SMALL (LESS-THAN-OR-EQUAL-TO-3 CM) HYPERECHOIC RENAL MASSES - COMPARISON OF HELICAL AND CONVENTIONAL CT FOR DIAGNOSING ANGIOMYOLIPOMA

OBJECTIVE. Because hyperechoic renal masses may represent angiomyolipo mas or small renal cancers, CT is often used to reveal the fatty compo nent, which allows diagnosis of angiomyolipoma myolipoma 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 wo uld improve our detection of fat and allow more of these masses to be diagnosed as angiomyolipomas. SUBJECTS AND METHODS. We used helical an d conventional CT to examine 20 masses (5-29 mm in diameter) in 17 pat ients who had a small hyperechoic mass detected sonographically. Densi tometry was performed by three readers and the mean attenuation values were compared. RESULTS. 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 neg ative on helical CT scans than on conventional CT scans. In five masse s, we found the opposite to be true. In the remaining four masses, we were unable to diagnose angiomyolipoma. Of the masses that we diagnose d as angiomyolipoma, the mean attenuation value when examined with hel ical CT (-44 H) was more negative than with conventional CT (-35 H) bu t 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 atte nuation values on helical CT were significantly lower than on conventi onal CT (-40 H versus -30 H, p < .05). Likewise, for masses with atten uation values that differed by more than 6 H (n = 8), when imaged by t he two techniques we again found that mean attenuation values on helic al CT were significantly lower (-43 H versus -24 H, p < .05). CONCLUSI ON. Helical CT revealed angiomyolipoma across all cases as well as con ventional 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 atten uations of the two CT techniques differed by a significant amount. We preferred helical CT over conventional CT when examining small hyperec hoic masses for the purpose of diagnosing angiomyolipoma.