Brain CT Anatomy and Basic Interpretation Part II

DR SAKHER AL-KHADERI CONSULTANT RADIOLOGIST

AMC

BRAIN CT ANATOMY AND BASIC INTERPRETATION PART II

VENTRICLES

OBJECTIVES

Illustrate and describe the ventricles.

Describe the structure of the ventricles.

Illustrate and describe the cerebrospinal fluid (CSF) formation, absorption and circulation.

VENTRICLES(Ventricular System) A ventricle is an

internal cavity of the brain. Within the brain, which is filled with cerebrospinal fluid(CSF).

The ventricular system is composed of two lateral ventricles and two midline ventricles( third and fourth ventricles).

VENTRICLES(Ventricular System) The chambers are

connected to allow the flow of cerebrospinal fluid via two interventricular foramen (referred to as the foramen of Monro) and the cerebral aqueduct (referred to as the aqueduct of Sylvius).

Lateral view to show the ventricular system of the CNS

Central canal of medulla oblongata & spinal cord

Fourth ventricle

Lateral ventricle

Third ventricle

Interventricular foramen (Monro)

Cerebral aqueduct

VENTRICLES(Ventricular System)

CONSISTS OF :1) Lateral ventricle2) Third ventricle3) Fourth ventricle 4) Central canal of

the medulla oblongata & spinal cord

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Lateral Ventricles

The lateral ventricles are two curved shaped cavities located within the cerebrum.

The lateral ventricles are separated by the septum pellucidum and do not communicate directly

Lateral ventricle

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

C-shaped cavity & may be divided into :

2. Anterior horn

1. Body

3. Posterior horn

4. Inferior horn

Third ventricle

Fourth ventricle

Lateral view of the ventricular cavities of the brain

Lateral ventricle

Anterior horn

Inferior horn

Posterior horn

Lateral view to show the ventricular system of the CNS

The third ventricle is a narrow cavity or a slitlike cleft between the 2 thalamus Communicates ;

• Anteriorly with lateral ventricles through interventricular foramina (of monro)

• Posteriorly with fourth ventricle through cerebral aqueduct (of sylvius)

Posterior view to show the ventricular system of the CNS

Third ventricle

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

Third ventricle

Third ventricle

Hypothalamus

Coronal section of the brain (posterior view)

Third ventricle

Thalamus

ROOF

FLOOR

Lateral wall

Body of fornix

Fourth ventricle The fourth ventricle Is

a rhomboid or diamond shaped cavity.

It is a wide and flattened space located just anterior to the cerebellum and posterior to the upper, or superior, half of the medulla oblongata and the pons.

Cerebellum

Pons

Medulla oblongata (superior half)

Sagittal section of the 4th ventricle

Cerebral aqueduct

Central canal (spinal cord)

Fourth ventricle

Fourth ventricle

ANTERIORPOSTERIOR

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

Fourth ventricle

Pons

Medulla oblongata (superior half)

Fig. : Sagittal section of the 4th ventricle

Cerebral aqueduct

ANTERIOR

POSTERIOR

Superior part of the roof ;Superior medullary

velum

Inferior part of the roof ;

Inferior medullary velum

Roof or posterior wall of fourth ventricle :

CENTRAL CANAL

Opens superiorly into the fourth ventricle

Fourth ventricle

Inferior ½ of medulla oblongata

Entire length of spinal cord

Central canal(Lined with

ependyma but no choroid plexus in the central canal)

Extends ;

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

CENTRAL CANAL

Conus medullaris-Terminal ventricle

CEREBROSPINAL FLUID

CHOROID PLEXUS

It is formed by invaginating of vascular pia mater into the ventricular cavity

It becomes highly convoluted & produce a spongy-like appearance

It enters the 3rd and 4th ventricles through their roofs, and the lateral ventricles through the choroid fissure

produces cerebrospinal fluid (CSF)

Lateral ventricle

Third ventricle

Fourthventricle

What is cerebrospinal fluid (CSF) ?• Clear, colorless fluid• Produced by the choroid plexus • Found in the :

Ventricles of the brain Subarachnoid space (between Arachnoid + Pia mater) around the

brain & spinal cord

The pressure of the CSF is kept remarkably constant.

Based on the Monro-Kellie doctrine : “Volume of BLOOD, CSF & BRAIN at any time

must be relatively constant”

Physical characteristics and composition of the CSF

Appearance Clear and colourlessVolume 130 mlRate of production 0.5 ml/minPressure 60-150 mm of waterComposition protein 15-45 mg/100 ml glucose 50-85 mg/ 100 ml chloride 720-750 mg/100 mlNo. of cells 0-3 lymphocytes/cu mm

Function of the CSF :

1. Cushions & protects the CNS from trauma2. Provides mechanical buoyancy & support for

the brain3. Serves as a reservoir & assists in the

regulation of the contents of the skull4. Nourishes the CNS5. Removes metabolites from the CNS6. Serves as a pathway for pineal secretions to

reach the pituitary gland

Sites of formation :1. Choroid plexus of the ventricle cavities,

mostly is formed in the LATERAL VENTRICLES 2. Some originate from the ependymal cells

lining the ventricles3. Some from the brain substances through

perivascular spaces

Movement of CSF inside the ventricle is controlled by the:1. Pulsation of the artery in the choroid plexus2. By the aid of the cilia & microvilli of the

ependymal cells

cerebrospinal fluid (CSF) The CSF is formed in the

lateral ventricles escapes by the foramen of monro into the third ventricle

From the third ventricle by the aqueduct into the fourth ventricle.

Then from the fourth ventricle the fluid is poured into the subarachnoid spaces through the medial foramen of majendie and the two lateral foramina of luschka.

There is no evidence that functional communications between the cerebral ventricles and the subarachnoid spaces exist in any region except from the fourth ventricle.

Choroid plexus of the lateral ventricle

Site of formation

1. Lateral ventricle

2. Third ventricle

Interventricular foramina

3. Fourth ventricle

Cerebral aqueduct

3.2 Lateral foramina (Luschka)3.1 Median

foramen (Magendie)

3.2 Lateral foramina (Luschka)

4. Subarachnoid space

Inferiorly

Superiorly

Absorbed

Superiorly

Absorbed

Median sagittal section to show the subarachnoid cisterns & circulation of CSF

Superior cistern

Interpeduncular cistern

Cerebellomedullary cistern

Chiasmatic cistern

Pontine cistern

Circulation of CSF in subarachnoid space :

Median foramen of 4th ventricle

Factors that facilitate the flow of CSF in subarachnoid space ;

1. Pulsation of the cerebral & spinal arteries2. Movements of the vertebral column3. Respiration & coughing4. Changing of the positions

Absorption of CSF into dural venous sinuses Main sites - arachnoid villi

(project into dural venous sinuses, especially, superior sagittal sinus)

Arachnoid villi are covered by endothelium of the venous sinus

Arachnoid villi tend to be grouped together & form elevations known as arachnoid granulations

CSF pressure >> the pressure in the sinus

The rate of absorption of CSF through the arachnoid villi controls the CSF pressure

BLOOD SUPPLY OF THE BRAIN

OBJECTIVES

Illustrate and describe the formation of the circle of willis

Describe the blood supply of the brain

Arterial supply Venous drainage

Blood Supply of The Brain The brain receives

it arterial supply from two pairs of vessels, the vertebral and internal carotid arteries which are interconnected in the cranial cavity to produce an arterial circle (of Willis).

Internal carotid artery

Internal Carotid Artery Begins – bifurcation of Com Carotid A Perforates base of skull – carotid canal Enters middle cranial fossa beside dorsum sellae In the cavernous sinus

Horizontal Emerge out – medial side of Ant clinoid process –

perforates dura & arachnoid mater – enters subarachnoid space

Turns posteriorly – below optic nerve Turns upward – lateral to optic chiasma Now is under anterior perforated susbtance Divides – into ANTERIOR & MIDDLE cerebral

arteries

Vertebral Artery Branch of first part of subclavian A Passes – foramen transvesarium C6 –

C1 Enters through foramen magnum –

perforates dura & arachnoid mater – enters subarachnoid space

Turns upward, forward, medially – medulla oblongata

Lower border of pons – joins opposite side BASILAR artery

Blood Supply of The Brain

VERTEBRAL Basilar Posterior cerebral

artery

INTERNAL CAROTID Middle cerebral Anterior cerebral Anterior

communicating artery

Posterior communicating artery

CIRCLE OF WILLIS

Branches of :-

VERTEBRAL Basilar PCA Pontine Labyrinthine Ant Inf CA Sup cerebellar Choroidal

INTERNAL CAROTID ACA MCA Ophthalmic Ant ComA Post Com A Choroidal

Circle of Willis

Interpeduncular fossa – base of brain

Anastomosis 2 internal carotid

arteries 2 vertebral arteries

In the subarachnoid space

Vertebral arteries

Basilar APosterior cerebral artery

Posterior communicating artery

Internal carotidartery

Middle cerebral artery

Anterior cerebral artery

Anterior communicating artery

Post Inf cerebellar A

Sup cerebellar A

Ant Inf cerebellar A

Middle cerebral artery

Anterior cerebral artery

Posterior cerebral artery

MIDDLE CEREBRAL ARTERYLOBE AREA

FRONTAL Motor – except for paracentral lobuleMotor speech – esp left side

PARIETAL Sensory – except for paracentral lobuleSensory speech

TEMPORAL Auditory

POSTERIOR CEREBRAL ARTERYLOBE AREA

OCCIPITAL Visual

TEMPORAL Olfactory

ARTERIES to specific brain areas

Corpus striatum Middle & lateral striate

Anterior & Middle cerebral arteryInternal capsule

Thalamus PComA, basilar, PCAMidbrain PCA, supCerebellarA, basilarPons Basilar, Ant, inf, supCerebellarA,Medulla oblongata

Vertebral, ASA,PSA,PICA, basilar

Cerebellum supCerebellar, AICA,PICA

VEIN of specific areasMidbrain Basal, great cerebral

Pons Basal, cerebellar

Medulla oblongata Anterior & posterior spinal

Cerebellum Great cerebral

Superior sagittal sinus

Inferior sagittal sinus

Straight sinus

Superior cerebral vein

Medial aspect of hemisphere

Great cerebral vein

Transverse sinus (R & L)

Sigmoid sinus (R & L)

Confluence of sinus

IntJugular vein

IntJugular vein

Cavernous sinus

Middle cerebral vein

Inferior petrosal sinus

Superior petrosal sinus

The subarachnoid cisterns are areas within the subarachnoid space where the pia mater and arachnoid membrane are not in close approximation. The subarachnoid tissue is not as abundant here as in the normal subarachnoid space and cerebrospinal fluid (CSF) gathers to form pools or cisterns (Latin: "box").Some major subarachnoid cisterns:cisterna magna (cerebellomedullary cistern): the largest of the subarachnoid cisternspontine cisternsuprasellar cisterninterpeduncular cisternquadrigeminal cistern (superior cistern or cistern of the great cerebral vein)ambient cistern

Sulcus : A sulcus is depression or fissure in the surface of the brain. ( valleys )

Gyrus : A gyrus is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci ( hills )

Typical continous fissure

Interhemispheric fissureSylvian fissure ( lateral sulcus )Parieto-occipital fissure Collateral sulcusCentral sulcusCalcarine Sulcus

Interhemispheric fissureDeep sulcus

upto corpus collosum

Divides brain into two hemisphere

Sylvian fissure

deep, mostly horizontal

insula is buried within it

separates temporal lobe from parietal and frontal lobes

Parieto - occipital fissure

very deepoften Y-shaped

from sagittal view

X-shaped in horizontal and coronal views

Collateral sulcus

Divides lingual and parahippocampal gyri from fusiform gyrus.

Central sulcus

usually freestanding (no intersections)

Seperates frontal and parietal lobe.

Calcarine sulcus

Lobes of brain

Frontal lobe.Parietal lobe.Temporal lobe.Occipital lobe.

Limbic lobe.Insular lobe.

• Frontal lobe:Anterior region of hemisphere; anterior to central sulcus, superior to sylvian fissure• Parietal lobe: Posterior region of hemisphere; posterior to central sulcus, anterior to parietooccipital sulcus• Occipital lobe: Posterior to parietooccipital sulcus• Temporal lobe: Inferior to sylvian fissure, anterior to angular gyrus

Lateral surface of brain

Medial surface of brain

Basal surface of brain

THE END