Ultrasound-Guided Attenuation Parameter（UGAP）A Valuable Alternative in Differentiation between Renal Angiomyolipoma without Visible Fat and Clear Cell Renal Cell Carcinoma? A Pilot Study

Background: To assess the utility of the ultrasound-guided attenuation parameter (UGAP) for distinguishing between and differential diagnosis of renal angiomyolipoma without visible fat (AML.wovf) and clear cell renal cell carcinoma (ccRCC). Methods The study included 74 patients with pathological renal tumor (60 ccRCC and 14 AML.wovf from 46 men and 28 women). The UGAP, CT attenuation values, signal intensity (SI), and tumor-to-spleen SI ratios were determined for each renal mass. The mean of five consecutive scanning lines of UGAP was used. A radiologist, blinded to the pathology results, measured CT attenuation values and assessed decreased SI on opposed-phase images compared to in-phase images. Clinical and imaging variables were analyzed using the Student’s t-test and two-tailed Fisher exact test. The diagnostic performance of UGAP between MRI-determined SI index, tumor-to-spleen SI radio and CT attenuation values were compared. Results AML.wovf showed significantly higher UGAP value than ccRCC (0.7 ± 0.2 vs 0.4 ± 0.1, respectively, P  < 0.001). The area under the receiver operating characteristic curve for UGAP was 0.89, which is better than MRI-based SI index (AUC = 0.74) and CT attenuation values (AUC = 0.81). UGAP had a lesion-level sensitivity of 93.3 (95% CI: 83–98); specificity, 57.0 (95% CI: 30–81); an accuracy of 83.8 (95% CI: 73–90). Test-retest reliability of UGAP was low. MRI-based SI index ( P  = 0.04) and CT attenuation values ( P  = 0.01) show significant difference between these two types of renal lesions. Kendall’s W coefficient of the UGAP test-retest reliability for ccRCC and AML.wovf was 0.888 and 0.805, respectively, both showing a strong consistency. Conclusion UGAP can be used to identify AML.wovf from ccRCC, and may offer a new way to ensure those with renal AML.wovf tumors avoid unnecessary surgery.