Kidney cysts

Overview

Kidney cysts are round pouches of fluid that form on or in the kidneys. Kidney cysts can occur with disorders that may impair kidney function. But more often, kidney cysts are a type called simple kidney cysts. Simple kidney cysts aren't cancer and rarely cause problems.

It's not clear what causes simple kidney cysts. Often, one cyst occurs on the surface of a kidney. But more than one cyst can appear on one or both kidneys. Simple kidney cysts aren't the same as cysts that form with polycystic kidney disease. Simple cysts also differ from complex cysts. Complex cysts need to be watched for changes that could be cancer.

Simple kidney cysts are often found during an imaging test for another condition. Treatment usually isn't needed unless simple cysts cause symptoms.

Symptoms

Simple kidney cysts typically don't cause symptoms. But if a simple kidney cyst grows large enough, symptoms may include:

• Dull pain in the back or side
• Fever
• Upper stomach pain

When to see a doctor

Make an appointment with your health care provider if you have symptoms of a kidney cyst.

Causes

It's not clear what causes simple kidney cysts. One theory suggests that kidney cysts develop when the surface layer of the kidney weakens and forms a pouch. The pouch then fills with fluid, detaches and develops into a cyst.

Risk factors

The risk of having simple kidney cysts increases as you get older. But they can occur at any age. Simple kidney cysts are more common in men.

Complications

Kidney cysts may sometimes lead to complications, including:

• An infected cyst. A kidney cyst may become infected, causing fever and pain.
• A burst cyst. A kidney cyst that bursts causes severe pain in the back or side. Sometimes a burst cyst may cause blood in the urine.
• Blocked urine flow. A kidney cyst that blocks the typical flow of urine may lead to kidney swelling.