Kidney stones

What are kidney stones?

Kidney stones (or calculi) may be as small as a grain of sand or as large as a pearl, with some even as big as golf balls. They may be smooth or jagged and can form in any part of the urinary tract, from the kidneys to the ureters (the tubes leading out of the kidneys), to the bladder.

About three in 20 men and one in 20 women in the UK develop a kidney stone at some stage in their life. They can occur at any age, but are most common between the ages of 20 and 40.

The problem often recurs, with 60 per cent of people developing another stone within seven years.

Causes and risk factors

In most cases, there's no obvious cause, although dehydration, prolonged bed-rest and urinary tract infection may all play a part.

In about 70 per cent of cases, the stone is made of calcium oxalate and/or calcium phosphate. Oxalate is a product of metabolism naturally found in urine, which can be found in the following foods:

• Rhubarb
• Coffee
• Spinach and leafy vegetables

Occasionally, calcium stones occur due to an overactivity of the parathyroid glands, which control calcium metabolism in the body.

In about 20 per cent of cases stones are caused by chronic urinary tract infections. The bacteria break down urea in the urine to form ammonia and make the urine alkali. This leads to the formation of stones containing calcium, magnesium and ammonium phosphate.

In severe cases, the stones fill the middle of the kidney, causing a large stone known as a ‘staghorn calculus’ because of its shape.

About one in 20 stones are uric acid stones, often linked to gout, but also to some cancers and chronic dehydration. Very rarely, stones are the result of inherited metabolic disorders such as cystinuria.

Symptoms

These depend largely on the position of the stone:

• Small stones in the kidney itself may cause no symptoms, and go unnoticed. But once stones enter the ureter, they can cause extreme and sudden pain in the loin (in the lower back), which moves down towards the groin. This pain, known as renal colic, is very sharp, may come in waves, and can cause nausea and vomiting.
• Blood may be noticed in the urine.
• Once the stone reaches the bladder, the pain may disappear, but there may be problems passing urine - with a slow stream and dribbling, as the stone can block the exit to the bladder. If the stone is passed, it is important to try to catch a stone in a strainer (the best way to determine the type of stone, is to test the stone itself).
• Urinary tract infection can also be a symptom.

Treatment and prevention

Most stones will pass by themselves, but the pain of renal colic is very severe and many patients will require hospital admission with strong painkillers and intravenous fluids, during the attack.

If the stone doesn’t pass by itself, a urologist (kidney surgeon) may need to take steps to get rid of it. In the past, the only way to remove a problem stone was through surgery, but new treatments have been developed:

• Shock wave machine. A machine can send shock (sound) waves directly to the kidney stone. The shock waves break a large stone up, which pass through the urinary system in the urine.
• Tunnel surgery. The doctor makes a small cut into the patient’s back and makes a narrow tunnel through the skin to the stone inside the kidney. With a special instrument that goes through the tunnel, the stone can be found and removed.
• Ureteroscope. This looks like a long wire. It is inserted it into the urethra (the tube fom the outside world to the bladder), and passed up through the bladder, to the ureter where the stone is located. The ureteroscope has a camera that allows the stone to be seen and removed or destroyed in the bladder.
• Stone removal can be completed by a traditional operation where the skin has to be cut to allow access to the ureter and kidney. This is only needed in a very small number of cases where the above, newer techniques have not worked or are not possible. It may be done if there is a very large stone in the kidney.

Depending on the causes, prevention can include:

• Drinking lots of water (some doctors think fluid intake of at least two to three litres a day can help to keep the urinary tract flushed out).
• Rapid treatment of urinary tract infections.
• Specific treatments for metabolic disorders and gout.