Genitourinary involvement of lymphomas on FDG-PET

Primary extranodal lymphomatous involvement of the genitourinary tract is rare and secondary extranodal involvement in disseminated disease occurs more frequently. Imaging of metabolic activity with 2-(fluorine-18) fluoro-2-deoxy-d-glucose (FDG) used in PET facilitates the identification of these extranodal sites of disease, particularly in the absence of structural lesions on conventional imaging modalities. Primary extranodal lymphoma affecting the genitourinary system is often caused by high-grade Non-Hodgkin's Lymphoma (NHL) with the most common subtype being diffuse large B-cell lymphoma (DLBCL). Although rare, the incidence of extranodal lymphoproliferative disease is increasing and a delay in diagnosis holds a poor prognosis. Familiarity with benign and physiological causes of FDG uptake, particularly due to the urinary tracer excretion is crucial in identifying sites of lymphomatous involvement in the genitourinary system. Additionally, non-lymphomatous malignancies are usually treated surgically, whereas lymphoma is primarily treated with chemotherapy and/or radiotherapy. Therefore, accurate identification and staging together with histological confirmation significantly impacts management of these patients. This article serves to review and illustrate the imaging findings on FDG-PET/CT of primary extranodal lymphoma affecting the genitourinary system.