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.