The difference would be so small it's probably impossible to detect. Plus they're looking in the wrong places. Ever since leftists who have no idea what this is about took over, everyone thinks it's a nice new way to have gender norms again. So they look for personality differences rather than where they would actually lie, which is probably body mapping, sensory perception, and instincts. Dissociation and loss of most talent is probably a sign too, because while it isn't easily visible from the outside the sexes do have different ways of thinking up similar results for some reason. The problem is it's only the inclination to think one way that manifests in GD, the rest of the brain still responds to hormones and develops assuming it's going to think the other (probably because this mostly doesn't happen until puberty). So I doubt it would be visible on a brain scan, but it could cause someone to suddenly lose their mind when they start puberty because they don't like or don't know how to use their remodeled one.