Optic Nerve Abnormalities in Morning Glory Disc Anomaly: An MRI Study

Background: The morning glory disc anomaly (MGDA) is a rare congenital malformation of the optic disc. The association with a significant enlargement of the optic nerve has been recently reported in a few cases, raising the question of potentially associated optic nerve gliomas. The objective was to report the anatomy of optic nerves on MRI in patients with MGDA. Methods: In this retrospective single-center study, files of patients with a clinical diagnosis of MGDA were identified through a rare disease database (CEMARA) and included. We reviewed every cerebral and orbital MRI available, performed between 2008 and 2018. Anatomy of the optic nerve from the optic disc to the chiasm was evaluated on MRI. Results: Nine patients were included. All presented unilateral MGDA. Age at first MRI was 0.6-62 years, median = 3.8 years. MRI showed posterior protrusion of the globe (staphyloma) centered by the optic disc in all cases (100%). Ipsilateral optic nerve abnormalities were found in all cases (100%). The optic nerve was found thinner than the contralateral one in its intraorbital, intracanalar, and intracranial portions in 1 case (11%); in 8 cases (89%), the thickness of the optic nerve was irregular and varied along its pathway: thick, normal, and/or thin. When gadolinium injection had been performed (3 cases), none exhibited gadolinium enhancement. When serial MRI scanning was available (4 cases), there was no evolution of the abnormalities. Conclusion: In patients with MGDA, optic nerve and chiasm abnormalities are the rule, with most often a unique pattern of irregular optic nerve thickness-hypertrophy and hypoplasia-from the orbit to the chiasm. Such pattern should be recognized and points to a developmental abnormality, rather than an optic nerve glioma.