Reservoir calculi: A comparison of reservoirs constructed from stomach and other enteric segments

Purpose: The intestinal augmented bladder has an increased propensity to form urinary calculi. Predisposing risk factors include chronic bacteriuria, urinary stasis and mucus production. Gastric reservoirs have negligible mucus production and the ability to acidify the urine. We determined whether they also have a decreased incidence of stones. Materials and Methods: We retrospectively reviewed the records of all patients undergoing augmentation cyptoplasty (215) or creation of a freestanding reservoir (44) between May 1976 and March 1996. Of these cases 83 were augmented with stomach and 179 were constructed from other intestinal segments, (that is ileal, ileocecal, sigmoid and/or a combination of these). Presenting diagnosis, patient age, gender, additional surgical procedures, interval to stone formation and calculous composition were recorded. Patients were excluded from study when there was less than 1 year of followup, as were those with renal or pre-augmentation bladder calculi. Results: Stones formed in 32 of 207 patients (15%) after an average interval of 3.6 years (range 0.5 to 8.6). The majority of stones were composed of struvite (magnesium ammonium phosphate). Reservoirs containing gastric segments were significantly less likely to form calculi than those augmented with other intestinal segments (2 of 70 versus 30 of 137, p<0.0001 Fisher's exact test). Seven additional patients with pre-augmentation bladder stones who subsequently underwent gastrocystoplasty remain stone-free at an average followup of 3.0 years. Conclusions: Calculous formation is rare in reservoirs that incorporate a gastric segment. In patients with gastric augmentation stones appear only to develop when the patient is on histamine blockade or has a propensity to form stones that only favor an acidic environment, such as uric acid.