According to the National Kidney Foundation, more than half a million people visit emergency rooms each year for kidney stones. Kidney stones are crystalized masses that develop from substances in the urine. One of the main causes of kidney stones is the lack of fluids in the body.Listen in as Steven A. Johnson, MD explains that in most cases, kidney stones pass out of the body unnoticed, but sometimes they can become too large and lodge in the urinary tract, causing extreme pain or bleeding. Several surgical options are available if a stone does not pass on its own.