J Urol 187(2):739-43 (2012)

PURPOSE: A persistent stone burden after renal stone treatment may result in future patient morbidity and potentially lead to additional surgery. This problem is particularly common after treatment of lower pole stones. We describe a potential noninvasive therapeutic option using ultrasound waves to create a force sufficient to aid in stone fragment expulsion.

MATERIALS AND METHODS: Human stones were implanted by retrograde ureteroscopy or antegrade percutaneous access in a live porcine model. The calibrated probe of a system containing ultrasound imaging and focused ultrasound was used to target stones and attempt displacement. To assess for injury an additional 6 kidneys were exposed for 2 minutes each directly to the output used for stone movement. Another 6 kidneys were exposed to more than twice the maximum output used to move stones. Renal tissue was analyzed histologically with hematoxylin and eosin, and nicotinamide adenine dinucleotide staining.

RESULTS: Stones were moved to the renal pelvis or ureteropelvic junction by less than 2 minutes of exposure. Stone velocity was approximately 1 cm per second. There was no tissue injury when tissue was exposed to the power level used to move stones. Localized thermal coagulation less than 1 cm long was observed in 6 of 7 renal units exposed to the level above that used for ultrasonic propulsion.

CONCLUSIONS: Transcutaneous ultrasonic propulsion was used to expel calculi effectively and safely from the kidney using a live animal model. This study is the first step toward an office based system to clear residual fragments and toward use as a primary treatment modality in conjunction with medical expulsive therapy for small renal stones

Comment:

Very interesting preliminary work in an animal model. Could external energy like this facilitate ureteroscopic or percutaneous treatment? Perhaps we could move fragments out of the lower pole, or move small fragments out of the kidney during the procedure, eliminating the need to pass them later. It might be possible to avoid a second puncture, or move that elusive fragment into the renal pelvis during percutaneous nephrolithotomy. I look forward to updates from the UW group.

Department of Urology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA.

Comment in:

• J Endourol. 2009 Nov;23(11):1919.

Outcomes after treatment for urolithiasis vary greatly depending upon the imaging modality used to evaluate for residual stones. Commonly used modalities such as plain film “KUB”, renal ultrasound, and in the past, IVP can easily miss small residual fragments. Stone protocol abdominal CT scans are now used more often for the diagnosis and monitoring of patients with urolithiasis. All residual fragments after treatment including tiny, perhaps clinically insignificant fragments, are visualized using CT postoperatively. This is a nice study presenting their stone free rate following ureteroscopic treatment as determined by CT scan for follow-up. They present the results of 92 patients (113 ureteroscopies) for renal and ureteral stones. Stone free was determined by the strictest definition of no stone fragment on CT scan/ The overall stone free rate was 50.4% (80% for ureteral only, 34.8% for renal).

These results likely come as no surprise to most urologists. As the authors point out, the fate of these remaining fragments after ureteroscopy found on CT, most of them tiny, have not been specifically studied. There is no question that reporting of results after treatment for urolithiasis should be standardized, and include other outcomes such as quality of life measures. For now, it will have to suffice that the methods of postoperative imaging and definitions of success be clearly described in each study.

Hermans T, Sauerman P, Rufibach K, Frauenfelder T, Sulser T, and Strebel RT

A recent randomized double blinded study that did not show different rate of successful stone passage for Tamsulosin vs. placebo (86.7% vs 88.9%), but the Tamsolosin group did pass their stones earlier (7 d vs. 10 d on average) and required less pain medications. It is quite possible that the advantage of the use of alpha blockers relates less to an improved ability to pass the stones, but rather less pain, and therefore more likely to tolerate the time required to pass the stone.