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


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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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1 99 4; 1 5 24

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m at io n A JN R 1 99 2; 1 3: 46 3 4 82

3. O senback RK , M enezes A H. D iagnosis and

m anagem ent of the D andy-W alker m atfon-m ation: 30 years of experience. P ediatr N eu-r os ur g 1 99 2; 1 8: 17 9 1 89

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graphic signs of the Chiani II m alform ation.

I. S kull and dural partitions. R adiology 1980;

1 3 4 : 6 5 7 1

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