Simple kidney cysts are usually small round sacs that are filled with a watery fluid. Most people who have them don't even know they have them. You might have to have treatment if your cyst bursts and bleeds, or grows big enough to press on other organs.
A cyst is a closed pouch or sac filled with air or liquid. Kidneys are bean-shaped organs located in the lower back that help to control the amount of salt and water in the body. They also remove waste products by filtering the blood and making urine.
Inside the kidneys are small working parts called nephrons. Each nephron is made up of a filter and a tube. As blood flows through the kidneys to be filtered, the nephrons remove extra water and waste products, which leave the body as urine.
Simple kidney cysts are usually small round sacs that have a thin wall and are filled with a watery fluid. As people get older, cysts can form on the surface or in the nephrons of the kidneys. They can range in size from a small pea to as large as a grapefruit. Cysts can also grow over time.
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Simple kidney cysts are very common as people begin to age; up to half of all people 50 years of age and older have at least 1 kidney cyst. Most people have a cyst in only 1 kidney, but the number of cysts and the risk of getting cysts in the second kidney increase as we get older.
Simple kidney cysts are almost always harmless. They are called "simple" because there is very little chance they will develop into something more serious. However, some cysts do have thickened walls, may look irregular on X-rays, and could be associated with kidney cancers.
Kidney cysts occur when the tube of a nephron begins to get bigger and fill with fluid. Researchers don't know what causes this to occur, but they do know that simple cysts aren't inherited. It is believed that injury or microscopic blockages in the tubules may lead to the development of some simple kidney cysts.
Simple kidney cysts usually don't cause any symptoms. In fact, most people who have them don't know they have them. The cysts become a problem if they rupture (break open) and start to bleed, become infected, or grow so large that they push against other organs within the abdomen.
When simple kidney cysts do cause symptoms, they might include:
Depending on where the cyst is located, it can affect how the kidney works. It can also lead to a type of high blood pressure if the cyst prevents the kidney from filtering extra fluid from the blood.
Simple kidney cysts are often found while the patient is seeing the doctor about another condition. The most common tests used to diagnose simple kidney cysts include:
In most cases, simple kidney cysts don't need to be treated. However, if a cyst is putting too much pressure on another organ or is affecting the way a kidney works, it might be necessary to shrink or remove the cyst. There are 2 procedures that are most commonly used to treat simple kidney cysts:
Simple kidney cysts can't be prevented. You can reduce your risk by drinking plenty of water and making sure you use less than 2,300 mg of sodium a day (less than 1,500 mg if you are older than 51, African-American, or have high blood pressure or long-term kidney disease).
It is very important that a specialist evaluate the type and location of the kidney cysts. There are often characteristics — such as wall thickness, calcifications, fluid density, and irregular borders of the cyst — that may make it more likely to be associated with a kidney cancer. Urologists use a grading system for cysts called the Bozniak Scoring System (named after the doctor who first described it). Higher Bozniak grades are associated with a greater chance for kidney cancer. Bozniak grade 1 cysts are virtually always benign (not cancer).
Since simple kidney cysts are almost always harmless, the outlook is excellent. Treatment, when necessary, is very effective and has few complications.
You should call your doctor if you experience any of the symptoms listed above (pain in the side between the ribs and hip, stomach, or back; fever; frequent urination; blood in the urine, or dark urine). This might mean that you have a kidney cyst that has burst or become infected.
Last reviewed by a Cleveland Clinic medical professional on 01/04/2021.
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