Optic nerve MRI
MRI findings in ON can include T2-hyperintense lesions, nerve swelling,
and gadolinium enhancement of the affected optic nerve on T1-weighted
imaging. In MOG-ON, optic nerve lesions are frequently extensive, also
termed longitudinally extensive ON (LEON), affecting more than half of
the pre-chiasmatic optic nerve length (40,85,86). Moreover, MOG-ON
predominantly affects the anterior part of the optic nerve. This can
help with differentiating MOG-ON from AQP4-ON, which is also often
extensive, but predominantly affecting the posterior part of the optic
pathway (including the optic chiasm) (40,87–89). In contrast, MS-ON
typically involve shorter segments of the optic nerve compared to both
MOG-ON and AQP4-ON. Meanwhile, bilateral ON is specifically more
frequent in MOG-ON than in MS-ON, and in paediatric patients have been
associated with higher MOG-IgG titers (38,40). Another characteristic
feature described in MOG-ON is perineural or periorbital gadolinium
enhancement in the orbital soft-tissue that is not typically found in
MS-ON (51,85,86,90–92).