Xanthogranulomatous pyelonephritis

Case contributed by Ryan Thibodeau
Diagnosis certain


Abdominal pain. History of nephrolithiasis.

Patient Data

Age: 30 years
Gender: Female

There is a globally enlarged right kidney with an associated thinned cortex and dilated low-density calyces. There is a large branching right renal stone which follows the contours of the calyces and pelvis, consistent with a staghorn calculus. There are multiple additional large stones in the mid and lower calyces. There is mild right-sided perinephric fat stranding. Furthermore, there is discrete contrast retention in the lower calyceal system in the delayed phase, suggestive of severe calyceal obstruction in this region. Patient is status post right double-J stent placement.

The left kidney is normal in appearance, size, and enhancement in all three phases.

Lymph nodes: There is a prominent pericaval lymph node, measuring 2.5 cm in diameter.

Soft tissue: There is a small fat-containing umbilical hernia.

Case Discussion

This is a case of pathologically proven xanthogranulomatous pyelonephritis (and a staghorn calculus). This case demonstrates the classic "bear paw appearance" of xanthogranulomatous pyelonephritis.

The pathologic examination from the right radical nephrectomy grossly demonstrated cysts with tan-green purulent material. Further dissection revealed diffusely scatted, multiloculated cysts that contained yellow to tan-gray pus-like material. Multiple stones were seen within the calyces and pelvis. Histopathologically, the renal parenchyma contained foamy histocytes, occasional giant cells, "thyroidization" of the kidney, and marked acute and chronic inflammatory changes. The enlarged pericaval lymph node was dissected, which only revealed a reactive lymph node without evidence for malignancy.

Michael Schuster, MD
Christine Cooley, MD

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