Ventral Pontine Stroke and Internal Carotid Artery Lesions
Definition and Classification
A stroke in the ventral pons is not considered a symptomatic internal carotid artery (ICA) lesion because the ventral pons is supplied by the vertebrobasilar circulation, not the carotid circulation. 1
- The ventral pons contains corticospinal, corticobulbar, and corticopontine tracts, while the dorsal pontine tegmentum contains white matter tracts and cranial nerve nuclei V through VIII 1
- Pontine lesions can affect cranial nerves V, VI, VII, and/or VIII, with ischemic and hemorrhagic infarcts being the most frequent cause of acute brainstem syndromes 1
- The pons is primarily supplied by branches of the basilar artery, which is part of the vertebrobasilar circulation system, not the carotid circulation 1
Vascular Supply and Stroke Etiology
- The internal carotid artery (ICA) primarily supplies the anterior circulation of the brain, including the anterior and middle cerebral arteries 1, 2
- Strokes in the distribution of the right internal carotid artery or middle cerebral artery typically cause left-sided weakness, left-sided sensory loss, and other left-sided deficits 2, 3
- The ventral pons is supplied by branches of the basilar artery, which is formed by the union of the vertebral arteries 1
- Pontine infarctions are most commonly caused by small vessel disease, basilar artery atherosclerosis, or emboli to the basilar artery 1
Diagnostic Considerations
- When evaluating stroke location, it's important to recognize that symptoms typically manifest contralaterally to the affected brain hemisphere due to the crossing of neural pathways 2
- MRI with diffusion-weighted imaging is the preferred imaging modality to identify the location and extent of infarction in patients with suspected brainstem stroke 1, 3
- Vascular imaging (CTA or MRA) can evaluate for occlusions or stenoses in multiple vascular territories 3
- Reviewing patterns of cerebral ischemia on DWI is particularly useful if additional acute lesions are present in brain areas supplied by the contralateral carotid artery or in the vertebrobasilar territory 1
Unusual Scenarios and Exceptions
- In rare cases, anomalous vascular connections between the carotid and vertebrobasilar systems, such as a persistent trigeminal artery, can allow emboli from carotid disease to reach the posterior circulation 4
- These embryonic vascular connections that may persist between the carotid and basilar arteries are uncommon but should be considered in evaluating patients with vertebrobasilar stroke who have carotid disease 4
- Such anomalies will likely be overlooked by ultrasound techniques and depend on good intracranial arteriographic images 4
Clinical Implications
- When determining the etiology of stroke, it's essential to match the clinical symptoms and imaging findings with the known vascular territories 1
- For patients with stroke symptoms and both carotid stenosis and atrial fibrillation, determining the true underlying cause can be challenging 1
- Arguments for carotid etiology include a severe degree of stenosis, clinical or imaging evidence for repetitive ipsilateral emboli, or imaging features of plaque instability and/or thrombotic content 1
- The presence of acute lesions in brain areas supplied by the contralateral carotid artery or in the vertebrobasilar territory suggests a proximal (i.e., aortic or cardiac) rather than carotid lesion-related source of embolism 1
Management Implications
- Treatment approaches differ significantly between carotid and vertebrobasilar strokes 1
- For symptomatic carotid stenosis, carotid revascularization (endarterectomy or stenting) may be indicated 1, 5
- For vertebrobasilar strokes, including those in the ventral pons, management focuses on medical therapy, risk factor control, and in some cases, evaluation for basilar or vertebral artery disease 1
- A multi-disciplinary Neuro-Vascular Team approach is recommended for optimal management of stroke patients 1