how do they know for sure its a dermoid

i am scheduled for a hysterectomy in aug i have endo., fibroid, and a dermoid cyst. from my understanding a dermoid cyst is my twin, that i absorbed while the cells were spliting in my mothers womb. it could contain glands, teeth, hair..... how can they tell for sure that that's what the cyst is???? i had an ultra sound and a ct scan. my ob/gyn didn't give me any measurements only that it was a dermoid mass on my left ovary. i did do a ca-125 test about 2 weeks ago. i haven't heard anything from the doc office. and my belief is no news is good news. plus he told me not to worry about it due to having endo, fibroids, and cyst, it will give that test a high reading. plus twins don't run in my family. so i'm worried it might be cancer.

Hello. Cancerhead does strike us when we least wish to have it strike. I had my BSO surgery in part due to encysted ovaries (both sides). In tests that were run, the problems with the cysts were inconclusive, so they took my ovaries. If they did a needle biopsy, it could be that helped them determine it was dermoid cyst. And if not, it could be the shape or size of the cyst or its seeming texture on scan that makes them have this conclusion. The important thing is that you are having it removed. Your hunch is probably correct: only after the cyst is removed will they know for absolute certainty that it is not cancer. But in the meantime, I hope you will rest assured that you found your troubles sufficiently early and that they will be treated. My surgery was in August, also. It seems far off right now, but it will come and go very fast from here on for you! Good wishes to you.