MRI in NMO: How to differentiate from MS

Abstract

Neuromyelitis Optica (NMO) is characterized by simultaneous or sequential acute transverse myelitis and optic neuritis. Spinal cord lesions extending over 3 or more vertebral segments are the typical MRI finding in NMO. Shorter MRI lesions can be found very early during relapse or in residual atrophic stages. Some of the lesions may appear hypointense on corresponding T1-weighted images which reflects sever inflammation with necrosis. T1-weighted hypointensities may help in differentiating NMO lesions from MS in spinal cord. “Snake-eye” or “owl-eye” sign a common feature of spinal artery ischemia has been reported to be transiently observed at an early stage of NMO. Brain MRI is initially normal in most patients with NMO but serial imaging may depict lesions in up to 85% of the patients at later stages. Brain lesions are usually nonspecific but may fulfill the Barkhof criteria for dissemination in space. Acute, large, edematous callosal lesions with a heterogeneous intensity occasionally develop in patients with NMO (marbled pattern). In contrast, in MS, callosal lesions are small, non-edematous, and the intensity was homogeneous in the acute phase and located at the lower margin of the corpus callosum. Multiple patchy enhancements with blurred margins (cloudlike enhancement) have been reported to be typical for NMO. Pencil-like ependymal enhancement is another type of enhancement around the anterior horns of lateral ventricles. Extensive hemispheric lesions, periependymal lesions surrounding the aqueduct, the third and fourth ventricles and brain stem lesions should raise the diagnosis of NMO. Actually NMO should be considered in any atypical lesion for MS in appropriate clinical settings. The extensive hemispheric lesions differed from those observed in regions of high AQP4 expression and were likely related to vasogenic edema; they sometimes looked like “spilled ink” and followed the white-matter tracts.