'Playing Pool' Is New Approach to Dislodge Kidney Stone Fragments

Maureen Salamon

December 16, 2021

Ultrasound technology that moves small, lingering kidney stones toward the ureter to avert episodes of pain or additional surgery may be ready for US Food and Drug Administration (FDA) approval next year, researchers report.

A 60-patient randomized clinical trial in progress at the University of Washington has produced encouraging findings from using focused ultrasound to dislodge persistent kidney stones left after surgery, said investigator Mathew Sorensen, MD, an associate professor of urology at the university.

In its third year, the study will likely enroll another 10 patients, he added.

"These fragments that are left after surgery are ripe to set up and grow new stones," Sorensen explained. "Somewhere between 20% and 40% of patients with fragments left over will get into trouble later, which can mean another emergency room visit or another surgery."

"If we can clear them while they're small after their first surgery, the hope is we prevent a surgery down the line," he told Medscape Medical News. "We are very excited at what the preliminary results look like. There's likely to be a significant difference between the control and the treatment group."

A Sweeping Movement Similar to a Blower

Participants in the trial were equally split into intervention and control groups. The intervention group underwent a type of image-guided, focused ultrasound developed over the past decade using an external transducer placed over the affected kidney area.

"Patients don't feel much of anything" during the 30-minute procedure, which doesn't require anesthesia, Sorensen said. "Sometimes there's a little tingling sensation or the probe gets a little warm, but otherwise there's no discomfort associated with it."

Some participants underwent two such sessions to continue clearing tiny stone fragments from their kidneys, he said. 

"Essentially, we use the acoustic energy of ultrasound, which gets focused on the stone and creates movement, like a blower," said Sorensen, who is also urology residency program director at the University of Washington. "A push of energy lasts a second or two, sort of a sweeping movement to try to get fragments to move out of what's usually the bottom of the kidney, toward the exit."

"Because the energy moves in one way, away from the probe, it's sort of like playing pool," he added.

Nearly all study participants had undergone kidney stone surgery in the UW system, Sorensen said, where it's routine to perform imaging tests about 8 weeks post-surgery to determine if any stone fragments remain.

Researchers tracked the participants periodically to assess both imaging and clinical differences between study groups. The treatment appears safe, raising few concerns, Sorensen noted.

Special Interest From NASA

NASA is especially interested in the ultrasound technology because more than 30 astronauts have reported kidney stones within 2 years of space flight. No surgical option exists to treat stones in flight, Sorensen said.

The trial, based at the Kidney Stone Center at UW Medical Center-Northwest, is set to conclude in 2022, with the hopes of final FDA approval by the end of next year.

"Once it's approved, we could get it into clinicians' hands and they could use it on a daily basis," he said.

The trial is being funded by the National Institutes of Health. Sorensen is a member of the advisory board for and holds equity interest in SonoMotion, which develops technology to treat kidney stone disease.

Maureen Salamon is a New Jersey-based freelance health journalist with bylines in The New York Times, The Atlantic, CNN.com, and other major outlets.

Follow Medscape on Facebook, Twitter, Instagram, and YouTube.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.