Stones start small and gradually grow larger.
Stone formation, shape, and growth are dependent on the total amount and types of crystals and all chemicals in the urine. Stones nearly always form in the kidney, where they may remain without symptoms and do not require treatment. However, they may cause obstruction or break loose and try to pass with the normal flow of urine through the urinary tract. More commonly, a stone will enlarge or move and cause pain and obstruction. The pain of trying to pass a kidney stone has been described as the most severe pain in the back, side, or abdomen that a person may experience.