Primary malignant melanoma of the sinonasal cavity: MR imaging evaluation.

To evaluate the magnetic resonance (MR) imaging characteristics of primary malignant melanoma of the sinonasal cavity, T1- and T2-weighted MR images of 12 patients with primary sinonasal melanoma were retrospectively reviewed. Gadolinium-enhanced imaging was performed in seven cases. The MR images were compared with histopathologic results. There were seven melanotic melanomas and five amelanotic melanomas; hemorrhage was present in three melanotic and two amelanotic melanomas. The seven melanotic melanomas were hyperintense to gray matter on T1-weighted images (whether hemorrhage was present or not), consistent with the paramagnetic effect of melanin. Four of the five amelanotic melanomas had intermediate signal intensity on T1-weighted images; one was not detected. On T2-weighted images, all of the melanomas detected had intermediate though variable signal intensity compared with that of gray matter. On gadolinium-enhanced images, all cases demonstrated mild to moderate enhancement. The signal intensity of sinonasal melanoma appears to vary according to the histopathologic components of the tumor. High signal intensity within the lesion on T1-weighted images suggests the presence of melanin.