Lower pole stones quickly repositioned with ultrasound device

Seattle-An experimental new device may be able to help clinicians in the surgical treatment of lower pole stones by using ultrasound to move stones through the kidney collecting system.

The device, researchers say, may help improve clearance of stones in the lower pole that are left behind after shock wave lithotripsy. Natural clearance is effective for most patients and most stone fragments, but lower pole stones are noted for low rates of fragment clearance, noted Anup Shah, MD, a urology resident at the University of Washington School of Medicine, Seattle, working with Michael Bailey, PhD, and colleagues.

Half of patients with residual stone fragments return for further treatment within 5 years, Dr. Shah noted during a podium presentation at the AUA annual meeting in San Francisco.

"To date, there is no technology developed to aid in active expulsion of lower pole stone fragments," Dr. Shah said. "We believe that ultrasound can move stones through the kidney using a portable device in an office environment. With the device we have developed, there is no evidence, gross or microscopic, of any thermal or mechanical injury to animal kidneys from moving stones to a more superior position within the kidney."

"This is the kind of power output we are all accustomed to using in ultrasound imaging," Dr. Shah said. "It is orders of magnitude lower than the power used in high-intensity focused ultrasound. Ultrasound energy moves stones and stone fragments into the natural path of exit out of the kidney."

The system has not yet been tested in humans, he added, but it works well in transparent phantom kidneys and in live porcine kidneys. Operators could guide stones into a new, more superior position up to 3 cm from their original position within the kidney. Newer versions of the unit offer deeper tissue penetration, Dr. Shah said, which makes the technology practical for patients with deeper kidneys.

"Deeper penetration will be useful in the higher body mass patients we are seeing today," he explained. "We have also found that we can conglomerate multiple small fragments into a single area to move them more easily and quickly into a more desirable position within the kidney collecting system."