Intracranial intermediate-grade meningeal melanocytoma with increased cellular proliferative index: an illustrative case associated with a nevus of Ota

Solitary primary melanocytic tumors of the central nervous system (CNS) represent a spectrum of lesions ranging from well-differentiated melanocytoma to melanoma. The association of a meningeal melanocytoma with an ipsilateral nevus of Ota is extremely rare, with only six cases reported in the literature to date. Only a minority of melanocytic tumors correspond to lesions of intermediate-grade malignancy, whose biological behavior and outcome remain undetermined. We report a new case of a 25-year-old man with a giant fronto-temporal intracranial meningeal melanocytoma associated with a congenital nevus of Ota, who suffered an acute neurological deterioration requiring an emergent surgical procedure. Despite total removal of the lesion, the patient did not recover from the operation due to a malignant infarct of the right hemisphere. The lesion showed no histological criteria of malignancy but did exhibit an elevated (8%) MIB-1/Ki-67 cell proliferative index, which suggested an intermediate-grade melanocytoma. In addition, its metabolic profile, determined by in vivo proton magnetic resonance spectroscopy (MRS), was similar to that observed in most high-grade gliomas. To our knowledge, this is the first case of a meningeal melanocytoma of intermediate grade associated with a nevus of Ota reported in the literature. Only two additional intermediate-grade melanocytomas showing an elevated MIB-1/Ki-67 labeling index have been previously reported. The MIB-1/Ki-67 labeling index may have potential prognostic value in helping the clinician to predict an aggressive clinical behavior and/or malignant progression for primary melanocytic neoplasms of the CNS.