Background: According to the recently popularized classification of superior oblique (SO) palsy based on congenital variations of the tendon, the primary pathology is the abnormality of the SO tendon rather than an innervational problem in congenital cases. If this hypothesis is true, denervation atrophy of SO muscle should not occur in patients with congenital SO palsy.
Methods: Eight patients with traumatic and nine patients with definite congenital SO palsy underwent magnetic resonance imaging (MRI) of the orbit. SO muscle width and cross-sectional area measurements were taken from coronal images and compared with the clinically uninvolved superior oblique muscles.
Results: Atrophy of varying degrees was observed in the SO muscle both in congenital and acquired cases. No significant difference was found in the appearance of the SO muscle between acquired and congenital SO palsy groups.
Conclusion: We have been unable to demonstrate abnormalities of the SO tendon in both groups. The MRI appearance of the SO muscle suggested that in congenital SO palsy, the pathology is not limited to the tendon; there also is an abnormality of the muscle itself.