kidney stone

A kidney stone, known medically as a calculus (plural: calculi), is a small, hard, pebble-like mass formed in the kidney from an accumulation of mineral substances. Passage of a kidney stone through the ureter (the tube leading from the kidney to the urinary bladder) causes intense pain known as renal colic. Kidney stones can be removed by surgery or, if the stones are small, they can be passed out in the urine after treatment, which includes drinking large amounts of water.