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Am Fam Physician. 2001;63(2):299

What are kidney cysts?

Your kidneys remove waste products from your blood. They do this by filtering the blood and making urine.

As people get older, fluid-filled sacs, called “cysts,” can form in the kidneys. These cysts are usually small, oval or round thin-walled sacs with water in them.

Kidney cysts are almost always benign (not cancer). Usually, the cysts cause no problems. In fact, people can go through life without knowing that they have them.

How common are kidney cysts?

Cysts can form almost anywhere in the body, but they are especially common in the kidneys. Up to 50 percent of people older than 50 years have kidney cysts.

How are kidney cysts found?

Almost all kidney cysts are found on radiology studies, like ultrasound, CT or MRI exams that are done because of problems in other parts of the body. The cysts are called “incidental” because they are found while a doctor is looking for something else and because of their benign nature.

If I have a kidney cyst, what will my doctor want to do?

First, your doctor will ask if you're having any problems because of the kidney cyst. The cyst could cause pain on your side between your ribs and your hip, pain in your belly, a fever, frequent urination or blood in your urine. If you're having any of these problems, your doctor will examine you and order lab tests.

If you're not having any of those problems and your kidney cyst is small, you probably don't need any treatment. Your doctor might want to check the cyst again with a CT scan in 6 to 12 months. If you start having problems, your doctor might want you to have a CT or MRI scan of your kidney to see if the cyst is growing. Remember that most people with kidney cysts never have problems and never need extra CT scans.

If your kidney cyst is large or if it contains calcifications (hard, stony pieces) or dense tissue, you might need to have CT scans every so often so that your doctor can watch for changes in the cyst. To get more information about the cyst, your doctor might also want you to have an MRI scan.

Will I need surgery to remove a kidney cyst?

Probably not. Most kidney cysts are harmless and don't need to be removed. Your doctor will send you to a urologist (a doctor with special training in kidney problems) if your kidney cyst keeps getting bigger, if you have problems because of the cyst or if there is any concern that the cyst might be a cancer.

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