This patient went on to have a posterior fossa craniotomy and resection of the tumour. 

MICROSCOPIC DESCRIPTION: Specimens show fragments of laminated keratin and segments of thin keratinizing squamous epithelium with an underlying layer of collagen. Laminated keratin with focal calcification abuts this membrane. No appendageal structures are identified. The overall features are of an epidermal cyst. No evidence of tumour is seen in the specimens submitted.

FINAL DIAGNOSIS: Epidermal cyst.