Occurrence of acute large and edematous callosal lesions in neuromyelitis optica

Background: The corpus callosum is commonly involved in multiple sclerosis (MS), but the characteristics of callosal lesions in neuromyelitis optica (NMO) are unknown. Objective: To reveal the features of callosal lesions in NMO in comparison to MS. Methods: We retrospectively reviewed the medical records and the brain magnetic resonance imaging films of 56 patients with MS and 22 patients with NMO. Results: In MS, 36 (64.3%) of 56 patients had callosal lesions, but only four patients had acute lesions. All such acute lesions were small, isolated and non-edematous, and the intensity was homotonic. Chronic lesions were observed in 34 patients with MS, and 32 (94%) of them presented small lesions located at the callosal lower margin ("hemi-oval pattern"). Meanwhile, four (18.2%) patients with NMO had callosal lesions, and three of them had acute lesions. Those acute lesions were multiple, large edematous ones with heterogeneous intensity ("marbled pattern"). In the chronic stage, the lesions shrank or disappeared. Conclusions: Acute large, edematous callosal lesions occasionally occur in NMO. Similar to longitudinally extensive transverse myelitis, such callosal lesions may reflect severe edematous inflammation in NMO, and may provide additional evidence that the pathogenesis in NMO is different from that in MS.