Intra-axial Brainstem Malignant Melanoma Mimicking Cavernous Angioma―Case Report

A 41year-old female presented with repeated pontine hemorrhage. Magnetic resonance imaging showed the pontine hemorrhage as a heterogeneously enhanced mass mimicking cavernous angioma. The mass lesion was removed via a midline suboccipital approach. Histological examination showed malignant melanoma cells. No cutaneous lesion was found and positron emission tomography found no abnormalities. Our presumptive diagnosis was primary intra-axial brainstem malignant melanoma. The possibility of malignant melanoma should be considered in patients with intra-axial brainstem lesion associated with repeated hemorrhages. 「Introduction」Intracranial primary malignant melanoma is quite rare, despite being first reported in 1859, 9)accounting for only 3 of 6402 cases(0.05%)of intracranial tumors according to the Brain Tumor Registry of Japan. 1)Primary central nervous system(CNS)melanoma is considered to be derived from melanocytes in the neural crest. 4,10)The pia mater is the main source of melanocytes in the CNS. Therefore, primary CNS melanoma generally occurs on the neural surfaces including the cerebellopontine angle. 4,5,7)However, melanocytes are also found in the brainstem reticular formation, substantia nigra, and locus coeruleus. 3)