Bilateral solid multifocal intrarenal and perirenal lesions: differentiation with ultrasonography, computed tomography and magnetic resonance imaging.

The differential diagnosis of bilateral solid multifocal intrarenal and perirenal lesions includes neoplastic, infiltrative, inflammatory, and vascular disorders. In a retrospective study 560 solid lesions were examined with cross-sectional imaging modalities (computed tomography (CT), ultrasonography (US), and magnetic resonance imaging (MRI). The results suggest that focal inflammatory disease can often be recognized because the lesions are poorly defined and may show a rather characteristic peripheral rim enhancement following the administration of intravenous contrast. Angiomyolipomas can be accurately diagnosed with CT, MR and US imaging. Because of their unique histomorphology they show fat-equivalent attenuation values at CT, hyperintense signal on T1 and hypointense signal on T2-weighted MR images, and appear homogeneous and hyperchoic with smooth margins at US. By the radiologic appearance alone renal metastases cannot be distinguished from lymphoma or renal cell carcinoma or adenoma. However, when multiple bilateral solid intrarenal or perirenal lesions are found with synchronous metastatic involvement of other organs or occur in the setting of a known primary tumour, the diagnosis of renal metastases is very likely. In the absence of these additional findings, malignant lymphoma has a higher probability. Infiltration of perinephric fat and thickening of the perinephric fascia may occur in inflammatory disease and lymphoma. CT remains the most suitable imaging technique to screen for these additional perirenal and extrarenal findings because of ready availability and relatively short scanning time as compared to MR imaging.