The ratio of CT attenuation values of the ureter above/below ureteral stones is a useful preoperative factor for predicting impacted ureteral stones.

Impacted stones typically make it difficult to perform ureteroscopic lithotripsy (URSL), so it is useful to preoperatively predict such impaction. We focused on CT attenuation values of the ureter above and below the stone ('HU above' and 'HU below') and calculated their ratio (HAB ratio; HU above/HU below ratio). The aim was to investigate whether HAB ratio could predict impacted stones preoperatively. Between 2011 and 2019, 171 patients from our hospital that had URSL for ureteral stones with pretreatment non-contrast computed tomography (NCCT) were retrospectively identified. Ureteral wall thickness (UWT), ureteral wall volume (UWV) and HAB ratio ('HU above' divided by 'HU below') were recorded. Impacted stones were defined as fixed stones that did not move by means of ureteroscopic manipulation or water pressure. Of the 171 procedures, 46 (27%) involved patients with impacted stones. Comparing patient characteristics and stone parameters according to impaction status, factors with significant difference included grade of hydronephrosis, UWT, and HAB ratio (all P < 0.01). Multivariate analysis indicated that significant independent predictors of impacted stones were thicker UWT and lower HAB ratio (all P < 0.01). HAB ratio was a significant preoperative predictor of stone impaction in patients undergoing URSL for ureteral stones. HAB ratio may be informative for selecting the treatment and preoperative preparations.