Primary intracranial sarcomatoid carcinoma arising from a recurrent/residual epidermoid cyst of the cerebellopontine angle: a case report.

Primary intracranial squamous cell carcinomas (SCCs) are rare and mostly associated with an intracranial epidermoid or dermoid cyst. Sarcomatoid carcinoma is a rare biphasic tumor composed of both carcinomatous and sarcomatous components and has not previously been reported as a primary intracranial tumor. Here, we present a case of a 60-year-old man with a primary intracranial sarcomatoid carcinoma, arising from the remnants of the previously resected epidermoid cyst in the cerebellopontine angle. The resected material had portions of an epidermoid cyst lined by normal and dysplastic squamous epithelia and invasive keratinizing SCC. This area was in continuity with areas of highly pleomorphic, anaplastic sarcomatoid cells. Brisk mitotic activity and extensive areas of necrosis were found. On immunohistochemical staining, the cells of the conventional SCC were positive for cytokeratin 5/6, pancytokeratin, epithelial membrane antigen, p63, and p53. The sarcomatoid cells were diffusely and strongly positive for vimentin, p53, smooth muscle actin, and, focally, muscle-specific actin. Occasional sarcomatoid cells coexpressed cytokeratin 5/6, pancytokeratin, p63, and S100 protein. The patient subsequently developed leptomeningeal spread and died 4 months after the second surgery. This rare entity expands the morphologic spectrum encountered in primary intracranial carcinoma.