Overview

What are kidney cysts?

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.

Who gets simple kidney cysts?

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.

Are simple kidney cysts dangerous?

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.

Symptoms and Causes

What causes simple kidney cysts?

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.

What are the symptoms of 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:

Pain in the side between the ribs and hip, stomach or back.
Fever.
Frequent urination (having to go the bathroom often).
Blood in the urine, or dark urine.

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.

Diagnosis and Tests

How are simple kidney cysts diagnosed?

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:

Ultrasound: High-frequency soundwaves and echoes create images of the inside of the body.
Computed tomography (CT): X-rays and computers produce images of a cross-section of the body.· The scans require an injection of iodinated contrast n order to distinguish fluid-only filled cysts from solid masses.
Magnetic resonance imaging (MRI): Magnets, radio waves and a computer create images of inside the body. They also can be used to tell the difference between cysts filled with fluid and solid masses. Because they don't require iodinated contrast, MRIs are used for patients with iodine allergy.

Management and Treatment

How are simple kidney cysts treated?

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:

Aspiration and sclerotherapy: The doctor inserts a long needle under the skin to puncture the cyst and drain the fluid. A strong solution is then injected into the cyst to shrink it. This procedure can be repeated, if necessary.
Surgery: Surgery to remove a cyst can usually be done laparoscopically, using thin instruments inserted through small holes in the abdomen. During surgery, the doctor first drains the cyst and then cuts or burns away the cyst itself.

Prevention

Can simple kidney cysts be prevented?

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).

Does a simple kidney cyst need to be watched over time?

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).

Outlook / Prognosis

What is the outlook for someone with simple kidney cysts?

Since simple kidney cysts are almost always harmless, the outlook is excellent. Treatment, when necessary, is very effective and has few complications.

Living With

When should I call my doctor about kidney cysts?

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.

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Kidney Cysts