A 60-year-old man presented with recurrent episodes of septicemia, nephrolithiasis, and right-sided hydronephrosis. Blood counts showed leukocytosis and anemia, and urinalysis revealed pyuria with microbiological evidence of Proteus mirabilis. In the past history, there were several interventions for recurrent stone disease and repeated transurethral resections for superficial bladder tumors in the 1990s. Also, an intraperitoneal perforation of the bladder due to severe cystitis with peritonitis had occurred several years before. No other systemic diseases were known. More recently, there had been short intervals between stone interventions and hospital readmissions due to septicemia. US showed an enlarged right hydronephrotic kidney and nephrolithiasis. CT yielded no additional information. For emergency treatment, a ureteral stent was inserted and parenteral antibiotic therapy was given.

After resolution of septicemia, ureterorenoscopy was performed. An amorphous mass with the consistency of chewing gum was removed from the ureter. Renal scintigraphy showed a nonfunctioning right kidney, and for this reason the kidney was removed. The pathology report gave the diagnosis of xanthogranulomatous pyelonephritis (a granulomatous inflammatory infiltrate composed of neutrophils, lymphocytes, plasma cells, xanthomatous histiocytes, and multinucleated giant cells). The renal parenchyma was markedly reduced. Grossly, the chronic inflammatory and fibrous process involved the perirenal fat (perinephritic stage II). The postoperative course was unremarkable.

Discussion

Xanthogranulomatous pyelonephritis is a rare chronic destructive inflammation of the medulla and cortex (incidence 1.4/100,000), usually due to an intrarenal urinary outflow obstruction, which primarily affects middle-aged women. The inflammatory areas are interspersed with characteristic xanthoma cells (lipid-laden histiocytes). The changes are almost always unilateral. Symptoms of xanthogranulomatous pyelonephritis are flank pain (70%), fever and chills (70%), flank tumor, persistent bacteriuria, general malaise, and weight loss.^1–6 This entity was first described by Schlagenhaufer in 1916.⁷

This unilateral disease of the kidney is associated with nephrolithiasis, urinary tract infection, and obstruction. The most commonly isolated bacteriae are Escherichia coli, Proteus mirabilis, Klebsiella, and staphylococci.⁵ The urine sediment shows leukocyturia, bacteriuria, and possibly xanthoma cells. The urine culture is often positive, but not necessarily. Kidney US usually shows an enlarged kidney with a mixed echogenic mass that cannot be reliably distinguished from a tumor. Possibly, nephrolithiasis can be detected. CT is the diagnostic tool of choice.^1–6 A renal mass can be seen with inhomogeneous contrast enhancement, reduced renal function, and evidence of nephrolithiasis. Findings include hydronephrosis (90.9%), renal calculus (72.7%), pyonephrosis (45.5%), intraparenchymal collection (45.5%), cortical renal atrophy (45.5%), nonfunctioning kidney (36.4%), abscess (36.4%), and perinephric fat accumulation (18.2%).⁸

In summary, the combination of a nonfunctioning enlarged kidney, a central calculus within a contracted renal pelvis, expansion of the calices, and inflammatory changes are typical for this disease. A renal cell carcinoma cannot be ruled out with certainty based on image morphology. Three forms of xanthogranulomatous pyelonephritis have been recognized: diffuse, segmental, and focal. The segmental form is characterized by segmental involvement of the kidney, while the focal form is located within the cortex without pelvic communication. It mimics other neoplastic and inflammatory renal diseases.⁶

The exact etiology of xanthogranulomatous pyelonephritis is unknown, but it is generally accepted that the disease process is associated with long-term obstruction and infection. Additional predisposing factors are ureteropelvic junction syndrome, ureteropelvic duplication, bladder tumor, and chronic interstitial nephritis. Comorbid conditions were also noted including pregnancy, diabetes mellitus, rheumatoid arthritis, chronic viral hepatitis C, cirrhosis, and obesity.⁶

The standard treatment for xanthogranulomatous pyelonephritis is complete or partial nephrectomy. Perioperative antibiotic therapy is important, which may have to be modified according to the results of the intraoperative swabs. In individual cases of segmental involvement, the kidneys may be salvaged by antibiotic therapy and internal ureter splinting alone.^1–6

Clinical Practice Points

Xanthogranulomatous pyelonephritis is a rare form of chronic pyelonephritis in association with long-term urinary tract obstruction and infection that results in kidney destruction. The diagnosis can often only be made postoperatively by the pathologist. Preoperative and postoperative broad-spectrum antibiotics and symptomatic management are key factors for successful management of this condition. The prognosis is considered to be good after treatment.