The optic chiasm and, more rarely, the optic tracts (often bilaterally [171]) may be affected as well in AQP4-IgG-positive NMOSD, whereas these structures are mostly spared in MS [171]; according to recent data, chiasmal lesions are also not uncommon in MOG-EM/MOGAD and then often extend from the anterior part of the optic nerve to the chiasm [84, 203]. The gene discussed is AQP4; the disease is myeloid sarcoma.