CT Urography: The Value Of IVU With Add-on CT In Evaluating Urinary Tract Abnormalities And Renal Function

Objective To evaluate the value of CT following IVU in evaluating urinary tract abnormalities and renal function in selected situations.Materials and methods 68 patients had CT following IVU without using additional contract medium. Of the 68 patients, 26 patients were prospectively selected for CT within 2 hours of IVU because of uncertain diagnosis on IVU. The other 42 patients were referred for CT within 2 hours and 24 hours of IVU because the separate renal functions were inadequate to allow visualization in delayed images up to 2 hours owing to urinary obstruction. The patients with nonopacification of the urinary collecting system in delayed images up to 2 hours were investigated by means of dynamic renal scintigrapy to assess renal functions(GFR).Results All the patients were classified into three groups: in the first group including 21 patients with normal renal functions , questions were raised that could not be answered on IVU. By CT , questions on IVU were successfully answered and abnormalities were proved to be tumors, renal cysts, duplications of collecting system, and pesudomass. The second group included 5 patients suffering from acute urinal obstruction. Sign of "white kidney" were seen on IVU and CT. The causes of urinal obstruction which could not be found on IVU were proved ,by CT, to be urinal stones and blood clot. The third one consisted of 42 patients with nonopacification of collecting systems in delayed images up to 2 hours. Chronic urinal obstructions were identified by CT in all patients. Stones, tumors and cicatricial stenosis were the causes of obstructions. In CT images, the collecting systems contain no or certain amount of contrast medium. Dynamic renal scintigraphies show different degrees of impairment of renal function with GFR varying from 3-36ml/min.Conlution IVU is the radiographic standard for evaluating urinary tract abnormalities, however, IVU is limited in the evaluation of renal masses, and can also be technically limited in patients who are obese or have extensive bowel gas. Another weakness of IVU is its low specificity. Questions are frequently raised that cannot be adequately answered. Furthermore, the cause and site of chronic urinal obstruction cannot be found on IVU when the renal function is inadequate to allow visualization even in delayed images up to 24hours. CT following IVU is a kind of CT urography(CTU) that combines portions of IVU and CT into one examination. The CT portion of CTU is more sensitive and specific in the detection and characterization of renal masses, stones and other urinary abnormalities. Also, CT with its high spatial resolution can demonstrate a little amount of contrast medium contained in the dilated colleting system, which cannot be visualized on IVU because of the impairment of renal function. The main advantage of CT following IVU is its abilities to answer questions raised by IVU without additional intravenous contrast medium. Because a formal CT study would have been required in most cases to answer these questions, this reduce-charge study is a less expensive alternation. The increased accuracy of CTU over IVU alone and gain in the speed of workup make it an effective technique in appropriate situations.