Meningeal melanocytoma. An uncommon diagnostic pitfall in surgical neuropathology.

Objective: To describe the neuropathologic findings in four cases of meningeal melanocytoma, a rare benign melanocytic tumor of the central nervous system.
Design: Retrospective analysis of surgical pathology and autopsy material.
Results: Grossly, all four tumors were well-circumscribed pigmented lesions, and three of four were attached to dura. Microscopically, the neoplasms were composed of spindle cells with epithelioid foci. Mitoses were not seen and only one case exhibited minimal necrosis. Immunohistochemistry and electron microscopy demonstrated the melanocytic nature of the lesions; all four cases showed S100 protein and neuron-specific enolase staining, and three cases exhibited melanoma-specific antigen staining. Immunostaining for epithelial markers and vimentin was uniformly negative. The single case in which electron microscopy was performed demonstrated premelanosomes.
Conclusions: Meningeal melanocytoma is a benign pigmented neoplasm that can easily be confused with melanoma, especially on frozen section analysis. Practicing surgical pathologists should be aware of this entity.