Pontine metastasis with dissociated bilateral horizontal gaze paralysis.

A clinicopathological case of pontine metastatic tumour is reported with an oculomotor syndrome including bilateral horizontal gaze paralysis affecting saccades and foveal pursuit. During full-field pursuit, oculocephalic movement, and after caloric stimulation, the right eye alone was able to move slowly only 30 degrees to the right of the midline. Convergence and vertical eye movements were unaffected in either eye. The lesion lay in the whole left pontine tegmentum and partly in the right pontine tegmentum which was also strongly compressed and displaced to the right. The bilateral horizontal gaze paralysis resulted from damage to both paramedian pontine reticular formations. The unusual combination of an absence of foveal pursuit with the persistence of a rightward full-field pursuit analysed in the light of recent experimental work, suggested a clear separation between the brainstem pathways of these two types of pursuit movement. Lastly, according to our data and other clinicopathological findings previously reported, it appeared also that the paramedian pontine reticular formation role in the triggering of voluntary vertical saccades is less significant in man than in the monkey.