Comparison of nephrographic with excretory phase helical computed tomography for detecting and characterizing renal masses.

OBJECTIVE: A retrospective study was performed to compare nephrographic phase (NP) with excretory phase (EP) renal helical computed tomographic (CT) images with respect to detection of renal masses 10 mm or more in diameter, and reviewer confidence in mass characterization. METHODS: Two reviewers evaluated 39 renal helical CT examinations. All masses measuring 10 mm or more in maximal diameter were classified as simple cysts, complex cysts, solid lesions, or indeterminate lesions. Reviewers graded their confidence in the characterization of the masses and decided whether the NP or EP contrast-enhanced images were superior. RESULTS: The 2 reviewers confidently characterized 71 (reviewer 1) and 65 (reviewer 2) of 72 detected masses 10 mm or more in diameter on NP images and 70 (reviewer 1) and 67 (reviewer 2) of 71 detected masses on EP images. There was strong agreement between the 2 sets of images in respect to the characterization of renal masses (kappa = 1.00 and 0.86). Only one mass (a focus of acute pyelonephritis) was not detected by either reviewer on EP images. Collecting system artifact degraded the quality of the EP image in images from only 1 patient. CONCLUSION: Although EP images are often aesthetically inferior to NP images, use of EP images results in a similar rate of detection and confidence in characterization of renal masses measuring 10 mm or more in diameter.

Different phases of renal enhancement: role in detecting and characterizing renal masses during helical CT.

Although helical CT offers greater flexibility in data acquisition and reconstruction than does conventional axial CT, new opportunities for error must be understood so that optimal protocols are used that minimize the likelihood of misdiagnosis. Most nonrenal abdominal helical CT scans are obtained late in the corticomedullary phase of renal enhancement because of the preferable enhancement of other parenchymal organs. CT evaluation of the kidneys during the corticomedullary phase or at an intermediate phase between the corticomedullary and nephrographic phases has significant limitations. Therefore, dedicated renal CT performed for the detection of suspected renal masses or for the characterization of known renal masses must include images obtained during later phases of enhancement (i.e., nephrographic or excretory phase). Nephrographic or excretory phase images appear to be similar to one another but superior to corticomedullary phase images in the ability to both detect and characterize renal masses. Corticomedullary phase images should always be obtained when information about the renal vasculature is desired or when there is a possibility that a detected renal mass may represent an aneurysm or an arteriovenous malformation or fistula. Optimal technique of helical CT for staging renal cancers may require use of both corticomedullary and nephrographic or excretory phase images, although work in this area is still preliminary.

Helical CT for detection and characterization of renal masses.

Helical CT permits the radiologist to image the kidney continuously, eliminating the chances of scanner misregistration. In addition, the kidneys can now be imaged during essentially any phase of contrast material enhancement. Although this offers greater flexibility to the imager, a number of potential problems with helical CT must be considered, particularly when it is performed during the cortical phase of renal enhancement. This article reviews both the advantages and potential pitfalls of helical CT when used for both detection and characterization of renal masses.