Abstract: PD35-06
Sources of Funding: None.

Introduction

A stone is considered impacted if it is not passable with a guide wire or contrast. These stones are more difficult to treat and have a higher morbidity with ureteral stricture rates as high as 24%. Factors predicting stone impaction have not been clearly identified. We sought to evaluate if pre-operative Computed tomography (CT) findings can predict the presence of an impacted stone.

Methods

From our prospectively maintained database of 1049 kidney stone formers between 01/2014 - 06/2016, we identified 47 patients with impacted stones (IS) and compared them to 34 who had non-impacted stones (NIS). All patients were treated with ureteroscopic laser lithotripsy by a single surgeon. We excluded patients who had prior stents or surgery for their stone. CT was reviewed to calculate stone size, stone volume, degree of hydronephrosis (0-3) and Hounsfield units (HU) of the stone as well as distal and proximal to the stone. Demographic data, CT imaging, labs, and intraoperative factors were used for comparison between groups.

Results

There were no differences in age, gender or BMI between IS and NIS. IS patients had a greater stone size, volume, HU under the stone, HU under/above ratio and degree of hydronephrosis compared to NIS patients. No differences in pre- or post-operative creatinine, stone density or HU above the stone was noted between the two groups. Patients above the cut-off value of 27 HU for the ureter distal to the stone were noted to have impacted stones with a sensitivity of 85%, specificity of 85%, positive predictive value of 89% and negative predictive value of 81%.

Conclusions

Impacted stones are associated with greater ureteral density distal to the stone, higher stone volumes and greater degrees of hydronephrosis on pre-operative CT. These criteria may help predict which patients are more likely to have impacted stones.

Funding

None.