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An 81-year-old woman presents to the emergency department with left upper quadrant pain associated with constipation and fever for the last 3 months. The patient had recently been examined by her primary care provider and told that her left kidney ”was not working right” and that she had kidney stones. She is concerned about a hard lump on the left side of her abdomen.

On physical examination, the patient‘s vital signs are temperature 36.2°C, blood pressure 155/67 mm Hg, pulse 85 beats per minute, respiratory rate 18 breaths per minute, and O2 saturation 97% on room air. In general, the patient is a pleasant, talkative, alert woman in no acute distress. Her heart and lung findings are unremarkable. She has mild abdominal distention with normal bowel sounds and tenderness in the left upper quadrant with a palpable mass along the left colic gutter. The patient has no rebound, guarding, or rigidity, but mild tenderness over the left costovertebral angle is elicited.

Laboratory data reveal an international normalized ratio of 1.24, an activated partial thromboplastin time of 27 seconds, and a creatinine value of 1.7 mg/dL. The patient‘s WBC count is 13.8 X 109/L with a hematocrit of 29% and platelets of 379 X 103/µL. Urinalysis shows 61 WBCs per high-powered field, but the results are otherwise normal, with no bacteria.

Abdominal and pelvic CT with intravenous and oral contrast enhancement was performed.

What is the diagnosis?


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.


  • Cotran RS, Kumar V, Collins T. Robbins Pathologic Basis of Disease. 6th ed. Philadelphia: W. B. Saunders; 1999: 977.
  • Davidson AJ. Radiology of the Kidney. Philadelphia: W. B. Saunders; 1985: 315-7.

Link to further Information on:

For more information on XGP, see the eMedicine articles Xanthogranulomatous Pyelonephritis (within the Radiology specialty) and Xanthogranulomatous Pyelonephritis and Renal Corticomedullary Abscess (within the Internal Medicine specialty).