To evaluate the magnetic resonance (MR) imaging characteristics of pri
mary malignant melanoma of the sinonasal cavity, T1- and T2-weighted M
R images of 12 patients with primary sinonasal melanoma were retrospec
tively reviewed. Gadolinium-enhanced imaging was performed in seven ca
ses, The MR images were compared with histopathologic results, There w
ere seven melanotic melanomas and five amelanotic melanomas; hemorrhag
e was present in three melanotic and two amelanotic melanomas. The sev
en melanotic melanomas were hyperintense to gray matter on T1-weighted
images (whether hemorrhage was present or not), consistent with the p
aramagnetic effect of melanin. Four of the five amelanotic melanomas h
ad intermediate signal intensity on T1-weighted images, one was not de
tected. On T2-weighted images, all of the melanomas detected had inter
mediate though variable signal intensity compared with that of gray ma
tter, On gadolinium-enhanced images, all cases demonstrated mild to mo
derate enhancement. The signal intensity of sinonasal melanoma appears
to vary according to the histopathologic components of the tumor. Hig
h signal intensity within the lesion on T1-weighted images suggests th
e presence of melanin.