Malignant melanoma of the sinonasal cavity: Explanation of magnetic resonance signal intensities with histopathologic characteristics

Purpose: To evaluate the magnetic resonance (MR) findings of malignant mela noma of the sinonasal cavity and compare these findings with those of the h istopathological examination. Materials and Methods: The MR images of 11 patients with malignant melanoma of the sinonasal cavity were retrospectively reviewed. Ten patients had pr imary malignant melanoma of the sinonasal cavity and one had a local recurr ence. The imaging findings were evaluated with special attention given to t he signal intensity of the tumor, internal characteristics, and growth patt ern on MR. Signal intensity and enhancement patterns of the tumors were com pared with the histopathological findings. Results: On T1-weighted image, 6 tumors were hyperintense (5 melanotic and one amelanotic melanoma), and 5 tumors were isointense or hypointense (4 am elanotic and one melanotic). On T2-weighted images, 2 amelanotic tumors sho wed hyperintensity, and 5 melanotic tumors showed hypointensity. Four tumor s (one melanotic and 3 amelanotic) were isointense. Four of the 7 tumors wi th hyperintensity on TI-weighted images showed patchy, higher-signal intens ity areas. In 3 of them, patchy areas of a higher degree of pigmentation we re found on histopathological examination. There were multiple linear dark signal intensities on T2-weighted images and/or linear-enhancing areas on e nhanced T1-weighted images within the masses in 5 of the 11 patients. These findings could be explained as intratumoral vessels in 4 tumors and fibrou s septa in one tumor on histopathological examinations. Conclusion: Malignant melanoma of the sinonasal cavity shows characteristic MR signal intensity, which is mainly attributable to the degree and distri bution of melanin pigmentation, and partly attributable to hemorrhage withi n the mass. The linear, low-signal intensity on T2-weighted images or enhan ced lines are intratumoral vessels or fibrous septa. Copyright (C) 2000 by W.B. Saunders Company.