Diagnostic challenge: primary leptomeningeal melanoma with melanomatosis, illustrative case report.

Primary leptomeningeal melanoma is an extremely rare type of intracranial melanoma. It cannot be reliably distinguished from metastatic melanoma on neuroimaging and histopathological characteristics alone; its diagnosis is established only after exclusion of secondary metastatic disease from a cutaneous, mucosal or retinal primary. Prognosis is poor, partly due to its high rate of misdiagnosis.