ABSTRACT
PRIMARY MELANOCYTIC LESIONS Primary benign and malignant melanocytic lesions of the nervous system include diffuse melanosis, melanocytoma and malignant melanoma. Primary melanocytic lesions originate from melanin-containing cells found in the leptomeninges. Though widespread throughout the neuraxis, these cells are normally most prominent over the lower ventral medulla oblongata, and may be grossly visible in some individuals. Meningeal melanocytic lesions may arise in association with cutaneous melanocytic lesions, for instance large congenital naevus (see later), cellular blue naevus, and naevus of Ota (oculodermal melanocytosis).31 The rare primary leptomeningeal melanocytic tumours should be distinguished from the more common scenario of malignant melanoma spreading to the nervous system. Immunohistochemically, melanocytic lesions are positive with ‘melanosome-specific’ antibodies (such as HMB-45, MART-1 or Melan-A, microphthalmia transcription factor), vimentin and S-100 protein, but it is important to recall that all tumours bearing melanosomes (e.g. melanotic schwannomas) may stain with these antibodies.
