21 cm ovarian neoplasm?

[cvg2002]

I have just received my results from a recent ultrasound and have questions about the medical terms. My GYN (who is wonderful) is currently on vacation for 2 weeks. My husband and family are having questions that I can not answer, and can not seem to find on the internet.I am 24 years old with no children or pregnancies, and have a family history of "female plumbing" problems.

Results say: "There is a large right adnexal cystic mass with internal septations. It measures up to 21 cm in size. Septations are thin and there are also areas of low level echogenicity between several of the septations. The left ovary is normal, the right ovary is not seen."

Impression says: "21 cm right adnexal cystic mass. From the size, ovarian neoplasm is a consideration. Both benign and malignant ovarian tumors can arise to this size. It is likely this represents an endometrioma or pelvic duplication cyst."
First, all research I have found do not mention cysts over 4 in....mine has been identified as 21 cm or 8-9 in. Is this uncommon?

Second, what is "ovarian neoplasm," "adnexal," "septations," "echogenicity," "endometrioma," and "pelvic dupication cyst?"

Third, I am not a hospital person nor have I ever had surgery or have been admitted to a hospital. Most research I have seen states over a 4 in cyst would recommend surgery. Is this inpatient and a long recovery time?

Last, my father is concerned is the cyst ruptures (considering it's size) what would happen? I did not know what to tell him.

Thank you for your time and this forum.