[A study of superior oblique muscle changes in superior oblique palsy using magnetic resonance imaging]

Objective: To observe the magnetic resonance imaging(MRI) changes of superior oblique muscle and to study the relationship between changes and clinical signs in superior oblique muscle palsy. Methods: Cross-sectional study. Data was collected from January 2014 to January 2016 in Tianjin Eye Hospital. Twenty-three(30 eyes) patients who were diagnosed with superior oblique palsy included 15 patients with congenital superior oblique palsy [9 males and 6 females aged (32±13) years (range, 12-53 years)] and 8 cases with acquired superior oblique palsy [3 males and 5 females aged (36±15) years(range, 17-62 years)]. Twenty normal volunteers [11 males and 9 females aged (35±13) years (range, 15-60 years)] were also observed. Coronal MRI was used to detect superior oblique muscle morphological changes, as well as the maximum cross-sectional area and volume changes. The relationship between the morphological changes and vertical deviation and cyclotorsion in the primary gaze was analyzed. Rank sum test, t-test and Person correlation analysis were used for statistical analysis. Results: Two morphological changes were obtained using MRI in superior oblique muscle palsy, including round (19 eyes) and oval changes (11 eyes). The maximum cross-sectional area in eyes with the palsied superior oblique muscle [round, (10.38±1.76) mm(2); oval, (11.16±2.02) mm(2)] was significantly smaller than fellow eyes [(14.16±1.88) mm(2); Z=6.208, 5.178, both P<0.001] and eyes with normal superior oblique muscle [(15.40±1.71) mm(2); Z=8.215, 6.330, both P<0.001], and the volume changes [round, (104.92±13.36) mm(3); oval, (110.43±16.11) mm(3)] were also significantly different from fellow eyes [(254.57±20.15) mm(3); Z=7.511, 5.396, both P<0.001] and eyes with normal superior oblique muscle [(258.04±16.36) mm(3); Z=10.040, 6.936, both P<0.001]. There was no significant difference in vertical deviation between round and oval superior oblique muscle palsies (P>0.05). The cyclotorsion effect of the round change in superior oblique muscle palsy was significantly less than that of the oval change (5.47°±1.05° vs. 7.36°±0.97°, t=3.083, P=0.005). The correlation of the volume changes with vertical deviation angle in the primary gaze was not significantly different (round and oval, both P<0.05), but there was a correlation between the morphological changes and cyclotorsion strabismus (r=0.631, P=0.004; r=0.801, P=0.003). Conclusions: In the patients with superior oblique palsy, MRI scans shows that the maximum cross-sectional area decreased and the volume was smaller, which indicated superior oblique muscle atrophy. Deformation of superior oblique muscle do not significantly affect the vertical deviation, but is in correlation with cyclodeviation. (Chin J Ophthalmol, 2019, 55:20-24).