Squamous cell carcinoma developing in an intracranial prepontine epidermoid cyst.

Intracranial epidermoid cysts represent around 0,2 to 1 % of all intracranial tumours. Rare malignant transformation of these benign lesions may occur. A 66-year-old man presented with a state of confusion. MRI demonstrated a heterogeneous signal in front of the pons and ventricular dilatation. Cerebrospinal fluid examinations disclosed inflammatory cells. The patient died six months after his first admission to hospital. At autopsy, a firm greyish tumour (3 cm-long and 1 cm-thick) was present in front of the brain stem encasing the basilar artery. Microscopic examination revealed a well-differentiated epidermoid carcinoma arising from a cystic lesion whose wall was lined by a squamous epithelium with a benign appearance. The walls of all the ventricles were lined by carcinomatous cells. There was no leptomeningeal metastasis. Twenty three other cases of such squamous cell carcinoma have been reported and most of them had died within a few months.