MR findings of renal angiomyolipoma containing minimal fat

Abstract

Objective To document the MRI features of renal angiomyolipoma (RAML) containing minimal fat and to explore whether the MR features vary depending on the tumor size. Methods The MR findings of 15 cases of pathologically-proved RAML containing minimal fat were reviewed retrospectively from January 2008 to March 2010. All patients underwent MR in a 1.5 T or 3.0 T scanners. The MR features of the lesions were analyzed, with emphasis on the signal intensity and homogeneity on T2WI, in regards to pseudocapsule, lipid component, hemorrhage, cystic degeneration or necrosis, blood vessels, interface with renal parenchyma and enhancement pattern. All lesions were categorized into 2 groups; those with diameter ＞4 cm and those with diameter ≤4 cm. The difference of imaging characteristics between these two groups was analyzed using Fisher exact test. Results All 15 lesions demonstrated hypointensity on T2WI compared to the renal parenchyma. Homogeneous signal intensity on T2WI was seen in 6 lesions (6/15); peritumoral pseudocapsule in 3 lesions (3/15); cystic degeneration or necrosis, hemorrhage in 5 lesions (5/15); flow void of blood vessels in 2 lesions (2/15); lipid component in 4 lesions (4/15); angular interface with renal parenchyma in 10 lesions (10/15); homogeneous enhancement in 8 lesions (8/15). Fifteen lesions were divided into two groups; 9 categorized into group 1 (the maximum diameter ≤ 4 cm) and 6 into group 2 ( the maximum diameter ＞ 4 cm). Cystic degeneration or necrosis was seen in 0 of 9 in group one and 5 of 6 in group two respectively, hemorrhage(0 of 9 and 5 of 6 respectively) and pseudocapsule(0 of 9 and 3 of 6 respectively. The difference between these findings in the two groups demonstrated statistical significance (P ＜ 0. 05). Conclusion The MR features of RAML containing miminal fat were hypointensity on T2 WI,angular interface with renal parenchyma and homogeneous contrast enhancement, however, these findings can vary depending on the tumor size. Key words: Kidney neoplasms; Magnetic resonance imaging