Computed tomography and magnetic resonance imaging of nonhemorrhagic, metastatic melanoma of the brain--case report.

Malignant melanoma frequently metastasizes to the central nervous system. Characteristic features of such lesions are increased density on computed tomography (CT) and shortening of the T1 and T2 on magnetic resonance (MR) imaging. Intratumoral hemorrhage, rather than melanin, is considered to be mainly responsible for these unique radiological features. The authors report a case involving a nonhemorrhagic, metastatic intracerebral melanoma. CT revealed a high-density mass, and MR imaging demonstrated a hyperintense mass both on T1- and T2-weighted images. These observations suggest that melanin is in fact a major determinant of the increased density on CT scans and the high signal intensity on T1-weighted MR images. On T2-weighted images, the paramagnetic effect appears to vary according to the melanin content.