Presentation
Signs of raised intracranial pressure.
Patient Data
Well-circumscribed midline intra-axial mass of the posterior cranial fossa centered on the cerebellar vermis. It elicits a low signal on T1, a heterogeneous/dirty signal on FLAIR, and a high signal on T2 with very high DWI signal and ADC values similar to cerebellum, and no enhancement on the postcontrast sequences. A mass effect is noted on the brainstem and cerebellar hemispheres as well as on the 4th ventricle which is displaced superiorly. Dilated 3rd and lateral ventricles with transependymal edema and effacement of the cerebral sulci (obstructive hydrocephalus).
Case Discussion
MRI features of posterior cranial fossa epidermoid cyst of intra-axial location centered on the cerebellar vermis.
Intra-axial location of epidermoid cysts within the cerebellar vermis is rarely seen and only a few cases were reported in the literature 1,2.
Historically, the main differential diagnosis for such an appearance would include an arachnoid cyst, dermoid cyst, hydatid cyst, cystic metastasis and primary cystic neoplasm 1,2. With modern imaging, however, particularly FLAIR and diffusion-weighted imaging, the diagnosis can be made with near-certainty in almost all cases.
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