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20 August 2014 - Case of the Week #323

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Case of the Week #323

Clinical History:
A 68 year old man with cirrhosis of the liver due to NASH was found to have a left renal mass in the mid-pole, measuring 2.9 x 2.6 x 2.6 cm. The lesion was 1.6 cm 20 months earlier, and so was suspicious for a renal cell carcinoma. A core needle biopsy was performed.

Micro images:

What is your diagnosis?

Xanthogranulomatous pyelonephritis


Immunostains were obtained:


Xanthogranulomatous pyelonephritis is an uncommon, severe form of chronic pyelonephritis due to infection, stones or other obstruction, but resembling clear cell renal cell carcinoma. Common symptoms include flank or abdominal pain, lower urinary tract symptoms, fever, palpable mass, gross hematuria and weight loss (Arch Pathol Lab Med 2011;135:671), although some patients are asymptomatic (Acta Radiol Short Rep 2014 Jan 3;3(1)). Imaging often shows unilateral renal enlargement and inflammation (J Clin Imaging Sci 2011;1:45). Patients commonly have anemia and leukocytosis, with positive urine cultures for E. coli or Proteus mirabilis.

Macroscopic appearance shows an enlarged kidney with a thickened capsule, yellow nodules with variable central necrosis, and a dilated renal pelvis with stones or purulent material. Histologically, there is replacement of renal parenchyma with CD68+ foamy histiocytes, occasional multinucleated giant cells and inflammatory cells.

Correct preoperative diagnosis is unusual, but focusing on clinical and laboratory findings, including the presence of stones and the association with obesity may be helpful (Int Urol Nephrol 2011;43:15, ANZ J Surg 2014 Mar 25 [Epub ahead of print]). The main differential diagnosis is clear cell renal cell carcinoma, whose cells have clear cytoplasm that may resemble histiocytes, but are usually in compact, tubulocystic or alveolar patterns accompanied by a delicate, chicken wire vasculature. The RCC cells often contain glassy hyaline globules, have nuclear grade 2-3, are keratin+ and CD68-.

Treatment is with antibiotics or surgery.

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and Shivani Thakore, Associate Medical Editor
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