[A case of vertical gaze palsy associated with a unilateral infarct in the thalamo-mesencephalic junction on MR imaging].

We report a case of a 54-year-old man with sudden-onset double-vision. On admission, neurological examination showed upward and downward gaze palsy on voluntary and smooth pursuit movements, and vertical oculocephalic maneuver elicited a full upward and downward response. Bell's phenomenon, horizontal eye movements and convergence were not impaired. Based on these findings, supranuclear dissociated vertical gaze palsy was diagnosed. T1-weighted MR images revealed low intensity on the medial side of the right thalamo-mesencephalic junction, which impaired the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). T2-weighted MR images revealed a high-intensity area. The posterior commissure was spared. The clinical signs gradually improved, and the vertical gaze palsy almost disappeared one month after onset. Based on these findings, unilateral infarct in the thalamo-mesencephalic junction in the distribution of the right paramedian thalamic artery was diagnosed. Only two cases of upward and downward gaze palsy in association with unilateral upper midbrain lesion without posterior commissure have been previously reported. Since we did not perform a pathological examination, we cannot deny that there may have been some denervation of fibers at the posterior commissure. Cases of upward and downward gaze palsy in association with unilateral upper midbrain lesion without posterior commissure are rare, and it is very interesting that the lesion in our patients, like that seen in the two pathological reports, was right-sided.