A fluid-filled sac in the kidney. Cysts frequently occur in those people over 50, and can arise either singly or multiply in one or both kidneys. The majority of cysts arise for no particular reason, are noncancerous, and do not usually create symptoms unless they become big enough to cause lower back pain due to pressure on the surrounding tissue. Large numbers of kidney cysts, however can be associated with polycystic kidney disease, which generally leads to kidney failure.
Simple cysts do not often need treatment. For cases in which the cysts are recurrent or painful, however, aspiration (withdrawal of fluid) or surgical removal can be undergone.