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.

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.

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.