What is papillary necrosis?
The renal papilla is the portion of the medullary pyramid that projects into the cup of the renal calyx. In patients with sickle cell disease, diabetes mellitus, nonsteroidal anti-inflammatory drug (NSAID) abuse, and occasionally severe infections, the renal papillae can become ischemic and undergo necrosis. The calyces then become deformed and lose their normal cup shape. Contrast material from the calyces can extend into the necrotic papilla on the excretory phase of imaging studies; this appearance is known as a “lobster claw” or “ring” sign.