Chronic renal inflammation usually associated with longstanding urinary calculus obstruction (75%)

Renal parenchyma is gradually replaced by lipid-laden macrophages

Diffuse (> 80%) and focal (< 20%) forms

3 stages of xanthogranulomatous pyelonephritis: Intrarenal → perirenal → perinephric ± retroperitoneal involvement

Diffusely enlarged kidney with hypoechoic round masses replacing normal parenchyma on US

“Staghorn” calculus with renal enlargement and perirenal fibrofatty proliferation

Renal sinus fat obliterated with large central “staghorn” calculus

Perinephric extension ± adjacent organs or structures may include sinus tracts or abscesses

Multiple focal, low-attenuating renal masses with rim enhancement on CT

Ultrasound ideal at initial investigation; CT good for assessing excretory function and retroperitoneal involvement

Lipid-laden, “foamy” macrophages, diffuse infiltration of plasma cells and histiocytes

Flank pain, fever, palpable mass, and weight loss

Rare complications: Hepatic dysfunction, extrarenal extension, fistulas

Long-term chronic process with good prognosis if treated and rare mortality

Antibiotic treatment is sometimes effective

Severe disease or perinephric extension usually requires nephrectomy