= benign lesion arising from resident melanocytic cells found within leptomeninges

Age: any; 5^th decade (majority); F >M

Path: darkly pigmented mass

Histo: tight cellular nests / whorls ± abundant melanin pigment within cytoplasm: NO mitotic activity, NO nuclear pleomorphism, NO hyperchromaticity; S-100 + melan-A + HMB-45 positivity (similar to melanoma)

• myelopathy, radiculopathy
• seizures, hydrocephalus, cranial nerve deficits

Location: posterior fossa, Meckel cave, spinal canal (cervical + thoracic spine)

• avidly enhancing iso- to hyperattenuating mass
• indolent growth pattern
• typically iso- to hypointense on T2WI ± T1 hyperintensity ← melanin

Rx: surgical resection (in up to 22% recurrence within 3 years)

DDx: melanoma