How to choose ROI?

Hi, friends, I want to track facial nerve in Vestibular schwannoma patients. But in the step of ‘tractography seeding’, I always can’t choose the right ROI in Editor module or put the right fiducial. The target ROIs are REZ of FN VII, and inner inner orifice of IAC. Because of the tumor supressing, the normal anatomy of FN VII has changed. It’s very difficult to find right label. I will appreciate if anyone could help me.