A 52-year-old woman comes to the physician because of a 2-day history of fever and left flank pain. She has been treated for multiple episodes of pyelonephritis during the past 3 years. Her temperature is 37.8°C (100.1°F). Physical examination shows left flank tenderness. Urinalysis shows 12–18 WBC/hpf with occasional lymphocytes and mononuclear cells with features of macrophages. Cultures of urine grow 80,000 colonies/mL of Proteus mirabilis. An x-ray of the abdomen shows a 3-cm mass in the lower pole of the left kidney. Gross examination of the mass after it has been resected shows that it is yellow, 3.2-cm in diameter, and centrally but not marginally necrotic. Histologic examination of the mass shows a predominance of epithelioid cells with partially clear and granular-to-foamy cytoplasm. Nuclei are eccentric, normochromic, symmetric, and without significant pleomorphism. Scattered lymphocytes and plasma cells are intermixed. Which of the following is the most likely diagnosis?
(A) Acute pyelonephritis
(C) Renal cell carcinoma, clear cell type,intermediate grade
(D) Renal cell carcinoma, granular cell type
(E) Xanthogranulomatous pyelonephritis
Correct answer : (E) Xanthogranulomatous pyelonephritis