Xanthogranulomatous pyelonephritis is an uncommon form of chronic bacterial pyelonephritis
It manifests as the destruction of renal parenchyma and the presence of granulomas, abscesses, and collections of lipid-filled macrophages.
It is usually a unilateral process.
Women are affected more often than men (2:1).
It is a complication of chronic pyelonephritis that is locally destructive and has deleterious effects on renal function.
It occurs in 0.5 N1% of cases of chronic pyelonephritis.
The majority of cases follow chronic urinary obstructive or infectious processes.
Patients typically present between 40-55 years of age, with a strong female to male predominance.
Symptoms include: flank pain, weight loss, fever, leukocytosis, anemia, and pyuria.
The majority of patients present with renal pain, recurrent UTI, malaise, anorexia, weight loss, and constipation.
Up to 90% of cases urine cultures grow E.coli and Proteus mirabilis.
Most patients have a history of previous calculous disease, obstructive uropathy, or diabetes mellitus.
About 38% of patients have undergone urologic procedures.
Sterile urinary cultures are not uncommon in the presence of obstructive disease.
On CT findings cortical atrophy and calyceal dilatation are present suggesting “bear paw” sign is present.
Gross findings of the kidneys include yellow to orange nodules and histologically demonstrate fibrosis with granulomatous infiltration and lipid-laden macrophages.
Complications of the process include renal abscesses and parenchymal destruction with cortical kidney scarring.
The process may extend beyond the renal parenchyma with the development of fistula’s to the skin.
Treatment is usually nephrectomy.
The diagnosis is considered in patients with a history of chronic infection and
radiologic features: unilateral renal enlargement, a nonfunctioning kidney on intravenous urogram, the presence of renal calculi, angiographic demonstration of an avascular mass or masses with stretched attenuated intrarenal vessels, and an irregular impaired nephrogram with prominent avascular areas.
Bacterial cultures of the urine are almost invariably positive.
A correct preoperative diagnosis is made infrequently
The diagnosis can be made by a combination of clinical and radiologic features in 40% of cases.