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Xanthogranulomatous Pyelonephritis: Symptoms, Diagnosis and Treatment

Definition of Xanthogranulomatous Pyelonephritis

Xanthogranulomatous pyelonephritis (XP) is a rare, chronic, destructive form of pyelonephritis characterized by granulomatous inflammation that destroys the renal parenchyma and by lipid-laden foam cells (Bingol-Kologlu et al., 2002) (Zorzos et al., 2003). Depending on the extent of renal involvement, XP may be focal or diffuse. Malek and Elder classified the disease into the following stages:

• Stage I: Nephric, confined to the kidney
• Stage II: Perinephric, involving the perinephric fat
• Stage III: Paranephric, involving adjacent organs

Epidemiology

XP is rare (incidence 1.4 per 100,000); women are affected more often than men.

Etiology

XP is a unilateral renal disease that develops in association with persistent urinary tract infection and obstruction, often caused by infection stones. Other risk factors include diabetes mellitus, immunosuppression, anatomical abnormalities of the urinary tract, and vesicoureteral reflux. The most commonly isolated organisms are E. coli, Proteus mirabilis, Klebsiella, and Staphylococcus. The pathophysiology is not fully understood; an impaired macrophage response leading to progressive tissue destruction has been proposed.

Pathology of Xanthogranulomatous Pyelonephritis

Gross pathology

The kidney is enlarged, and the enlarged renal pelvis is filled with pus (pyonephrosis). Orange-yellow inflammatory lesions occur alongside tissue necrosis and small abscesses. Renal involvement is initially segmental; as the disease progresses, inflammation may spread diffusely throughout the kidney. Granulomatous inflammatory tissue replaces the renal parenchyma. The disease may extend into adjacent retroperitoneal structures.

Histology

The inflamed tissue contains neutrophils, lymphocytes, plasma cells, necrosis, and large macrophages with foamy, lipid-containing cytoplasm (foamy histiocytes). Giant cells or epithelioid granulomas may also be present.

Signs and Symptoms of Xanthogranulomatous Pyelonephritis

Symptoms are often nonspecific and may persist for weeks to months.

• Flank pain
• Fever and chills
• Persistent bacteriuria
• General malaise and weight loss
• Uncommonly, a palpable flank mass

Diagnostic Workup

Urine sediment

Urine sediment may show leukocyturia and bacteriuria; xanthoma cells are rarely detected.

Urine culture

Urine culture is often positive but is not specific for XP.

Laboratory tests

Findings may include leukocytosis, increased ESR, and increased CRP. Obtain blood cultures in patients with severe disease. Also measure creatinine and electrolytes; depending on the clinical presentation, liver enzymes and lipase may also be indicated.

Renal ultrasound

Renal ultrasound may show an enlarged kidney with a mass of mixed echogenicity that cannot reliably be distinguished from a tumor. Other typical findings include dilation of the renal pelvis and calyces and nephrolithiasis.

Computed tomography

CT is the diagnostic tool of choice. Typical findings include nephrolithiasis, decreased contrast uptake in the surrounding renal tissue (bear paw sign), and hydronephrosis. The inflammatory process may involve the perinephric tissue; renal cell carcinoma cannot always be ruled out.

MRI

MRI is an alternative to CT, especially in patients with renal impairment or contrast-media allergy.

Renal scintigraphy

Renal scintigraphy can be used to assess residual renal function when organ preservation appears possible.

Intravenous urography

Intravenous urography is a historical investigation. CT should be performed when XP or a renal abscess is suspected. Typical findings included nephrolithiasis, lack of contrast opacification on the affected side, and an enlarged renal shadow.

Differential diagnosis

The differential diagnosis includes renal cell carcinoma, upper tract urothelial carcinoma, renal abscess, pyelonephritis, renal tuberculosis, and other chronic destructive renal inflammatory diseases. XP is often confirmed histologically only after surgery.

Treatment of Xanthogranulomatous Pyelonephritis

The standard treatment for XP is radical nephrectomy. Before definitive surgery, temporary drainage with a nephrostomy or ureteral stent is useful in patients with pyonephrosis or significant obstruction. Perioperative antibiotic therapy is important and may need to be adjusted based on urine culture or intraoperative swab results. Surgery is technically difficult because of adhesions; a laparoscopic approach may be considered in selected patients at experienced centers.

In selected cases of segmental renal involvement, an organ-preserving approach with antibiotic therapy, internal ureteral stenting, and partial nephrectomy may be considered.

References

Zorzos u.a. 2003 ZORZOS, I. ; MOUTZOURIS, V. ; KORAKIANITIS, G. ; KATSOU, G.: Analysis of 39 cases of xanthogranulomatous pyelonephritis with emphasis on CT findings.
In: Scand J Urol Nephrol
37 (2003), Nr. 4, S. 342–7

  Deutsche Version: Xanthogranulomatöse Pyelonephritis

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