Kidney cross section showing renal papillary necrosis! The pale white areas involving some or all of many renal papillae are areas of ischemic papillary necrosis. This is an uncommon but severe complication of acute pyelonephritis, particularly in persons with diabetes mellitus. Papillary necrosis may also accompany analgesic nephropathy, sickle cell disease, and renal transplant rejection. The condition can lead to secondary infection of desquamated necrotic foci, deposition of calculi, and/or separation and eventual sloughing of papillae, with impending acute urinary tract obstruction. Multiple sloughed papillae can obstruct their respective calyces or can congregate and embolize to more distal sites such as the ureteropelvic junction, ureter, and ureterovesical junction. There is no definitive treatment. Underlying cause should be identified and the offending agent stopped.