Primary central nervous system malignant melanoma with leptomeningeal melanomatosis: a case report and review of the literature.

Leptomeningeal melanomatosis is an extremely rare variant of primary central nervous system (CNS) melanoma and has a poor prognosis and no standard treatment. Primary CNS melanoma is derived from the melanocytes of the leptomeninges. Here, we describe a case of a 37-year-old male who visited our hospital due to worsening headaches. Characteristic imaging findings of this tumor type include hyper-dense lesions that are enhanced by contrast medium on computed tomography and hyper-intensity on T1-weighted magnetic resonance images and iso- to hypo-intensity on T2-weighted magnetic resonance images. Imaging of the CNS in our patient showed several lesions of this type. Pathological diagnosis and exclusion of systemic melanoma are required to confirm primary CNS malignant melanoma. Partial resection of the mass in the left temporal lobe of this patient was performed, and histological analysis showed pigmentation, melanin black-45 positivity, and BRAF mutation. Because no lesions were found outside the CNS following a thorough whole-body search, he was diagnosed with primary CNS malignant melanoma with leptomeningeal melanomatosis. He was treated with whole-brain radiation and the BRAF kinase inhibitor vemurafenib. His condition worsened, and he was given the anti-programmed cell death-1 antibody nivolumab as second-line therapy. This was also unsuccessful, and he died 5 months after treatment initiation. Further studies are needed to improve treatment and prognosis of this rare but serious disease.