They either left an ovary or you have an ovary remnant. Do come on over and join the Ovarian Cysts forum. The Health Pages attached to it describe the different types of cysts which you may find helpful. Us ladies over there will help you walk through this whole process. I am also 45 and just had a grapefruit sized fluid filled cyst plus my right ovary and tube removed 3 weeks ago.
All the best,