Renal cysts: Is attenuation artifactually increased on contrast-enhanced CT images?

PURPOSE: To determine if the attenuation values of simple renal cysts are a rtifactually increased on contrast material-enhanced, clinically acquired s piral computed tomographic (CT) images. MATERIALS AND METHODS: Dual-phase renal spiral CT studies (5-mm collimation ; pitch, 1.0) were retrospectively analyzed in 24 consecutive patients who had ultrasonographic (US) documentation of simple renal cysts. Forty-eight cysts were identified. The attenuation values of each cyst were measured on nonenhanced, cortical phase, and nephrographic phase images. The size and the location of each cyst in relation to the renal parenchyma were also rec orded. RESULTS: The cysts were 0.6-10.8 cm in diameter (mean, 2.6 cm; SD, 2.0). Th e mean attenuation change in the cysts from nonenhanced to contrast-enhance d images was statistically significant in a comparison of cortical phase an d nephrographic phase images (P < .01): +1.8 HU (SD, 3.8) for cortical phas e and +3.6 HU (SD, 5.6) for nephrographic phase images. Renal cysts 1.0 cm or smaller showed a higher attenuation increase (mean, +4.0 HU for cortical phase and +11.0 HU for nephrographic phase). None of the renal cysts large r than 1.0 cm demonstrated an increase greater than 10 HU (mean, +1.4 HU fo r cortical phase and +2.3 HU for nephrographic phase). Intraparenchymal cys ts showed higher mean attenuation changes than the exophytic cysts. CONCLUSION: Attenuation Values in the renal cysts increased artifactually o n contrast-enhanced images, but this pseudoenhancement was not substantial and was less than 10 HU when the cyst was larger than 1.0 cm in diameter.