Chapter 17 - Melanocytic tumors

Abstract

Melanocytic tumors in the central nervous system are believed to form from leptomeningeal melanocytes derived from the neural crest. Primary melanocytic tumors may be diffuse or localized. Diagnosis is based on recognizing tumor cells with melanocytic differentiation, usually via histopathological examination. The majority of these tumors have finely distributed melanin pigment in their cytoplasm, but coarsely distributed melanin in the tumor stroma and the cytoplasm of macrophages that are referred to as melanophages. Primary CNS melanocytic tumors must be distinguished from other melanotic tumors, including metastatic melanoma, and tumors undergoing melanization, such as schwannomas, gliomas, medulloblastomas, and paragangliomas. Though there have been rare cases of melanocytic colonization in meningiomas, there is only slight evidence of any true melanotic meningioma. Most melanocytic tumors react with antimelanosomal antibodies such as human melanoma black 45 (HMB45), melan-A, and microphthalmia-associated transcription factor (MITF), while also expressing the S-100 protein. Staining for neuron-specific enolase and vimentin are variable. Normally, CNS melanocytes are localized at the base of the brain, around the ventral medulla, and along the upper cervical portion of the spinal cord.