Xanthogranulomatous pyelonephritis is a type of chronic pyelonephritis. A significant number of the inflammatory cells are lipid laden histiocytes and account for the yellow appearance of the gross specimen. The renal parenchyma immediately adjacent to the calyces is yellow compared to the background native renal parenchyma. The disease process is essentially infectious. Proteus is a frequent associated causative organism.
Chronic obstruction plays a part in the development of the disorder.
Pathogenesis Most cases are due to ascending infections from urine flow abnormalities. Urinary outflow obstruction results in urine stasis providing an environment for bacterial proliferation. Obstruction also predisposes to vesicoureteral reflux which can enable bacteria to reach the kidney. Xanthogranulomatous pyelonephritis is usually unilateral and may involve all or portion of a kidney. The affected renal parenchymal is brightly yellow and may take on a nodular quality mimicking renal cell carcinoma.