Xanthogranulomatous pyelonephritis (XGP): The CT scan demonstrates a markedly dilated left renal pelvis and calyces with a large staghorn calculus in the renal pelvis. The left kidney is mildly enlarged and multilobulated. The renal cortex has a thin rim of relatively intense enhancement. These findings are consistent with XGP.

XGP is a chronic renal infection that leads to scarring of the renal cortex, dilatation of the calyces and renal pelvis, and diffuse infiltration of the renal parenchyma with lipid-laden macrophages intermingled with lymphocytes, plasma cells, polymorphonuclear leukocytes, and occasional giant cells. Xanthogranulomatous refers to the yellow masses that form in the kidney as a result of the high lipid content of the infiltrating macrophages.

A calculus in the renal pelvis occurs in greater than 75% of all cases of XGP. The calculus is usually staghorn in shape and composed of struvite. This process develops from long-standing partial obstruction of the renal pelvis due to stones, stricture, or uroepithelial tumor. The histologic response is thought to result from the liberation of lipid from the cells destroyed by bacterial infection. The inflammatory process often extends into the psoas muscle and the perirenal space. The renal parenchyma usually does not become calcified. XGP is often observed in patients with diabetes mellitus or those who are otherwise immunocompromised.

XGP is 4 times more common in women than men and typically observed in the fifth or sixth decades of life. Typical signs and symptoms are weight loss, malaise, anorexia, low-grade fever, and abdominal and flank pain. The pain of XGP is not colicky; it is usually dull and persistent. Patients often have no lower urinary tract symptoms. The kidney may be palpable on examination. Pyuria, leukocytosis, anemia, and albuminuria may be present. Bacteria are not typically cultured from urine. If they are, the most common organisms are Proteus mirabilis or Escherichia coli, though Pseudomonas species can also be involved. XGP can lead to fistulae; pyelocutaneous, ureterocutaneous, and pyeloenteric fistulae are all well described.

Radiographs of XGP usually demonstrate the staghorn calculus in the enlarged, multilobulated kidney that does not opacify during excretory urography. Retrograde pyelography shows irregular filling defects in the dilated renal collecting system. Ultrasonography depicts pelvocaliectasis with many fine echoes in the collecting system because the products of inflammation fill the calyces. A CT scan can show the pelvocaliectasis, staghorn calculi, lobulated and enlarged kidney, and a thin rim of intensely enhancing renal cortex due to inflammatory tissue in the calyceal wall and renal parenchyma. CT scanning is also helpful for demonstrating extension into the psoas muscle or the perirenal and pararenal spaces.

Treatment with antibiotics alone is inadequate, but it may be used as a temporizing measure in patients requiring a medical workup before nephrectomy. The choice of antibiotic should be specific to any organism isolated on urine culture. Nephrectomy is the definitive treatment for XGP. All involved granulomatous tissue should be removed to minimize the risk of remaining infected tissue leading to cutaneous fistulae. Open nephrectomy is typically preferred because of the technical difficulties often encountered with laparoscopic techniques. This patient underwent left nephrectomy. Her symptoms resolved, but she continued to have mild chronic renal failure.



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