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HI Janito,

I asked this question on another forum got this answer from a dr on there. Hope it helps.

The Life History of an MS Lesion

MS does it's damage by causing the nerves in localized areas in the brain and spinal cord to lose their protective sheaths, called myelin. At first, when the myelin is being attacked, the body brings a higher blood supply to the area to fight the attack and the area becomes iswollen and inflamed. These areas now become "lesions." At this point, when they are inflamed and blood engorged, they are called "active lesions." At first the nerves, themselves, haven't changed much and they appear (and have the same density) as the healthy areas around them. The body attempt to repair the damage that is being done and sometimes these areas re-myelinate. They may disappear from the next MRI. They aren't perfect in their function, but the area may return to a normal appearance.

If the nerves do not remyelinate and the damage continues, for a long time the lesions sit as scars. These scarred areas have damaged and dying cells in them, the blood supply shrinks, and the areas become more dense - more dense than the normal brain around them. These are the classic MS plaques and are considered old lesions. They show up as the bright areas most of us have seen in pictures and on our films.

If the attack on the myelin sheath is too strong for the immune system to repair, more and more myelin disappears and the area of nerves eventually dies. Then it contracts and scars. The blood flow is decreased to that area and the body tries to reabsorb the dead area. It becomes "less dense" then the surrounding normal nerve tissue. After a longer time - probably years - the scar can reabsorb completely and the area becomes "empty." It's called a black hole.

How the MRI Shows These Different Stages of MS Lesions

When you image these lesions with an MRI you can see different things, depending on the technique, the age (stage) of the lesion, the power of the MRI, and whether contrast is used.

The first MRI image is done without contrast. This technique will show old lesions that are big enough to be seen by the power of that MRI machine. WE KNOW that many lesions in MS are too small to be seen. If the newer, more powerful MRI with a 3 Tesla magnet is used many more lesions will be seen (by at least 25%) than on the older 1.5 Tesla machines. The classic old, scarred, mature MS lesion is a little bit oval, will have well-defined borders and will be in the white matter. Characteristic places (but not the only places) are subcortical, peri-ventricular and in the corpus callosum. The classic MS lesion will also have it's long axis perpendicular to the ventricles of the brain. Also, important and very symptomatic lesions are found in the brainstem, the cervical and the thoracic spine. The spinal cord ends at the bottom of the thoracic spine, so there is no such thing as a lumbar spinal cord lesion in the normal spine.

The scarred lesions will show up as light, bright areas. These are the classic, MS lesions or "plaques." But, with just the regular MRI image one can NOT say if it is old and dormant or if it has active inflammation in it.

Now the very old, scarred ones that have been reabsorbed will show up as a black (empty) space or black hole. If there are many of these empty areas the brain will contract around them eventually and show up as a loss of brain volume. This is also know as brain atrophy. This is particularly seen in the progressive types of MS. In brain atrophy there will be an increased space between the skull and the brain. Also the deep folds in the brain will appear widened.

However, a newly active MS lesion may not show up on a regular MRI because the area of nerves, though inflamed, is still pretty much intact and has normal brain density. On the MRI it will look like normal brain. Without contrast it won't show up and will be missed.

When the next phase of MRI is done the contrast is in the blood vessels. Anywhere the blood vessels are more dilated than usual, bringing more blood to the area, as in inflammation, the areas will "highlight" or "enhance." They show up as even brighter than the brain around them and brighter than an old, scarred lesion. So new lesions will show up as "enhancing," or "active". Also, older lesions, that have undergone a new attack right around them (also called reactivation) will show an enhancing rim or ring. When you compare the regular MRI to the Contrast MRI you can see this reactivated, old lesion.

That's how some reports can call active lesions or some report no newly enhancing lesions (these say the same thing). Also since some new ones heal they can be compared to old films and show they disappeared. In addition, between different sets of MRI done after a time has passed, the radiologist can see an increase in old and in new activity.

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