What is the role of urography suspected urinary tract obstruction?
If the patient has renal insufficiency with elevation in the serum creatinine level, administration of a contrast material is contraindicated. Renal US is the best study to evaluate such a patient for a dilated collecting system, which would indicate obstruction. Renal scintigraphy may also be useful in this clinical scenario. Nondilated obstructive uropathy is rare. In patients with normal renal function and suspected obstruction, renal US and renal scintigraphy remain the mainstays for evaluation. In an occasional patient with equivocal results from other diagnostic tests, CTU or IVU may help. Prompt and symmetric nephrograms with bilateral contrast excretion and complete drainage of the collecting systems on an erect postvoid radiograph effectively exclude significant urinary tract obstruction. In postoperative patients in whom urinary diversion has been performed, a study in the first few months after surgery serves as a baseline to exclude strictures at the ureteral anastomotic sites.