Fundal uterine fibroid not responding to hormone treatment (not shrinking) injections 6months - concerns of sarcoma - will sarcoma show on mri?

Very very unlikely: Unfortunately gynecological oncologists and radiologists have not found an accurate imaging technique to diagnose a uterine sarcoma which is very unlikely to "show on MRI". The lack of response of "your fundal uterine fibroids to hormone treatment" is not a reliable sign either. Consult an experienced gynecologist about uterine fibroid biopsy or a laparoscopic myomectomy if you remain "concerned"