Teaching Case

A 2-week-old boy had a small midline scalp swelling since the time of birth located in the midline parietal region. It was soft and fluctuant and the overlying scalp appeared normal. No cutaneous markers of neural tube defects were evident in the region of back and spine.

MR imaging of brain revealed a small midline calvarial (osseous) defect in the posterior parietal region in the midline. Through this calvarial defect the meninges were seen herniating into the subgaleal soft tissues of the scalp, forming an ovoid swelling. This scalp swelling demonstrated fluid-signal-intensity and contained predominantly CSF. No overt neural elements were evident. The intracranial brain parenchyma demonstrated interdigitating gyri with mild ventriculomegaly. MR venogram exhibited a vertically oriented persistent primitive falcine. These MR imaging findings suggested the diagnosis of an atretic parietal cephalocele, which was subsequently confirmed peroperatively.

Parietal cephaloceles are uncommon, comprising less than 10% of cephaloceles. Atretic cephalocele is considered to be an abortive form of meningomyelocele. It refers to a subscalp lesion that consists of meninges and rests of glial and/or cerebral tissues. In 1972, James and Lassmam introduced the concept of an abortive form of meningomyelocele and termed it 'meningocele manque', meaning spontaneous arrest in the development of the malformation. This has also been referred to as abortive/ atretic/ rudımentary or occult cephalocele. Other theories which have been postulated regarding their development include: persistence of neural crest remnants, persistence of a fetal nuchal bleb caused by early embryonic cerebral "blow-out." Atretic parietal cephaloceles present clinically as a soft-to-firm midline scalp lesion which may be noticed immediately after birth or may go undiagnosed into adolescence or adulthood. Its association with intracranial anomalies is highly variable and some children may have normal clinical outcome with no associated intracranial anomalies. Associated anomalies include DandyWalker malformation, Arnold Chiari-II, heterotropia, cerebellar and corpus callosum dysgenesis. Intracranial venous anomalies have also been described. These include: vertıcal straight sinus, persistent falcine sinus, absent or hypoplastic straight sinus, focal splitting of the superior sagittal sinus or double superior sagittal sinus. These can be depicted well using noninvasive 3D-MR-venography. It has been seen that these venous anomalies are encountered predominantly when the cephalocoeles lie above the torcular. CT or MR imaging have proven to be highly helpful in diagnosing atretic cephaloceles. On CT and MRI, atretic cephaloceles are visualised as a midline sub-scalp swelling in the parietal or occipital region with underlying calvarial defect. There is often a fibrous stalk seen along the base of the atretic cephaloceles which is attached to the dura mater, which is better visualised on sagittal T1- or T2-weighted MR images. Other imaging findings which have been described include: "spinning-top" configuration of the tentorial incisura on axial CT or MRI. A "cigar-shaped" CSF tract within the posterior interhemispheric fissure and "peaking" of the tentorium on the coronal scan. The most frequently encountered venous anomaly includes vertical straight sinus with persistent falcine sinus. Differential diagnosis of the atretic cephalocele includes other scalp lesions such as haemangioma, cystic hygroma, lipoma, teratoma, sinus pericranii and dermoid cyst. The prognosis of the atretic parietal cephaloceles depends on whether there is an accompanying central nervous system or other systemic malformation. Treatment is surgical with good post-operative prognosis, in case of absence of other intracranial malformations.