[Meningeal melanocytoma].

A 38-year-old man presented with an intracranial extra-axial tumour at the base of the left posterior fossa which proved to be a meningeal melanocytoma. Meningeal melanocytoma is a rare, benign melanotic tumour of the leptomeninges occurring predominantly in the posterior fossa or the upper spinal cord in adults. It shows characteristic cytologic features with isomorphic epitheliod or spindle-shaped cells, often with prominent nucleoli and a variable content of intracytoplasmic melanin. It usually lacks signs of malignancy such as high mitotic rate, necroses or infiltrative growth and shows a low labeling index in proliferation marker studies. Its immunohistological profile with S-100 protein-, vimentin- and HMB-45-positive tumour cells is similar to that of (primary or metastatic) malignant melanoma. This differential diagnosis is crucial because of the totally different therapeutic and prognostic implications. Therefore, everyone dealing with surgical neuropathology should be familiar with the rare, but clinically important diagnosis of meningeal melanocytoma.