A fluid filled cylinder is applied to the back. Soundwaves are generated that pass through the body and are focused on the stone. The stone is pulverized to small particles that can more readily pass down the ureter. SWL is non-invasive and works best on smaller stones of the kidney or upper ureter. SWL requires heavy sedation or full anesthesia. Even though it is non-invasive, there are limitations. It may not fully pulverize a large stone, a very dense stone, or a stone in the lower pole of the kidney. When a large stone is treated with SWL, it can occasionally lead to fragments that line up in the ureter and cause obstruction and pain. This is called a “Steinstrasse” or street of stones. If this occurs, a ureterostomy may need to be performed to remove the fragments.