(UroToday.com) On the third day of the annual World Congress of Endourology and Technology 2024, the fourth plenary session entitled “Stone Disease and Treatment” included an expert panel on new approaches for stone retrieval. This session was moderated by Paksi Satyagraha, MD of Saiful Anwar General Hospital, Indonesia, with panelists including: Han Kyu Chae, MD, PhD of Kangdong Sacred Heart Hospital in Seoul, Republic of Korea, Sundaram Palaniappan, MD of Sengkang General Hospital, Singapore, Joseph C. Liao, MD of Stanford Medicine, and Steffi Yuen, MD of New Territories East Cluster Hospitals, Hong Kong.
At the initiation of the panel, Dr. Satyagraha briefly introduced various approaches to stone removal. Following this portion, Dr. Han Kyu Chae opened the session with his presentation titled “Basket with Various Design/Function”. Given that modern practice operates in a time characterized by laser dusting, this has become a primary method for stone fragmentation; however, stone retrieval baskets remain crucial. Indeed, various studies have suggested that basketing is as effective as dusting, contributing to higher stone-free rates, which Dr. Han Kyu Chae notes as an advantage. Rather than highlighting known benefits of basketing, he opted to review various designs and features of stone basketing (Figure 1).
Figure 1. Various features of stone baskets.
A majority of baskets in-use are made from nitinol for its “shape memory” effect which confers super elasticity and fatigue resistance, further attributed to decreased intraoperative trauma to the renal system, able to achieve a closer proximity to the stone, and excellent kink resistance. Furthermore, basket wires can be categorized to flat, round, or delta; wherein delta is associated with the largest wire mass possible. An additional feature includes the shape and tip design of the basket; whether it be straight vs helical and tipped vs tipless. Both straight and tipless wires are associated with reduced trauma, while tipped baskets can serve as a guide, and helical offer increased stone capture. He also considered the action of opening, whether there be front or side action, as well as the number of wires (3 vs 4). While front action baskets are better for relocation, side action baskets may be more appropriate for stone fragments. In a similar vein, 3-wire baskets are ideal for Randall stones, and 4-wire baskets may maximize stone retention. Overall, it is crucial to understand various basket types and components in order for urologists to make informed choices that lead to improved surgical efficiency and reduced complications.
Dr. Palaniappan then proceeded to introduce a presentation on “Suction Device Technique”, reviewing the standard for treatment for stones >2 cm, which may include digital scopes, single-use scopes, and new laser technologies for the disintegration of stone. However, at the end of a dusting session, surgeons are left with a “snow globe effect” and residual fragments, requiring baskets or further intervention associated with increased costs. Therefore, suction may pose as a solution in dust and fragment removal, as well as provide improved visualization and decreased intrarenal pressure and temperature.
There are various mechanisms for suction, however the primary three include ureteric catheters, direct scope suction, and suction access sheaths. He then proceeded to share a comparison of manual suction and irrigation to suction ureteral access sheath (UAS); there was no difference in residual fragments, wherein 33% of patients required repeat RIRS in the manual group. A further compromise to this was a 7.5Fr suction scope with integrated channels that did not require manual suction. Next, a steerable catheter (CVAC aspiration system) was reviewed in a randomize trial with 101 patients, which resulted in significantly higher stone clearance (97%) vs standard URS with basketing (93%). Currently under investigation, CVAC was then redesigned to a 12Fr scope, that can be introduced to a 12/14Fr sheath, allowing for further stone collection. Lastly, Dr. Palaniappan reviewed suction UAS, which was initially seen in PCNL. Although rigid, early models did show promising results in improved dust aspiration. Dr. Palaniappan then addressed previous faults in prior iterations where such sheaths were unable to dust and remove remnants effectively. Chen Y et al. demonstrated that such shortcomings were related to the level of the sheath and scope during suction. When the two instruments are equal in level, the clearance of stone dust is optimized (Figure 2). Therefore, the sheath must be brought towards the stone. In total, numerous suction devices on the horizon are proving to be essential to stone surgery, with suction UAS as the most promising.
Figure 2. An image from Chen Y et al. Optimal placement of flexible ureteral access sheath in retrograde intrarenal surgery, demonstrating the various levels of UAS and scope. Notably, there are areas of high flow at the tip of the scope and UAS. Aspiration and stone dust clearance is optimized when these are equal in level, as seen in the first image of the sequence.
In introducing novel technology, Dr. Liao then resumed the conversation, reporting on “Stone Retrieval Using Magnetic Hydrogel”, a preclinical study. Although ureteroscopy is the most common stone surgery with ongoing advancements, stone-free rates remain sup-optimal. Despite the utility of basketing as suggested by an earlier panelist, Dr. Liao suggests that basketing is tedious and time-consuming, while stone dusting is linked to poor stone-free rates and visualization. Herein, Dr. Liao and colleagues at Stanford have developed “MagSTONE” based upon two innovations: a magnetic hydrogel deployed following lithotripsy, and a magnetic guide wire utilized for stone retrieval (Figure 3).
Figure 3: MagSTONE System.
There are two components of the magnetic hydrogel, including Ferumoxytol which serves to coat the stone surface, and Chitosan, a polymer that crosslinks iron oxide particles and forms a 3D coating around stone fragments. The subsequent magnetic wire contains alternating polarities in an effort to remove stone fragments along the length of the wire. In an in-vitro model using patient-derived stone fragments ranging from 1-4 mm, MagSTONE was able to capture nearly 100% of stone fragments of various stone types, whereas isolated Ferumoxytol was inadequate. They have also continued to validate their approach with a head-to-head comparison to conventional wire baskets, demonstrating 57% greater efficiency for smaller stone fragments. With regard to toxicity, safety, and feasibility, Dr. Liao and colleagues have explored these parameters in ex-vivo human urothelium, in vivo mouse urothelium, and in vivo porcine models. He reports that results thus far are promising with minimal cytotoxicity and disruption to the urothelium. In sum, MagSTONE may offer a more efficient strategy compared to standard stone baskets, with efficient retrieval of stone fragments regardless of composition.
Dr. Yuen then proceeded with “Deflectable Ureteral Access Sheaths”, initially reviewing the history of ureteral access sheaths. Though suction UAS were available in 2020, they were limited by calyceal anatomy and therefore unable to clear all stone dust and fragments. In 2022, a flexible tip was released, deemed Flexible and Navigable Suction UAS (FANS) by Dr. Yuen and colleagues (Figure 4).
Figure 4: Flexible and Navigable Suction UAS (FANS) intraoperative configuration.
In this configuration, the UAS is brought directly to the stone. Two designs include the Clearpetra and YiGao. These ultimately connect to suction and can be withdrawn for stone retrieval, but may also be employed without suction for the retrieval of larger fragments. FANS is able to accomplish hefty stone-free rates, regardless of dusting or fragmentation settings. In clinical studies (30 days post-op), there was an Endourological Grade A + B 97.3% stone-free rate, with a 2.8% reintervention rate. Overall, FANS can be utilized for active suction to increase stone-free rates and reduce intervention rates.
At the end of the presentation, there was an audience member with a question regarding FANS stone-free rates, inquiring about the residual volumetric burden for patients who were not considered stone-free. In response, Dr. Yuen stated that preoperative stone volume was established in the global registry, however, stone volume was not measured for post-operative volume, however, residual linear metrics were obtained.
Moderated by: Paksi Satyagraha, MD, Saiful Anwar General Hospital, Indonesia
Expert Panel:- Han Kyu Chae, MD, PhD – Kangdon Sacred Heart Hospital, Seoul, Republic of Korea
- Sundaram Palaniappan, MD – Sengkang General Hospital, Singapore
- Joseph C. Liao, MD – Stanford Medicine, California, United States
- Steffi Yuen, MD – New Territories East Cluster Hospitals, Hong Kong
Written by: Mariah Hernandez, Research Specialist, Department of Urology, University of California Irvine, @mariahch00 on Twitter during the 2024 World Congress of Endourology and Uro-Technology: August 12 -16, 2024, Seoul, South Korea