Eight-and-a-half syndrome from pontine infarction in the context of a stenotic persistent trigeminal artery with vertebrobasilar hypoplasia: a case report and literature review

Background Eight-and-a-half syndrome (EHS)—a rare brainstem syndrome combining one-and-a-half syndrome with ipsilateral peripheral facial palsy—typically localizes to the dorsal pontine tegmentum. The persistent trigeminal artery (PTA) is the most common carotid-basilar anastomosis, but its role as a hemodynamic cause of brainstem infarction is rarely documented with direct angiographic evidence. Case presentation A 72-year-old woman with hypertension and prior trigeminal neuralgia presented with acute binocular diplopia. Examination revealed right horizontal gaze palsy, right internuclear ophthalmoplegia with abduction nystagmus of the left eye on leftward gaze, and right peripheral facial palsy, consistent with EHS. Diffusion-weighted MRI showed a small acute infarct in the right pontine tegmentum. Digital subtraction angiography (DSA) unexpectedly revealed a left-sided Saltzman type I PTA with approximately 60% proximal stenosis and post-stenotic ectasia, alongside bilateral hypoplastic vertebral arteries that failed to form a functional basilar artery—rendering the posterior circulation entirely dependent on this stenotic PTA. Dual antiplatelet therapy (aspirin and clopidogrel) was initiated. Her ophthalmoplegia resolved completely within days, and facial weakness improved significantly by discharge. Conclusions This is the first reported angiographically documented case of EHS associated with a stenotic PTA and vertebrobasilar hypoplasia, in which a hemodynamic mechanism is strongly suspected. This underscores that PTA should be considered a potential low-flow stroke mechanism even without an embolic source, and highlights the indispensability of comprehensive vascular imaging (including DSA) in unexplained brainstem syndromes.