High-grade transitional cell carcinoma masquerading as a xanthogranulomatous pyelonephritis and perinephric abscess.

Xanthogranulomatous pyelonephritis (XGPN) is an atypical long-term pyelonephritis with destruction of renal parenchyma and a long-term inflammatory infiltrate of macrophages. Reported presentations of transitional cell carcinoma (TCC) are different. A 73-year-old woman presented with loin pain, prostration, and fever. Computed tomography scan revealed poor cortical enhancement of the kidney, but some of the images bore resemblance to the characteristic "bear's paw" sign, consistent with XGPN with a 7-cm perinephric collection. She was provisionally diagnosed as severe acute pyelonephritis, possibly XGPN, with abscess. In view of the poor clinical condition, decision was made to perform nephrectomy. Histology revealed a G3pT4 high grade TCC with perineural and vascular invasion and reactive xanthogranulomatous inflammatory response. There are few reports of concomitant XGPN and TCC affecting the kidney. However, there has not been any mention of XGPN and TCC presenting as acute pyelonephritis and perinephric abscess so far.