Xanthogranulomatous Pyelonephritis

Updated: Mar 22, 2024
  • Author: Samuel G Deem, DO; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Overview

Practice Essentials

Xanthogranulomatous pyelonephritis (XGP), is a rare, serious, chronic inflammatory disorder of the kidney characterized by the replacement of normal renal or perirenal tissue with granulomatous tissue containing lipid-laden foamy macrophages. Those macrophages appear yellow on pathologic section, which is the source of the disease's name (xantho is the Greek term for yellow). XGP was named by Osterlin in 1944, but was first described in 1916 by Schlagenhaufer. [1, 2]

XGP most commonly involves infection with Proteus or Escherichia coli. [3, 4] Pseudomonas species have also been implicated. The kidney is usually nonfunctional. Most cases of XGP involve a diffuse process; however, up to 20% are focal. (See Etiology and Pathophysiology.)

XGP typically occurs in patients with a history of nephrolithiasis, urinary tract obstruction, and recurrent urinary tract infection. [5] Other common risk factors are diabetes and immunocompromise. [3] Most patients are middle-aged women, [6] but rare reports exist of pediatric cases, with most occurring in boys. [7]

Patients with XGP often appear chronically ill. Signs and symptoms include anorexia, fever, chills, weight loss, and flank pain. The pain of XGP is not colicky in nature; it is usually dull and persistent. [8] XGP is notorious for fistulization, often to the skin. (See Presentation.)

XGP shares many characteristics with true renal neoplasms in terms of its radiographic appearance and its ability to involve adjacent structures or organs. Typical CT findings include a staghorn calculus with contraction of the renal pelvis, multiple rounded hypoechoic foci in the kidney, enlargement of the kidney, and perinephric inflammation or abscess. [9]  The arrangement of multiple rounded hypoechoic foci around the contracted renal pelvis has been described as the bear paw sign and is considered characteristic of XGP. [3, 4]  (See Workup.)

Open radical nephrectomy has historically been the hallmark of management and it remains the most common treatment method for XGP. [6]  In selected cases, however, laparoscopic nephrectomy may be preferable, as it may result in less postoperative pain and faster recovery. The renal and perirenal inflammatory changes in XGP can pose a formidable challenge, however, and conversion of laparoscopic to open surgery may prove necessary. Rarely, partial nephrectomy is feasible. [6]  (See Treatment.)

Most cases of XGP are unilateral, but bilateral disease has been reported. Bilateral XGP is usually fatal, but bilateral nephrectomy and long-term dialysis is a treatment option in such cases, and Perez et al described successful treatment with partial nephrectomies in one patient [10]  (See Treatment.)

The overall prognosis for patients with XGP is good. Death from this entity is exceedingly rare, although morbidity is substantial.

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Anatomy

The kidneys are paired organs in the retroperitoneum. They are covered in a thin, fibrous capsule that is in turn covered by Gerota’s fascia. On the right, the liver and adrenal gland abut the superior pole of the kidney. The second part of the duodenum is medial to the right kidney and may be reflected medially to gain exposure to the inferior vena cava (Kocher maneuver). On the left, the superior pole of the kidney is attached to the spleen superolaterally (splenorenal ligament) and is very near to or in direct contact with the tail of the pancreas medially.

The colon is anterior to the kidneys and is easily reflected anteriorly and medially when transabdominal exposure is required. The renal hilar structure, from anterior to posterior, includes the vein, the artery, and the collecting system. The left renal vein has 3 draining tributaries: the adrenal, gonadal, and posterior lumbar veins.

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Etiology and Pathophysiology

The exact etiology of xanthogranulomatous pyelonephritis (XGP) is unknown, but it is generally accepted that the disease process requires long-term renal obstruction and infection. XGP is most commonly associated with Proteus or Escherichia coli infection; Pseudomonas species have also been implicated. [11]

Stones (frequently of staghorn proportions) are found in 80% of patients with XGP but are not required to make the diagnosis. XGP is often observed in patients with diabetes, immunocompromise, or both. Abnormal lipid metabolism has also been hypothesized as an etiologic factor in XGP.

XGP displays neoplasmlike properties; it is capable of local tissue invasion and destruction and has been referred to as a pseudotumor. Adjacent organs, including the spleen, pancreas, or duodenum, may be involved. Malek and Elder proposed the following stages of XGP involvement [12] :

  • Stage I: Confined to the kidney
  • Stage II: Infiltration into the perinephric space within the Gerota fascia
  • Stage III: Extension into adjacent paranephric space and other retroperitoneal structures

The term focal XGP is increasingly used for the earliest stage of the disease, in which only part of the kidney is involved and some kidney function remains preserved. Stage II and beyond are often called diffuse XGP. [5]

The gross appearance of XGP is that of a mass of yellow tissue with regional necrosis and hemorrhage, superficially resembling renal cell carcinoma. The pathognomonic microscopic feature is the lipid-laden foamy macrophage accompanied by both chronic- and acute-phase inflammatory cells. Focal abscesses may be observed.

The primary mechanisms involved in XGP include nephrolithiasis, collecting system obstruction, and infection. No single factor can explain the process; rather, an inadequate host response to the acute inflammatory response occurs in the obstructed, necrotic kidney. [13]

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Epidemiology

XGP occurs in approximately 1% of all renal infections. It is 4 times more common in women than in men and is usually noted in the fifth and sixth decades of life. The left kidney is more often affected. [6]

Although XGP is rare in the pediatric population, it is found in approximately 16% of pediatric nephrectomy specimens. In children, XGP is more common in boys and usually affects those younger than 8 years.

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