Radiologic Differentiation Between Homogeneously Solid Renal Cell Carcinoma and Muscle-Predominant Renal Angiomyolipoma

Kim, Joo Hyung; Cho, Jae Ho; Chang, Jay Chun; Park, Bok Hwan

Abstract

PURPOSE: To compare the differential radiologic findings of renal cell carcinoma presenting as a homogeneous solid mass (HS-RCC) and muscle-predominant angiomyolipoma (MP-AML).
MATERIALS AND METHODS
Nine of 76 surgically and pathologically proven RCCs presenting at CT or magnetic resonance (MR) imaging as a homogeneous solid mass, and four cases of MP-AML were included in this study. Echogenicity at sonography, attenuation at non-enhanced CT (NECT), the contour of the mass, signal intensities at T1- and T2-weighted MR imaging, the existence of a capsule, and the pattern and degree of enhancement at CT and MR imaging were retrospectively analyzed.
RESULTS
Two of five HS-RCCs were isoechoic and three were hyperechoic. Two of three MP-AMLs, however, were isoechoic, and one was mixed echoic. All nine HS-RCCs were round or oval in shape, but three MPAMLs were lobulated and one was round. At NECT, seven of eight HS-RCCs were isodense and one was hypodense compared to surrounding normal renal parenchyme, but three MP-AMLs were hyperdense masses and one was isodense. At enhanced CT, HS-RCCs showed various degrees of homogeneous enhancement, but all MP-AMLs showed moderate homogeneous enhancement. All three MP-AMLs demonstrated heterogeneous hypointensity at T2-weighted MRI and homogeneous hypointensity at T1-weighted MRI. HS-RCCs showed various signal intensities at both T1- and T2-weighted MRI, and in five cases, heterogeneous high signal intensity at T2-weighted MRI. Capsules were observed in seven of nine HS-RCCs but not in any of the three MP-AMLs. At enhanced T1-weighted MRI, MP-AMLs showed mild to moderate enhancement, but HSRCCs showed mild, moderate, and strong enhancement in two, two, and five cases, respectively.
CONCLUSION
Echogenicity, density at NECT, signal intensity at MR T2-WI, the contour of the mass, and the existence of a capsule are features which are useful in the differential diagnosis of HS-RCC and MP-AML.