They have a tendency to be confluent. Usually plaques are found to involve the posterior and lateral segments of the cord and they do not respect boundaries between grey and white matter and specific white matter tracts. The plaques are usually wedge shaped with it's apex pointing to the centre of the cord. There is destruction of the myelin with axonal sparing. Usually they occur in a perivenular distribution.
Interstitial edema is noted.
White matter is more severely involved than the grey matter. There is a transient break in the blood-cord barrier. Chronic MS plaques They usually show gliosis, atrophy and cavitation. Remyelination may be noted. A thin rim of active myelin breakdown with perivenous lymphocytic cuffing is noted at the edge of the chronic active plaque.