Cerebellar Squamous Cell Carcinoma Due to Malignant Transformation of Cerebellopontine Angle Epidermoid Cyst, Report an Interesting Case and Review the Literature

Malignant transformation of an epidermoid tumour is a rare entity that in almost all patients occurs at the same site of the primary lesion. We report a case of an epidermoid tumour with malignant transformation to squamous cell carcinoma (SCC) at the adjacent site but without any relation to the primary site of the tumour. A 30-year-old patient with a history of cranial surgery and resection of cerebellopontine (CP) angle epidermoid cyst five years ago, presented with a headache, nausea, and vomiting. Physical examination showed no neurological deficit. The brain magnetic resonance imaging (MRI) demonstrated a well-defined lesion within left middle cerebellar peduncle with no relation to CP angle cistern (the previous tumour site). It was isointense on T1, isointense on T2 and had a rim enhancement on gadolinium (GD) injection. Via retrosigmoid and transcortical approach, total resection of the tumour was performed. During the surgery, there was no visible relationship between the current lesion and the previously resected lesion site. Histopathology revealed squamous cell carcinoma. The systemic survey to finding a probable origin of the tumour was negative and the patient referred for performing brain radiotherapy. We are reporting a case of malignant transformation of epidermoid cyst separate from primary location. Moreover, malignant transformation can occur years after index surgery even after gross total resection.