Kidney cysts are round pouches of fluid that form 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 being done for another condition. Simple kidney cysts that don't cause signs or symptoms usually don't require treatment.