Mapping of brainstem lesions by the combined use of tests of visually-induced eye movements

To determine the diagnostic value of visually-induced eye movements for indicating the lateralization of the lesion, optokinetic nystagmus (OKN), fixation-suppression of caloric nystagmus and pursuit eye movements were investigated in 28 patients who showed discrete unilateral brainstem lesions. In all patients, pursuit gains decreased in parallel with the direction of the impairment of slow-phase OKN velocity with a significant left/right difference. Decreases of gains were predominantly towards the affected side in 22 patients, whereas they were predominantly towards the contralateral side in 2 patients with dorsal tegmental pontine lesions and in 4 out of 8 patients with Wallenberg's syndrome. The relationship of pursuit gains to percentage reduction of fixation-suppression of caloric nystagmus (%FS) showed no correlation. The following four groups were classified. In group A, which was the largest, pursuit gains and %FS decreased predominantly towards the lesioned side. This group consisted of 5 patients with lesions in the midbrain, 6 patients with lesions in the ventral pons and 4 out of 8 patients with Wallenberg's syndrome. The opposite of group A was group D, showing reverse electro-oculographic (EOG) patterns to those in group A in relation to the lesioned side. Group D consisted of 2 patients with lesions in the dorsal pontine tegmentum. This observation, taken together with the decreases of pursuit and OKN gains in relation to the lesioned side, might indicate that lesions of ascending fibres are responsible for pursuit and OKN abnormalities. Group B, consisting of 7 patients with lesions either in the superior or middle cerebellar peduncles, showed decreased pursuit gains predominantly towards the lesioned side and %FS reduced predominantly towards the side contralateral to the lesion. EOGs of these patients were consistent with the results of floccular ablation in the monkey. In group C, these two parameters showed patterns opposite to those in group B in relation to the lesioned side and this group consisted of the other 4 patients with Wallenberg's syndrome. In patients of this group, the inferior cerebellar peduncle might be involved. The combined use of these tests is thus useful for lateralizing the lesion in the brainstem.