Comparison of T2-weighted MRI with and without fat suppression for differentiating renal angiomyolipomas without visible fat from other renal tumors.

OBJECTIVE: The purpose of this study was to retrospectively compare the usefulness of T2-weighted imaging with and without fat suppression for differentiating angiomyolipomas (AMLs) without visible fat from other renal tumors.

MATERIALS AND METHODS: MRI was performed in 111 patients (66 men and 46 women; age range, 17-78 years) who had pathologically diagnosed (14 AMLs, 86 renal cell carcinomas [RCCs], and three other tumors) and clinically diagnosed (eight AMLs) renal masses without visible fat or a cystic portion on unenhanced CT. The signal intensity (SI), tumor-to-kidney SI ratio, tumor-to-spleen SI ratio on T2-weighted imaging and fat-suppressed T2-weighted imaging, and tumor-fat subtraction index were measured for each tumor. Receiver operating characteristic (ROC) analysis was used to evaluate diagnostic accuracy of SI ratios.

RESULTS: The highest area under the ROC curve was 0.886 for tumor-to-kidney SI ratio on fat-suppressed T2-weighted imaging. With a tumor-to-kidney SI ratio of 0.9 on fat-suppressed T2-weighted imaging, the sensitivity, specificity, positive predictive value, and negative predictive value were 90.9%, 71.1%, 43.5%, and 97%, respectively. The highest tumor-to-kidney SI ratio of AMLs without visible fat was 1.09. Ninety-eight percent of renal tumors with a tumor-to-kidney SI ratio greater than 1.09 were RCCs (51/52), especially clear cell RCCs (82.7%, 43/52).

CONCLUSION: Fat-suppressed T2-weighted imaging is more useful than T2-weighted imaging for differentiating AMLs without visible fat from non-AMLs. The high SI of solid renal masses on fat-suppressed T2-weighted imaging can be indicative of non-AMLs, especially RCCs.