Chronic Pyelonephritis Presenting as Multiple Tumor-Like Renal Lesions

We encountered a 49-year-old Japanese man in whom tumor-like renal lesions developed as a result of chronic Staphylococcus aureus pyelonephritis. The patient complained of general fatigue, weight loss, and anorexia for 6 months. Contrast-enhanced computed tomography (CT) of the abdomen revealed multiple low-density lesions in both kidneys and paraaortic lymphadenopathy. A strong uptake of Ga67 citrate in the lesions and elevation of serum soluble interleukin-2 receptor and thymidine kinase activity were strongly suggestive of primary renal lymphoma; however, histologic examination of renal biopsy specimens revealed severe tubulointerstitial change, consistent with chronic pyelonephritis. Following systemic antibiotic treatment, multiple tumor-like lesions regressed 4 months later. This case suggested that chronic pyelonephritis could present as bilateral renal tumors.