how big can kidney cysts grow

Kidneys are bean-shaped organs located in the lower back.The kidneys help to control the amount of salt and water in the body, and also remove waste products by filtering the blood and making urine.A cyst is a closed pouch or sac filled with air or liquid.Simple kidney cysts are usually small round sacs that have a thin wall and are filled with a watery fluid.As people get older, cysts can form on the surface or in the nephrons of the kidneys.Renal (or kidney) cysts are very common, occurring in 50 % of adults.About 2/3 of people over 80 years old will have a cyst detectable by x-rays or ultrasound.
They can range in size from a small pea to as large as a grapefruit.Cysts can also grow over time.Cysts usually do not grow during follow up examination, but they can grow to be very large, even larger than the kidney itself.
What causes simple kidney cysts?Kidney cysts occur when the tube of a nephron begins to get bigger and fill with fluid.Cysts can cause pain due to growth and stretching of the wall of the cyst,pressure on the kidney,pressure on the drainage of the kidney, causing blockage,pressure on other organs (stomach, intestines).Rarely, cysts can bleed, rupture, or become infected.

Are simple kidney cysts dangerous?Simple kidney cysts are almost always harmless.They are called "simple" because there is very little chance they will develop into something more serious.However, some cysts do have thickened walls, may look irregular on X-rays, and could be associated with kidney cancers.While no surgery is without risks, and no surgery can be 100% successful, all patients treated so far have had successful surgery and no recurrence of their symptoms.
http://www.pkdclinic.org/kidney-cyst/