Bladder stones are more common in those who have nerve impairment affecting the bladder, such as a spinal cord injury. Individuals who have had specific forms of bladder surgery (such as intestine-to-bladder expansion) are also at risk of bladder stones. A bladder stone is very seldom the outcome of a kidney stone that could not pass through the bladder. This can happen to persons who have trouble emptying their bladder, such as men with BPH. Bladder stones form when pee remains in the bladder for an extended period of time. The bladder is a component of the urinary system in the human body.