Stone size on endoscopic view as a predictor of successful stone retrieval during flexible ureteroscopy: an in vitro analysis

Abstract

Purpose: Basketing plays an important role during flexible ureteroscopy, but it can be time-consuming, especially when fragments are too large to pass through the ureteral access sheath. We aim to present the optimal on-screen, endoscopic stone size that predicts successful basketing through various access sheaths.

Methods: A tipless basket, individually extended to 5 mm from multiple ureteroscopes: (Flex-Xc, Karl Storz; Flex-X2s, Karl Storz; LithoVue, Boston Scientific; or URF-P6R, Olympus) and via differently sized access sheaths (10-12 Fr through 13-15 Fr), was used in retrieval attempts of various artificial stone sizes (2 mm through 5 mm). A relative endoscopic stone size was recorded as the stone's maximum diameter on endoscopic view compared to the total image diameter.

Results: Basketing of stones up to 2.5 mm, yielding relative endoscopic stone sizes of 0.38 (Flex-Xc), 0.30 (Flex-X2s), 0.32 (LithoVue), and 0.34 (URF-P6R), was successful using all access sheaths. Only the 12-14 Fr and greater sheaths allowed for successful basketing of 3 mm stones. Larger stones did not successfully pass through any of the access sheaths.

Conclusion: Successful stone retrieval can be predicted by estimating the stone's size on screen, which is influenced by the type of flexible ureteroscope and access sheath. In our testing, stones of approximately one-third of the screen size passed successfully in all cases.

Keywords: Access sheath; Basket; Flexible ureteroscopy; Lithotripsy; Stone size; Urolithiasis.