Endoscopic Combined Intrarenal Surgery Can Accurately Predict High Stone Clearance Rates on Postoperative CT

To determine stone clearance rates using endoscopic combined intrarenal surgery (ECIRS) and assess the accuracy of intraoperative prediction of stone-free (SF) status compared to postoperative CT scan.

A single institution, prospectively maintained database of ECIRS was queried for procedures performed 8/2017 to 1/2018. Retrograde access was performed using a ureteral sheath and flexible ureteroscope. Percutaneous nephrolithotomy was performed through a 30fr or 18fr sheath in prone position. Residual stone status was estimated at the end of each procedure and was verified with postoperative CT scan. SF was defined as no single stone >2mm³ on CT.

One hundred and ten procedures were reviewed. Average age was 58.9 ± 12.6 years (range 26-87) and 69 (63%) were male. The mean stone size was 33.3 ± 23.5 mm (range 4-140 mm). Ninty-three patients (84.5%) were endoscopically estimated to be SF, of which 84 (90% of predicted SF cohort, 76% of total cohort) were confirmed SF via CT scan. The sensitivity for estimating SF status with ECIRS was 65.4% (95%CI 44.3%-82.8%), specificity was 100% (95%CI 95.7%-100.0%) and accuracy was 91.8% (95%CI 85.0%-96.2%). SF patients had significantly smaller stones than those with residual fragments (28.5 ± 2.1 vs 48.4 ± 5.7mm, P <.0001). On logistic regression, the factors associated with residual stones were preoperative stone burden (OR 1.03 per mm, 95%CI 1.01-1.05, P = .0004) and fluoroscopy time (OR 1.01 per minute, 95%CI 1.0-1.02, P = .0081).

ECIRS accurately predicts clinical SF status and may obviate the need for additional CT scans. Consistent with prior studies, the primary determinant of residual stone after percutaneous nephrolithotomy is initial stone size.