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8/18/2019 Front Foramina in Hydroceph
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8/18/2019 Front Foramina in Hydroceph
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Findings at C T in Infants and C hildren with Hydrocephalus ii 99 )
N o. w ith F inding N o. w ith Fronta l
Finding at CT (H = 99 ) Foramina n = 10 )
Achondroplasia 1 0A quedu ctal stenosis 1 0A rachnoid cysts 2 0O ccip ital horn dilatation (cotpocephaly) 1 1Cerebral palsy 2 0Chian II m alform ation 61 8Cran iosynostosis 1 0D iastem atom yelia , syningom yelia 1 1D an dy W alk er m alfo rm ation 1 0Encephatocele 2 0Ischem ic insu lt 2 0
M eningitis 2 0M yelom eningocete 3 0Prim itive neuroectoderm at tum or 2 0S chizencephaly 1 0
V AC TERL* association I 0
H ydrocephalus, origin unknow n 15 0
-
Figure 2. A xial head CT scan of the sam epatient as in Figure 1 d epicts frontal fo -ram ina w ithout soft-tissue m ass or extra-axialfluid collection. Typical features of Chiani IIm alform ation are seen.
* VACTERL = vertebral, anal, cardiac, tracheo-esophageal, renal, and lim b (acronym to desc
tern o f a ss oc ia te d c on gen ita l a no malie s) .
3. 4.
Figures 3, 4 . (3) Three-dim ensional reconstruction of the skull show s frontal fonam isam e patient as in F igures 1 and 2. (4) In a 22-m onth-old fem ale infant w ith Chiani II m
m ation, three-dim ensional reconstruction of the skull show s fronta l foram ina.
49 8 {149}adiology N ovem ber 1995
scalloping. These findings were con-
sistent with Chiani II m alform ation.
This patient also had tw o palpab le
soft spots on the panam id line of her
forehead . F igure 1 is a radiograph
that shows tw o sharply m anginated,
slightly irregu larly bordered, ovoid
frontal foram ina that m easured ap-
proxim ately 4 cm long and 1.5 cm
w ide, separated by a bone bridge of
about 2 cm . Both tables of the sku ll
tapered sm oothly, w ithout sclerosis on
peniosteal reaction. There w as no cra-n io lacunia calvan ial change. The su-
tunes were norm al for her age. The
axial head CT scan (Fig 2) did not
depict increased extra-axial flu id or
the presence of abnorm al soft tissue
w ithin the defects. There was a m m -
im al focal bu lge of the neural tissue
locally at the defects. These bifrontal
foram ina w ere also depicted in a
three-d im ensional reconstruction of
the skull (F ig 3). The fonam ina w ere
also dep icted in a second child (F ig 4).
Frontal fonam ina were initially
identified in three fem ale patients
with C hiani II m alform ation , and 10
additional cases were discovered at
retrospective analysis of the head CT
scans in 99 cases of congenital hydro-
cephalus. The head C T scans of 116
patients in the control group , w ho did
not have hydrocephalus, depicted no
evidence of frontal bone abnorm ali-
ties (Table). Therefore, a total of 13
children (seven fem ale and six m ale
patients, aged 6’/ weeks to 9 years)
were found to have frontal foram ina,
which varied in size and shape. A ll of
these children even tually underwent
ven tn icu loperitoneal shunt placem ent
for hydnocephalus. E leven of these 13
children had C hian i II m alform ation ,
one had D andy-W alker m alform ation ,
and one had occipital horn dilatation
(colpocephaly). The cases of 61 chil-
d ren w ith Chiani II m alform ation w ere
retrospectively reviewed, and eight
(13% ) w ere found to have frontal fo-
ram ina. The m ale-to-fem ale ratio of
the Chian i II group w as 1.3:1, w hereas
the ratio in the subgroup w ith frontal
fo ram ina w as 1:1.
Sequential axial C T exam inations
of the head, w hich w ere available for
three children, depicted gradual de-
crease in the size of the fron tal fo-
ram ina. O ne child underw ent initial
head CT at 6/2 w eeks of age and fol-
low -up head C T 4 m onths later. An-
o ther child underw ent head CT at
ages 2, 4, and 6 years. The third child
underw ent head C T at ages 6, 11, a
13 m onths. F igure 5 depicts the ab-
sence of a large portion of the m idline
frontal bone in the child w ho under-
w ent initial axial head CT at age 61/
weeks. There is a sm all focal hyper-
attenuating area oven the m etopic
tune that suggests calcification. F igur
6, a head C T scan obtained 4 m onths
later in the sam e child, depicts a sub
stantial decrease in the size of the c
vanial defect.
DISCUSSION
There is an apparent association
tw een the existence of frontal fo ram ina
and congenital hydrocephalus relate
to central nervous system m alform a-
tion . The presence of hydnocephalus
alone is not sufficient to cause fron tal
fonam ina because the m ajority of th
8/18/2019 Front Foramina in Hydroceph
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6.
Volum e 197 {149}um ber 2 Radiology {149}99
Figures 5, 6 . (5) A xial head CT scan ob-tam ed in a 6V 2-w eek-otd fem ale infant w ith
Chiani II m alform ation. O nly the m eninges
separa te the cortex from the scalp in the
frontal bone defect. (6) A xial head CT scan
obtained 4 m onths later in the sam e patient
shows bone form ation in the param edian
frontal bone on either side of the m etopic
suture.
patients with hydrocephalus do not
have these bone defects. There m ay
be m any other factors that affect the
presence and size of frontal fonam ina,
includ ing associated congenital neu-
nal anom alies; onset, severity , and du-
ration of hydrocephalus; and inter-
vention and treatm ent.
Chiani II m alform ation occurs early
in utero w hen, recent ev idence sug-
gests, the neural fold fails to develop
norm ally, w hich results in inadequate
distention of the prim itive ventricular
system (1,2). This alters the inductive
effect of pressure and volum e on the
surrounding m esenchym e, w hich
form s the neural tissue and the skull.
These patients have sm all posterior
fossae; m yelom eningocele; and in-
creased prevalence of sp inal dysra-
phism , aqueductal stenosis, and con-
genital hydro cep halu s.
Dandy-W alker m alform ation is a
disorder of the m idline central nen-vous system that also occurs early in
fetal developm ent. Insu lts of varying
severity to both the developing cen-
ebellar hem ispheres and the fourth
ventricle are believed to be the gen-
esis (1). E ighty percent of patients
w ith D andy-W alker m alform ation are
sym ptom atic in the first 3 years of life,
and as m any as 91% have hydroceph-
alus (3). The early onset of these neu-
ral tube defects and high rate of as-
sociation with hydrocephalus m ay
adversely affect the norm al frontal
calvarial developm ent.
The exact cause of form ation of
frontal foram ina is unknow n but m ay
be associated with central nervous
system m alform ation and increased
intracranial p ressure, w hich result in
abnorm al induction of bone form a-
tion. The m etop ic suture appears to
develop norm ally as a nonossified
grow th center, w hich indicates nor-
m al tissue in teractions are m aintained
(4). C losure of the frontal foram ina
m ay occur as bone form s in growth
centers that expand laterally within
the param edian frontal bone on either
side of the m etopic su ture and asbone grows inward from the lateral
m argins of the frontal foram ina. This
pattern of grow th is distinctly differ-
en t from that of the norm al skull, in
which progressive closure of the m id-
line suture and fontanelle is a result
of m edial expansion of the calvanial
plates.
Serial head CT exam inations in
three patien ts depicted progressive
closure of the frontal foram ina over
tim e. The foram ina w ere present be-
fore ventriculopenitoneal shunt place-
m ent, and the procedure m ay have
accelerated closure of the foram ina
by norm alizing intracranial p ressure.
Therefore the true prevalence and
size of the fron tal foram ina in an un-
treated population could be underes-
t imated.
Fron tal foram ina appear to be dis-
tinct from cran io lacunia (luckenschadel),
which is seen in som e patients w ith
Chiani II m alform ation (5). In p atie nts
with cran io lacunia, the radial grow th
of the developing calvanium is pro-
foundly altered in utero secondary to
dysplastic m em branous bones, which
result in m ultiple areas of skull thin-
ning and a “scooped-out” appear-
ance, which is m ost prom inen t near
the torculan H erophili and the vertex.
The lacunae are m ost pronounced at
b irth , dim inish with age, and usually
disappear by 6 m onths. Since cnan io-
lacunia is not a result of increased in-
tracranial pressure, its resolution isnot altered by surgical in tervention
and ventricular shunt placem ent (1).
The differences in pathogenesis, loca-
tion, age distribution, and association
w ith o ther central nervous system
m alform ation m ake frontal fonam ina
and cran io lacunia distinct entities.
A nother calvarial defect that differs
from frontal foram ina is panietal fo-
ram ina, w hich is seen in about tw o-
thirds of sku ll series. Parietal foram ina
are norm al findings w ith no know n
patholog ic sign ificance (6).
Frontal foram ina do not appear to
have direct pathologic consequences
but, m ore im portantly, are associated
w ith central nervous system m alfor-
m ations. An understand ing of w hat
fron tal foram ina represen t will help
d irect a focused diagnostic and treat-
m ent effort. Since these calvarial de-
fects m ay be palpable at physical ex-
am ination and can be visualized on
skull or sinus nadiographs, the find ing
of this entity m ay help recognition of
undiagnosed hydrocephalus second-
ary to cen tral nervous system m alfon-
mation. U
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