BERKELEY, CA (UroToday.com) - Over the last decade, there have been incremental advancements in stone management. The main options for treating patients with kidney stones remain observation, medical expulsive therapy, shockwave lithotripsy, ureteroscopy with laser lithotripsy or basketing, and percutaneous nephrostolithotomy. With the goal to ultimately render a patient stone free, the development of technologies to further improve stone-free rates while minimizing morbidity are necessary.
Most recently, ultrasonic propulsion has been developed as a new technology that may radically change how urologists manage stone disease. A review of this technology is highlighted in the October 2013 Journal of Endourology. This technology generates focused ultrasound waves to deliver an acoustic force to move kidney stones. The pressure applied to the tissue is approximately half of current shockwave lithotripters, at about one quarter of the energy exposure. The acoustic force is delivered transcutaneously with real-time ultrasound guidance.
In animal studies, the device has been shown to be safe and effective in repositioning calyceal stones to the renal pelvic, ureteropelvic junction, or proximal ureter. In the latest published study, 65% of stones 2-8mm in size were successfully relocated. Stone size and type did not appear to be associated with success. Injury studies have demonstrated that the exposure settings used are an order of magnitude below the threshold of mechanical and thermal injury.
There are several possible applications of ultrasonic propulsion in the management of stones. First, ultrasonic propulsion may be used to treat and facilitate passage of small stones ≤ 5mm, that otherwise would be managed with observation. Patients may want to induce stone passage in a more predictable setting combined with medical expulsive therapy due to personal preference or occupational requirements, such as pilots. Second, ultrasonic propulsion may be used to identify and clear residual fragments after lithotripsy and reduce the rates of stone recurrence and retreatment. Third, ultrasonic propulsion may be used to push back an obstructing stone to a nonobstructing position during an acute stone event. This may obviate an emergent stenting procedure and delay stone treatment to an elective setting. Fourth, ultrasonic propulsion may be utilized in the perioperative setting to improve the effectiveness of current techniques, such as during ureteroscopy to reposition a difficult-to-reach stone or during shockwave lithotripsy to relocate a lower pole stone. Finally, ultrasonic propulsion may be used to provoke movement of a suspected stone to distinguish true stones from renal sinus fat or parenchymal calcifications. This and other applications may have the potential to reduce radiation exposure in stone-forming patients.
In summary, ultrasonic propulsion has the potential to dramatically change how urologists manage stone disease. A curriculum has been developed to train urologists how to image and reposition stones with ultrasonic propulsion (J Endourology, in revision). Ultrasonic propulsion has gained FDA approval for a pilot study in humans, and the clinical data from this trial is anticipated to further refine the technology.
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Written by:
Ryan Hsi, MDb and Mathew Sorensen, MD, MSa, b as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
aDivision of Urology, Department of Veteran Affairs Medical Center, Seattle, Washington.
bDepartment of Urology, University of Washington School of Medicine, Seattle, Washington.
Focused ultrasonic propulsion of kidney stones: Review and update of preclinical technology
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