Kidney cysts are round pouches of fluid that form on or in the kidneys. Kidney cysts can be associated with serious disorders that may 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. Typically, only one cyst occurs on the surface of a kidney, but multiple cysts can affect one or both kidneys. However, simple kidney cysts aren't the same as the cysts that form with polycystic kidney disease.
Simple kidney cysts are often detected during an imaging test performed for another condition. Simple kidney cysts that don't cause signs or symptoms usually don't require treatment.
Simple kidney cysts typically don't cause signs or symptoms. If a simple kidney cyst grows large enough, symptoms may include:
- Dull pain in your back or side
- Upper abdominal pain
When to see a doctor
Make an appointment with your doctor if you have signs or symptoms of a kidney cyst.
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 (diverticulum). The pouch then fills with fluid, detaches and develops into a cyst.
The risk of having simple kidney cysts increases as you get older, though they can occur at any age. Simple kidney cysts are more common in men.
Kidney cysts can occasionally 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 your back or side.
- Urine obstruction. A kidney cyst that obstructs the normal flow of urine may lead to swelling of the kidney (hydronephrosis).