Imaging Findings of an Epidermoid Cyst Undergoing Malignant Transformation.

Malignant transformation of epidermoid cyst into squamous cell carcinoma (SCC) is rare. We report the case of a 39-year-old woman presenting with dizziness and cerebellar ataxia. MR scan revealed a mass in the left cerebropontine angle compressing the brainstem and the cerebellum, with two main components, a cystic and a solid one. The cystic component displayed imaging findings consistent with an epidermoid cyst. The solid component showed dense calcifications, low signal intensity on T1W, T2W and DW images and peripheral nodular enhancement. MR spectroscopy detected high lipid/lactate peaks and choline/creatine ratio. Imaging findings raised suspicion for malignant transformation, which was confirmed by histopathologic examination revealing an SCC. MR imaging with intravenous administration of gadolinium, DW images and MR spectroscopy can play a critical role in the diagnosis of malignant transformation of an epidermoid cyst.