Morphometry of the Oculomotor Nerve in Duane's Retraction Syndrome

Abstract

Objective: To investigate the morphometric characteristics of the oculomotor nerve and its association with horizontal rectus muscle volume in patients with Duane's retraction syndrome (DRS) according to the presence of the abducens nerve.

Methods: Fifty patients diagnosed with unilateral DRS were divided into two groups according to high-resolution magnetic resonance imaging (MRI) findings; DRS without an abducens nerve on the affected side (absent group, n = 41), and DRS with symmetric abducens nerves on both sides (present group, n = 9). Oculomotor nerve diameter was measured on high-resolution MRI in the middle of the cisternal space. The medial rectus muscle (MR) and lateral rectus muscle (LR) volumes were measured on T2-weighted coronal MRI of the orbit. Associations of oculomotor nerve diameter and horizontal rectus muscle volumes were performed according to the presence and absence of the abducens nerve.

Results: Oculomotor nerve diameter on the affected side was thicker than that of the non-affected side in the absent group (p < 0.001), but not in the present group (p = 0.623). In the absent group, there was a positive correlation between oculomotor nerve diameter and MR volume (r = 0.779, p < 0.001), as well as the LR volume (r = 668, p = 0.023) of the affected eye.

Conclusions: In DRS patients with an absent abducens nerve, the oculomotor nerve diameter was thicker in the affected eye compared to the non-affected eye. Oculomotor nerve diameter was associated with MR and LR volumes in the absent group. This study provides structural correlates of aberrant innervation of the oculomotor nerve in DRS patients.

Keywords: Duane’s retraction syndrome; extraocular muscle; high-resolution magnetic resonance imaging (MRI); oculomotor nerve; strabismus.

Figure 1

T2-weighted axial magnetic resonance imaging of the brain shows the cisternal segments of both oculomotor nerves (arrows) coursing in an anterior lateral direction at the level of the lower midbrain. The diameters of the oculomotor nerves were measured at three contiguous planes (A–C).

Figure 2

Medial rectus (MR) (A) and lateral rectus (LR) (B) muscle volumes in Duane’s retraction syndrome patients according to the presence and absence of the abducens nerve (CN6). MR and LR volumes were both smaller in the affected eye than the non-affected eye in the absent group (p = 0.001, p = 0.006, respectively). In the present group, there was no significant difference between the affected and non-affected eyes regarding MR and LR volumes (all p > 0.05). MR and LR volumes in the affected eye were both smaller in the absent group compared to patients in the present group (p = 0.005, p = 0.017, respectively).

Figure 3

Correlations between oculomotor nerve diameter and horizontal rectus muscle volumes in patients without an abducens nerve in Duane’s retraction syndrome. (A) The medial rectus muscle (MR) volume of the affected eye showed a positive correlation with oculomotor nerve diameter (r = 0.779, p < 0.001). (B) The lateral rectus (LR) muscle volume of the affected eye also showed a positive correlation with oculomotor nerve diameter (r = 668, p = 0.023).