This term refers to stones in the urinary system. They form in the kidneys but can be found anywhere in the urinary system. They vary in size and the amount of pain they cause. Many of these stones can pass though without help but some require medical intervention. Extracorporeal shockwave lithotripsy (ESWL) is the most frequently used procedure for the treatment of kidney stones. In ESWL, shock waves that are created outside the body travel through the skin and body tissues until they hit the denser stones. The stones break down into very small particles and are easily passed through the urinary tract in the urine.