Kidney Stones

Kidney stones are very common with a lifetime risk of developing a kidney stone of about 5%. Kidney stones are more common in adults than children but can occur at any age, with the average age being 30-50 years.

Men are more likely than women to develop kidney stones although the reason for this is not clear.

Kidney stones are a feared condition as they can be extremely painful. Many stones cause no symptoms at all for long periods and people may not realise they have a kidney stone until it causes them an episode of severe pain.

What are kidney stones?

Kidney stones are solids made of various chemicals which are produced in urine. Kidney stones are usually as hard as hard as rocks but some are made of softer substances.

The stones are initially produced in the kidneys, but may travel further downstream into the ureter (tube between the kidney and bladder), the bladder or the urethra (water pipe draining the bladder externally). Some stones are stuck to the internal walls of the kidney and do not move around, while others are floating loose within the kidney and can change location. Some stones will pass downstream from the kidney into the ureter when they are tiny and may not even be seen or felt. Other stones will only travel out of the kidney into the ureter when they are bigger and may get stuck in the ureter and cause pain.

Kidney stones vary in size greatly from tiny crystals of less than a millimetre (not visible to the naked eye) up to 10 centimetres (cm). They can vary in colour but are usually brown, black or yellow. Some stones are perfectly round, others are triangular, elongated, irregular or sharp.

Other names for kidney stones

Kidney stones have many names which are synonymous:

  • Kidney stones
  • Renal stones
  • Renal calculi
  • Ureteric calculi – when a stone made in the kidney has travelled down the ureter
  • Urolithiasis
  • Renal lithiasis
  • Nephrolith
  • Kidney pebble
  • Kidney concretion

It is important to note that kidney stones are not related to other stones in the body. Having stones in the gallbladder is not a risk factor for developing kidney stones at all. Stones can also occur in salivary glands, stomach, and ear but none of these are at all related to renal stones.

Anatomy of the urinary system

There are usually two kidneys although some patients have only one. The kidneys are located in the upper abdomen, closer to the back than the front. They lie just in front of the back muscles and behind the intestines. The kidneys are solid organs surrounded by a layer of fat. The central part of the kidney is hollow – this is called the renal pelvis and is where the urine is stored just prior to flowing downstream into the ureter.

In some patients the kidneys are located in the pelvis (pelvic kidney) or the two kidneys are joined together across the midline (horseshoe kidney).

Each kidney produces urine which drains down a ureter into the base of the bladder. Some patients have two ureters draining out of one kidney – a duplex system. Very rarely patients have three ureters draining a kidney. The ureters are very narrow which is not a problem as urine can easily flow though this. However, the narrow diameter of the ureter is a major problem for patients who have stones in the kidney as these frequently get stuck in the ureter causing a blockage.

The two ureters drain into the bladder. The bladder is an organ designed to store urine until such time as it is convenient to empty the bladder. The bladder is located deep in the pelvis just behind the pubic bone. It has a capacity of 400-700 ml in most people although this is extremely variable.

The bladder drains out of the body through the urethra, also known as the water pipe. The urethra is short in women and long in men. The urethra is much wider than the ureters and kidney stones usually do not get stuck in the urethra. Nearly all stones which manage to pass through the ureter into the bladder will pass from the bladder without further difficulty or pain.

The prostate is an organ found only in men. It encircles the urethra just under the bladder and is involved in making semen. The prostate may, if is enlarged, cause a blockage to the urethra.