Epidermoid cyst: frontal and cerebellopontine angle
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A sharply circumscribed left posterioinferior frontal mass approaches CSF signal on most sequences, with areas of ill-defined incomplete FLAIR suppression. The presence of marked high signal on diffusion-weighted imaging with ADC values similar to brain parenchyma in the lesion is characteristic of an epidermoid cyst.
Mass effect effaces and displaces superiorly and to the right the left frontal horn, and causes subfalcine herniation of the left inferior frontal parenchyma. The mass extends posteriorly to the level of the foramen of Monro, which is partially effaced but not obstructed. Faint linear enhancement about the periphery of the mass. Minimal surrounding gliosis or oedema.
Additional epidermoid cyst material extending posteriorly into the prepontine and left cerebellopontine angle.
The patient went on to have a resection.
Sections show acellular keratinous debris with foci of dystrophic calcification and multinucleated giant cell reaction. There are several small foci of intact squamoid epithelium present, consistent with an epidermoid cyst. No skin adnexal structures are seen. There is no evidence of malignancy.
FINAL DIAGNOSIS: Epidermoid cyst.