Multiphasic helical CT of the kidney: increased conspicuity for detection and characterization of small (< 3-cm) renal masses.

PURPOSE To evaluate the potential of thin-section multiphasic helical computed tomography (CT) in the detection and characterization of small (< 3.0-cm) renal masses. MATERIALS AND METHODS Identically collimated helical CT of the kidney was performed before and after administration of contrast material in 93 patients with small renal masses. Helical CT scans were obtained during the corticomedullary and nephrographic phases. Differences between attenuation of the lesion and that of the kidney were measured quantitatively. The presence of a mass or absence of disease was confirmed with clinical, imaging, and histologic findings. RESULTS The number of masses smaller than 3.0 cm detected on corticomedullary-phase scans (n = 211) was statistically significantly fewer than those on nephrographic-phase scans (n = 295) (P < .01). Mean differences in enhancement between the renal cortex and masses were 148 HU +/- 54 and 137 HU +/- 44 during the corticomedullary and nephrographic phases, respectively, and the difference in attenuation of the renal medulla and that of the masses was statistically significantly greater during the nephrographic phase (P < .01). False-positive results (n = 9) occurred only on corticomedullary-phase scans because of lack of enhancement of the renal medulla. CONCLUSION Nephrographic-phase scans enabled greater lesion detection and better characterization of small renal masses than corticomedullary-phase scans. Nephrographic-phase scans should be obtained when only monophasic scanning is used to detect small renal masses.