Presentation
Signs of raised intracranial pressure.
Patient Data
Intradiploic expansile osteolytic lesion of the left occipital bone, hypodense with no enhancement, containing foci of calcification with destruction of the skull vault mainly the inner table of the skull. There is an intracranial extension compressing the left cerebellar hemisphere, brainstem and 4th ventricle with tonsillar herniation and mild to moderate dilatation of the 3rd and lateral ventricles.
On the MRI, the intradiploic lesion elicits a low signal on T1, heterogeneous signal on FLAIR and high signal on T2 with restricted diffusion and no enhancement seen on the postcontrast sequence. It extends along the left cerebellar hemisphere and vermis, compressing the brainstem and cerebellar parenchyma with tonsillar herniation and mild to moderate dilatation of the 3rd and lateral ventricles (obstructive hydrocephalus).
Small vessel ischaemic changes are noted.
Case Discussion
CT and MRI features are in keeping with an intradiploic epidermoid cyst with intracranial extension, compressing the brainstem and left cerebellar hemisphere with tonsillar herniation and mild to moderate obstructive hydrocephalus.