Is PET Scan Recommended To Test Results On Glioma Of Brain?

I have an oncologist who has reviewed my triple contrast MRI and believes I have a brain glioma. This was the original notation from the radiologist. My neurologist believes I have MS even though there are no lesions on the rest of my brain. I m scheduled for a PET scan later in the month but am highly concerned about the differences in opinion and the affects the waiting, guessing, and traveling are having on my family. How many opinions are considered too many?