Understanding the kidneys

The kidneys are 2 bean-shaped organs near the middle of your back. They filter large amounts of blood each day. They also help control the fluid and salts (electrolytes) in your blood. They release waste products through your urine. The kidneys have tiny tubes (tubules). These structures collect newly formed urine. Cysts may happen when the tubules get blocked. Small sacs sometimes form on the tubules. They may detach and become simple kidney cysts.

What causes simple kidney cysts?

Experts are not sure what causes simple kidney cysts. 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. In most cases, a person has only one cyst. Over time, the cyst may slowly increase in size.

Some health conditions can cause kidney cysts to grow. For example, a person with polycystic kidney disease develops a large number of kidney cysts. Too many cysts can keep the kidney from working properly. Polycystic kidney disease is genetic. It's a different problem from simple kidney cysts.

Other health conditions that can cause simple kidney cysts include:

• Chronic kidney disease.

• Dialysis for chronic kidney disease.

• Medullary cystic kidney disease.

• Autosomal dominant polycystic kidney disease.

• Von Hippel-Lindau disease.

• Tuberous sclerosis complex.

If you smoke or have high blood pressure, you may have a higher risk for a simple kidney cyst.

Symptoms of simple kidney cysts

Simple kidney cysts often don’t cause symptoms. In rare cases, they may cause symptoms such as:

• 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 is infected.

• High blood pressure if the cyst compresses the rest of the kidney.

• Trouble peeing if the cyst blocks the tube that sends urine from the kidneys to the bladder (ureter)

Diagnosing simple kidney cysts

Simple kidney cysts are often first found with an imaging test that was done for another reason. Your health care provider will ask about your health history and symptoms. They will also give you a physical exam. Blood and urine tests can also be done to see if simple kidney cysts are affecting kidney function.

It's important to distinguish simple kidney cysts from complex cysts. Complex cysts are a different kind of cyst that may be cancer. A complex cyst needs to be removed. For this reason, you may need tests such as:

• Kidney ultrasound.

• Kidney CT scan, if a detailed picture of the cyst is needed.

• Kidney MRI, if more information is needed about the cyst.

A radiologist will look at these pictures to see if your kidney cyst is simple or complex. A cyst may be rated with the Bosniak system. This has 5 categories based on how the cyst looks. If your cyst is a category I, you likely won’t need any more tests. A kidney cyst with a higher rating may need more tests or treatment. A category IV cyst is most often linked with cancer.

Your provider will also check for other conditions that may be causing the cysts. You may need to have genetic testing. It can find other problems, such as polycystic kidney disease.

Treatment for simple kidney cysts

Many people with simple kidney cysts don’t need treatment. Your provider may want to keep track of the cyst over time. You may need ultrasound of the kidneys periodically

If you have symptoms, or if the cyst is blocking the flow of urine, you may need treatment such as:

• Over-the-counter pain medicine.

• A procedure to puncture the cyst with a long needle inserted through the skin (sclerotherapy).

• Surgery to drain the cyst and remove its outer tissue.

• Blood pressure medicine.

• Antibiotics and drainage to treat a kidney cyst infection.

When to contact your doctor

Contact your provider right away if:

• There's blood in your urine.

• You have pain in your back or upper belly.

• You have trouble peeing.

• You have a fever of 100.4°F (38.0°C) or higher, or as advised by your provider.

• You have chills.