Intracranial epidermoid cyst
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Large extra-axial posterior fossa mass lesion epicentered upon the right cerebellopontine angle with an irregular creeping borders. It elicits a low signal on T1WI, a high signal on T2WI, heterogeneous/dirty signal on FLAIR, and restricted diffusion.
It exerts marked mass effect displacing the brainstem to the left and compressing the fourth ventricle with consequent mild supratentorial hydrocephalic changes. No transependymal CSF permeation around both lateral ventricles. The lesion also compresses the cerebellum, notably the right cerebellar hemisphere.
This case shows typical MRI features of an intracranial epidermoid cyst, with creeping borders, partial suppression of the T2 signal on FLAIR and diffusion restriction with low-intensity on ADC map. Epidermoids are the third most common mass lesion at the cerebellopontine angle, which is also its most common intracranial location.
The lesion causes important mass effect over the posterior fossa structures with consequent mild obstructive hydrocephalus.