A kidney cyst is a fluid-filled sac that grows in your kidneys, which are the bean-shaped organs that filter wastes out of your bloodstream to produce urine. You might have a single cyst on one kidney or many cysts on both kidneys.
There are two types of cysts: simple cysts and polycystic kidney disease. Simple cysts are individual cysts that form on the kidneys. They have thin walls and contain a water-like fluid. Simple cysts don’t damage the kidneys or affect their function. Polycystic kidney disease (PKD) is an inherited condition that causes many cysts to form on the kidneys. These cysts can damage the kidneys as they grow.
Cysts are usually harmless. Because they often don’t cause symptoms, you might not even realize you have them until you get an imaging scan for another reason.
Some cysts are so small that you can’t see them without a microscope. Others can grow to be as large as a tennis ball. As they get larger, cysts can press on nearby organs and cause pain.
A simple cyst may not cause any symptoms. However, if the cyst grows large or becomes infected, it may cause symptoms such as:
- pain in your back or side between your ribs and pelvis (the pain is usually dull, but it can become severe if the cyst bursts)
- pain in your upper abdomen
- swelling of the abdomen
- urinating more often than usual
- blood in your urine
- dark urine
PKD can cause symptoms and signs such as:
- pain in your back and side
- high blood pressure
- blood in your urine
Doctors don’t know exactly what causes simple kidney cysts. They do have a few possible explanations. For example, each kidney has about a million tiny tubules that collect urine. Cysts may start to grow when a tube becomes blocked, swells up, and fills with fluid. Another possibility is that cysts start when pouches called diverticula form in weakened areas of the tubules and fill with fluid.
You’re more likely to have kidney cysts as you get older. By age 40, about 25 percent of people will have them. By age 50, about 50 percent of people will have kidney cysts. Men are at greater risk than women of developing kidney cysts.
PKD is an inherited condition, meaning it’s caused by changes to genes that are passed down through families.
Usually cysts don’t cause any problems. However, sometimes they can lead to complications, including:
- infection in the cyst
- burst cyst
- blockage of urine out of the kidney
- high blood pressure
PKD can damage the kidneys over time. About half of people with this condition will develop kidney failure by age 60.
To diagnose a kidney cyst, you might see a specialist called a urologist. Your doctor may take a blood or urine sample to see how well your kidneys are working.
You might also need one of these imaging tests:
- computed tomography (CT) scan, which uses powerful X-rays to create 3D images of your kidneys
- magnetic resonance imaging (MRI), which uses magnets and radio waves to take pictures of your kidneys
- ultrasound, which uses sound waves to create pictures of your kidneys and can show if a cyst has grown bigger
If the cyst is small and doesn’t cause any problems with your kidneys, you might not need to treat it. You may just have imaging tests done every 6 to 12 months to make sure the cyst hasn’t grown.
For larger cysts or ones that cause symptoms, treatments include sclerotherapy and surgery.
Sclerotherapy is done to drain the cyst. You’ll first get a local anesthetic so you won’t feel any pain. Using ultrasound as a guide, your doctor will place a thin needle into the cyst through your skin and drain all the fluid from the cyst. Sometimes, the doctor fills the cyst with an alcohol solution afterward to prevent it from growing again. You’ll likely go home on the same day as the procedure.
A larger cyst that affects your kidney function may need to be removed with surgery. You’ll be asleep under general anesthesia during the procedure. Surgeons often remove cysts laparoscopically through several small incisions. This means they perform the surgery using a camera and tiny instruments. First, the surgeon will drain the cyst. Then they’ll cut or burn the walls of the cyst. You’ll need to stay in the hospital for a day or two after your procedure.
Most simple kidney cysts are harmless and don’t cause problems. If a cyst grows, sclerotherapy or surgery can remove it without any long-term complications.
Polycystic kidney disease can be more serious. Without treatment, PKD can cause complications such as high blood pressure and kidney failure.