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From the Archives of the AFIP. Xanthogranulomatous pyelonephritis
W S Hayes1, D S Hartman, I A Sesterbenn
1Department of Radiology, Georgetown University Hospital, Washington, DC 20007-2197.
Abstract:
Xanthogranulomatous pyelonephritis is a form of chronic infection of the kidney and surrounding tissues characterized by destruction and replacement of renal parenchyma by lipid-laden macrophages. Gross pathologic features include massive renal enlargement, lithiasis, peripelvic fibrosis, hydronephrosis, and lobulated yellow masses replacing renal parenchyma. Typically, the disease is diffuse and has characteristic imaging features. Less commonly, the process is focal and is difficult to differentiate from malignant disease on radiologic studies. Ultrasound demonstrates renal enlargement with multiple anechoic or hypoechoic masses replacing the normal corticomedullary differentiation and a contracted pelvis. Peripelvic fibrosis may obscure acoustic shadowing from a central staghorn calculus. On computed tomographic scans, a staghorn calculus may be seen in a contracted renal pelvis of an enlarged kidney, with characteristic low-attenuation, peripherally enhancing rounded masses. Extrarenal extension of the inflammatory process is frequently seen.
Insights
Xanthogranulomatous pyelonephritis (XGP) is a chronic kidney infection causing renal destruction by lipid-laden macrophages. Imaging reveals enlarged kidneys, masses, and often staghorn calculi, sometimes mimicking malignancy.
Area of Science:
- Nephrology
- Pathology
- Radiology
Background:
- Xanthogranulomatous pyelonephritis (XGP) is a rare, destructive inflammatory condition of the kidney.
- It involves the infiltration of renal parenchyma by lipid-laden macrophages.
- XGP can present diffusely or focally, posing diagnostic challenges.
Purpose of the Study:
- To describe the gross pathologic and characteristic imaging features of xanthogranulomatous pyelonephritis.
- To highlight the diagnostic considerations, especially differentiating focal XGP from renal malignancy.
Main Methods:
- Review of gross pathologic findings in XGP.
- Analysis of imaging characteristics on ultrasound and computed tomography (CT).
Main Results:
- Gross features include massive renal enlargement, lithiasis, peripelvic fibrosis, hydronephrosis, and parenchymal replacement by yellow masses.
- Ultrasound shows renal enlargement, anechoic/hypoechoic masses, and a contracted pelvis, with fibrosis potentially obscuring staghorn calculi.
- CT scans reveal enlarged kidneys with contracted pelves, staghorn calculi, low-attenuation peripherally enhancing masses, and frequent extrarenal extension.
Conclusions:
- Xanthogranulomatous pyelonephritis is characterized by distinct gross and imaging findings.
- Focal presentations of XGP can mimic renal tumors, necessitating careful radiologic evaluation.
- Understanding these features aids in differentiating XGP from other renal pathologies.