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Atherothrombotic occlusion of vertebrobasilar and posterior cerebral arteries

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Atherothrombotic Occlusion of Vertebrobasilar and Posterior Cerebral Arteries: Overview

At the pontomedullary junction (where the pons meets the medulla oblongata), the two vertebral arteries unite to form the single basilar artery. The basilar artery then travels upwards and bifurcates (splits) into the two posterior cerebral arteries (PCAs) within the interpeduncular fossa (a space at the base of the brain). Each PCA gives rise to long and short circumferential branches, as well as small, deep penetrating branches. These collectively supply blood to the cerebellum, medulla oblongata, pons, midbrain, hypothalamus, thalamus, hippocampus, and the medial (inner) portions of the temporal and occipital lobes of the brain [1, 2].

Absence of blood flow in the right vertebral artery (white arrow) on MRI angiography of neck and brain vessels [3].

Specific regions within the vertebral, basilar, and posterior cerebral arteries are particularly susceptible to developing atherosclerotic lesions (plaques). The initial segments (origins) of both vertebral arteries and the proximal (lower) portion of the basilar artery are most commonly affected sites. Additionally, there is a tendency for atherosclerotic plaque formation in the proximal segments (near the origin) of the posterior cerebral arteries [4, 5].

The location of these atheromatous lesions holds prognostic significance because it influences the natural progression (natural history) of the disease, often leads to characteristic clinical syndromes based on the affected brain region, and necessitates tailored therapeutic strategies depending on the site of occlusion or stenosis [4, 6].

Differential Diagnosis of Posterior Circulation Stroke Symptoms [7]

Symptoms arising from occlusion or stenosis in the vertebrobasilar or posterior cerebral arteries (e.g., dizziness, vertigo, ataxia, visual disturbances, cranial nerve palsies, altered consciousness) can overlap with other conditions. Differentiating posterior circulation ischemic stroke (often due to atherothrombosis) from its mimics is crucial.

Condition Key Features / Distinguishing Points Typical Investigations / Findings
Posterior Circulation Ischemic Stroke (Thrombotic/Embolic) Sudden onset of brainstem, cerebellar, thalamic, or occipital/temporal lobe deficits (vertigo, ataxia, diplopia, dysarthria, hemianopia, sensory loss, weakness, altered LOC). Vascular risk factors common. MRI (esp. DWI) confirms acute infarct in corresponding territory. CTA/MRA shows vessel occlusion/stenosis (atherosclerosis) or identifies embolic source (e.g., vertebral artery dissection, cardiac source).
Posterior Circulation Hemorrhage (ICH/SAH) Sudden onset, often with severe headache, vomiting, decreased consciousness. Signs depend on location (brainstem/cerebellar hemorrhage vs. SAH). Often associated with hypertension. Non-contrast CT head is diagnostic, showing hemorrhage in posterior fossa or subarachnoid space. CTA/DSA may identify underlying aneurysm or AVM.
Migraine with Brainstem Aura (formerly Basilar Migraine) Transient neurological symptoms (vertigo, dysarthria, diplopia, ataxia, bilateral sensory/visual changes) followed by headache (often occipital). Usually history of migraine. Symptoms fully reversible. Clinical diagnosis based on history/pattern. Neurological exam normal between attacks. Imaging normal (rules out stroke/hemorrhage).
Peripheral Vestibular Disorders (e.g., Vestibular Neuronitis, Labyrinthitis, BPPV) Acute vertigo, nausea, vomiting, nystagmus. Usually NO other brainstem signs (dysarthria, diplopia, weakness, sensory loss). BPPV is positional, brief. Labyrinthitis includes hearing loss. Clinical exam key (HINTS exam for vertigo). Audiometry for hearing loss. Imaging usually normal. Specific positional tests for BPPV.
Seizure (esp. Occipital Lobe) Can present with visual phenomena, altered awareness, or post-ictal focal deficits mimicking stroke. History of event, post-ictal state. EEG may show epileptiform activity. MRI to rule out structural cause.
Metabolic/Toxic Encephalopathy Diffuse brain dysfunction (confusion, altered LOC). May have ataxia or visual symptoms, but typically symmetric and accompanied by other signs of systemic illness/intoxication. Lab tests identify underlying metabolic derangement (glucose, electrolytes, liver/kidney function) or toxin. Imaging usually non-specific.
Multiple Sclerosis (MS) Relapse Acute/subacute onset of brainstem or cerebellar symptoms (diplopia, ataxia, vertigo, dysarthria). Usually younger adults. History of prior neurological events possible. MRI shows characteristic demyelinating lesions (T2/FLAIR hyperintense) in posterior fossa, +/- enhancement.
Posterior Fossa Tumor Usually progressive symptoms (headache, ataxia, cranial nerve palsies). Can present acutely due to hemorrhage into tumor or obstructive hydrocephalus. MRI with contrast is diagnostic, showing mass lesion. CT may show mass/hydrocephalus.
Vertebral Artery Dissection Neck pain/headache common. Can cause posterior circulation stroke/TIA symptoms. Often younger patients, may follow trauma or neck manipulation. CTA or MRA confirms dissection (intimal flap, pseudoaneurysm, occlusion). MRI brain checks for infarct.
Hypoglycemia Can mimic stroke with focal neurological signs, confusion, altered LOC. History of diabetes relevant. Low blood glucose. Symptoms resolve with glucose administration.

References

  1. Blumenfeld H. Neuroanatomy through Clinical Cases. 2nd ed. Sinauer Associates; 2010. Chapter 18: Brainstem III: Vascular Supply.
  2. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor's Principles of Neurology. 11th ed. McGraw Hill; 2019. Chapter 34: Cerebrovascular Diseases, section on Anatomy and Physiology of the Cerebral Circulation.
  3. Osborn AG, Hedlund GL, Salzman KL. Osborn's Brain: Imaging, Pathology, and Anatomy. 2nd ed. Elsevier; 2017. Section on Vascular Diseases.
  4. Caplan LR. Caplan's Stroke: A Clinical Approach. 5th ed. Cambridge University Press; 2016. Chapter on Posterior Circulation Stroke Syndromes.
  5. Grotta JC, Albers GW, Broderick JP, et al. Stroke: Pathophysiology, Diagnosis, and Management. 7th ed. Elsevier; 2021. Chapter on Intracranial Atherosclerosis.
  6. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor's Principles of Neurology. 11th ed. McGraw Hill; 2019. Chapter 34: Cerebrovascular Diseases, sections on Posterior Cerebral Artery Occlusion and Basilar Artery Occlusion.
  7. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor's Principles of Neurology. 11th ed. McGraw Hill; 2019. Chapter 34: Cerebrovascular Diseases (sections on Differential Diagnosis of Stroke and Posterior Circulation Syndromes); Chapter 15: Dizziness and Vertigo.

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