Diagnostic Ultrasound - Abdomen and Pelvis

Xanthogranulomatous Pyelonephritis
TERMINOLOGY
Abbreviations
• Xanthogranulomatous pyelonephritis (XGP/XGPN)
Definitions
• Chronic renal inflammation usually associated with
longstanding urinary calculus obstruction (75%)
• Renal parenchyma is gradually replaced by lipid-laden
macrophages
○ Greek prefix "xantho-" refers to yellow color of fat
• Diffuse (> 80%) and focal (< 20%) forms
○ Diffuse: Due to obstruction at ureteropelvic junction
○ Focal or segmental: Due to obstruction of single
infundibulum or 1 moiety of duplex system
• 3 stages of XGP: Intrarenal → perirenal → perinephric ±
retroperitoneal involvement
IMAGING
General Features
• Best diagnostic clue
○ Staghorn calculus with renal enlargement and perirenal
fibrofatty proliferation
• Location
○ Unilateral (most cases) > bilateral
Ultrasonographic Findings
• Grayscale ultrasound
○ Appearance varies depending on pattern of XGP
○ Diffusely enlarged kidney; highly reflective central
calculus
○ Anechoic or hypoechoic round masses replacing normal
parenchyma
○ Parenchymal thinning ± hydrocalyces or pyonephrosis
○ Segmental XGP: Anechoic or hypoechoic masses
surrounding calculus-obstructing calyx
○ Perinephric inflammatory tissue ± fluid collection
CT Findings
• Multiple focal low-attenuating renal masses with rim
enhancement
○ Pockets of lipid-laden macrophages appear cystic on CT
and may mimic hydronephrosis
• Impaired contrast excretion into collecting system
• Renal sinus fat obliterated with large central "staghorn"
calculus
• Perinephric extension ± adjacent organs or structures may
include sinus tracts or abscesses
Imaging Recommendations
• Best imaging tool
○ Ultrasound ideal at initial investigation; CT good for
assessing excretory function and retroperitoneal
involvement
DIFFERENTIAL DIAGNOSIS
Renal Neoplasm
• XGP may simulate cystic renal cell carcinoma
• Urothelial cancer obstructing pelvis or secondarily invading
parenchyma may look similar
• Renal lymphoma may appear very similar to XGP due to its
low density on CT
Pyonephrosis or Renal Abscess
• Pyonephrosis: Purulent material within collecting system,
usually no staghorn
• Renal abscess: Ill-defined hypoechoic masses, acute rather
than chronic presentation
Papillary Necrosis
• Due to analgesic abuse, diabetes mellitus, chronic
pyelonephritis, and sickle cell anemia
PATHOLOGY
General Features
• Etiology
○ Chronic obstruction of ureteropelvic junction by
longstanding calculus
– Complication by secondary infection
○ Pyonephrosis leads to mucosal destruction, extension
into adjacent cortex & medulla, and papillary necrosis
Microscopic Features
• Lipid-laden "foamy" macrophages, diffuse infiltration of
plasma cells and histiocytes
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Flank pain, fever, palpable mass, & weight loss
Demographics
• Epidemiology
○ Peak age: 40-50 years; F > M
Natural History & Prognosis
• Rare complications: Hepatic dysfunction, extrarenal
extension, fistulas
• Long-term chronic process with good prognosis if treated,
and rare mortality
Treatment
• Antibiotic treatment is sometimes effective
• Severe disease or perinephric extension usually requires
nephrectomy
DIAGNOSTIC CHECKLIST
Consider
• Histologic diagnosis in equivocal XGP
SELECTED REFERENCES
1. Ifergan J et al: Imaging in upper urinary tract infections. Diagn Interv
Imaging. 93(6):509-19, 2012
2. Arvind NK et al: Laparoscopic nephrectomy in xanthogranulomatous
pyelonephritis: 7-year single-surgeon outcome. Urology. 78(4):797-801,
2011
3. Li L et al: Xanthogranulomatous pyelonephritis. Arch Pathol Lab Med.
135(5):671-4, 2011
4. Kim JC: US and CT findings of xanthogranulomatous pyelonephritis. Clin
Imaging. 25(2):118-21, 2001
Diagnoses: Urinary Tract
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