Small, solid masses called kidney stones may form when salts or minerals, normally found in urine, become solid crystals inside the kidney. Normally, these crystals are too small to be noticed and pass harmlessly out of your body. However, they can build up inside your kidney and form much larger stones. If a stone becomes large enough, it may begin to move out of your kidney and progress through the ureter-a tube that carries urine from the kidney to your bladder. A kidney stone can become stuck at various parts of the ureter causing pain, infection and occasionally kidney damage.
Attribution: BUPA