Calculocutaneous sinus.

Extrusion of a urinary calculus is a rare occurrence, and to date only 7 cases have been previously documented. Three patients are described, all of whom had a persistent discharging calculocutaneous sinus as a manifestation of the extruded calculus. The 3 cases had similar features of presentation with a perinephric abscess, a staghorn calculus within a nonfunctioning kidney, and a classic radiologic feature of a portion of calculus clearly distinct from the main bulk of the stone.