Preliminary study on the differentiation between parapelvic cyst and hydronephrosis with non-calculous using only pre-contrast dual-energy spectral CT scans

Objective: To investigate the value of using the quantitative parameters from only the pre-contrast dual-energy spectral CT imaging for distinguishing between parapelvic cyst and hydronephrosis with non-calculous (HNC). Methods: This retrospective study was approved by the institutional review board. 28 patients with parapelvic cyst and 24 patients with HNC who underwent standard pre-contrast and multiphase contrast-enhanced dual-energy spectral CT imaging were retrospectively identified. The parapelvic cyst and HNC were identified using the contrast-enhanced scans, and their CT number in the 70-keV monochromatic images, effective atomic number (Z(eff)), iodine concentration (IC) and water concentration in the pre-contrast images were measured. The slope of the spectral curve (lambda) was calculated. The difference in the measurements between parapelvic cyst and HNC was statistically analyzed using SPSS (R) v. 19.0 (IBM Corp., New York, NY; formerly SPSS Inc., Chicago, IL) statistical software. Receiver-operating characteristic analysis was performed to assess the diagnostic performance. Results: The CT numbers in the 70-keV images, Z(eff) and IC values were statistically different between parapelvic cyst and HNC (all p < 0.05). The sensitivity, specificity and accuracy of these parameters for distinguishing between parapelvic cyst and HNC were 89.2%, 73.3% and 82.1%; 86.5%, 43.3% and 67.2%; 91.9%, 40.0% and 68.7%; and 64.9%, 73.3% and 83.6%, respectively, and the combined specificity was 92.9%. There was no statistical difference in lambda between the two groups (p > 0.05). Conclusion: The quantitative parameters obtained in the pre-contrast dual-energy spectral CT imaging may be used to differentiate between parapelvic cyst and HNC.