Characterization of small renal lesions: Problem solving with MRI

With the widespread use of cross-sectional imaging, many renal masses are incidentally found. These need to be accurately characterized as either lesions potentially requiring surgery such as renal cell carcinoma or as nonsurgical lesions including cyst, angiomyolipoma, abscess, hematoma, lymphoma, or metastasis. MRI and CT can both accurately characterize renal masses and frequently, both exams are complimentary to each other. Advantages of CT include a short imaging time, familiarity to referring clinicians, the ability to detect calcium and to quantify enhancement. The advantages of MRI include better intrinsic soft tissue contrast, primary multiplanar capability, lack of radiation exposure, and safer contrast material. MRI is especially useful in those patients who require follow-up imaging studies and who would otherwise be exposed to additional radiation and iodinated contrast material during follow-up CT exams. This includes patients with indeterminate cystic masses, with a history of renal cell carcinoma, and with a genetic predisposition (Von HippelLindau) to develop renal cell carcinoma. The concepts of evaluating a renal mass with MR imaging are the same as those used in CT. An enhancing mass indicates a vascular mass, which is indicative of a neoplasm. A combination of T1-weighted images with and without fat saturation and T2-weighted images should be obtained prior to gadolinium administration. This is followed by fat suppressed T1-weighted images after gadolinium. Diffusion weighted imaging may also