One-and-a-half syndrome in pontine infarcts: MRI correlates

The one-and-a-half syndrome is characterised by a lateral gaze palsy in one direction and internuclear ophthalmoplegia in the other. It is due to a un ilateral lesion of the dorsal pontine tegmentum, involving the ipsilateral paramedian pontine reticular formation, internuclear fibres of the ipsilate ral medical longitudinal fasciculus and, usually, the abducens nucleus. The main causes of this rare syndrome are stroke and multiple sclerosis. Few c ases have been reported since the introduction of MRI. Our aim was to exami ne clinicoradiological correlations in six patients with a one-and-a-half s yndrome due to a stroke. Ophthalmological symptoms were diplopia, oscillops ia or blurred vision. Four patients had an associated facial nerve palsy, t hree a hemiparesis and one a unilateral hemihypoaesthesia. MRI revealed an infarct in the pans in all patients. The cause of the infarct was a basilar artery dissection in one patient, bilateral vertebral artery dissection in a second and unknown in the other four. All patients recovered within 2 da ys to 8 weeks. This study showed a good correlation between the site of the lesion (superior, inferior or extensive pontine ischaemia) and clinical de ficits.