Epidermoid cyst - posterior cranial fossa
Chronic headaches, vertigo, and peripheral facial nerve palsy. The patient had history of surgery at the posterior cranial fossa 20 years ago.
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The MRI sequences demonstrate an extra-axial mass of irregular margins filling the posterior fossa cisterns, mainly the subpontine, prepontine, and supracerebellar cisterns with extension to the 4th ventricle which is dilated. It is of low signal intensity on T1WI, heterogeneous low signal on FLAIR and high signal on T2WI with no enhancement following IV contrast. It shows a high signal on DWI with low ADC (restricted diffusion).
A mass effect is noted on the brainstem and right cerebellar hemisphere which shows an area of encephalomalacia and gliosis from the previous surgery. Mild dilatation of the 3rd and lateral ventricles.
Typical MRI features an epidermoid cyst of the posterior cerebral fossa. DWI an important sequence to differentiate an epidermoid cyst from an arachnoid cyst. Given the remote history of posterior fossa surgery, the possibility of epidermoid recurrence is considered as it is a slowly growing mass lesion or acquired epidermoid, although rare.