Epidermoid cyst (cerebellopontine angle)

Case contributed by Dr Bruno Di Muzio


Few months of intermittent bilateral hand numbness and headache, tonight first tonic clonic seizure.

Patient Data

Age: 30 years

CT Brain

There is an extra-axial hypodense lesion within the right cerebellar pontine angle, extending over the free edge of the right tentorial leaf and into the floor of the right middle cranial fossa. The lesion has no internal calcification or hemorrhagic foci. There is mass-effect upon the right middle cerebellar peduncle and midbrain which are displaced to the left. There is also minor effacement of the 4th ventricle without entrapment. No hydrocephalus. Normal grey-white matter differentiation is maintained with no CT evidence of acute infarction. There is extensive coarse dural calcification, predominantly along the falx and tentorium cerebelli, the cause of which is unclear.  


MRI Brain

Extra-axial mass centered in the right ambient cistern is again demonstrated extending anteromedially into the interpeduncular cistern, medial to the free edge of the left tentorium, laterally into the middle cranial fossa, inferiorly into the prepontine and cerebellopontine angle cisterns, and posteromedially into the tectal cistern. No convincing extension into the right internal acoustic meatus. The mass demonstrates high T2 signal, low T1 signal, and almost complete FLAIR suppression. It demonstrates increased diffusion restriction relative to CSF. A thin rim of enhancement (presumably leptomeningeal ) at the anterior margin of the mass. Mass-effect on the brain stem resulting in deformity of the right cerebral peduncle, left lateral displacement and compression of the midbrain and superior pons. Mass effect on the medial left temporal lobe with scalloping of the medial surface of brain parenchyma. Further mass-effect on the right cerebellar hemisphere. Mass surrounds the right posterior communicating artery and right posterior cerebral artery. It causes elevation of the right mesial temporal lobe. There is abnormal T2 and FLAIR hyperintensity and affecting the entire right hippocampus. Signal loss due to extensive dural calcification, particularly on the gradient echo sequence. 

Case Discussion

This case illustrates an extra-axial CSF density lesion on CT that has MRI signal characteristics consistent with an epidermoid cyst.

The MRI study has also demonstrated hyperintensity in the right hippocampus that was probably related to recent seizure activity rather than mass effect. 

The patient underwent surgery for partial resection of the lesion: 

MICROSCOPIC DESCRIPTION: Sections show multiple pieces of keratinising stratified squamous epithelium together with acellular keratinous debris. No skin adnexal structures are seen. There is no evidence of malignancy.

DIAGNOSIS: Epidermoid cyst.

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Case information

rID: 55442
Published: 11th Sep 2017
Last edited: 11th Sep 2017
Inclusion in quiz mode: Included

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