Intracranial epidermoid cyst: atypical location
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A sharply circumscribed 3.9 x 4.7 x 3.7 cm left posterior inferior frontal mass approaches CSF signal on most sequences, with areas of ill-defined incomplete flair suppression. The presence of marked diffusion restriction in the lesion is characteristic of an epidermoid.
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 edema.
A few small T2 hyperintense white matter foci compatible with mild age-related change chronic small vessel ischemia. No parenchymal susceptibility artefact. No further mass lesion or pathological contrast enhancement. No hydrocephalus.
Conclusion: Large left frontal epidermoid.
In this case, although the unusual location, the lesion signal features are typical and characteristic for an epidermoid: sharply circumscribed lesion which approaches CSF signal on most sequences, with areas of ill-defined incomplete FLAIR suppression, and marked diffusion restriction.
Because of their avascular nature and composition (cholesterol and keratin) epidermoid tumors typically have no enhancement on post-contrast images.
Intracranial epidermoid cysts are benign tumors that are commonly found in the cerebellopontine angle (40-50%), suprasellar cistern (10-15%), and fourth ventricle (~17%), however, they can also happen in unusual locations such as exposed in this case.
The tumor in this case was surgically removed and confirmed as an epidermoid cyst.