Patient Data
Selected images from a non-contrast CT demonstrate a hyperdense lesion located anterior to the brainstem.
Selected images from an MRI demonstrate the mass to be markedly hypointense on T2/FLAIR and with intrinsic T1 hyperintensity. The mass demonstrates intermediate diffusion restriction on ADC, only slightly values than normal brain. On DWI it does not demonstrate high signal.
Sitting position to the posterior fossa approach with suboccipital craniectomy, with surgical exposure of a white mass prior to resection.
Histology
No malignant cells.
Cystic lesion with stratified, keratinizing squamous epithelium with anucleated squames, with surrouding granulomatous reaction presumably due to rupture.
The Findings are consistent with epidermoid cyst.
Note, that one of the differentials is that of a neuroenteric cyst which have ciliated mucin-producing epithelium but can show squamous metaplasia. However, no anucleated squames or keratohyaline granules should be present, which are in this case.
Case Discussion
This lesion is challenging radiologically as it is atypical for all lesions.
The differential is that of an epidermoid cyst (white epidermoids are recognized) and neurenteric cyst (which can be low on T2). Epidermoid cysts are of course much more common, but when features are odd it is difficult to know which would be the favored diagnosis.
In this case the histology is needed and consistent with an epidermoid cyst.
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