Background: The trochlear (fourth) nerve is the only cranial nerve that decussates before emerging from the posterior aspect of the brainstem. Lesions involving the trochlear nucleus or fascicles mostly give rise to contralesional superior oblique palsy (SOP).
Methods: We report 2 patients with SOP on the side of intraaxial lesions with a literature review on central trochlear palsy.
Results: The lesions are more commonly located posterior to the cerebral aqueduct in patients with ipsilesional SOP than in those with contralesional SOP.
Conclusions: Intraaxial lesions may cause ipsilesional or contralesional SOP depending on the lesion location along the course of trochlear fascicle in the brainstem.