Basilar Artery Occlusion

Basilar artery occlusion is acute thrombotic or embolic blockage of the basilar artery, causing brainstem, cerebellar and thalamic infarction with high rates of death or severe disability. It is an emergency in which early reperfusion changes outcome.

It accounts for about 1 to 4% of ischaemic strokes, and about 10% of strokes with large vessel occlusion. Mean age is about 60 to 65 years, with a male predominance.

Causes. Atherosclerotic in situ thrombosis (often proximal or at the vertebrobasilar junction), cardioembolism or vertebral artery embolism (distal), dissection, and rarely vasculitis and hypercoagulability.

Prognosis. Without recanalisation mortality is 70 to 90%; outcomes improve with early reperfusion.

Severity. NIHSS under scores brainstem deficits. A prodrome of vertigo, headache or neck pain, or transient symptoms, occurs in many patients in the days before occlusion.

Pathophysiology.

Occlusion cuts off perfusion to the pons, midbrain, cerebellum, thalamus and occipital lobes via perforators, causing infarction and loss of the reticular activating system.

Collateral supply through the posterior communicating arteries determines whether the occlusion causes mild or catastrophic deficits.

• Prodrome: stuttering vertigo, nausea, headache, neck pain, dysarthria, diplopia or transient limb weakness.
• Progressive or sudden quadriparesis, bulbar palsy, abnormal gaze, pupillary changes and impaired consciousness; locked in syndrome with preserved vertical eye movement.
• Top of the basilar syndrome: visual loss, oculomotor and pupillary signs, amnesia and somnolence.
• Examination may show a gaze palsy, nystagmus, bilateral long tract signs and ataxia.

Red flags.

• Decreasing level of consciousness or new bulbar signs.
• Abnormal gaze or pupils with limb weakness.
• Stuttering vertigo with headache or neck pain.

• Immediate non-contrast CT (excludes haemorrhage; may show a hyperdense basilar sign), then CT angiography of the head and neck.
• Posterior circulation ASPECTS on CT or MRI diffusion weighted imaging to estimate infarct extent; low scores (under 6) predict poor outcome.
• MRI with diffusion weighted imaging if there is no delay; CT has poor sensitivity for posterior fossa infarction.
• Blood tests: glucose, coagulation, full blood count, troponin; ECG.

Differential diagnosis. Brainstem or cerebellar haemorrhage, basilar migraine, encephalitis, Wernicke encephalopathy, hypoglycaemia, intoxication, central pontine myelinolysis, seizure, Guillain-Barré syndrome and functional disorders.

• Time is critical: airway protection and breathing support when consciousness is impaired, blood pressure control, glucose correction and early transfer to a thrombectomy centre.
• 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. Do not delay transfer for thrombectomy.
• 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.
• Mechanical thrombectomy: recent randomised studies show benefit when the NIHSS is 10 or more and treatment is within 12 hours of onset, with some benefit when the NIHSS is 6 or more in the 6 to 24 hour window; benefit in milder deficits and later windows is less certain. Posterior circulation ASPECTS of 6 or more favours treatment.
• After reperfusion: aspirin 300 mg orally once (or rectally) after 24 hours and a repeat scan excluding haemorrhage, then 75 mg orally once daily long term. Maximum 300 mg daily. Monitor bleeding and full blood count. Avoid in active peptic ulcer and bleeding disorders; use caution when eGFR is under 10.
• Basilar stenosis or occlusion unsuitable for reperfusion: antiplatelet therapy or anticoagulation by cause, and intensive risk factor control.
• 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.
• Intensive care, dysphagia management, early rehabilitation and prevention of aspiration, venous thrombosis and pressure ulcers.

Monitoring. Neurological observations in a stroke or neurocritical unit; repeat imaging at 24 hours; swallow screen before feeding.

Referral and escalation. Immediate stroke team and thrombectomy centre referral; neurosurgery for cerebellar swelling; palliative care discussion in devastating disease.

Special groups. Pregnancy: thrombolysis and thrombectomy are not absolutely contraindicated and are decided by a multidisciplinary team. Children: rare and managed in specialist centres.