Stenotic Persistent Trigeminal Artery Triggers Rare Brainstem Stroke in Case Report

A clinical report published in BMC Neurology describes a rare neurological condition known as eight-and-a-half syndrome resulting from an acute ischemic stroke within the pontine tegmentum in a patient with unusual vascular anatomy. Researchers Junya Gao and Yinbao Hu documented the presentation of a seventy-two-year-old woman with a documented medical history of hypertension and prior trigeminal neuralgia who sought emergency medical care after suddenly developing acute binocular diplopia. Detailed neurological assessment confirmed that her ocular motility impairments and accompanying facial deficits aligned with eight-and-a-half syndrome, an infrequent brainstem disorder. Advanced diagnostic evaluations linked her localized ischemic injury to an underlying left-sided Saltzman type I persistent trigeminal artery showing marked narrowing, occurring alongside congenital hypoplasia of the vertebral arteries that left the posterior brainstem circulation unusually dependent on carotid inflow.

On physical and neurological examination, clinicians identified a precise combination of neuro-ophthalmologic and cranial nerve signs that localized the pathology directly to the dorsal brainstem. Specifically, the patient exhibited a right horizontal gaze palsy along with right internuclear ophthalmoplegia, accompanied by characteristic abduction nystagmus of the left eye during leftward gaze. In addition to these complex gaze abnormalities, she demonstrated an ipsilateral right peripheral facial palsy. Together, these clinical findings established the diagnosis of eight-and-a-half syndrome, an entity that characteristically combines the conjugate and internuclear gaze deficits of one-and-a-half syndrome with peripheral weakness of the seventh cranial nerve on the same side. The medical literature notes that such clinical manifestations typically reflect a localized structural lesion situated within the dorsal pontine tegmentum.

To confirm the anatomical origin of the patient’s acute symptoms, neuroimaging was performed using diffusion-weighted magnetic resonance imaging. The resulting brain scans demonstrated a distinct area of restricted diffusion corresponding to a small acute infarct confined to the right pontine tegmentum. This restricted lesion provided an exact structural correlation for the patient’s right-sided horizontal gaze impairment, internuclear ophthalmoplegia, and ipsilateral facial palsy.

Subsequent vascular investigation using catheter-based digital subtraction angiography uncovered an unexpected and critical congenital vascular anomaly that explained the patient’s compromised posterior circulation. Angiographic imaging revealed a persistent trigeminal artery originating from the left internal carotid system, classified anatomically as a Saltzman type I variant. Although the persistent trigeminal artery is recognized as the most common embryonic carotid-basilar anastomosis surviving into adulthood, direct angiographic evidence documenting it as the primary hemodynamic source of an acute brainstem infarction has been exceptionally rare. In this patient, the persistent vessel demonstrated approximately sixty percent proximal stenosis along with downstream post-stenotic ectasia, indicating localized structural compromise in the dominant lumen delivering blood flow to the brainstem.

The hemodynamic vulnerability of the patient’s brainstem was further intensified by profound developmental anomalies affecting the standard posterior arterial supply. The digital subtraction angiography demonstrated that both the right and left vertebral arteries were bilaterally hypoplastic and failed to join to form a functional basilar artery. As a direct consequence of this severe vertebrobasilar hypoplasia, the posterior cerebral circulation was entirely dependent on the single left-sided Saltzman type I persistent trigeminal artery for its perfusion.

Following the angiographic identification of this precarious intracranial vascular configuration, medical management was directed toward preventing further ischemic progression through medical antithrombotic therapy. The patient experienced a favorable clinical trajectory, with her complex ophthalmoplegia resolving completely within a few days of starting treatment.

The authors emphasized that this report represents the first angiographically confirmed case of eight-and-a-half syndrome arising in the specific setting of a stenotic persistent trigeminal artery combined with bilateral vertebrobasilar hypoplasia. The findings underscore that a persistent trigeminal artery should be recognized as a viable cause of low-flow ischemic stroke even in the absence of an identifiable embolic source or cardiac embolus. Gao and Hu concluded that the case reinforces the critical clinical necessity of conducting comprehensive intracranial vascular imaging, including digital subtraction angiography, whenever patients present with unexplained or complex brainstem stroke syndromes where underlying developmental vascular variations may alter expected cerebral hemodynamics.

Subject of Research: Eight-and-a-half syndrome caused by pontine infarction with persistent trigeminal artery stenosis and vertebrobasilar hypoplasia

Article Title: 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

Article References: Gao, J., & Hu, Y. (2026). 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. BMC Neurology. https://doi.org/10.1186/s12883-026-05520-1

Image Credits: AI Generated

DOI: 10.1186/s12883-026-05520-1

Keywords: eight-and-a-half syndrome, pontine infarction, persistent trigeminal artery, vertebrobasilar hypoplasia, dorsal pontine tegmentum, digital subtraction angiography, Saltzman type I, one-and-a-half syndrome, peripheral facial palsy, horizontal gaze palsy, internuclear ophthalmoplegia, abduction nystagmus, diffusion-weighted MRI, carotid-basilar anastomosis, hemodynamic stroke, dual antiplatelet therapy, clopidogrel, aspirin