Atretic parietal cephalocele

Clinical History

A 4 year old child presented with complaints of a small scalp swelling since birth and delayed milestones.

Imaging Findings

A 4 year old child presented with complaints of a small scalp swelling since birth and delayed milestones. On physical examination a soft and fluctuating mass over the posterior part of the high parietal region near the mid line was found. CT scan revealed a nodular soft tissue density lesion beneath the scalp in the mid line high parietal region with an underlying bone defect (Fig.1). Straight sinus appeared unusually high and vertically positioned extending up to the scalp lesion (Fig.2). High lying cerebellar tentorium and superior cerebellar cistern were seen showing the typical "spinning-top" configuration of the tentorial incisura (Fig.3).The parallel orientation of the lateral ventricles with probost bundles separating them is suggestive of partial agenesis of callosum. Combining all these features, a diagnosis of atretic parietal cephalocele with partial agenesis of corpus callosum was made.

Discussion

Cephaloceles are extensions of one or more intracranial structures through a skull defect. Depending on the content they are classified in to meningoceles, encephaloceles and meningo-encephaloceles. Parietal cephaloceles are uncommon entities and are usually atretic. Among cephaloceles, the incidence of atretic cephaloceles is reported to be 4-17%, of which parietal cephalocele accounts for 37.5-50 % of cases [1,3].Multiple schools of thought exist regarding the pathogenesis of atretic cephaloceles. Few consider them as the neural crest remnants, few consider it to result from "remnant nuchal bleb" whereas others consider them as result of near complete resolution of a larger meningoencephalocele formed in early foetal life [1,2].
Pathologically parietal cephaloceles are considered to be of two types. Type I cephalocele has a lesion consisting mainly of arachnoid tissue found at the lesion stalk; and is accompanied by a multitude of anomalous blood vessels. The dome consists of dermal tissue with normal hair follicles. In Type II cephaloceles, the blood vessels extend towards the dome and have ectopic foci of neural/glial elements. Atretic parietal cephaloceles usually have a very high association with Dandy Walker spectrum malformations, Holoporencephaly, Interhemispheric cysts, Chiari type II malformations and corpus callosal agenesis [3].
The abnormal vertically positioned straight sinus is the most consistent finding in these patients [4]. This is proposed to have resulted from the arrest of normal migration from vertical to transverse position of the straight sinus and the tentorium by a mid-line fibrous strand extending up to the calvarium. This fibrous strand also causes fenestration of the superior sagittal sinus resulting in a "cigar like" CSF tract extending up to the calvarium.
The usual differential diagnoses of these patients include dermoid cyst, sinus pericranii, lipoma and other scalp lesions. Presence of the embryonic straight sinus is classical of atretic cephaloceles and is usually sufficient to differentiate from others. Sinus pericranii are dilated superficial veins that communicate with the dural sinuses by way of an emissary vein. Sagittal MRI allows differentiation of this lesion by showing its relationship to the underlying dural venous sinus [5].
Atretic parietal cephaloceles usually have a very high association with Dandy Walker spectrum malformations, Holoporencephaly, Inter-hemispheric cysts, Chiari type II malformations and corpus callosal agenesis.[3] As mentioned earlier, this patient showed longitudinally running white matter fibers, called ‘Probost’ bundles, separating the lateral ventricles and aligning them parallel to each other (Fig.2). This finding is seen in the agenesis of corpus callosum. Absence of the other classical findings of complete agenesis, such as high lying third ventricle, rules out the possibility of complete agenesis. [6]
Surgical excision of the scalp lesion and the fibrous tract at the level of dura is the treatment of choice. Postoperative complications are very rare. The prognosis of these patients depends upon the presence or absence of the associated anomalies .[4] In any patient with a fluctuant mass lesion in the parietal region, along with the other common causes; the possibility of atretic parietal cephalocele should be considered and excluded.

Differential Diagnosis List

Final Diagnosis

Atretic parietal cephalocele

URL:	https://www.eurorad.org/case/7870
DOI:	10.1594/EURORAD/CASE.7870
ISSN:	1563-4086