Primary leptomeningeal melanomatosis

37-year-old with extremely rare leptomeningeal melanomatosis on T2- (A), T2*-gradient echo (B, C), T1- (D, E), and postcontrast T1-weighted (F) MRIs of the brain. Melanin appears as micronodular and linear hyperintense foci on leptomeningeal surfaces of both the cerebrum and cerebellum on noncontrast T1-weighted MRIs (D, E). Melanin is hypointense on T2*-weighted gradient echo images (B, C) because of its paramagnetic effect (stable free radicals in melanin shorten both T1- and T2-relaxation times). Enhancement of these foci (F) indicates a neoplastic process.