AUA 2017: Can CT Imaging Predict Stone Impaction

Boston, MA ( Parkhomenko et al. conducted a retrospective study attempting to identify factors that may correlate with stone impaction. The presenting author noted that hydronephrosis, stone size, previous treatment failure, elevated Hounsfield unit (HU) density of the ureter distal to the stone, and duration of previous stone impaction all have been shown in the literature to correlate with stone impaction. They performed a review of 1151 patients who were treated with ureteroscopic laser lithotripsy; impacted stones were defined as ureteral stones that failed to progress over 2 months, or ones beyond which a guidewire could not be passed, or visible edema on endoscopy. A blinded reviewer evaluated CT scans of 47 patients with, and 47 patients without, stone impaction for stone size and volume, degree of hydronephrosis, stone HU, and ureteral HU proximal and distal to the stone.

They found on univariate analysis that stone size, stone volume, ureteral HU distal to the stone, and the degree of hydronephrosis were significantly greater for those with stone impaction. Upon multivariate analysis, the only factor that remained significant was the ureteral HU distal to the stone. They followed this with a sensitivity analysis which determined that a cutoff value of 27 HU accurately distinguished between impacted and non-impacted stones (sensitivity, specificity, and PPV of 85%).

These findings seem promising in that a stone may potentially be identified as impacted, and thus can particularly benefit surgeons by providing them the insight to alter operative plans and preoperative management (e.g. withholding anti-platelet therapy). Dr. Parkhomenko notes that they plan to conduct a validation study using the 27 HU cutoff to prospectively predict impacted ureteral stones.

Speaker: Egor Parkhomenko

Written By: Shoaib Safiullah, MS4 for

at the 2017 AUA Annual Meeting - May 12 - 16, 2017 – Boston, Massachusetts, USA