Specific Imaging Findings

Atretic parietal encephaloceles (APE) are located at the midline superior to the posterior fontanel. Non-enhanced CT images show a sharply marginated central calvarial defect (cranium bifidum) with associated extracranial soft tissue mass located under the scalp. Small cranium bifidum may only be seen with thin slices and 3D reconstructions. MRI shows an extracranial/subscalp mass just above the lambda with heterogeneous T1 signal intensity and hyperintense T2 signal. The APE may insinuate intracranially or show a fibrous band extending into the cranium bifidum. There is embryonic vertical positioning of the straight sinus, which is seen as a flow void connecting the vein of Galen with the superior sagittal sinus (SSS). There may be a “cigarshaped” CSF tract within the interhemispheric fissure and fenestration of the SSS. The lower posterior aspect of the SSS shows a bifid configuration, best appreciated on axial or coronal T2WI. The tentorium is displaced upward with a large superior cerebellar cistern and prominent suprapineal recess of the third ventricle, giving a “spinning-top” configuration to the tentorial incisura. Variations of occipital cortical infolding may be present. The position of the dural venous sinuses with respect to the encephalocele is best seen on post contrast images. APE can be associated with other anomalies, such as callosal dysgenesis, heterotopia, Dandy–Walker syndrome, Walker–Walburg syndrome, and holoprosencephaly. Persistent falcine venous sinus (horizontally connecting the vein of Galen with the SSS) and parietal foramina (persistent bilateral symmetric calvarial defects) may be the only findings in individuals with incidentally found APE.