A cyst is a swelling. In the kidney, cysts are round, have a very thin, clear wall and are usually filled with watery fluid. They can range in size from 5 centimetres (the size of a tennis ball) to something so small it can only be seen clearly under the microscope.
The kidney is made up of blood vessels, which carry blood to tiny filters. Each filter is connected to a tube. There are about a million units of filter and tube in each kidney. A cyst occurs when a single tube expands, often to a very large size. The exact cause of a swollen tube is not known.
One or two isolated cysts are a common finding in normal kidneys. Normal kidneys can occasionally have up to 5 cysts in each kidney. More cysts are an abnormal finding, but may not be due to serious disease. Other cysts may be a form of kidney cancer and these do not look the same as normal cysts.
These are the main causes of kidney cysts:-
- Normal - Cysts may be found in normal kidneys (up to 5 cysts per kidney).
- Cancer - Cysts can be a form of kidney cancer and these cysts do not look the same as normal cysts. If a cyst looks abnormal it will be reviewed by further scans and it may need to be removed.
- Medullary sponge kidney - Very small cysts are found in both kidneys, and there can be kidney infections, small kidney stones and kidney pain. Medullary sponge kidney does not usually lead to kidney failure.
- Medullary cystic kidney (sometimes called Nephronophthisis) - Very small cysts are found in both kidneys, and kidney failure may develop, requiring dialysis treatment.
- Autosomal Recessive polycystic kidney disease - There are hundreds of cysts in each kidney, and this condition is found in childhood. Click here for more information
- Autosomal Dominant Polycystic Kidney Disease - There are hundreds of cysts in each kidney: this condition is usually found in adults. Click here for more information.
The majority of cysts found in kidneys are normal and therefore you will not develop kidney disease. Even with multiple cysts, many people will not develop kidney damage. Given that there are as many as one million tubes in each kidney, it is easy to imagine that thirty cysts in each kidney may cause no problem to the other 999,970 tubes in each kidney.
However, in some conditions, such as Autosomal Dominant Polycystic Kidney Disease, you may develop kidney failure.
Cysts in normal kidneys only cause problems in very rare cases. Diseases with multiple cysts in the kidneys cause more frequent problems.
Cysts can swell up and cause pain in the upper back. Sometimes you may bleed from the cysts and there may be blood in the urine. Infections can occur, with pain passing urine, or fevers with sweats and pain in the back. These can be hard to treat, requiring long courses of antibiotics.
It is rare for cysts to require drainage. If so, this can be done with a needle, with some local anaesthetic to dull the pain and an X-ray (ultrasound) machine for guidance. However, polycystic kidneys contain so many cysts that drainage of a single cyst cannot cure the condition. Even if one cyst is painful, there may be hundreds of cysts in each kidney, and needling the one causing the problem can be very hard.
Most kidney specialists regard cyst drainage as rather experimental, but it can sometimes help. In extreme cases, particularly if severe infection has been a problem, the whole kidney can be removed at an operation.
This depends on the exact type of cystic kidney disease, some conditions run in families whilst others do not. Cysts in normal kidneys (up to 5 cysts in each kidney) do not require testing of family members.
The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.