Gross pathologic features of xanthomatous pyelonephritis:
(1) The condition is usually unilateral with an enlargement of the kidney.
(2) There is evidence of chronic inflammation in and around the renal capsule with adhesions or scarring.
(3) There is severe chronic pyelocalyceal inflammation with scarring, deformed papillae and dilated calices.
(4) Renal calculi may be present.
(5) The calices show a yellowish, friable material with or without calcifications.
Histologic features:
(1) foamy lipid-laden macrophages predominate
(2) evidence of acute and/or chronic inflammation
(3) variable numbers of multinucleated giant cells
(4) renal cortex and medulla show interstitial inflammation and fibrosis
Complications:
(1) secondary amyloidosis
(2) perirenal abscess
(3) psoas abscess
