Shadow on CT scan mastoid bone area, MRI results clear, had ear infection and still do. Would MRI only show intercrainial and not bone disease?

Probably. Mri and ct are complementary studies so there is always the possibility that one study will show an abnormality that the other doesn't. Typically a 'shadow' in the mastoid bone means fluid and that should show up on mri. But not knowing for sure what is meant by 'shadow' in your case, i can't be 100% about that. Ask your doctor about your case specifically or an ENT specialist or a neurologist.
CT or MRI? Ct is the superior study to define issues within the ear and temporal bone. Mri is the superior study to define issues involving soft tissue such as brain.