What causes an ovarian serous cystadenoma to rupture do i need surgery if rupture?

Depends: One would not know it a cyst is a serous cystadenoma unless it was removed and d examined by path. It is got too large or was under a lot of pressure it could rupture. When a cyst ruptures surgery may be needed if there is internal bleeding or severe pain.

Pressure: The increased pressure and weak wall of the ovary can cause it to rupture - you do not need surgery if it does. You might consider getting it removed before it does though.