Background Malignant sinonasal melanoma （MSM） is a rare tumor with a perplexing signal intensity due to variable histopathologic components. This study was undertaken to delineate its MR imaging features. Methods MR imaging findings of 10 patients （6 women and 4 men, mean age 61.3 years old） with pathologically confirmed MSM were retrospectively reviewed. The location, size, signal intensity, enhancement, and internal imaging characteristics of all tumors were evaluated. Signal intensity and degree of enhancement was graded in comparison with the gray matter and adjacent muscle uptake, respectively. Results There were 8 tumors that were pathologically confirmed to contain melanin. Compared to gray matter of the brain, 7 of them demonstrated hyperintensity on T1WI and 6 （6/7） showed hypointensity on T2Wl. There was multiple linear, dark-signal intensity on T2Wl within the mass in 9 of the 10 patients＇ tumors. Evaluated with gadolinium-enhanced imaging, all 10 patients showed moderate enhancement within the areas that were isointense in the lesion on pregadolinium TlWl. Moreover, some parts which displayed hyperintensity on TlWl within the tumors of 7 patients showed mild enhancement that was similar to muscle on a time-intensity curve （TIC）. Conclusions MSM shows characteristic MR signal intensity （hyperintensity on TlWl and the linear, low-signal intensity on T2Wl）, which may provide valuable information for clinical diagnosis. Together with conventional MRI, TIC may be useful for indicating pleomorphic patterns of MSM.
