Splitting of the extraocular horizontal rectus muscle in congenital cranial dysinnervation disorders
(Séparation des muscles droits horizontaux dans les désinnervations des nerfs crâniens d'origine congénital )

Okanobu H, Kono R, Miyake K, Ohtsuki H.
Department of Ophthalmology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan. tankun@bj9.so-net.ne.jp

PURPOSE: To analyze the horizontal rectus extraocular muscles (EOMs) by orbital magnetic resonance imaging (MRI) in patients with congenital cranial dysinnervation disorders that arises from abnormal development of cranial nerve nuclei or their axonal connections.

DESIGN: Case series, retrospective analysis.

METHODS: The morphology of the horizontal rectus EOMs was analyzed in orbital MRI on 4 patients with congenital oculomotor palsy, 26 with congenital superior oblique palsy, and five with Duane syndrome. Orbital imaging was performed by 1.5 tesla (T) and 3T MRI, and quasi-coronal and sagittal images perpendicular and parallel to the long axis of the orbit were obtained at slice thicknesses of 3 and 2 mm.

RESULTS: The horizontal rectus EOMs were split in 4 of the 35 patients (11%). Splitting was observed in 2 of the five patients (40%) with Duane syndrome, one of the 26 patients (4%) with congenital superior oblique palsy, and 1 of the 4 patients (25%) with oculomotor palsy, but in none of the 6 normal subjects and 12 patients with acquired cranial nerve palsy.

CONCLUSION: Since splitting of the horizontal rectus EOMs was noted in patients with congenital dysinnervation disorders, including Duane syndrome, Sevel's theory that the horizontal rectus EOMs develop from the superior and inferior mesodermal complexes is considered to be reasonable.

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