A case of focal xanthogranulomatous pyelonephritis difficult to differentiate from renal cell carcinoma

: A 34-year-old female with left flank pain persisting for 3 months consulted us on 19 Feb, 2001. Ultrasonography (US), computerized tomography (CT), magnetic resonance imaging (MRI) and renal angiography revealed a cystic renal tumor in the upper pole of the left kidney invading the spleen, and paraaortic lymph node swelling. Left radical nephrectomy combined with splenectomy and partial diaphragmectomy was performed under a tentative diagnosis of renal cell carcinoma. However, histopathological findings revealed xanthogranulomatous pyelonephritis (XGP). XGP is a rare, severe, chronic inflammatory disease characterized by accumulation of lipid laden macrophages. XGP is classified as diffuse or focal type. Preoperative diagnosis of focal XGP is difficult because of radiological similarities to renal cell carcinoma. Our case was more difficult to diagnose because she showed few signs of inflammation and had no history of urinary tract infection or stones.