Abstract：Objective: To analyze the imaging findings of benign renal angiomyolipoma(AML) with minimal fat. Materials and Methods: Ultrasonography, CT and MRI findings in 20 patients(6 males, 14 females) of benign renal AML with minimal fat confirmed by surgery and pathology were analyzed retrospectively. All patients underwent ultrasonography. Unenhanced and biphasic CT scans were performed in 12 patients, 1 patient underwent biphasic CT scan only. Unenhanced and dynamic contrast-enhanced MRI were performed in 12 patients, 1 patient underwent unenhanced MRI only. Results: Ten lesions(50%) were of irregular or ellipsoidal shape. The tumor-kidney interface was straight in 9 lesions(45%). Fifteen lesions protruded from the renal margin, and 7 lesions(46.7%) with restricted growth pattern or “fungus sign”. Compared with the surrounding renal parenchyma, 9 lesions(75%) showed homogeneously high attenuation on unenhanced CT images. Of the 13 patients examined with MR imaging, all were hypo-intense on T2WI, homogeneous(4 lesions, 30.8%) or with micro hyper-intense spot(9 lesions, 69.2%). On double-echo GRE chemical shift imaging, focal or diffuse signal suppression were found in 5 lesions(41.7%). All lesions showed homogeneous or reticular enhancement on biphasic CT and dynamic contrast-enhanced MRI images. Twelve lesions(60%) showed hyperechogenicity on ultrasonography, and 18 lesions(90%) were homogeneous. Tortuous and enlarged vessels were found in 3 lesions(15%). Conclusion: Benign renal AML with minimal fat usually has irregular or non-expansive growth pattern, homogeneous hyperechogenicity on ultrasonography, homogeneously high attenuation on unenhanced CT images, homogeneously hypointense on T2WI with micro hyperintense spots, homogeneous or reticular prolonged enhancement on contrast-enhanced CT and MRI images, female predominance, and tortuous or enlarged vessels were found occasionally.
2010, Vol. 21 
