title: Comparison of T2-weighted MRI with and without fat suppression for differentiating renal angiomyolipomas without visible fat from other renal tumors.
abstract: 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.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: 1 Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Poong-nap-dong, Songpa-gu, Seoul 138-736, South Korea.
authors.forename: Mi Sun
authors.initials: MS
authors.lastname: Chung
authors.forename: Hyuck Jae
authors.initials: HJ
authors.lastname: Choi
authors.forename: Mi-Hyun
authors.initials: MH
authors.lastname: Kim
authors.forename: Kyoung-Sik
authors.initials: KS
authors.lastname: Cho
mesh_terms: D000273:Adipose Tissue / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D018207:Angiomyolipoma / Q000175:diagnosis*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity