BERKELEY, CA (UroToday Inc.) - The workup of the patient with suspected UPJ obstruction or chronic obstructive uropathy can become an expensive and cumbersome process for the patient. The importance of an anterior crossing vessel or significantly reduced renal function of the affected kidney are well recognized as major factors in determining the recommended surgical technique for management. Computed tomography angiography (CTA) provides very reliable and effective imaging to determine the presence of an anterior crossing vessel. However, determining differential function and an objective evaluation of obstruction usually dictates the performance of a diureteric renogram. This paper introduces a very appealing concept of being able to use the contrast enhanced spiral CTA to achieve the results of determining both the anatomy and function of the kidneys. This would reduce the radiographic imaging in the diagnosis of UPJ obstruction to one study.

These investigators used the CTA to cursor outline the enhancing renal parenchyma of both kidneys as regions of interest (ROIs) and calculate mean enhancement and renal volume. They determined that the corrected CT GFR was calculated to be 1/3 of the uncorrected CT GFR. The 65 patients in this study underwent both the CT calculation of GFR and the standard 99Tc-MAG3 GFR. These were then statistically compared using the t test. They also compared the CT scan and the reconstructed IVP to determine the sensitivity for identifying the cause of obstruction. They found that the CT scan had 100% sensitivity compared to a 74% sensitivity for the IVP in determining the cause and location of the obstruction. They also found that the radioisotope GFR of the obstructed kidney corresponded with the CT GFR with a perfect correlation (r = 0.78, p < 0.0001). The isotope and CT GFR's of the normal kidneys also showed an excellent correlation (r = 0.73, p < 0.0001).

The authors suggest that CT may be more precise in the determination of GFR than the gamma camera because of the more precise determination of the ROI than by isotope due to lack of background artifact. The concern with the technique described is that there may potentially be up to 50% difference in the corrected CT GFR compared to the actual GFR and that the level of radiation exposure may be unacceptable in children, adolescents and pregnant women. However, if this technique could provide one study to provide all of the necessary definitive information in patients with chronic obstruction, it may overall reduce radiation exposure and expense. It would be nice to see these results reaffirmed and confirmed by other centers using this same technique.

J Urol 172: 985-988, 2004