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.
These are the main causes of kidney cysts:-
This depends on the type of kidney disease. Each person with kidney cysts will need to be advised individually. However, many people with multiple cysts in their kidneys 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.
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. This can come in spasms, and sometimes there may be blood in the urine. Infections can occur, with pain passing urine, or fevers with sweats and pain in the back. Sometimes these are 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.
NKF Controlled Document No. 282, Kidney Cysts, written 22 July 2000. Last reviewed 6 June 2011.
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.