Kidney stones are a topic near and dear to my heart as I’m a member of the club. Stones are also known as calculi, from the Latin for pebble. They can form and stay in the kidneys (renal calculi or nephrolithiasis) or move down the ureters, the tubes connecting the kidneys to the bladder (ureteral calculi or urolithiasis). Stones may also be found in the bladder.
The ureters are very small tubes that contain smooth muscle cells. These cells rhythmically contract to help move the urine from the kidneys to the bladder. When a stone is too large to pass down the ureter it can partially or completely block the flow of urine causing pressure to build up. This pressure, along with contractions of the muscles in the ureter, causes deep, severe, unrelenting pain known as ureteral colic. Stones may also cause blood in the urine.
The peak onset of kidney stones is in the third and fourth decades. They rarely occur after age 60. Men have about a 12% lifetime chance of developing a kidney stone while women have a 7% chance. Interestingly, stones are more common in the Southeastern United States. The chance of developing recurrent stones is 14% at one year, 35% at five years, and 52% at ten years.
Stones form when the urine becomes supersaturated. This means that minerals and compounds in the urine become so concentrated that they start to form crystals. These eventually grow to form stones. It’s very important to maintain adequate fluid intake to keep the urine diluted to reduce the risk of stone formation. Certain types of kidney infections can also cause stones to form.
There are four primary types of stones that are associated with over 20 different conditions that are too numerous to discuss here. Most stones contain calcium. Chemical analysis of stones and urine identifies the cause in 95% of cases. This allows for specific therapy in most patients that can reduce recurrence rates by up to 90%. Even though most stones contain calcium, dietary restriction of calcium usually is not required.
Symptoms of kidney stones vary based on the size of the stones and their location in the urinary trac t. Renal calculi often have no symptoms. Ureteral calculi, on the other hand, can be extremely painful. Women who have given birth and also had stones often say the stones are more painful. Each year in the U.S., renal colic accounts for 2 million visits to physicians. The pain is often accompanied by nausea and vomiting. It’s also common for patients to be very restless and they often seek relief by pacing the floor.
The pain can be located anywhere from the back to the groin, testicle or vulva. The progression of the pain follows the anatomy of the urinary tract – it may start in the back or abdomen and move downward as the stone moves down the ureter. The pain may not move if the stone becomes stuck in the ureter. The most common places for stones to get lodged are where the ureter crosses over the pelvic bone or where it enters the bladder.
Normal X-rays may reveal some stones, depending on their composition. Most people get a special type of X-ray called a helical CT (CAT) scan that allows determination of the location and size of the stone, as well as giving much more information about the health of the ureter, kidney and other abdominal organs.
Small stones (less than 4 millimeters) usually pass spontaneously 80 to 85% of the time. Medications such as tamsulosin (Flomax) may be given to help speed the process. Large or irregularly shaped stones may become stuck and need to be removed, especially if they are over 8 millimeters in diameter. This can be done by inserting a lighted tube called a ureteroscope through the urethra, into the bladder and up the ureter. An instrument can then be used to grasp the stone and pull it out. Some stones need to be broken up into smaller pieces to allow them to pass. This can be done by using external sound waves (lithotripsy), or internally using an instrument, usually a laser, that is inserted through the ureteroscope.