Renal papillary necrosis is a form of nephropathy involving the necrosis of the renal papilla. Lesions that characterize renal papillary necrosis come from an impairment of the blood supply and from subsequent ischemic necrosis that is diffuse, n terms of cause, almost any condition that involves ischemia can lead to renal papillary necrosis. A mnemonic for the causes of renal papillary necrosis is POSTCARDS: pyelonephritis, obstruction of the urogenital tract, sickle cell disease, tuberculosis, cirrhosis of the liver, analgesia/alcohol abuse, renal vein thrombosis, diabetes mellitus, and systemic vacuities. Often, a patient with renal papillary necrosis will have numerous conditions acting synergistically to bring about the disease; this condition is due to ischemia of the renal papillae, the portion of the kidney that collects urine from the nephron. The papillae are vulnerable to ischemia as they are supplied by small caliber arteries which are liable to obstruction. All of the underlying causes of papillary necrosis cause diminished flow through these arteries, either through direct mechanical obstruction (sickle cell), obstruction secondary to inflammation (vasculatures), or vasoconstriction (NSAIDs). Papillary necrosis is more likely to develop when multiple of these underlying factors are present. Ultimately, necrosis of the papillae results in sloughing into the lumen, causing hematuria. If the degree of necrosis is substantial post-renal failure may occur, though this is uncommon.