Renal Diffuse Large B-cell Lymphoma Mimicking Acute Pyelonephritis on 18 F-FDG PET/CT.

A 58-year-old man with a history of lithotripsy for urolithiasis presented with persistent fever and pollakisuria. As empirical anti-infective therapy was ineffective, 18 F-FDG PET/CT was performed to detect potential malignancy, revealing bilateral renal enlargement with multiple nodular cortex uptakes and an enlarged left axillary lymph node, suggestive of pyelonephritis. However, biopsies of the axillary lymph node and right kidney confirmed high-grade diffuse large B-cell lymphoma (DLBCL). Following R-DA-EPOCH chemotherapy, the patient achieved sustained remission. This case highlights that renal DLBCL can mimic pyelonephritis on 18 F-FDG PET/CT, and PET/CT is instrumental in guiding biopsy for accurate diagnosis.