What Could A Gestational Sac Close To The Posterior Wall Of The Uterine?

Ok, I scanned a patient a week ago and noted in the uterus was a gestational sac but she s not pregnant. I asked her further questions and she said there as always been a gestational sac in her womb. Now the question is how will I write my report because am confused of which word to use. What kind of cyst should I write because the gestational sac like cyst is close to the posterior wall of the uterine cavity? Thank you.