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EDUCATION EXHIBIT |
Department of Radiology, University of California at San Francisco
Dr Joffe and his colleagues are to be congratulated for providing a timely and comprehensive review of multi–detector row CT urography in the evaluation of patients with hematuria (1). One of the most striking changes in the practice of genitourinary radiology over recent years has been the near disappearance of intravenous pyelography (IVP) as a routine test for hematuria. At our institution, we have gone from performing IVP several times a day to perhaps once a month. Three factors have contributed to this decline: first, the widespread acceptance of unenhanced spiral CT as the imaging test of choice in patients with suspected urinary stones; second, the clear superiority of CT over IVP in the evaluation of renal parenchymal masses; and third, the increasing acceptance of contrast-enhanced CT (including CT urography) in the evaluation of patients with hematuria. Our ability to produce detailed and compelling reformatted and 3D images from the nearly isotropic data sets of modern multi–detector row CT scans has also contributed to the embrace of this technology by our referring colleagues. However, with these new capabilities come new concerns. We would like to highlight four important issues that are raised by the increasing use of CT urography as a replacement for IVP in patients with hematuria.
First, do all patients with hematuria require a contrast-enhanced study? Unfortunately, no clear answer to this question exists, and the appropriate approach to the imaging of patients who have both flank pain and hematuria will depend on local practice and close cooperation with referring colleagues. At our institution, we perform unenhanced CT in patients who are referred with flank pain or a request to evaluate for suspected urinary stones. We do not proceed to a contrast-enhanced study without discussion with the referring physician. The primary reason for this approach is that the decision to administer contrast material in this setting is in effect a decision that the patient requires a work-up for hematuria. That is, the administration of contrast material is effectively suggesting that the patient requires cystoscopy because the latter is an essential investigation in a patient with hematuria. We do not believe that the radiologist is in a position to make this decision, and therefore we proceed to administer intravenous contrast material only after discussion with the referring physician.
Second, how many phases of CT enhancement are required for the work-up of hematuria? The authors are right to be concerned with reducing radiation dose and accordingly acquire CT scans only during noncontrast, nephrographic, and urographic phases of enhancement. Although this approach may be justified, omission of the corticomedullary phase is controversial because some studies have indicated that the combination of corticomedullary and nephrographic phases is superior to the nephrographic phase alone for renal mass detection (2,3). In addition to lesion detection, arterial- or corticomedullary-phase imaging may be helpful in demonstrating aberrant renal arteries that may be contributing to obstruction or that may be important for presurgical planning (4). One clever technical modification that the authors mention, and that we have found helpful in this setting, is to use a split bolus, whereby a portion of the bolus of contrast material is administered 5–10 minutes before the majority is given. In this way, corticomedullary- or nephrographic-phase images can be acquired at the same time as the excretory-phase images because the initial component of the bolus has passed into the collecting systems by the time the second part of the bolus is administered (5,6).
Third, how important is it to completely distend and opacify the ureters during CT urography? It is true that the use of a bolus of saline solution or abdominopelvic compression facilitates ureteral distention with excreted contrast material. Such distention helps generate pleasing 3D images, but is this distention of diagnostic importance? There appears to be a widely held perception that complete opacification of the ureters is a crucial endpoint of IVP, and this same perception has been transferred to CT urography. The source of this belief is unclear, and we believe it to be simply a radiologic myth that should be debunked. In an important but little-known study, no upper tract malignancies were identified on 187 retrograde pyelograms solely because of underfilling of the upper tracts at IVP (7). It would appear that upper tract malignancies manifest at imaging as filling defects or obstruction and do not manifest as underfilling of the ureter. The obsession with complete ureteral opacification may be misguided.
Fourth, can CT urography replace IVP in the detection of upper tract urothelial malignancy? To do so, the added benefit and convenience of the urographic phase of CT must outweigh the higher cost and radiation dose associated with CT urography. As previously noted, neither IVP nor CT urography is sufficiently sensitive to exclude bladder cancer, and therefore cystoscopy remains a crucial component of the work-up of patients with hematuria. However, one of the traditional reasons to order IVP is to assess the upper tract urothelium, and the question remains as to whether the higher contrast resolution and volumetric acquisition of CT urography make it sufficiently sensitive in the detection of upper tract malignancy to replace IVP with its higher in-plane spatial resolution and capacity for multiple upper tract image acquisition. Unfortunately, this is another question that cannot be readily answered because there is insufficient data, with only small preliminary studies having been published. Although the quality of CT urograms would suggest that the resolution of CT urography is adequate for the detection of upper tract malignancies, this conclusion is tentative and is not based on a strong body of evidence, and the referring physicians should be appropriately informed.
In conclusion, multi–detector row CT urography is emerging as a powerful and compelling tool that is replacing traditional IVP. Although this "changing of the guard" is probably appropriate, it is imperative that radiologists work closely with their referring physicians to ensure that the basis of practice is clear, that agreed technical protocols are in place, and that there is awareness of the strengths and weaknesses of CT urography. Local consensus is required to bridge the gaps in our knowledge, pending larger-scale and multi-institutional trials of CT urography, particularly about detection of upper tract urothelial malignancy.
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  A. Kawashima, T. J. Vrtiska, A. J. LeRoy, R. P. Hartman, C. H. McCollough, and B. F. King Jr CT Urography RadioGraphics, October 1, 2004; 24(suppl_1): S35 - S54. [Abstract] [Full Text] [PDF]
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