Kidney cysts are round pouches of fluid that form in the kidneys. Kidney cysts can be associated with serious disorders that can impair kidney function.

What is it?

Kidney cysts are round pouches of fluid that form in the kidneys. Kidney cysts can be associated with serious disorders that can impair kidney function. But more commonly, kidney cysts are a type called simple kidney cysts — noncancerous cysts that rarely cause complications.

It's not clear what causes simple kidney cysts. Simple kidney cysts typically occur as one cyst on the surface of a kidney. But simple kidney cysts can occur as multiple cysts affecting one or both kidneys.

Simple kidney cysts are often detected during an imaging test being done for another condition. Simple kidney cysts that don't cause signs or symptoms usually don't require treatment.

Symptoms

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

  • Dull pain in your back or side
  • Fever
  • Upper abdominal pain

Causes

It's not clear what causes simple kidney cysts.

Risk factors

The risk of simple kidney cysts increases as you get older, though they can occur at any age.

Complications

Kidney cysts can occasionally cause 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 your back or side.

Diagnosis

Tests and procedures used to diagnose simple kidney cysts include:

  • Imaging tests. Imaging tests, such as ultrasound, computerized tomography (CT) and magnetic resonance imaging (MRI), are often used to investigate simple kidney cysts. Imaging tests can help your doctor determine whether a kidney mass is a cyst or a tumor.
  • Kidney function tests. Testing a sample of your blood may reveal whether a kidney cyst is impairing your kidney function.