Is is possible for a woman that had a total hysterectomy due to endometriosis 12 yrs ago now have this inside the stomach if it was "caked" to uterine wall? Taken estro/progestine patches since then.

Adhesions. What you describe are adhesions or scar tissue which is a side effect of hysterectomy. The patches are not the cause, but a treatment for early menopause due to the surgery.
Yes, but... Yes but if there is something there that is measurable on some image it is important to make sure it is not cancer. Women with endometriosis in their lifetime have a higher risk of ovarian and peritoneal cancer which can still occur many years after a total hysterectomy. That is not to scare you but just to make sure you get properly evaluated.