That seems pretty big to me. They are probably worried that it could rupture. I would ask them why they are recommending surgery and go from there. Good Luck!
Laura :)
A cyst this size will seldom go away on their own, it is almost too big to be removed by scope also, either way it surely benefit you to get it removed as soon as possible before it gets larger and starts pressing on the other organs and causing you distress. A ruputured cyst causes pain and discomfort and spills the contents into the abdominal cavity. At your age, they might suggest removing the ovary also, especially if the cyst has compromised the ovary. With a laperotomy the surgeon can take a good look around for any other growths. Good Luck