Radiologic Characteristics of Renal Angiomyolipoma with Minimal Fat

Ha, Hong Koo; Seo, Ho Kyung; Chung, Moon Kee

Abstract

PURPOSE: Renal angiomyolipoma (AML) is a benign renal tumor composed of fat, blood vessels, and smooth muscle elements in variable proportion. Radiologic diagnosis of AML depends on the amount of fat in AML, but AML with minimal fat is difficult to differentiate with renal cell carcinoma. We evaluated the accuracy of the radiologic study in the diagnosis of AML and radiologic characteristics of AML with minimal fat.
MATERIALS AND METHODS
From 1993 to 2002, five AMLs with minimal fat of 14 AMLs, which were diagnosed radiologically or pathologically, and 26 renal cell carcinoma, which were classified pathologically as stage 1 (pT1N0M0), were included. The echogenecity on the sonogram, the attenuation on unenhanced and contrast material-enhanced computed tomographic (CT) images, and the signal intensity on T1-, T2-weighted magnetic resonance images (MRI) were investigated and compared retrospectively.
RESULTS
Nine of 14 AMLs were radiologically diagnosed (64.3%). Five AMLs with minimal fat were diagnosed pathologically (1 of renal biopsy, 3 of partial nephrectomy, and 1 of radical nephrectomy). Four of five AMLs with minimal fat showed homogeneous iso-echogenecity, and one showed low-echogenecity on the sonograms. Five AMLs with minimal fat showed homogeneously attenuation on unenhanced CT. Four showed mild enhancement, and one showed heterogenous enhancement. Capsules were not observed in the AMLs with minimal fat but were observed in 20 of 26 renal cell carcinoma on CT. All 4 AMLs with fat demonstrated high signal intensity on the T1- and T2-weighted MRI. AMLs with minimal fat demonstrated low and intermediate signal intensity in 2 and 1 on T1-weighted image, respectively, and demonstrated low and high signal intensity in 2 and 1 on T2-weighted images, respectively.
CONCLUSIONS
In the kidney, the renal mass that was homogenously minimal enhanced renal mass without capsule are suggestive of renal angiomyolipoma that contains abundant muscles and minimal fat and should be considered for nephron sparing surgery.