New radiologic classification of renal angiomyolipomas.
OBJECTIVE
To introduce a new radiologic classification of renal angiomyolipoma (AML).


METHODS
Between 1995 and 2014, CT or MR images in 98 patients with histologically proven 98 AMLs were reviewed independently by a radiologist and a resident. The lesions were classified as (a) 53 fat-rich AML (≤-10HU), (b) 22 fat-poor AML (>-10HU) with tumor-to-spleen ratio (TSR) <0.71 or signal intensity index (SII) >16.5%, and (c) 23 fat-invisible AML (>-10HU) with TSR ≥0.71 and SII ≤16.5%. Inter-reader agreement was assessed with a weighted kappa value. Fat-poor and fat-invisible AMLs were compared in terms of attenuation value, TSR, and SII using unpaired t-test.


RESULTS
The weighted kappa value was 0.956 (95% confidence interval, 92.0-99.1%). When a region of interest (ROI) was placed within the most hypodense area on unenhanced CT or within the most signal-dropped area on chemical shift image, the mean attenuation values, TSRs, and SIIs of fat-poor versus fat-invisible AMLs were 19.5±8.1 HU versus 38.1±9.9 HU, 0.59±0.19 versus 0.96±0.01, and 43.7±16.9% versus -5.4±21.1%, respectively (p<0.0001). When a ROI was placed within the other area on CT or chemical shift images, 90.1% (48/53) of fat-rich AMLs were mis-classified as fat-poor or fat-invisible AML and 50% (11/22) of fat-poor AMLs as fat-invisible AML.


CONCLUSIONS
The new radiologic classification of renal AML is feasible for clinical practice. ROI location is important in differentiating the types of AMLs.
Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
Sohee
S
Song
Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea. Electronic address: rapark@skku.edu.
Byung Kwan
BK
Park
Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
Jung Jae
JJ
Park
D000328:Adult; D000368:Aged; D018207:Angiomyolipoma / Q000000981:diagnostic imaging*; D002292:Carcinoma, Renal Cell / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
Angiomyolipoma; Classification; Computed tomography; Magnetic resonance imaging; Region of interest