Potential pitfalls in the obstructive renal scan in patients with double-pigtail ureteral catheters.

In 21 patients with a long-standing internal ureteral double-pigtail catheter we demonstrated the adverse effect of a full bladder on upper system drainage. A pseudo-obstructive pattern noted in these patients on routine scans was immediately rectified by mere bladder emptying and a normal pattern was demonstrated. We suggest the bladder be emptied in all patients with indwelling internal ureteral stents before renographic evaluation.