Urinary tract calculi that form on surgical staples: a characteristic radiologic appearance.

An autostapler is frequently used when bowel is interposed in the urinary tract during reconstructive urologic surgery in children. Usually the metallic staples are buried beneath the intestinal mucosa. However, if a portion of a staple is unintentionally left exposed or becomes exposed through migration and is then bathed by urine, it can become the nidus for formation of a calculus. The radiologic studies of 30 patients having surgery of this type in our hospital from 1980 to 1990 were reviewed prospectively, and stones were found to have developed on staples in eight patients. None of the patients had metabolic abnormalities. The stones were easily visible on plain radiographs because they were calcified. They formed in the lumen of the bladder or the bowel segment on the exposed portion of the staple. Thus, the staple was eccentric in the calculus and not central, as is usually the case with a stone forming on a foreign body. This experience suggests that stones forming on surgical staples during reconstructive urologic surgery have a characteristic radiologic appearance that may aid in their identification.