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Simple Kidney Cysts

What are simple kidney cysts?

Simple kidney cysts are fluid-filled sacs that form in your kidneys. These cysts usually don’t affect how the kidneys function. The kidneys are 2 bean-shaped organs located near the middle of your back. They filter large amounts of blood each day. They also help regulate the fluid and salts (electrolytes) in your blood. They release waste products through your urine.

Simple kidney cysts are very common. They rarely need treatment. Most people don’t even know that they have them. You might have a single kidney cyst. Or you might have more than one. You might have them on only one kidney or on both of them. Most commonly, you’ll have only a single cyst. Over time, the cyst might slowly increase in size.

Simple kidney cysts become more common with age. But sometimes they are present at birth. Men get these cysts more often than women do. As medical imaging becomes more frequent, more and more people are diagnosed with these cysts.

Simple kidney cysts are different from complex kidney cysts. Healthcare providers can identify the type of cyst based on its appearance with medical imaging. Simple kidney cysts are the most common type. These cysts have thin walls and a regular, rounded shape. They are filled only with fluid. In contrast, a complex kidney cyst might have thicker walls and an irregular shape. It might also contain solid material. A complex kidney cyst might be a sign of cancer. But simple kidney cysts are not cancerous and never will become so.

What causes simple kidney cysts?

Researchers are still not sure what causes simple kidney cysts. The kidneys have tiny tubules. These structures collect newly formed urine. Cysts may result when the tubules get blocked. Small sacs sometimes form on the tubules. These may detach and become simple kidney cysts.

Some medical conditions can cause kidney cysts to grow. For example, a person with polycystic kidney disease develops a large number of kidney cysts. (The cysts may be simple or complex.) Too many cysts can prevent the kidney from working properly.

Other medical conditions that can cause simple or complex kidney cysts include:

  • Chronic kidney disease from any cause (especially with dialysis)

  • Medullary cystic kidney disease

  • Autosomal dominant polycystic kidney disease

  • Von Hippel-Lindau disease

  • Tuberous sclerosis complex

Who is at risk for simple kidney cysts?

If you smoke or have high blood pressure, you might have an increased risk of getting a simple kidney cyst. It’s not clear whether stopping smoking or controlling your blood pressure might reduce this risk.

What are the symptoms of simple kidney cysts?

Most people don’t notice any symptoms from their simple kidney cysts. Rarely, they might cause:

  • Blood in your urine (if the cyst bursts)

  • Pain in your upper belly or back (if the cyst bursts)

  • Fever and chills (if the cyst becomes infected)

  • Elevated blood pressure (if the cyst compresses the rest of the kidney)

  • Problems passing urine (if the cyst blocks the ureter, the tube that passes urine from the kidneys to the bladder)

  • A mass detected on a physical exam

These cysts usually don’t majorly impair kidney function unless they block the ureter. More commonly, some cysts might cause a slight drop in kidney function. But that doesn’t tend to cause any medical problems or symptoms.

For most people who have both simple kidney cysts and high blood pressure, the cysts are not the cause of the high blood pressure.

How are simple kidney cysts diagnosed?

Simple kidney cysts are often first found with an imaging test that was done for another reason. Your healthcare provider will perform a medical history. He or she will ask about your recent symptoms and past medical problems. You’ll also need a physical exam.

It is important to distinguish simple kidney cysts from complex cysts. Complex cysts might be cancerous. They usually need to be removed. For this reason, your healthcare provider might order medical imaging tests like:

  • Kidney ultrasound

  • Kidney CT (computed tomography, if more detail about the cyst is needed)

  • Kidney MRI (magnetic resonance imaging, if the nature of the cyst is still unclear)

A radiologist will look at these images to see if your kidney cyst is simple or complex. Healthcare providers sometimes rate cysts with the Bosniak CT system. It places cysts into 5 categories, which are I, II, II-F, III, and IV. The categories are based on complexity and possible malignancy. If your cyst is ranked a category I cyst, you probably won’t need any more imaging. Kidney cysts with higher ratings might need more imaging or treatment. Category IV cysts are most often linked with cancer.

Your healthcare provider will also check for other conditions that may be causing the cysts. If the diagnosis is still unclear after medical imaging, you might need to have genetic testing. It can help rule out other conditions, such as polycystic kidney disease.

How are simple kidney cysts treated?

Many people with simple kidney cysts don’t need treatment. Healthcare providers may want to closely watch the cysts. You may need occasional ultrasounds of the kidneys.

If you have symptoms, or if the cyst is blocking the flow of urine, you might need one of the following treatments:

  • Sclerotherapy, a procedure to puncture the cyst with a long needle inserted through the skin

  • Surgical procedure to drain the cyst and remove its outer tissue

  • Antibiotics and drainage to treat a kidney cyst infection

When should I call my healthcare provider?

Call your healthcare provider right away if you start having possible symptoms from your kidney cyst. These may include blood in your urine, pain in your back, or problems passing urine.

Key points about simple kidney cysts

Simple kidney cysts are fluid-filled sacs that form in your kidneys. Though abnormal, these cysts usually don’t affect how your kidneys work.

  • Most simple kidney cysts don’t cause any symptoms. They also usually don’t need any treatment.

  • Using medical imaging, your healthcare provider can tell if your cyst is simple or complex. A complex cyst might be cancerous.

  • You may need repeat imaging to monitor your simple kidney cyst.

  • If your cyst causes symptoms, you may need to have it removed.

  • If you have many kidney cysts, you may need testing to see whether you have a condition causing them. One such condition is polycystic kidney disease.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

  • Know the reason for your visit and what you want to happen.

  • Before your visit, write down questions you want answered.

  • Bring someone with you to help you ask questions and remember what your provider tells you.

  • At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

  • Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.

  • Ask if your condition can be treated in other ways.

  • Know why a test or procedure is recommended and what the results could mean.

  • Know what to expect if you do not take the medicine or have the test or procedure.

  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.

  • Know how you can contact your provider if you have questions.

Online Medical Reviewer: Daphne Pierce-Smith RN MSN CCRC
Online Medical Reviewer: John Hanrahan MD
Online Medical Reviewer: Walead Latif MD
Date Last Reviewed: 2/1/2019
© 2000-2021 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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