Fulminant leptomeningeal carcinomatosis from a malignant melanoma arising in a cerebellopontine epidermoid cyst: A rare case with diagnostic pointers.

A malignant component in an epidermoid cyst is rare. We report an exceptionally rare case of a malignant melanoma arising in an epidermoid cyst located in the cerebellopontine (CP) angle. A 26-year-old woman presented with headache, vomiting, ataxia and difficulty in swallowing over the previous 3 months. The radiological finding suggested an epidermoid cyst and the lesion was excised. The histopathology confirmed a CP angle epidermoid cyst. Within 1 month of discharge, she developed hydrocephalus for which a ventriculo-peritoneal shunt was performed. Postoperatively she developed weakness in lower limbs. A contrast-enhanced MRI was done which showed dilated CSF cisternal spaces with a small enhancing lesion in the pineal region and enhancement of meninges extending to the spinal cord. Re-exploration showed gelatinous material with gross adhesions in the CP angle cistern. A dural biopsy was done which showed sheets of poorly differentiated tumor cells which expressed S100 and Melan A and were immunoreactive with Human Melanoma Black (HMB)-45 antibody, consistent with the diagnosis of malignant melanoma. Histology of the excised epidermoid cyst was re-evaluated in deeper sections and showed scattered atypical melanocytes in the basal layer of the epidermis which were highlighted with HMB-45 antibody. The patient expired within 3 days of the second procedure due to respiratory failure. A very aggressive fulminant course of the disease was evident after surgery for the epidermoid cyst. Treatment options are limited. Criteria for identification of malignancy in an intracranial epidermoid cyst were identified in our case retrospectively and have been highlighted.