Decreased renal parenchymal density on unenhanced helical computed tomography for diagnosis of ureteral stone disease in emergent patients with acute flank pain

Background: The purpose of this study was to determine the usefulness and optimal cutoff point of decreased renal parenchymal density (DRD) for diagnosis of ureteral stone disease (USD) in emergent patients with acute flank pain. Methods: A total of 85 emergency patients with acute flank pain who underwent unenhanced helical computed tomography (UHCT) were prospectively included in this study as the study group. An additional 30 patients with no USD undergoing UHCT were retrospectively included as the control group. The mean parenchymal density difference between both kidneys of the control group was compared to that of the study group. Within the study group, the DRD of patients with USD and with no USD was compared. The sensitivities and specificities of DRD for diagnosis of USD in a range of possible optimal cutoff points were analyzed. Results: There was a statistically significant difference in DRD between the study and control groups (p < 0.0001). In the study group, the DRD of patients with USD was significantly higher than that of patients with no USD [mean ± SD = 4.04 ± 3.4 Hounsfield units (HU) versus 0.08 ± 2.7 HU, p = 0.0001]. DRD using cutoff points of ≥ 8 HU, ≥ 5 HU and ≥ 2.06 HU had a sensitivity of 12.5%, 40.3% and 76.4%, and a specificity of 100%, 92.3% and 76.9%, respectively. Conclusions: DRD may be helpful in the diagnosis of USD in emergent patients with acute flank pain. When a DRD of ≥ 2.06 HU is selected as a cutoff point, its sensitivity and specificity are both acceptable and higher than 75%.