By Sally Robertson, BSc
Kidney (renal) cysts are fluid-filled sacs that form on one or both of the kidneys. Usually, these cysts do not cause symptoms or kidney damage, in which case they are referred to as simple kidney cysts.
Simple kidney cysts are very different from the type of cysts that develop when a person has the genetic condition polycystic kidney disease (PKD), which causes scarring of the kidney tissue that can eventually damage the kidney and lead to kidney failure.
Simple cysts sometimes cause symptoms if they have become large enough or have started to press on other organs. They can also become infected, leading to pain and fever.