Abstract
Purpose :
Anomalous orbital structures (AOS) are a cause of congenital atypical restricted strabismus. Embryologic disturbance of extraocular muscles (EOMs) is considered a possible mechanism. This study aims to provide imaging evidence for the pathogenic mechanism by analyzing the morphological and quantitative characteristics of AOS using MRI.
Methods :
Twenty-nine congenital atypical strabismus patients accompanied by AOS observed in MRI and twenty healthy volunteers between January 2006 to November 2022 were retrospectively reviewed. All patients and healthy volunteers had performed high-resolution MRI (FSE/T2WI, FSE/T1WI and 3D-FIESTA). Morphological features of AOS, EOMs and ocular motor nerves were evaluated. The quadrant distribution of anomalous orbital structures in all patients was analyzed. The mean diameters of ocular motor nerves were measured in patients and the control group, and Kruskal-Wallis tests were used to compare inter-group differences.
Results :
All patients exhibited unilateral AOS, which showed the identical signal as the EOMs on MRI. Wherein, twenty-seven patients (27/29, 93.1%) exhibited irregular retrobulbar mass, which was adhesion with the traction deformed EOMs. Two patients (2/29, 6.9%) showed an orbital band originating from the orbital apex to inserting the posterior wall of the globe closing to the optic nerve, there were no abnormalities observed in EOMs. The highly vulnerable quadrants of the globe were the nasal superior (16/29, 55.2%) and the nasal inferior quadrant (15/29, 51.7%). Meanwhile, the retrobulbar mass often involved the medial rectus (MR) (22/27, 81.5%) and superior rectus (SR) (20/27, 74.1%). Moreover, all patients showed normal morphology of the CN3 and CN6. The mean diameters of CN3 and CN6 in the affected eyes of patients were respectively 1.58±0.26 mm and 1.06±0.14 mm, no statistical difference was found between patients and the control group.
Conclusions :
The vast majority of AOS manifested as a unilateral irregular retrobulbar mass on MRI. AOS commonly occurred in the nasal superior quadrant, and the SR and MR were more likely to be involved. All patients exhibited normal course and size of the ocular motor nerves. Our study indicated that the blocked separation and growth in the wrong way of EOMs during embryonic development is a possible pathogenic mechanism.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.