I thought this article quite interesting.
http://www.medhelp.org/health_pages/...show/61?cid=36

The article also discusses the Brain.

THE BRAINSTEM AND SPINE

The nerves in the brainstem and spine are all "eloquent" to some extent. They drive the functions and the movement of the body and they relay information like sensations from the body back to the brain. A small area of damaged myelin in the spine is "more likely" to cause a direct symptom or problem. Spinal lesions are a little less common than brain lesions, but more directly connected (in an obvious way) to our disease. But, also many spinal lesions are still invisible. One of the reasons for them being invisible is that they are harder to get good clear MRI images on. This appears to be one of the strengths of the newer generation of MRI machines. They have a higher magnet strength and because of this they have a higher resolution. They can see smaller lesions. The strongest MRI machines currently in clinical use today use a 3 Tesla magnet. Tesla is the "unit of measurement" of magnets, like "amps" is the unit of measurement of an amplifier. Older MRI machines, which are by far the most common in use, may use a magnet that is 1.5Tesla or weaker. Much stronger magnet MRI machines are being developed, but currently are used only in research.

Lesions in the brainstem and spine are stronger evidence for the presence of MS than are lesions in the brain. This is because there are many disorders that cause brain lesions, but many fewer that cause lesions in the spinal cord or the brainstem. And even though there tends to be a better correlation between symptoms or abnormal physical findings and lesions here, it is still often hard to draw connections between all of them.