Primary meningeal malignant melanoma

Primary meningeal malignant melanomas, or merely meningeal melanoma, is a primary melanocytic tumor of the CNS and represent malignant neoplasms of the leptomeningeal melanocytes, derived from neural crest cells.

Unlike meningeal melanocytosis, which is diffuse, meningeal melanoma presents as a solitary mass.

Epidemiology

Meningeal melanomas are encountered in all age groups .

Pathology

These durally based extra-axial tumors occur anywhere in the central nervous system, but appear to have a predilection for the spinal cord and posterior fossa, similar to meningeal melanocytomas .

Macroscopic appearance

Meningeal melanomas appear as circumscribed masses of variable pigmentation from black to non-pigmented .

Microscopic appearance

Microscopically, meningeal melanomas appear similar to malignant melanomas elsewhere in the body. They demonstrate cellular pleomorphism and atypia, necrosis and are mitotically active, features which are helpful in distinguishing them from meningeal melanocytomas .

Immunophenotype

As is the case with other primary melanocytic tumors of the CNS, meningeal melanocytomas usually demonstrate the following immunohistochemical staining :

• HMB45: positive
• melan-A: positive
• MITF: positive
• S100: positive
• vimentin: variable
• neuron-specific enolase: variable
• GFAP, NFPs, cytokeratins, EMA: usually negative

Radiographic features

These tumors appear as extra-axial masses, with enhancement on both CT and MRI. They may have variable T1 signal hyperintensity depending on the degree of melanin present.

Treatment and prognosis

Meningeal melanomas are aggressive lesions with a generally poor prognosis, although as they are localized, they have a better prognosis than melanoma metastases to the dura .