Posterior Circulation Stroke

Posterior circulation stroke is ischaemic stroke in the territory of the vertebral, basilar and posterior cerebral arteries, affecting the medulla, pons, midbrain, cerebellum, thalamus and occipital lobes. It accounts for about 20% of ischaemic strokes and is often missed because symptoms are non-specific.

It is more common in men and with increasing age. Causes are large artery disease (vertebral origin, intracranial vertebral and basilar atherosclerosis), cardioembolism, small vessel disease and dissection.

Missed diagnosis. Early CT misses a high proportion; diffusion weighted MRI can be falsely negative in 10 to 20% in the first 24 to 48 hours, particularly in small brainstem lesions.

Syndromes. Lateral medullary (Wallenberg), medial medullary, Weber, Claude, Benedikt, locked in, top of the basilar and posterior cerebral artery syndromes.

Pathophysiology.

Occlusion or embolism in the vertebrobasilar system causes infarction of perforator and branch territories. Dissection of the vertebral artery is a leading cause in young adults.

Posterior cerebral artery occlusion causes occipital and medial temporal infarction with visual and memory deficits.

• Acute vestibular syndrome: sudden vertigo, nausea, vomiting, gait instability and nystagmus.
• Lateral medullary syndrome: ipsilateral facial and contralateral body pain and temperature loss, Horner syndrome, ataxia, dysphagia and hoarseness.
• Diplopia, dysarthria, crossed motor or sensory deficits and cranial nerve palsies.
• Posterior cerebral artery: homonymous hemianopia with macular sparing, alexia without agraphia, visual agnosia, Balint syndrome and amnesia.
• Isolated vertigo in a patient with vascular risk factors needs bedside testing.

Red flags.

• Acute vestibular syndrome with inability to walk or sit unsupported.
• New headache or neck pain with vertigo (dissection).
• Dysphagia, diplopia or reduced consciousness.

• Bedside examination with HINTS (head impulse, nystagmus, test of skew) in patients with continuous vertigo and nystagmus, by trained examiners within 48 hours: normal head impulse, direction changing nystagmus or skew deviation suggest a central cause.
• Neurological examination of gait and truncal ataxia; ability to walk unsupported is a strong predictor of central disease.
• MRI with diffusion weighted imaging; repeat after 24 to 48 hours if negative and suspicion persists. CT angiography or MR angiography of the head and neck.
• ECG and rhythm monitoring; echocardiography when a cardiac source is possible.
• Blood tests: glucose, lipids, full blood count, coagulation.

Differential diagnosis. Vestibular neuritis, benign paroxysmal positional vertigo, Ménière disease, vestibular migraine, cerebellar haemorrhage, demyelination, Wernicke encephalopathy, tumour and drug intoxication.

• Acute: airway and swallow assessment, glucose control and blood pressure management.
• Alteplase 0.9 mg/kg intravenously (maximum 90 mg), 10% as a bolus over 1 minute and the rest as an infusion over 60 minutes, within 4.5 hours of onset or last known well. Monitor neurological observations and blood pressure every 15 minutes for 2 hours, every 30 minutes for the next 6 hours, then hourly to 24 hours; keep blood pressure under 185/110 mmHg before and under 180/105 mmHg after treatment; repeat imaging at 24 hours or with deterioration. Contraindicated with previous intracranial haemorrhage, INR over 1.7, platelets under 100 x 10^9/L, glucose under 2.7 mmol/L, anticoagulant use within 48 hours or major surgery within 14 days; no renal adjustment.
• Tenecteplase 0.25 mg/kg intravenously as a single bolus over 5 to 10 seconds (maximum 25 mg), within 4.5 hours, with the same monitoring and contraindications as alteplase; no renal adjustment.
• Thrombectomy for basilar occlusion, which is a large vessel occlusion; for vertebral artery and posterior cerebral artery occlusions, selected cases only.
• Aspirin 300 mg orally once as a loading dose (300 mg rectally if swallowing is impaired), then 75 mg orally once daily with food. Maximum 300 mg daily. Monitor bleeding and full blood count. Avoid in active peptic ulcer, bleeding disorders and in children under 16 years; use caution when eGFR is under 10. For minor stroke, add clopidogrel 300 mg orally once, then 75 mg once daily, for 21 days; avoid omeprazole and esomeprazole, and avoid in pregnancy unless clearly needed.
• Atorvastatin 80 mg orally once daily, long term. Maximum 80 mg daily. Monitor lipids at 4 to 12 weeks and ALT at baseline and if symptoms occur. No dose change in renal impairment; avoid in active liver disease; limit to 20 mg daily with clarithromycin; contraindicated in pregnancy and breastfeeding.
• Vertebral dissection: antithrombotic therapy with antiplatelet or anticoagulant agents for 3 to 6 months, depending on the clinical situation.
• Atrial fibrillation: anticoagulation started after repeat imaging, from 48 hours after a minor or moderate stroke and about day 6 or 7 after a major stroke.
• Blood pressure under 130/80 mmHg long term, diabetes and smoking control, and rehabilitation with vestibular and gait training.
• Cerebellar infarct with swelling: neurosurgical monitoring for hydrocephalus and brainstem compression.

Monitoring. Neurological observations in the first days; repeat imaging for deterioration; review at 3 months and yearly.

Referral and escalation. Stroke unit admission; neurosurgery for swelling and hydrocephalus; vascular or cardiology review for the cause.

Special groups. Young adults: assess for dissection, patent foramen ovale and thrombophilia. Older adults: falls prevention and dysphagia management.