Meningeal melanocytosis

Meningeal melanocytosis is a benign form of primary melanocytic tumor of the CNS that represents proliferation of melanocytic cells within the subarachnoid space ¹. When associated with cutaneous melanocytic lesions, the conditions is known as neurocutaneous melanosis ³.

Meningeal melanocytosis is related to the more aggressive meningeal melanomatosis. As imaging is very similar, they are discussed together in the article on meningeal melanomatosis.

Pathology

The melanocytic cells found in the subarachnoid space are believed to arise from leptomeningeal melanocytes of neural crest origin ¹. Sometimes meningeal melanocytosis can extend to involve the perivascular spaces, importantly without direct invasion into the brain ¹. The cells appear bland without atypia, necrosis or significant mitotic activity. If these features are found then a diagnosis of meningeal melanomatosis should be made ¹.