[A Case of Malignant Transformation of Epidermoid Cyst with Cerebrospinal Fluid Dissemination]

An epidermoid cyst is a benign tumor, accounting for 0.2-1.8% of all brain tumors. Histologically, an epidermoid cyst has a wall consisting of squamous epithelium with keratinization and without skin components. An epidermoid cyst tends to develop in the cerebellopontine angle(CPA), middle cranial fossa, pituitary fossa, spinal cord, and other locations. We describe a rare case of malignant transformation of an epidermoid cyst with cerebrospinal fluid(CSF)dissemination. A 54-year-old man was referred to our hospital with chief complaints of dysesthesia of the right leg, persisting for 6 months, and dizziness and dysarthria for 2 months. Magnetic resonance(MR)imaging showed multiple neoplastic lesions with lobulated margins in the left frontal and temporal lobes, left cerebellum, right brainstem, and right CPA. Diffusion-weighted imaging showed a hyperintense cord-like lesion in the right CPA. Blood examination revealed squamous cell carcinoma(SCC)antigen positivity;however, systemic examination revealed no neoplastic lesion, except for the head lesion. Intracranial lesions were considered unlikely to be metastatic brain tumors. We performed surgical removal of the tumor in the left CPA via a left lateral suboccipital craniotomy. The histopathological diagnosis was SCC. MR imaging for the headache was taken at another hospital 2 years before the surgery, revealed an epidermoid cyst in the right CPA. The current MR imaging showed enhancement in part of the epidermoid cyst in the right CPA, strongly suggesting that the epidermoid cyst in the right CPA had disseminated to the left frontal and temporal lobes, left cerebellum, and right brainstem via the CSF.