You are here

Kidney stones

Kidney stones are a very common problem in hot climates and Australia is no exception. Kidney stones are not stones in the generic sense, but crystals composed of different types of salts that are found in the blood and excreted in the urine, including complexes of calcium, oxalate, uric acid, magnesium and phosphate. Less common stones arise from genetic defects, e.g. "cystine" stones. Stones typically form when the patient is dehydrated and the urine is very concentrated as a result, or when the kidney is excreting or "losing" too much of certain minerals into the urine, or both. Stones usually start as small granules and grow in size by progressive deposition of more crystal layers. Stones vary in size from 3-10mm at diagnosis, but some can be much larger, or even fill part or all of the urine collecting tubes of the kidney, a so-called "staghorn" stone, named after the antlers of a stag.

Stones cause severe pain when they drop out of the kidney collecting tubes and into the ureter, the thin, muscular tube that conveys urine from the kidneys to the bladder. The pain is caused by the stone blocking the ureter, causing build-up of urine in the kidney, swelling of the kidney and stretching of the tough covering of the kidney (the "capsule") which has many pain fibres. The pain is extremely severe and moves from the kidney area (the upper small of the back on the left or right) and moves down to the groin of the same side in waves. It is episodic, coming and going in waves, and often causes nausea or vomiting.

Many stones which become stuck in the ureter are small enough to be expelled by the body without surgery. This may take a number of weeks however. For stones that are too large to pass out on their own, treatment is usually by surgery. When stones are causing a blockage of the ureter, the urologist will usually place a "stent" (a hollow, flexible silicone rubber tube) in the ureter which lies between the bladder and kidney and allows urine to flow down into the bladder and relieve the build-up and pressure. This allows the swelling and any associated infection to clear, and the patient is usually booked for surgery to clear the stone in the coming weeks. This involves passage of a thin rigid or flexible telescope under general anaesthesia up the urethra, through the bladder and up the ureter tube to the level of the stone, which is then disintegrated with a small medical laser fibre. The resulting stone fragments and dust are very small and pass easily down the ureter into the bladder. For stones in the kidney, the same technique can be used.  For large stones in the kidney, and staghorn stones, another approach is to perform a PCNL procedure, in which a thin tunnel is made into the kidney from the skin of the back, and an operating endoscope is passed into the kidney to breakdown the stone using a lithotripter, a device which breaks down stones like a jack-hammer. The stone fragments are then removed with small graspers via the same tunnel, and a small drainage tube is left in the kidney overnight.

Kidney stones can be a difficult problem as they often recur in patients over many years. A person who has had one stone has an approximately 50% chance of having another kidney stone in the next 10 years. Furthermore, for unknown reasons, some patients make stones in only one kidney and not the other. Undiagnosed kidney stones which have blocked a kidney can result in severe damage to that kidney and ultimately complete loss of function. For this reason urologists are very careful in making sure that any stone which has caused a problem has been naturally passed out of the body or removed surgically.