AJR:167, October 1996 877 Small (3 cm) Hyperechoic Renal Masses: Comparison of Helical and Conventional CT for Diagnosing Angiomyolipoma Stuart 6. Silverman1 Gregory D. N. Pearson Steven E. Seltzer Maria Polger Clare M. C. Tempany Douglass F. Adams Douglas L. Brown Phillip F. Judy OBJECTIVE. Because hyperechoic renal masses may represent angiomyolipomas or small renal cancers, CT is often used to reveal the fatty component, which allows diagnosis of angio- 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 would improve our detec- tion of fat and allow more of these masses to be diagnosed as angiomyolipomas. SUBJECTS AND METHODS. 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 val- ues were compared. RESULTS. Of the 20 masses, we diagnosed angiomyolipoma in 16 masses using helical CT and in 14 masses using conventional CT. In 1 1 masses, we found the measured attenua- tion 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 con- ventional 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 heli- cal 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 (ii = 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). CONCLUSION. 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 small hyperechoic masses for the purpose of diagnosing angiomyolipoma. Received February 28,1996; accepted after revision April 15, 1996. Presented at the annual meeting of the American Roentgen Ray Society, Washington, DC, April-May 1995. tAll authors: Department of Radiology. Brigham and Women’s Hospital, Harvard Medical School, 75 Francis St., Boston, MA02115.Addresscorrespondenceto S.G. Silverman. AJR 1996;167:877-881 0361-803X/96/1674-877 © American Roentgen Ray Society M any small (3 cm) hyperechoic . renal masses, often discovered incidentally, represent angiomyo- lipoma, a benign renal tumor consisting of variable mixtures of blood vessels, smooth muscle, and fat. However, two recent reports suggest that the percentage of small renal can- cers that are hyperechoic is greater than previ- ously recognized. In one series, 61 % of small renal cancers were hyperechoic [1]. A second series reported that 32% of small renal can- cers were markedly hyperechoic and mim- icked angiomyolipomas [2]. These authors recommended that all incidentally discovered hyperechoic renal masses be further evaluated with CT to confirm the presence of fat within the mass, which is diagnostic of angiomyoli- poma in most cases [2, 3]. CT is considered the most reliable test to detect fat within small renal masses and thus make the diagnosis of angiomyolipoma [3-5]. However, conventional CT may fail to reveal the fat in small tumors or in tumors with small amounts of fat [6]. Because of respiratory misregistration (i.e., imaging at different degrees of inspiration that results in skip areas in the imaged organ or lesion), the portion of the lesion containing fat or the entire lesion could be missed. Helical CT eliminates respi- ratory misregistration and has been shown to Downloaded from www.ajronline.org by 52.73.204.196 on 05/16/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved