Perfusion disorders and debunking myths
Blood circulation insufficiency in the brainstem is divided into transient (transient ischemia) and permanent, which leads to brain tissue necrosis—infarction.
Contrary to popular belief, brainstem infarctions do not occur due to spasm or an awkward posture. The main cause is embolism. Sources of emboli include the heart chambers, atherosclerotic plaques directly in the vertebral arteries, and arterial wall dissection followed by secondary thrombosis.
The vascular angioarchitecture of the brainstem is relatively uniform. Due to the compact arrangement of numerous nuclei and tracts, the occlusion of a specific vessel produces distinct vascular syndromes. Infarction foci in the acute stage are reliably visualized on high-resolution T2-weighted MRI scans.
Subclavian steal syndrome
This is a classic example of transient ischemia. The pathology occurs when the right or left subclavian artery is occluded strictly proximal to the origin of the vertebral artery.
Hemodynamic steal pathway:
- Blood travels upward via the contralateral (healthy) vertebral artery.
- It reaches the confluence into the basilar artery.
- Flows retrograde (in the reverse direction) down the ipsilateral (affected) vertebral artery.
- Enters the axillary artery and fills the brachial artery, maintaining blood supply to the arm.
If the patient exerts physical effort with the affected arm, an increased volume of blood is diverted from the vertebrobasilar system. This causes symptoms of brainstem ischemia. The key sign on angiography is the detection of retrograde blood flow. Treatment is required only if hand ischemia or true steal syndrome with syncope and dizziness develops.
Wallenberg syndrome (dorsolateral medullary syndrome)
Brainstem infarctions most commonly present as alternating syndromes—conditions in which cranial nerve dysfunction occurs on the side of the lesion (ipsilaterally), while hemiparesis or another hemisyndrome occurs on the opposite side of the body (contralaterally).
A prime example of pathology in the vertebral artery basin is the dorsolateral medullary syndrome (Wallenberg syndrome). It develops due to occlusion or embolism of the vertebral artery itself or the posterior inferior cerebellar artery.
The onset of the syndrome is always sudden. The symptomatology strictly correlates with the affected structures:
- Dizziness and nystagmus—due to damage to the inferior vestibular nucleus and the inferior cerebellar peduncle.
- Nausea and vomiting—upon involvement of the vomiting center (area postrema).
- Dysarthria and dysphonia—upon damage to the caudal nerve group (nucleus ambiguus).
Aneurysms and cranial nerve compression
Saccular aneurysms can form in the vertebrobasilar system (accounting for about 10% of all cerebral aneurysms). The vertebral artery–posterior inferior cerebellar artery segment accounts for 3% of cases. Rupture of such an aneurysm leads to subarachnoid hemorrhage.
In addition, vascular loops of arteries in the vertebrobasilar system (including the vertebral artery) may lie close to the roots of cranial nerves. Contact between a pulsating vessel and the unmyelinated segment of a root causes irritation. A classic example of this mechanism is severe trigeminal neuralgia due to compression by a loop of the superior cerebellar artery.
To understand brainstem vascular disorders, remember the essence of alternating syndromes: "The face is affected on the same side as the vessel, and the body on the other side." This is due to the decussation of tracts below the level of the cranial nerve nuclei.
Class and exam questions
Can the vertebral artery be compressed during sleep and cause a stroke?
No, the theory that ischemia occurs due to kinking of the vertebral artery during sleep has not been confirmed. The true causes lie in embolism, atherothrombosis, or vascular dissection.
Why is the diagnosis of "vertebrobasilar insufficiency" no longer used?
In modern practice, this term is considered incorrect and is not recommended for clinical use, as it does not reflect the precise pathogenesis of vascular disorders and is frequently used to mask other diseases.
How is subclavian steal syndrome diagnosed?
The diagnosis is established based on the characteristic clinical picture (brainstem ischemia during physical work with the arm) and angiographic data, where the key sign is retrograde (reverse) blood flow in the vertebral artery.
What else to study on this topic
- Topographic anatomy of the brainstem and blood supply zones
- Clinical presentation and stages of subarachnoid hemorrhage
- Microvascular decompression in neurovascular conflict
- Differential diagnosis of facial pain and neuralgias
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