Epidermoid cyst of posterior cranial fossa with obstructive hydrocephalus
Presentation
Headaches and cerebellar symptoms.
Patient Data
There is a large lobulated cystic mass of the posterior cranial fossa (density similar to CSF) of retropontine location, centered on the 4th ventricle with prominent scalloped contours which is a characteristic feature. No solid component or peripheral enhancement seen. It shows downward extension filling the cisterna magna and foramen magnum. A mass effect is noted on the adjacent structures with mild dilatation of the supratentorial ventricular system (3rd and lateral ventricles).
The MRI confirms the intraventricular location of the cystic lesion which appears of inhomogeneous low signal on T1WI, high signal on T2WI, heterogeneous signal on FLAIR and high signal on DWI (restricted diffusion) with an ADC similar to the adjacent cerebellar parenchyma. A significant mass effect is noted on the adjacent structures (cerebellar hemispheres, tonsils, pons, and medulla) with triventricular hydrocephalus. No periventricular interstitial edema was seen.
Case Discussion
CT / MRI features of an intraventricular epidermoid cyst with obstructive hydrocephalus. The location within the 4th ventricle is the second most common after the cerebellopontine angle and account for around 17% 1. The differential diagnosis of an epidermoid cyst includes mainly an arachnoid cyst which follows the CSF signal on all sequences including FLAIR and DWI whereas an epidermoid cyst shows a high signal on DWI.
Additional contributor: R Bouguelaa, MD.
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