Snap - they changed their minds about the MRI because a CT scan images bone and neural tissue better than an MRI. MRI is better for diagnosing soft tissue lesions including disc and cartilage problems. My guess, and please keep in mind that it is a guess, is that they are looking for a Type 1 Chiari malformation or something similar. These are congenital and are not usually found until later on in life when people are undergoing treatment for something else. If that's what it is it could definitely have a lot to do with the arm problems.