Leptomeningeal melanoma of unknown primary site: two cases with an atypical presentation of acute meningitis

Primary melanoma of the central nervous system accounts for only 1% of the cases of melanoma, having a relatively rare frequency of being reported in the literature. We report two cases of leptomeningeal melanoma of unknown primary site diagnosed after post mortem examination. In the first case, the patient presented with resisting epilepsy, whereas in the second with persisting fever and mental slowness. Cranial CT in the first patient showed postgadolinium enhancement of the ependyma and the infundibulum, while in the second there was diffuse enhancement of the leptomeninges. Analyses of the CSF in both cases did not establish the presence of malignant cells but revealed altered CSF glucose and increased CSF protein levels. There were no extracranial abnormalities. Both patients were treated for infectious meningitis and died a few days afterwards. At autopsy, all body cavities including oral cavity and the entire integument were examined. In both cases the leptomeninges were diffusely covered with brownish material. Histological examination of the brain specimens revealed the presence of a malignant neoplasm of low differentiation. Diagnosis was established with the results of immunohistochemistry, tumor cells were positive for HMB-45 and S-100 whereas they were negative for cytokeratins, CD45 and GFAP. In conclusion, both patients, although presenting with symptoms and signs highly suggestive of meningitis, suffered from leptomeningeal melanomas of unknown primary site. Clinical, radiological and histological findings are discussed with a review of the literature.