- Last Updated: July 11, 2017
One in 20 people will develop a kidney stone, and the symptoms include flank pain, which may be severe and blood in the urine. Stones 4 mm and smaller are likely to pass on their own, and those greater than 9 mm are more likely to need intervention prior to passage. Staying hydrated can help prevent kidney stones and once you have had a kidney stone, you are more likely to have another one. They are most common in the 50-70 age group.
There are several methods of treatment, starting with hydration and pain relief and progressing to more invasive methods. Alpha blockers and calcium channel blockers can relax the spasm of the ureter and allow the stone to pass down to the bladder. For larger stones, Extracorporeal Shock wave lithotripsy (ESWL) can be used to break up the stone in your body, and then fragments will pass. For stones in the kidney, a percutaneous nephrolithotomy can use small scopes to penetrate to the kidney to help remove the stones. Some stones can be reached with a small scope that passes through your bladder and ureter to reach a smaller stone or fragment to remove it. A tube can also be places which allows the stones to pass down to the bladder to exit. Many of these procedures require general or regional anesthesia and limiting factor for many of them relates to the location of the stone. If the stone is not in a suitable location, a more invasive approach must be taken.
Focused Ultrasound Therapy
The ability to move stones in the genitourinary track can be very helpful in some patients. For patients with multiple stones or for those who have had ESWL, there is a potential for the fragments to locate in the lower pole. Treatment success is based on both stone fragmentation and clearance of the fragments. The tendency of accumulation in the lower pole can have longer term implications, as the fragments can grow in size resulting in the need for another removal procedure. Additional uses include treatment of asymptomatic calculi in pilots, pregnancy or in those with a solitary kidney. One can also reposition a stone for better access by ESWL, ureteroscopy or percutaneous nephrolithotomy.
The mechanism of moving the stones is based on the application of focused ultrasound to a location that is adjacent to the stone. As the energy is applied, there is an acoustic wave that spreads. When the wave hits the stone, the energy is transmitted to the stone, resulting in an acoustic radiation force. This force is transmitted to the stone, and acts along the propagation axis of the acoustic wave. The movement is based on the initial location of the wave and the position of the stone. Alterations in the location of the wave can enable directional control of the stone.
Another use of focused ultrasound is to break up larger stones, called Burst Wave Lithotripsy (BWL). This technique is not as far along the process as kidney stone movement, but the preclinical work is encouraging. The plan is to use repeated, smaller power applications that can break up the stones without causing damage to neighboring structures. Ongoing work is expected in both areas by the spin off company from the University of Washington, SonoMotion.
The ability to use focused ultrasound to move stones or stone fragments has been demonstrated in adult patients. The team used focused ultrasound to reposition stone fragments ranging from 5mm-10mm in 14 out of 15 patients. Of the 43 total targets, 28 (65%) showed some level of movement, while 13 (30%) were moved 3mm or more to a new location. Stone direction was controlled and 4 out of the 6 patients who had ESWL eliminated 30 fragments. The largest stone moved was 10mm, and one patient had temporary discomfort when a 10mm stone was moved at the ureteropelvic junction. There were no adverse events with the treatment.
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