Superior oblique muscle MRI asymmetry and vertical deviation in patients with unilateral superior oblique palsy.

Purpose: To evaluate the MRI cross sectional greater area of the unilateral superior oblique (SO) muscle in patients with congenital or acquired superior oblique palsy to detect asymmetries and to determine if there is any relationship between the degree of vertical deviation and the muscle size determined by imaging.

Methods: Magnetic Resonance Imaging coronal images were obtained in primary position, supraversion and infraversion. Interocular differences and intergroup differences were compared in 17 patients with unilateral acquired or congenital SO palsy and 15 orthotropic control subjects.

Results: Mean maximal difference was 3.56 +/-0.83 mm(2) (p 0.01) between healthy and paretic eye in the paretic group, and 1.08 +/-0.40 mm(2) (p 0.02) in the control group. Statistical Intergroup comparison was p 0.02 (conventionally statistically significant). In 9 patients the maximal interocular difference was detected in 44.4% in infraversion, 33.3% indistinctly in supra- and infraversion and 22.2% in primary position. The correlation coefficient between vertical deviation and interocular asymmetry was not conventionally statistically significant at p>0.05.

Conclusions: Patients with unilateral superior oblique palsy showed significant MRI asymmetry, which was represented by a relatively greater healthy SO muscle size, in the paretic congenital group. We found no association between the SO muscle size and the degree of any vertical deviation present.