medullary groove
in 36.4% and above the groove in 53% and below the groove in
35.5%.
56
De Caro R et al 1995 worked on the anatomy of segmental
duplication of the human basilar artery and its possible site of
aneurysm formation. In his work he studied 5 cases of basilar
fenestration without aneurysm was studied using scanning
electron microscopy and morphometry was done. In all cases it
showed thinning of tunica medial wall was seen towards the
junction of fenestration.
Mandiola,E. et al 1995 studied on anatomical consideration of
basilar artery in 70 Brazilian brain specimens, in this the basilar
artery average length is 24-45mm. The length of basilar artery
varied to 31-37mm in 50% of male specimens and 42.9% in
female specimens.
Gieliecki J et al 1996 studied the digital image analysis of the
brain base arteries in chinchilla luniger. The paper attempts to
quantitatively characterize the cerebral arterial circle using
computer image analysing system. The sole blood supply to the
brain in this animal is the vertebral and basilar arteries. And it was
found that the basilar artery diameter and volume was two times
larger than the cerebral arterial circle.
57
Grand Walter et al 1997 studied the micro vascular surgical
anatomy of the vertebrobasilar junction in 28 brains to make a
guideline for aneurysm surgery in the vertebrobasilar region
Jonas H. Goldstein et al 1998 studied the complete duplication
or extreme fenestration of the basilar artery seen in 42 year old
male patient with complete duplication of the basilar artery, with
each vertebral artery continuing separately to form a posterior
cerebral artery which demonstrated by catheter digital subtraction
angiography DSA.
PH Nakstad et al 1998 studied the basilar artery fenestration
aneurysms treated with Guglielmi detachable coils (GDC) in four
patients in Norway. And concluded that GDC embolisation, is a
useful treatment in basilar fenestration aneurysms.
Krabbe Hartkamp et al 1998 studied the circle of Willis:
Morphologic variation on three-dimensional, time of flight MR
angiograms. In his work the diameter of basilar artery is 3mm
Moore. S et al 2006 in his study on the 3D blood flow pattern in
cerebral arteries, the work was carried out in NewZealand. The
diameter of basilar artery is 3.17mm.
58
Gernot Schulte et al 2000 visualization of the basilar artery by
Transcranial Color – Coded Duplex Sonography (TCCDS) in
comparison with post-mortem results was done in 46 cases/ the
mean length of basilar artery in ultrasound measurements is
21.5±6.8mm and it ranged between 9 to 37mm. the mean length of
basilar artery was measured in autopsy specimen is 32.9±6mm ant
it ranged between 25-57mm.
Witold Brudnicki et al 2000 studied on the basilar arteries of the
brain in domestic goat in which starts at the posterior part of the
interpedunculate fissure, and then runs caudally over the pons and
then in the medial fissure of the medulla oblongata. The diameter
of the basilar artery gradually decreases caudally.
Nilda Turgut et al 2004 studied the isolated hypoplasia of distal
basilar artery: clinical and imaging findings. It was seen in 50 year
old male patient from turkey reported by MRI and 3-D-TOF MRA.
Nishikata M 2004 studied on the measurement of basilar artery
bending and elongation by magnetic resonance cerebral
angiography: relationship to age, sex and vertebral artery
dominance, in this the basilar artery bending mainly depends on
aging, and dominance of vertebral artery.
59
Mandiola.E et al 2004 studied on the biometrical analysis
between bioanthropological cephalics measurements of basilar
artery. In this the basilar artery presents an average length of 36.9
mm for a length of clivus of 54.4 mm, wide of the cerebellar fossa
of 108.0 mm and height of 46.0 mm.
Fernanado Gonzalez et al 2005 investigated on the skull base
approaches to the basilar artery. In his work the posterior
circulation lesions accounts approximately 10% of all intracranial
aneurysms. The different approaches and their nuances and
indications based on the area of aneurysm and its relationship to
the surrounding bones.
Fernanado Pico et al 2006 studied on the basilar artery diameter
and 5-year mortality in patients with stroke using MRI and in this
he concluded that the basilar artery diameter was independently
associated with cerebrovascular mortality and the diameter of
basilar artery greater than 4.3mm may be a marker for a high risk
of fatal stroke.
Sabtos Franco et al 2006 studied on the microsurgical
considerations of the anterior spinal and the anterior-ventral spinal
arteries, in 50 human cadaveric brain, in which the formation of
60
basilar artery at the ponto-medullary groove was present in 27.5%
and above the groove in 37% and below the groove is 35.5% .
Balaji. S. Pai et al 2007 studied the microsurgical anatomy of the
posterior circulation in the Indian population. In this he studied 35
cadaveric brain specimens, he found the mean diameter of the
vertebral artery was 3.4mm on the left and 2.9mm on the right, and
the diameter of the basilar artery varied from 3-7mm, mean
diameter is – 4.3mm. The length of basilar varied from 24-35mm
and mean length 24.9mm.
Ljiljana P vasovic et al 2007 studied the posterior part of the
human cerebral arterial circle from gestational weeks 13 to 24 in
Serbian population. The average diameter to posterior cerebral
artery and posterior communicating artery was done
Songur et al 2008 studied the variations in the intracranial
vertebrobasilar system in 109 subjects of Turkish population. The
diameter of vertebral and basilar artery and their branches were
measured. The dominancy and hypoplastic arteries and its
variations and location, were determined.
Ljilljana vasovic et al 2008 studied the reliability of basilar
bifurcation geometry obtained by microdissection, conventional
61
geometrical models of the fetal cerebral arterial circles in 200 fetal
brains to the adult human present in the available literature. Basilar
artery bifurcation angle ranged from 35 to 175 degrees and in two
thirds of the case the bifurcation angle is larger than 90 degrees.
J M Hong et al 2009 studied the diameter of basilar artery in
normal and the same in case of PICA infarction. The normal
diameter is 3.17mm and in PICA infarction it is 1.95mm.
O.A.Fomika et al 2009 worked on the age specific and sexual
variability of morophological and biomechanical parameters of the
basilar artery of 114 adult people in an experiment on monoaxonic
distension by tensile testing machine Tira test and determined
general solidity, breaking point, maximum and relative deformation
of the artery. And it is statistically proved the prevalence of the size
of wall thickness and general solidity of the men arterial wall. In
age aspect the external, lumen diameter and the wall thickness of
the basilar artery increases with age.
Liu Huai-Jun 2010 anatomical study of basilar artery in 108
subjects using MRA and conventional MRI, in his work he
mentioned the straight length of basilar artery 2.35+0.30cm, the
straight length of the basilar artery in en was longer than that in
women. The average diameter of basilar artery was 0.26+0.05cm
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and there was no difference between the diameter of upper,
middle and lower segment of basilar artery.
O.E.Idowu et al 2010 studied the surgical anatomy of
vertebrobasilar territory and posterior circle of Willis in 50 Nigerian
brains. The average length of basilar artery is 31.42+3.82mm. The
origin of basilar artery at the ponto-medullary junction is seen 68%
of specimens, above the ponto-medullary junction in 22% and
below the junction is 10%. The bifurcation at the upper border of
pons in 98%, and early bifurcation in 2%. The diameter of basilar
artery was constant throughout the course except at the bifurcation
where there is slight widening is seen. The mean diameter of
basilar artery is 3.82mm and it ranged between 2.5 to 5.5mm.
Mohamed Abdelaziz Maaly et al 2011 A three dimensional MRA
of the circle of willis was done in 250 Egyptian population was
done in this the Basilar artery diameter in Males is 3.06mm and in
Females is 2.98mm. In patient below 40 years the diameter of
basilar artery is 2.91mm and above 40 years is 3.09mm.
A.Dodeviski et al 2011 in his studied he has mentioned about
Wollschaleger who studied the length of basilar artery which
ranges between 24.80 to 38.50mm and the diameter ranges
between 2.70 to 4.28mm.
63
Padmavathi. G et al 2011 studied on the variations in the origin
and termination of basilar artery from 54 autopsy specimen from
the regions of Mysore. In this he tabulated the variations in the
level of formation of basilar artery and the variations in the level of
termination of the basilar artery.
Fellgiebel. A 2011 studied the basilar arery diameter as a
potential sceening tool for fabry disease in young stroke patients.
In this he reported that in patients with stroke, the diameter of
basilar artery was significantly lower – 2.45±0.5mm
Haripriya et al 2011 studied the basilar artery using magnetic
resonance imaging angiography. The study was done in 50
patients and two cases showed stenosis and bulbosity.
Ana Rodriguez - Hernandez et al 2011 studied the segmental
anatomy of cerebellar arteries – a proposed nomenclature. In his
work an analogous nomenclature for cerebellar arteries has been
described, the superior cerebellar artery was divided into 4
segments: s1 – anterior ponto mesencephalic segment, s2 –
lateral pontomesencephalic segment, s3- cerebellomesencephalic
segment, s4 – cortical segment. The anterior inferior cerebellar
artery was divided into 4 segments: a1 – anterior pontine segment,
a2 – lateral pontine segment, a3 – flocculopeduncular segment,
64
and a4 – cortical segment. The posterior inferior cerebellar artery
was divided into 5 segments: p1 – anterior medullary segment, p2
– lateral medullary segment, p3 – tonsillomedullary segment, p4 –
telovelotonsillar segment and p5 – cortical segment. In this work
the microsurgical anatomy of the cerebellar arteries is reviewed,
and a numbering system for cerebellar arteries is proposed.
Anjuman Ara Sultana et al 2012 studied on the variation in the
site of formation of basilar artery in 70 autopsy specimens. The
normal formation of basilar artery at the level of Pontomedullary
junction was seen in 72.2% and above the junction is 27.8%.
Hosapatna Mamatha et al 2012 worked on the morphological
study of basilar artery in 20 cadaveric brain specimens, the
average length of basilar artery is 32mm and the diameter is 2.6 -
3.5mm. The formation of basilar artery at the normal position
(Ponto-Medullary junction) is seen in 65%, below the normal
position in 25% and above the normal position in 10% of the
specimens. The termination of basilar artery was normal (at the
upper border of pons) in 70% and below the normal position is
25% and above the normal position is 5%. The mean angle of
formation was 60degree+8.7.
65
Ogeng.O.J.A et al 2012 made a study on the pattern of
termination of basilar artery in 173 black Kenyan population aged
between 20-79years. He observed bifurcation in 82.1%, trifurcation
in 10.4%, quadrifurcation in 5.8% and pentafurcation in 1.7% of the
population.
Witold Brudnicki et al 2012 studied the brain base arteries in
European otter and he investigated it in 30 brain specimens. In his
study a well developed basilar artery which was formed as a result
of the anastomosis of equally well developed vertebral arteries and
ventral spinal artery.
Deng D et al 2012 morphological analysis of the vertebral and
basilar arteries in the Chinese population provides greater
diagnostic accuracy of vertebrobasilar dolichoectasia and reveals
gender differences by MRI, in the study the basilar artery diameter
in males were 2.2-4.2mm and female is 2.0-4.0mm and the
vertebral artery diameter in males were 1.7-3.7mm on the left side
and 1.5-3.5mm on the right side and in females is 1.5-3.5mm on
the left side and 1.1-3.1mm on the right side. No significant gender
difference was found in the height of the basilar artery bifurcation
and the position of the basilar artery.
66
Iqbal. S. 2013 studied on the vertebrobasilar variants and their
basic clinical implications in 50 adult human brains. In this he
made a note on the length of basilar which ranged between 18-
37mm and average is 30mm and the diameter of the basilar artery
ranged between 2.8 -5.1mm and average 3.9mm.
Pedro Luis Forera et al 2013 studied in 100 autopsy specimens
in Colombian population, the length of basilar artery is 30.2mm
SD4.07, and the length of basilar artery in relation to the origin of
superior cerebellar artery is 28.1mm, SD3.84mm. the diameter of
basilar artery at the proximal point is 3.96mm SD0.48, and at the
distal point is 3.7mm SD0.48. The origin of basilar artery at the
level of ponto-medullary groove is seen in 43%, above the groove
is 30% and below the groove is 27%.
Polguj M. et al 2013 studied an asymmetrical fenestration of the
basilar artery coexisting with two aneurysms in a patient with
subarachnoid haemorrhage: case report and review of literature. In
this the diameter of basilar artery is 2.8mm and the study was
done using CT angiography.
Ljiljanana Vasovic et al 2013 worked on the human basilar artery
abnormalities in the prenatatal and postnatal period in 120 fetuses
and in 112 adult cadavers. In which the basilar fenestrations in
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adult specimens shared similar features with festal ones and
without aneurysms, lead us to hypothesis that the basilar
fenestration is a vascular developmental variant related to the
maintenance of vascular symmetry in the midline of the human
brain base.
Manju bala et al 2013 studied the trifurcation of basilar artery and
its importance was reported.
Veysel akgun et al 2013 worked on the normal anatomical
features and variations of the vertebrobasilar circulation and its
branches: an analysis with 64-Detector row CT and 3TMR
angiographies was done in 135 patients. The anatomical relations
of the branches of the vertebrobasilar circulation may be different
from well know normal anatomy. Hence CT and MR angiographies
will help us to precise and detailed evaluation of vertebrobasilar
circulation.
Marco Antonio Stefani et al 2013 the influence of the gender on
cerebral vascular diameters observed during the magnetic
resonance angiographic examination of Willis circle, in this they
have mentioned about the mean diameter of basilar artery is
2.9mm and the maximum diameter is 3.7mm and minimum is
2.1mm.
68
Anel Mehinovic et al 2014 worked on the variations in diameters
of vertebro-basilar tree in patients with or with no aneurysm in 60
consecutive adult patients of both sexes in Bosnian population, in
his study on the diameter of vertebral, posterior cerebral and
basilar artery. The basilar artery diameter ranged between 3.8mm
to3.43mm.
Maryna Alfaouri-Kornieieva et al 2014 worked on the
morphology of the vertebral artery in Asian population in 68
patients by MRA in Jordan. The V3 segment of vertebral has
lesser outer diameter than other ethnic groups. The right dominant
type of the vertebral artery is in the contribution of formation of
basilar artery is seen in 9% of Asian patients.
S.A.Gunnal et al 2014 on his work on the variations in the circle
of willis of 150 cadaveric human brain and in his work the diameter
of basilar artery minimum is 3mm and maximum is 6mm and mean
4.9mm SD0.06mm.
Alma Efendic et al 2014 studied the vascular geometry of
vertebrobasilar tree with and without aneurysm in 60 adult patients
using MRI and CTA. He divided the patients into two groups. One
group of 30 patients without aneurysm of vertebrobasilar tree, and
another 30 patients with aneurysm. In the patient without
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aneurysm the average angle at the junctions of vertebral artery
was 65.43° and the group of aneurysm the angle is 68.46°. The
average diameter of basilar artery in the caudal part (in the
vertebral artery joint area) is 3.8mm and the average diameter in
the rostral part (in the basilar artery bifurcation into posterior
cerebral artery) is 3.43mm. In the patients with aneurysm, the
average diameter at the caudal part is 5.08mm and in the rostral
part is 4.57mm.
Allen L. Ho et al 2014 studied the posterior cerebral artery angle
and the rupture of basilar tip aneurysms in 33 patients by CTA and
multivariate logistic regression proved that a larger angle between
the posterior cerebral arteries was most strongly associated with
aneurysm rupture
Fatilh Tutuncu et al 2014 studied the widening of basilar artery
bifurcation angle.
Zhang DP et al 2014 studied on the basilar artery bending length,
vascular risk factors, and pontine infarction, in this basilar artery
with a bending length greater than 3.77mm was an independent
predictor of pontine infarction.
70
Nurcan Uceyler et al 2014 worked on the increased arterial
diameters in the posterior cerebral circulation in men with Fabry
disease. In this the basilar artery diameter in male Fabry patients
is 3.5(2.7-4.4) and female Fabry patients is 3.1(2-5mm). In stroke
male patients is 3.2 (2.6-4.2mm) and in female is 3.2mm (.3-3.6),
in normal male patients is 2.9mm (2.3-5.5) and in female is 2.9mm
(1.2-3.6). It was done in 87 Fabry patients, 20 patients with stroke
and 36 normal patients using TOF MRA in Germany.
Shilpa Patel et al 2015 studied on the Morphometry of basilar
artery in Gujarat population in 60 adult human brains. In her
studies she has mentioned about the dimensions of basilar
arteries, variations in the level of formation of the basilar artery and
variations in the level of termination of basilar artery.
Can A 2015 studied on the effect of vascular anatomy on the
formation of basilar tip aneurysms, in this he correlated the
morphological parameters of basilar artery with the formation
basilar artery tip aneurysms. And he concluded that smaller basilar
artery diameters are associated with formation of basilar tip
aneurysm.
S. Gunnal et al 2015 studied the anatomical variability in the
termination of basilar artery in 170 human cadaveric brains in
71
Maharashtra. In his work he observed variations in the termination
of basilar artery as Bifurcation 82.39%, Trifurcation in 5.29%,
Quadrification in 5.88%, Pentafurcation in 3.52% and Nonfurcation
in 2.94%. The knowledge of variations in termination of basilar
artery are important in neurovascular procedures.
Witold Brudnicki 2015 studied the arteries of brain in Hare Lepus
europaeus. It was studied in 38 adult hares. The largest diameter
of the arteries of brain was observed in basilar artery.
Ronald A Bergman illustrated the basilar artery in his
encyclopedia of human anatomic variation.
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3. NEED FOR THE STUDY
Many works are done in the circulation of the brain,
especially anterior circulation, however, the studies on the
Vertebro-basilar circulation or Posterior circulation) are very few.
Basilar artery is the important artery which supplies the hind brain
and it is also subjected to aneurysms, it is a favoured site for
atherosclerotic changes, and occlusion leading to stroke. Hence,
the knowledge of basilar artery is mandatory in surgery,
radiography so that it can help us in better understanding. Many
studies are made on by imaging techniques MRA, TCD, and CTA,
these indirect methods have limited resolution and sometimes
makes distinguishing variations like hypoplasia from aplasia in an
arterial segment. Furthermore, the operator-dependant nature of
these methods may detract from the accuracy of the results
compared to the direct visualization. Only a few studies have
described the exact method of arterial measurement, and they
have mentioned the morphometry of the arteries but they failed to
explain the technique or instrument of measurement used. And the
studies on the Indian population are very few and the number of
specimens used in the previous studies ranges from 20 – 60
numbers of specimens which is not a sufficient number. And the
73
studies undertaken in Tamilnadu are not reported so far. So, we
have taken this study to ascertain the morphology in Tamilnadu
population.
74
4. OBJECTIVES
1. To find the formation of the basilar artery by the vertebral artery
2. To find the level of formation of the basilar artery in relation to the
Ponto-medullary junction (P-M junction)
3. To find the level of termination of the basilar artery in relation to
the Midbrain-pons junction (MB-P junction)
4. To find the length of basilar artery between the following points,
i) From the point of formation of basilar artery by the union of right
and left vertebral arteries
ii) To the termination where it divides into right and left posterior
cerebral arteries
5. To find the diameter of basilar artery at three different points:
i) At the point of formation
ii) At the midway
iii) At its termination
6. To find the angle of formation of basilar artery.
7. To find the variation in the course of basilar artery
75
5. METHODOLOGY
A) TOOLS:
Figure 10: Dissection Instruments
• Manual Goniometer,
• Digital Vernier caliper,
• Dissection forceps (pointed, tooth, blunt),
• Scalpel with blade
• Scissors long and short
• Bone saw
• and Magnifying Hand lens
• SPSS Software version 18.0
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5.1) Manual Goniometer:
A Goniometer is an angle measuring device. Goniometer is
derived from two Greek words, Gonia meaning angle, and metron
meaning measurement. It measures angles or gives an accurate
support to an object to be moved at a particular angle. It is widely
used in industries and various fields of science.
Figure 11: Manual Goniometer
.
77
5.2) Digital Vernier Caliper:
The French scientist Pierre Vernier invented the vernier
caliper was by It is used to measure length and diameter with
accuracy to hundredth of a millimeter. The caliper comprises of
two graduated scales, a primary scale which resembles a ruler and
a moment scale of the vernier, which slides parallel to the ruler
scale. Our study uses a digital vernier caliper (sensitivity –
0.01mm) which has an electronic display that displays the
diameter measurement in millimeters or inches (Fig 12).
Figure 12: Digital vernier calliper
78
B.METHODS TO BE USED: Dissection method
DISSECTION METHOD:
1.EMBALMING PROCEDURE:
Embalming is a method to preserve the dead bodies (cadaver) so
that it can be used for further anatomical studies. In modern day
embalming is usually done with formalin, salt, sodium citrate,
borax, rectified spirit, glycerine and thymol crystals dissolved in
water. The study was done on already embalmed cadaver.
REMOVAL OF BRAIN FROM CADAVER:
REMOVAL OF CALVARIA:
1. The cadaver should be in the supine position. Reflect the scalp
inferiorly.
2. Use the scalpel to detach the temporalis muscle from the calvaria
and reflect the temporalis muscle inferiorly, and reflect down over
the reflected scalp.
3. Observe the pericranium that covers the calvaria and use the
scalpel to scrape the bones of the calvaria clean of pericranium
and muscle fibers.
4. Mark a point 2cm above the superior orbital margin in front and
another point 2cm above the external occipital protuberance
79
behind. Connect these two points by a pencil line passing around
the skull. Use the saw to cut the outer table of the bone but not
completely through the bone along this line. Moist red bone
indicates that the saw is within the diploe. We should be careful
when cutting the squamous part of the temporal bone, which is
very thin. While sawing, turn the body alternately from supine to
prone and back to supine as we work around the skull. After
making a complete circumferential cut, break the inner lamina of
the calvaria by repeatedly inserting a chisel into the saw cut and
striking the chisel gently with a mallet. Continue this procedure
until the calvaria can be pried loose.
REMOVAL OF BRAIN:
5. Remove the calvaria of the skull from the duramater with the
handle of a forceps or a chisel blade. Work form anterior to
posterior and do not use more force than is necessary. Violent
pulling may result in tearing of the dura and damage to the brain.
Slit open the outer layer of dura in the midline longitudinally and in
the midline present the superior sagittal sinus. Make a incision
through the dura on either side of superior sagittal sinus and on
seeing the median dural fold extending between the two cerebral
hemisphere is the falx cerebri formed by the inner layer of
80
duramater. Cut the anterior attachment of the falx cerebri close to
the crista galli and pull it backwards. Make a coronal incision in the
duramater on both sides starting from above the ear and passing
towards the midpoint of the falx cerebri and the four triangular flaps
downwards.
6. Allow the head to hang over the edge of the table to facilitate the
removal of the brain. Pull the frontal lobes of the cerebral
hemispheres gently backwards from the anterior cranial fossa.
Identify and cut the following structures close to the brain.
1. Olfactory nerves from beneath the olfactory bulbs which lie on the
cribriform plate of the ethmoid bone on either side of crista galli.
2. Optic nerves close to the optic canals.
3. Internal carotid arteries immediately behind the optic nerves
4. Infundibulum of the pituitary gland near the centre of the
hypophyseal fossa.
5. Oculomotor nerves behind and lateral to the infundibulum
6. The slender trochlear nerves behind the oculomotor nerves.
Slowly pull the temporal lobes from the middle cranial fossa. Turn
the head to one side and cut the tentorium along its attached
border up to the internal occipital protuberance. Repeat this
procedure on the opposite side while supporting the overhanging
81
brain as otherwise it may be torn at the tentorial notch. And the cut
the following structures close to the brain –
1. Trigeminal nerves near the apices of the petrous part of the
temporal bones.
2. Abducent nerves behind and medial to the trigeminal nerves.
3. Facial and vestibulocochlear nerves near the internal acoustic
meatus
4. Glossopharyngeal, vagus and accessory nerves opposite the
jugular foramina.
5. Hypoglossal nerves close to the hypoglossal canal.
Slowly cut the two vertebral arteries at the level of foramen
magnum and also cut through the lower limit of brain stem. The
brain was then gently lifted out of the cranium. After removal of the
brain, it was washed in running tap water for 5 to 10 minutes and
the arachnoid and piamater close to the brain stem were carefully
removed, excess water is removed by using filter paper from the
arteries to facilitate the accurate measurements. The specimens
were duly numbered.
The morphology of basilar artery was studied in detail in each
specimen with reference to parameter mentioned.
82
Digital vernier caliper (sensitivity – 0.01mm) was used to
measure the length and diameter of the basilar artery and Manual
Goniometer used for measuring the angle of the formation of
basilar artery was mentioned by. Magnifying lens was used to
observe the vessels closely. Each specimen was photographed
using Nikon digital camera with different magnifications for better
clarity of the vessels was noticed.
D.SAMPLING METHOD USED:
Sampling method used in the study is Purposive sampling.
The study was conducted in 100 adult human brain specimens,
removed during routine dissection. The fifty specimens from the
Department of Anatomy of Vinayaka Mission’s Medical College,
Karaikal, thrity brain specimens from Aarupadai veedu Medical
College, Puducherry and twenty specimens from Dr.A.L.M. Post
graduate Institute of Basic Medical Sciences, Taramani, Chennai.
Male and female differentiation was not made since the numbers
of female specimens was less. The study was approved by
Scientific Review and Ethical Committee, Vinayaka Missions
Medical College, Karaikal.
83
E.STATISTICS USED:
Statistical significance was determined with help of Chi-square
test, One way Anova and Duncan Multiple Range test (DMRT)
using SPSS version 18.0.
84
6. RESULTS AND DISCUSSION
A wide range of variability with regard to length, origin,
termination and position of basilar arteries was seen in our study.
Variation in the basilar artery can be attributed to ageing and
haemodynamic factors, variations in branching pattern are mostly
congenital in origin with embryological explanations behind them.
Voljevia A et al 2005 Cerebrovascular disorders are one of the
leading ailments affecting the modern mankind with high incidence
of mortality rate and with high levels of disabilities among those
who survive cerebrovascular accidents.
Gernot Schulte et al 2000 on the visualization of the basilar artery
by Sonography in measuring the artery in case of abnormal course
of basilar artery. Sinous course of the basilar artery leads to
chances of losing Doppler signal at the point of change of direction
and the summation of segmental measurements have yielded in
an incorrect overall length measurement.
Can A et al 2015 mentioned that increase in posterior cerebral
angles and decrease in basilar artery diameter are closely
associated with the formation of basilar tip aneurysms
85
Nishikata M et al 2004 the basilar artery length mainly depends on
aging, and the presence of larger vertebral artery. While the
bending of basilar or curvature of artery depends upon the
dominance of vertebral artery in contralateral direction.
Formation of Basilar artery Percentage
Left VA larger than right
VA 35%
Right VA larger the Left VA 11%
Right VA equal to Left VA 50%
Right VA hypoplastic 2%
Left VA hypoplastic 1%
Left VA absent 1%
Table 1: Variation in the formation of basilar artery
86
FIG 13: APLASIA OF LEFT VERTEBRAL ARTERY
87
GRAPH 1: THE FORMATION OF BASILAR ARTERY
The bar diagram shows the formation of basilar artery, the
symmetrical vertebral artery is seen in 50% of our studies. And
larger left vertebral artery is seen in 35%.
Left VAlarger than
right VA
Right VAlarger the
Left VA
Right VAequal to Left
VA
Right VAhypoplastic Left VA
hypoplastic Left VAabsent
35%
11%
50%
2% 1% 1%
VARIATION IN THE FORMATION OF BASILAR ARTERY
Percentage
88
FIG 14: LEFT VERTEBRAL ARTERY DIVIDING INTO PICA AND VERTEBRAL ARTERY
89
Level of formation Percentage
Chi- square test P - value
At P-M junction 77%
85.940
<0.001** Above P-M junction 10%
Below P-M junction 13%
Note: ** denotes significant at 1% level
Table 2: Variation in the level of formation of the basilar artery
Level of formation of basilar artery by Stoppard 1916 and
A.M.Vare and Bansal the level of formation at the level of PM
junction is nearly 75% at the PM junction, Wojtowicz et al 1989
found the formation of basilar at the PM junction is 44.60% and
above the junction 15.10% and below 40.40%. Akar et al 1994 in
11 cadaveric specimens mentioned the formation of basilar at the
PM junction is 36.40%, above 53% and below the junction
35.50mm. Sabtos et al 2006 found the formation at the PM
Junction is 27.50% and above 37% and below the junction
35.50%.
90
FIG 15: LEVEL OF FORMATION ABOVE PM JUNCTION
91
LEVEL OF FORMATION OF BASILAR ARTERY
NAME YEAR
NUMBER OF SPECIMENS STUDIED
PM JN ABOVE BELOW
Stoppard 1916 150 73% 8% 19%
A.m. Vare et al 1970 175 79.4% 4.5% 16%
Songur et al 2008 110 20% 12% 67%
H. Mamatha et al 2012 20 65% 10% 25% Anjuman ara sultana et al 2012 70 72.2% 27.8% Nil
O.e. Idowu et al 2012 50 68% 22% 10%
Iqbal 2013 50 70% 44% 26%
Shilpa et al 2015 60 88.33% 6.67% 5%
Our study 2016 100 77% 10% 13%
TABLE 3: COMPARISON OF LEVEL OF FORMATION
Padmavathi et al 2011 studied the formation in 54 brain
specimens, the formation at the PM junction 44.40% and above
the junction 16.60% and below 38.80%. Mamatha.H et al 2012
found the formation at the PM junction is 65% and above 10% and
below the junction 25%. Anjuman et al 2012 mentioned the
formation of basilar at PM junction is 72.20% and above the
junction is 27.80%, below the junction the formation was not seen.
92
O.E.Idowu 2012 in African population the formation of basilar at
the PM junction is 68% and above 22% and below 10%. Pedro luis
et al 2013 mentioned the formation at PM junction in 43% of
cases, and above the junction 30% and below the junction 27%.
Iqbal 2013 found the formation of basilar in PM junction 70
percentage, above 44% and below the junction in 26%. And Shilpa
Patel et al 2015 studied the formation of basilar in Gujarat
population mentioned at the level of PM junction is seen 88.33%
and above 6.67% and below the junction in 5%.
93
GRAPH 2: THE LEVEL OF FORMATION OF BASILAR ARTERY
Level of formation in our study is 77%, Vare and Bansal is 79.4%
and and Stoppard is 73% at PM Junction. Below PM junction in
our study is 13% and in Stoppard 19% seen below PM Junction.
And above PM junction is 10% in our study and Stoppard 8% and
H.mamatha10%. Atheromatous lesions occur frequently in the
proximal basilar artery and distal vertebral artery.
Sylvia Kamath 1979 mentioned an idea of the normal dimensions
of these vessels may contribute significantly to a surgeon’s
assessment of the feasiblility of shut operations.
0%
10%
20%
30%
40%
50%
60%
70%
80%
At P-M junction Above P-Mjunction
Below P-Mjunction
LEVEL OF FORMATION
Percentage
94
Length of the basilar artery in cm
Number of
specimens
2.0 – 2.5 14
2.6-3.0 36
3.1-3.5 32
3.6-4.0 14
4.1-5.0 04
Table 4: Length of the basilar artery
95
FIG 16: LEVEL OF FORMATION –
BELOW PM JUNCTION
96
GRAPH NO: 3 LENGTH OF BASILAR ARTERY
The Pie-Chart showing the basilar artery, length in correlation with
the number of specimens. The average length of basilar artery in
our work is 30.98±5.06mm, range between 21-45mm. Adachi
studied in 83 cadaveric specimens in Japanese population found
the range between 25-30mm, Lang and Kollmannsbeger 1961
mentioned the length of basilar artery is 23-28mm in his studies,
and by Sylvia Kamath on her studies mentioned the range is 22-
45mm, in recent study by Padmavathi et al 2011 noted the range
between 25-38mm reported average length is 25-48mm,Saeki and
Rhoton 1977 studied on the 50 cadaveric brain ranged between
14
3632
144
Number of specimens
2.1 – 2.5
2.6-3.0
3.1-3.5
3.6-4.0
4.1-5.0
97
LENGTH OF BASILAR ARTERY
NAME YEAR METHOD OF STUDY
LENGTH OF BA
ADACHI 1928 CADAVERIC 25-30mm LANG & KOLLMANNSBEGER 1961 CADAVERIC 23-28mm
NOAKATSU SAEKI et al 1977 CADAVERIC 15-40mm
S.KAMATH 1979 CADAVERIC 22 -45.2mm
MANDIOLA et al 1995 CADAVERIC 24-45mm
GERNOT SCHULTE et al 2000 TCCS 25-57mm
BALAJI.S.PAI et al 2007 CADAVERIC 24-35mm
O.E.IDOWU et al 2010 CADAVERIC 25-40mm
PADMAVATHI et al 2011 CADAVERIC 25-38mm
H.MAMATHA et al 2012 CADAVERIC 25-37mm
SHILPA PATEL et al 2015 CADAVERIC 20-42mm
GUNNAL et al 2015 CADAVERIC 25-35mm
OUR STUDY 2016 CADAVERIC 21-45mm
TABLE 5 : COMPARISON OF LENGTH OF BASILAR ARTERY
15-40mm, Smoker.W et al 1986 studied the basilar artery in CT
the mean length is 28.1 ± 1.35mm, the range was between
15-40mm. Torche M et al 1992 studied on the 20 cadaveric brain
the length is 28.1 ± 1.35mm, Nishijima Y 1994 is 35 ± 5.1mm,
Mandiola et al 1995 the basilar length ranged between 24-45mm,
Balaji S.Pai et al 2007 studied the length in 35 brain specimens
98
which ranged between 24-35mm, Liu Huai Jun 2010 in 108
patients by MRA is 23.5 ±3.0mm, O.E.Idowu et al 2010 in 50
specimens the length of basilar is 31.41±3.82mm, Iqbal 2013 in 50
brain specimens the length ranged from 18-37 mm, Pedro Luis et
al 2013 studied in Brazilian population of 100 autopsy brain
specimens the length is 30.2mm, Shilpa Patel et al 2015 et al
studied the length of basilar in 60 Gujarat specimens it is ranged
from 20.2 to 42.02mm and average length is 27.76mm. Gunnal S
et al 2014 in his study mentioned the length ranged between 24.6
– 35mm, and the mean length of basilar is 30.27±3.5mm.
Morels-Vidal S et al 2012 specified the basilar artery is a favoured
site for atherosclerotic changes among the intracranial vessels,
and the clinical picture of the basilar artery in the occlusive
diseases vary according to the site and nature of the vascular
occlusion. The impediment of the proximal and middle segments of
the basilar artery results in unilateral or bilateral pontine
dysfunction, whereas distal occlusion produces signs of midbrain
and thalamic ischemia.
99
Table 6: One way ANOVA for significant difference among
level of formation with respect to the length of basilar artery
Since P-value is greater than 0.05, there is no significant
difference among the level formation with respect to length of
basilar artery
Level of formation
Length of basilar artery
F value
P value Mean(mm) SD
At PM junction
30.36
5.18
2.845
0.063
Above PM junction
33.20 5.63
Below PM junction
33.62 6.69
100
Alma Efendic et al 2014 the anatomical variations in the angle of
formation of basilar artery, the angle of bifurcation, and the calibre
of the basilar are some of the elements for the rise of the incidence
of aneurysm in this anatomic area.
Level of formation
Angle of formation
F value
P value Mean SD
At PM junction 63.25 13.00
0.143
0.867
Above PM junction 65.50 13.63
Below PM junction 63.85 10.03
Table 7: One way ANOVA for significant difference among
level of formation with respect to the angle of formation of
basilar artery
101
ANGLE OF FORMATION
NAME ANGLE OF
FORMATION
CLARKE et al 70°-90°
PADMAVATHI et al 50°-90°
MAMATHA et al 45°-70°
OUR STUDY 55°-75°
TABLE 8: Comparison of Angle of Formation of Basilar Artery
Angle of formation in our study ranged between 55° to 75°
and by Padmavathi et al 2011 ranged between 50°-90°, H.
Mamatha et al 2012 is between 45° to 70° ,the ideal angle is 60°-
75°. The length and angle of formation of basilar artery can be
assumed to determine the rate of flow of blood and its
haemodynamic effect can cause weakness in the wall of the
vessel.
102
Diameter in mm Maximum Minimum Mean ±
At Origin 4.00mm 3.00mm 3.65
At Mid level 3.90mm 3.00mm 3.51
At Termination 3.80mm 3.00mm 3.45
Table 9: Diameter of basilar artery
Akimoto et al 1979 examined 130 vertebral angiogram, in which he
noted the diameter of basilar artery being 3.5±0.7mm. Sylvia
Kamath 1979 studied the basilar artery in 97 brain specimens the
diameter ranged between 1.9 to 6.0mm. Smoker W et al 1986 in
126 CT found the diameter 3.17mm. Wojtowicz et al 1989 in his
cadaveric approach mentioned the diameter 4mm. Nishijima et al
1994 studied in 52 Japanese specimens the mean diameter
3.14±0.58mm. Krabbe harkamp et al 1998 noticed the diameter
3mm in 150 MRA patients. Balaji.S.Pai et al 2007 mentioned the
basilar diameter ranged between 3 to 7mm. Hong JM et al 2009 in
103
91 CT the diameter is 3.17mm.O.E.Idowu et al 2010 the diameter
of basilar 3.82mm. Dodeviski.A et al 2011 in 50 CTA noticed the
diameter 2.70-4.28mm. Mohamed Adbelaziz et al 2011 studied the
basilar diameter in 3.06mm in 25- MRA in his studies on circle of
Willis in Egyptian population.
104
DIAMETER OF BASILAR ARTERY
NAME YEAR METHOD
OF STUDY DIAMETER OF BA
AKIMOTO 1979 X-RAY 3.5±0.7mm
S.KAMATH 1979 CADAVERIC 1.9-6.0mm
SMOKER 1986 CT 3.17mm
WOJTOWICZ 1989 CADAVERIC 4mm
NISHIJIMA 1994 CADAVERIC 3.14±0.58 KRABBE HARTKAMP 1998 MRA 3mm
BALAJI.S.PAI 2007 CADAVERIC 3-7mm
JM HONG 2009 CT 3.17mm
LIU HUAI JUN 2010 MRA 2.6±0.5mm
O.E.IDOWU 2010 CADAVERIC 3.82mm
DODEVISKI.A 2011 CTA 2.70-4.28mm M.ADBELAZIZ 2011 MRA 3.06mm
H.MAMATHA 2012 CADAVERIC 2.6-3.5mm
DENG 2012 MRI 2.2-4.2mm
IQBAL 2013 CADAVERIC 2.8-5.1mm MARCO ANTONIA STEFANI 2013 MRA 2.1 -3.7mm ANEL MEHINOVIC 2014 MRA 3.8-3.43mm
GUNNAL SA 2014 CADAVERIC 3 - 6mm ALMA EFENDIC 2014 MRA&CTA 3.8mm
SHILPA PATEL 2015 CADAVERIC 3.36mm
TABLE 10: COMPARISON OF DIAMETER OF BASILAR ARTERY
105
Mamatha.H et al 2012 in 20 cadaveric specimens found the
diameter ranged between 2.6-3.5mm. Deng et al 2012 mentioned
its range between 2.2-3.7mm in 200 MRI patients. Iqbal 2013 the
diameter ranged from 2.8 to 5.1mm. Marco Antonia Stefani et al
2013 in 30 MRA patients slated the diameter between 2.1-3-7mm.
Anel mehinovic et al 2014 in 60 MRA patients is 3.8 – 3.43mm.
Gunnal et al 2014 mentioned the basilar diameter ranged 3-6mm.
Alma Efendic et al 2014 noticed the diameter in 60 patients using
MRI and CTA is 3.8mm and Shilpa Patel et al 2015 in 60 cadaveric
Gujarat population the diameter ranged 2.02 -4.45mm and the
average 3.36mm.
Diameter of basilar artery at its origin was not quoted in the
previous study, in the present study it is mean 3.65mm, diameter
at mid level is 3.51mm, and in Smoker et al midlevel diameter is
3.17mm. The diameter at the level of termination in our study
3.45mm and in Saeki and Rhoton at termination is 4.1mm. The
data on the length and diameter of basilar artery is very important
for interventional radiologist to perform various endovascular
procedures and the neurosurgeon to perform a safer approach for
the surgery.
106
GRAPH 4: DIAMETER OF THE BASILAR ARTERY
Fischer CM et al 1965 demonstrated the hypoplastic
narrowing is additionally significance since atherosclerotic malady
may likewise show up at a prior age if the parent vessel is
hypoplastic and would get to be distinctly stenosed sooner than a
bigger vessel. Deng D et al 2012 slated that there is a significant
gender differences in noted in the diameter of both the vertebral
and basilar artery, demonstrasting that male and female difference
needs to be considered in the diagnosis of vertebrobasilar
Dolichoectasia in the Chinese population.
3.3
3.4
3.5
3.6
3.7
3.00mm 3.00mm 3.00mm
4.00mm 3.90mm 3.80mm
At Origin At Mid level At Termination
DIAMETER AT DIFFERENT LEVELS
Mean ±
107
Note: ** denotes significant at 1% level
Table 11: Variation in the level of termination of basilar artery
Stoppard 1916 in his studies the termination of basilar artery at the
Midbrain-pons junction is seen in 97.5% and below the junction in
2.5%. O.E. Idowu noted the termination at the MB-P junction at
98% and below in 2% and above junction no case was reported.
Padmavathi 2011 in her studies found the termination at MB-
P junction at 44.4%, above the junction 29.6% and below the
junction in 25.9%. Shilpa Patel 2015 mentioned the normal
termination i.e. MB-P junction in 99% of cases and above the
junction in 2% of cases and below the junction in 1% of cases.
Saeki and Rhoton noted the termination of basilar in 88%. Iqbal
2013 found the termination at MB-P junction in 64% and above the
junction in 4% and below the junction in 32%.Termination at MB-P
Level of termination Percentage
Chi-quare test P -value
At MB-P junction 85%
106.82
<0.001** Above MB- P junction 10%
Below MB- P junction 05%
108
Junction in our study is 82% and is 88% by Rand et al and 92% by
Smoker et al 1986. And above the junction is 11% and below is
7% in our study.
GRAPH 5: BASILAR ARTERY AT DIFFERENT LEVELS OF
TERMINATION
0%10%20%30%40%50%60%70%80%90%
At MB-P junction Above MB- Pjunction
Below MB- Pjunction
LEVEL OF TERMINATION
Percentage
109
TABLE 12: COMPARISON OF LEVEL OF TERMINATION
Basilar artery seems to show manifestation of arterial disease
much more frequently than the other arteries. The termination site
of basilar artery is one of the basic areas where the occurrence of
aneurysm takes place. Padmavathi et al 2011 in her studies
reviewed the surgical significance at the point of termination of the
basilar artery which helps us to determine the type of approach to
be made to the treatment of basilar tip aneurysms transylvian
pterion approach, and in order to minimise or prevent the injuries
to their nearby structures like the mamillary body, optic chiasma.
The position of formation and termination of basilar artery have
implications for the pathogenesis of occlusive disorder, forms the
site for initiations of aneurysm and its progress into giant aneurysm
LEVEL OF TERMINATION OF BASILAR ARTERY
NAME YEAR SPECIMENS STUDIED
MB-P JN
ABOVE BELOW
STOPPARD 1916 150 98% NIL 3% PADMAVATHI et al 2011 54 44.40% 29.60% 26% H. MAMATHA et al 2012 20 70% 5% 25% O.E. IDOWU et al 2012 50 98% 22% 10% IQBAL 2013 50 64% 4% 32% SHILPA et al 2015 60 99% 2% 1% OUR STUDY 2016 100 77% 10% 13%
110
Level of formation
Diameter at origin
Diameter at mid level
Diameter at
termination
Mean SD Mean SD Mean SD
At PM junction 3.61a 0.23 3.49 0.21 3.44 0.20
Above PM junction 3.85b 0.20 3.61 0.17 3.50 0.21
Below PM junction 3.74ab 0.24 3.59 0.18 3.54 0.19
F value 5.940 2.632 1.544
P value 0.004** 0.077 0.219
Note: 1. ** denotes significance at 1% level
2. Different alphabet among level of formation denotes significance at 5% level using Duncan Multiple Range Test (DMRT)
Table 13 : DMRT for significance difference among the level
of formation with respect to the diameter of basilar artery
111
Variation in the basilar artery
Percentage Chi- square test P -value
Normal or straight
77%
87.20
<0.001** Bent right side 16%
Bent left side 07%
Note: * denotes significant at 1% level
Table 14: Variation in the course of basilar artery
Pedro Luis et al 2013 noted the variation of course of basilar
artery it was straight in 68% and deviated to the right in 12% and
deviated to the left in 10% and sinous in 10% of the cases.
Wojotowicz et al 1989 mentioned the rectilinear course in 78.7%
and bulged on right or left in 20.5% and S type in 0.8%, in his work
he didn’t mention about the deviation of basilar right and left
separately. O.E.Idowu et al 2010 found the course of basilar artery
running straight in 60% and convex to the right in 18% and convex
to the left in 18% and S type in 4% of cases.
112
FIG 17: CURVATURE OF BASILAR ARTERY ON RIGHT SIDE
113
GRAPH 6: VARIATION IN THE COURSE OF BASILAR ARTERY
Zhang DP et al 2014 patient exhibiting basilar artery curvature not
dolichoectasia are at increased risk of posterior circulation
ischemic stroke. Both basilar bending length and diameter
differences between the vertebral arteries are positively correlated
with the risk of pontine infarction. And when basilar artery bending
was linked with other vascular risk factors, the probability of
pontine infarction increased. Basilar artery bending with basilar
0%10%20%30%40%50%60%70%80%
NORMAL OR STRAIGHT
BENT RIGHT SIDE
BENT LEFT SIDE
COURSE OF BASILAR ARTERY
Percentage
114
artery bending length greater than 3.77mm was an independent
predictor of pontine infarction.
FIG 18: CURVATURE OF BASILAR ARTERY TO THE
LEFT SIDE
Wendy R.K.Smoker et al 1986 Dolichoectasia in Greek Dolichos
means elongation and in Greek ectasia means distension was first
described by Morgagni in 1971, is a perceived clinical and
pathologic entity. Ectasia is analyzed if the diameter across of
basilar supply route is more noteworthy than 4.5mm. Patients with
elongated and convoluted, yet b\normal sized basilar conduits
115
have a tendency to have confined cranial nerve association,
whereas patients with ectasia of the basilar artery are far more
likely to suffer from multiple neurologic deficits. Conventional
angiography poses an increased risk of complications in patients
with severe VBD. And if vascular studies are necessary,
intravenous DSA or nonselective intrarterial DSA examinations
should be done.
Keele and Neil in 1971 mentioned that the volume of blood flow
through a vessel is inversely related to the length of the vessel and
directly related to its diameter that is fourth power to its radius.
Sylvia Kamath 1979 mentioned that the blood flow through shorter
and wider vessels is more efficient. From our study the smaller
diameter in the right part of the vertebral artery is seen then the left
vertebral artery as result a better blood supply. This is in keeping
with dominance of the left hemisphere and the commoner
occurrence of right handedness (Warwick and Williams, 1973)
116
FIG 19: STRAIGHT COURSE OF BASILAR
O.E.Idowu et al 2010 the endoscopic endonasal approach to the
skull base is a technique, which has established itself in the recent
years, and it demands a thorough knowledge of the surgical
anatomy and variations of the skull base vessels during surgery for
sellar and suprasellar tumours, cerebelllopontine angle tumours
and vertebrobasilar vascular malformations.
117
Chaturvedi et al 1999 suggested that the hypoplastic basilar artery
might be a predisposing factor for ischemic stroke in 49.8% of
cases he has examined.
Fischer CM et al 1965 demonstrated the hypoplastic narrowing is
also importance since atherosclerotic disease may also appear at
an earlier age if the native vessel is hypoplastic and would become
stenosed sooner than a larger vessel.
Fernanado Gonzales.L et al 2005 the posterior fossa aneurysms
are challenging lesions that demand ability in vascular and skull
base surgery for their treatment. The preference of reach depends
on the particular components of every aneurysm. Numerous
directions and edges of reach are accessible and ought to be
custom-made on a case-by-case basis. The favoured strategy is to
work with an edge that runs parallel to the parent vessel that is
orbitozygomatic and far sidelong methodologies. The transpetrosal
and retorosigmoid methodologies are constrained to appoint
cases.
The customary standards of skull base surgery as far as amplifying
bone resection to minimize brain withdrawal and to encourage
instrument manipulation registerly. In aneurysm surgery, a
definitive objective is to clip the aneurysm and to prohibit it from
118
the flow. It these objectives can't be accomplished, the aneurysm
can be trapped or the blood flow changed. It is critical to recognize
preoperatively whether revascularizaton is shown.
Hypothermic cardiac arrest encourages dismemberment of an
aneurysm from perforating arteries. The aneurysm is collapsed
and transmural pressure is insignificant. The strategy takes out the
hazard of rupture and the hypothermia instigated with barbiturate
treatment protects the brain. All things considered, this intricate
mean is connected with high mortality and morbidity rates and
ought to be held for chose patients treated just specialized centres.
Atherosclerosis is an unending, inflammatory, fibroproliferative
systemic malady basically of bigger and medium measured
conduits. Atherosclerotic plaques have a tendency to create in
central locales with confused stream designs, or with low or
oscillatory divider shear worry as in areas, for example,
bifurcations, curves and intersections.
Hong J M et al 2009 found that pontine infarcts all the more much
of the time happened inverse to the side of basilar artery bending
and PICA infarcts were more regular on the non-predominant
vertebral artery side, and that the distinction in the diameter of the
119
right verterbal and left VA was the main autonomous indicator for
direct to serious BA curvature.
FIG 20: DOLICHOECTASIA
120
In his review proposed that the uneven blood stream pattern of
VAs around the vertebrobasilar intersection may be a basic
mechanical forece in the source of BA curvature and flow and
additionally a causative part of peri-vertebrobasilar junctional
infarcts. It is likewise found that pontine infacrction tended to the
opposite side to the horizontal uprooting of the BA. What's more,
the bend of the BA was directionally inverse to the predominant
VA.
Such directional connections can be clarified by a few
haemodynamic systems. Firstly, Cunningham KS et al 2005 and
Hademenes GJ et al 1997 clarified that the internal wall of the BA
curvature and flow might be more thrombogenic in light of a low
divider shear stress and Passero SG et al 2008 said the traction of
the pontine perforators created by basilar course bend may prompt
to infarction. Also, a hypoplastic VA can bring about ipsilateral
PICA localized necrosis by directly diminishing blood stream in the
minimal intracaranial VA. Binns RL et al 1989 specified this can
happen in light of this simple collapsibility of a limited vessel as
aftereffect of Bernoulli's impact under the diminished VA rebuilding
limit. Hong JM et al 2009 clarified in this hypothesis that the vector
of basilar blood stream converging from unequal VAs makes the
121
BA stream bend to the side of the weaker VA and the chronic
process brought about by deviated VA stream can instigate more
prominent bending of the BA
divider. Along these lines, such twisting of the basilar supply route
can bring about atherogenesis, prompting to ischaemic stroke in
the vertebrobasilar framework. A hypoplastic vertebral can
likewise bring about the ipsilateral impediment of this vessel
because of direct diminishing in blood stream and simple collapse
of the vessel brought on by the smaller intracranial vertebral
diameter.
The diameter difference across the vertebral was the
independent indicator for the direct to sinous basilar course
dolichosis, even in the wake of changing for perplexing factors
including socioeconomics, radiological factors and haemodynamic
factors. By and large, the blood flow is relative to the fourth power
of radius of the artery indicated by Poiseuille's law. Thus the radius
of the vessel is the most basic determinant of blood flow, even in
the vertebrobasilar framework. Koller et al 2006 expressed that the
pressure, blood flow or both variables are generally perceived as
potential jolts for morphological changes or the functional
adjustment of vessels. Different reviews have inspected blood flow
122
dependent models and if such haemodynamic powers are
adjusted incessantly, an ensuing morphological or strructural
modifications of the supply route can occur to minimize the effect
of the modified haemodynamic pressure on the vascular wall,
consolidating changes in diameter and thickness.
It is the curvature of basilar conduit was fundamentally because of
unequal blood flow of right and left vertebral supply route which
plays a critical haemodynamic factor in deciding the bending and
flow of basilar artery and because of traction of pontine branches it
can prompts to advancement of intense infarcts in the
vertebrobasilar course The stream of blood in basilar artery
because of unequal size of vertebral conduit in the incessant
process can initiate bending and flow in basilar wall of artery,
which can prompt to atherogenesis prompting to ischaemic stroke
in the vertebrobasilar framework. The bending of basilar artery was
directionally inverse to prevailing vertebral supply route
Muhl-Benninghaus et al 2015 specified about the utilization of
intermediate catheters altogether lessens the length of mechanical
thrombectomy systems in intense basilar course impediments.
Surgical access to the vertebrobasilar intersection is exceedingly
troublesome, and it is unpredictable on account of its relationship
123
with lower cranial nerves and perforators to the stem of the brain.
Along these lines, endovascular treatment of aneurysms in the
basilar supply route is treated with detachable coils which are
broadly acknowledged.
124
7. CONCLUSION
Stroke due to basilar artery comprises approximately 10 to
15% of all stroke, and more common in man than woman.
Morphological aspects of the basilar artery in the local region
were highlighted in this cadaveric study. Variations in the
morphology of the basilar artery are common. Detailed knowledge
of the course of the basilar artery would help neurosurgeons,
interventional Neuroradiologist, to safely diagnose, as well as plan
and execute vascular bypass and shunting procedures for the
treatment of Stenosis, aneurysms and neuralgia.
125
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LIST OF PUBLICATIONS
1. The Formation of basilar artery and its significance. Scholars
Journal of Applied Medical Sciences, 2016; 4(4B):1237-
1239. (First author)
2. Morphometric analysis of basilar artery in Karaikal
population. Scholars Journal of Applied Medical Sciences,
2016; 4(7E):2596-2599.(First author)
3. . A Study of variation in termination of Short Saphenous vein.
Journal of evidence based medicine and health care 2016,
3(40):2010. (Second author).
4. A Study on Morphometry of articular cartilage of Talocrural
joint. Journal of evidence based medicine and health care
2016, 3(33):1594. (Third author)
