Small (< or = 3 cm) hyperechoic renal masses: comparison of helical and convention CT for diagnosing angiomyolipoma.

Abstract

Because hyperechoic renal masses may represent angiomyolipomas or small renal cancers, CT is often used to reveal the fatty component, which allows diagnosis of angiomyolipoma in most cases. Because conventional CT can fail to reveal fat in angiomyolipomas 3 cm or smaller, we conducted a study to determine whether helical CT would improve our detection of fat and allow more of these masses to be diagnosed as angiomyolipomas. We used helical and conventional CT to examine 20 masses (5-29 mm in diameter) in 17 patients who had a small hyperechoic mass detected sonographically. Densitometry was performed by three readers and the mean attenuation values were compared. Of the 20 masses, we diagnosed angiomyolipoma in 16 masses using helical CT and in 14 masses using conventional CT. In 11 masses, we found the measured attenuation values to be more negative on helical CT scans than on conventional CT scans. In five masses, we found the opposite to be true. In the remaining four masses, we were unable to diagnose angiomyolipoma. Of the masses that we diagnosed as angiomyolipoma, the mean attenuation value when examined with helical CT (-44 H) was more negative than with conventional CT (-35 H) but not significantly so (p = .058). However, in the subset of patients with masses that were 2 cm or less in diameter (n = 14), the mean attenuation values on helical CT were significantly lower than on conventional CT (-40 H versus -30 H, p < .05). Likewise, for masses with attenuation values that differed by more than 6 H (n = 8), when imaged by the two techniques we again found that mean attenuation values on helical CT were significantly lower (-43 H versus -24 H, p < .05). Helical CT revealed angiomyolipoma across all cases as well as conventional CT did. Also, helical CT was more sensitive in revealing fat in masses less than 2 cm in diameter and in masses in which the attenuations of the two CT techniques differed by a significant amount. We preferred helical CT over conventional CT when examining hyperechoic masses for the purpose of diagnosing angiomyolipoma.