Abstract
Neuromyelitis optica is an autoimmune disease of unknown etiology characterized by primary involvement of the optic nerves and spinal cord. Unlike in MS, astrocytes are primarily affected.
Lesions on MRI are mainly located in areas where aquaporin-4 is overexpressed. Lesions can be found in diencephalon periependymally around the lateral ventricles or fourth ventricle and in the corpus callosum.
Pyramidal pathway involvement may also be seen but it is not associated with increased aquaporin-4 expression. Intramedullary involvement is most frequent in the form of longitudinal extensive transverse myelitis, where the lesion extends over three or more vertebral bodies.
These lesions primarily affect the gray matter, often extend into periphery and occupy more than 50% of the spinal cord area in transverse cuts. Optic nerve involvement is typically bilateral in the dorsal part, also affecting the chiasma.