Preliminary MRI study in patients with congenital complex strabismus

Abstract

Objective Although the ocular motility examination has been traditionally used in the diagnosis of complex strabismus resulting from cranial nerve (CN) and extraocular muscles (EOM) abnormalities, magnetic resonance imaging (MRI) now permits the direct imaging of lesions in CNs and EOMs. Methods Twenty-six patients with complex strabismus underwent MRI examination on 1.5 T MR unit (Twinspeed, GE). Nerves to EOMs were imaged with T1 weighted in orbits in all patients using phase array surface colls. Results Patients with Duane syndrome ( 15 cases, 19 eyes) all exhibited absence or hypoplasia of abducens nerve (CN6), always with mild hypoplasia and apparent misdirection of oculomotor nerve ( CN3 ) to the lateral rectus muscle in the orbit, and there were no hypoplasia of EOMs. Patients with congenital fibrosis of EOMs (9 cases, 16 eyes) exhibited severe hypoplasia of CN3 and CN6, and EOMs appeared hypoplasia to a different degree, particularly severe for the superior rectus and levated palpted muscles. Multiple nerves displayed aplasia in patients with Mobius syndrome (1 case, 2 eyes) and there was abnormal branch from CN3 to lateral rectus. The tendons of bilateral superior oblique muscles were thin in the patients with Brown syndrome ( 1 case, 2 eyes). Conclusion MRI can directly demonstrate absence or hypoplasia of CNs and corresponding EOM abnormalities in congenital complex strabismus, which suggests that the mechanism of congenital complex strabismus is perhaps abnormal innervation or displasia of the ocular motor nerves. Key words: Strabismus; Oculomotor muscles; Ophthalmic nerve; Magnetic resonance imaging