Eight-and-a-half syndrome: a rare potentially life-threatening disease.

Purpose: To report a case of eight-and-a-half syndrome presenting with a conjugate horizontal gaze palsy, an ipsilateral internuclear ophthalmoplegia, and an ipsilateral lower motor neuron-like facial palsy. Methods: A 56-year-old male who came in for limitation of extraocular muscle motion - wherein the only remaining movement is abduction of the left eye - and right-sided facial weakness. Magnetic resonance imaging revealed a well-defined lesion resembling a cavernoma, at the level of the ponto-medullary junction. Results: Eight-and-a-half syndrome results from a lesion affecting the paramedian pontine reticular formation, the median longitudinal fasciculus, and the facial nerve fascicle on one side. In this case, a cavernoma at the level of the ponto-medullary junction was compressing the important pontine structures. Conclusion: Although eight-and-a-half syndrome is most commonly caused by an infarction or demyelination, in rare instances, a space-occupying lesion at the level of the pons can be the etiology. It is of utmost importance to recognize the features of this disease entity to be able to exhaust the proper diagnostic exams, localize the lesion and determine the proper treatment regimen catered to each patient.