An unusual case of pneumoperitoneum: nephrocolic fistula due to a giant renal staghorn calculus.

Gastrointestinal perforations usually lead to pneumoperitoneum and peritonitis. Rarely, if ever described, a complete giant staghorn renal stone might cause a nephrocolic fistula with sigmoid impaction and perforation similar to gallstone ileus. Few nephrointestinal fistulae have been described in the literature and none of them were presented as an acute abdomen with pneumoperitoneum and pneumoretroperitoneum. To our knowledge, this is the only case showing CT and radiographic findings of a pathology not yet described in the literature. We named the sigmoid perforation by a renal stone ileus "Lorenzi's syndrome" after the physician who hypothesized this rare differential diagnosis based only on history and clinical examination.