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.
When to see a doctor
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.
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 cause 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).