Rapid malignant transformation of an intracranial epidermoid cyst: Report of a case.

Intracranial epidermoid cysts (ECs) occur at various locations along the neuraxis and account for nearly 2% of all intracranial tumors. Considering the frequency of ECs, transformation of ECs into squamous cell carcinomas is a rare occurrence. Here, we report the case of a 39-year-old man who presented with a lesion in the left cerebellopontine angle and underwent gross total resection for the same. Histopathological examination revealed a benign EC with mild chronic inflammation. Five months later, the patient presented with another lesion at the same location with evidence of brainstem bleed. Histopathological examination revealed a moderately differentiated squamous cell carcinoma and remnants of the previous cyst in the form of lamellated keratin, indicating malignant transformation of the EC.