Walsh & Hoyt: Pathology

The gross pathology in patients with chronic MS is typical. In the majority of cases, the brain shows no obvious abnormalities, although the leptomeninges may appear thickened and the brain may appear covered with a cortical gray mantle. There may be a particularly prominent arachnoiditis in the region of the optic chiasm and intracranial optic nerves (optochiasmatic arachnoiditis). Gross examination of the brainstem sometimes reveals gray patches on the surface of the basis pontis, the roof and floor of the fourth ventricle, the cerebellar peduncles, and the surface of the medulla, where lesions have either developed superficially or broken through from deeper levels. Similarly, the spinal cord may be atrophic, showing disseminated, gray, firm, depressed surface patches along its entire length. There is no predilection for any specific level or tract. In patients with brainstem or spinal cord damage, the proximal segments of cranial nerves and spinal nerve roots may also be gray and atrophic, presumably from loss of CNS myelin in these areas or from an adjacent lesion in the brain parenchyma.