[A case of primary intracranial malignant melanoma showing leptomeningeal dissemination].

A 28-year-old woman was hospitalized in drowsy state with signs of increased intracranial pressure. CT scans revealed diffuse increased density with marked enhancement in the subarachnoid space, as well as ventricular dilatation. V-P shunt operation was performed to control intracranial pressure. Repeated cytological examinations of CSF couldn't determine the tumor origin. CT scan of thoracic spine showed a cystic tumor in its dorsal aspect. T2-weighted MRI revealed multiple spotty low intensity, specific to melanin granules, throughout the whole spine. Her thoracic spine was explored, and the intradural tumor was partially removed. Histopathological examination revealed the tumor cell which had dark nucleus with conspicuous nucleolus and cytoplasmic granules. These findings were compatible with malignant melanoma. Her general condition were deteriorated progressively and she died about 5 months after her admission. Postmortum examination showed diffuse leptomeningeal invasion of dark tumor throughout the entire central nervous system, and metastasis to peritoneum and omentum via V-P shunt system. Histopathological examination proved the tumor to be malignant melanoma. Electrone microscopic examination also revealed melanosome in the cytoplasm. Primary intracranial malignant melanoma is divided in two groups, nodular type and leptomeningeal type. In the latter type, early diagnosis is very difficult, just as in our case, because only a little tissue specimen can be obtained. In a case of leptomenigeal carcinomatosis, possibility of primary malignant melanoma, though rare, should always be kept in mind, and specific staining such as Fontana-Masson's staining should be tried.