Imaging of renal lymphoma: patterns of disease with pathologic correlation.

Extranodal spread of lymphoma often affects the genitourinary system, with the kidneys being the most commonly involved organs. Contrast material-enhanced computed tomography (CT) remains the modality of choice for the detection, diagnosis, staging, and monitoring of renal lymphoma. Magnetic resonance (MR) imaging is particularly useful in patients in whom intravenous administration of iodinated contrast material is contraindicated. Ultrasonography (US), although very valuable for diagnosing lymphoma in the testis or epididymis, is less sensitive than CT and MR imaging for detecting renal lymphoma. Typical imaging findings of renal lymphoma include multiple poorly enhancing or hypoechoic masses, retroperitoneal tumors directly invading the kidneys, bilateral renal enlargement, and perirenal soft-tissue masses. Cystic lesions and tumors predominantly affecting the renal sinus and collecting system are uncommon. Unless the renal lesions manifest in the setting of widespread lymphoma, percutaneous biopsy is indicated to differentiate lymphoma from metastases, hypovascular renal cell carcinoma, uroepithelial carcinoma, or atypical infection, with US routinely being used to guide the procedure. Current immunohistochemical techniques allow accurate diagnosis and characterization of renal lymphoma. Radiologists should be familiar with both typical and atypical manifestations of renal lymphoma and should recommend imaging-guided percutaneous biopsy for diagnostic confirmation to avoid unnecessary nephrectomy.