Watershed Cerebral Infarction

Watershed cerebral infarction is infarction in the border zones between major arterial territories, usually from reduced perfusion pressure or from microembolism. Cortical (external) border zones lie between the anterior, middle and posterior cerebral arteries, and internal border zones lie in the deep white matter, between deep and superficial middle cerebral branches.

It accounts for about 10% of ischaemic strokes. Common settings are severe carotid stenosis or occlusion, cardiac surgery, cardiac arrest, hypovolaemia and profound hypotension, and it also occurs with embolism.

Patterns. Anterior cortical (anterior to middle cerebral artery), posterior cortical (middle to posterior cerebral artery), internal (corona radiata and centrum semiovale) and, less often, cerebellar and spinal cord territories.

Mechanism. Haemodynamic and embolic mechanisms often coexist: reduced flow slows clearance of emboli from distal branches.

Pathophysiology.

Border zone regions sit at the end of arterial supply and have limited collateral flow, so a fall in perfusion pressure causes ischaemia first at these sites.

Impaired autoregulation in chronic carotid disease reduces tolerance to even brief hypotension.

• Proximal arm and leg weakness (man in a barrel syndrome) in bilateral anterior cortical infarcts.
• Transcortical aphasias, visual agnosia and Balint syndrome in posterior zone infarcts.
• Recurrent short stereotyped TIAs related to posture, exercise or hypotension; limb shaking.
• Cognitive impairment or fluctuating deficits in internal border zone infarcts.
• Often follows hypotension, cardiac surgery, bleeding or anaemia.

Red flags.

• Deficit after hypotension, cardiac arrest or major blood loss.
• Symptoms with standing or exertion.
• Contralateral carotid occlusion or bilateral severe stenosis.

• MRI with diffusion weighted imaging shows the pattern: cortical wedge shapes at territory borders or a linear string of internal lesions parallel to the ventricles.
• CT angiography, MR angiography or carotid duplex ultrasound for stenosis or occlusion; perfusion imaging for haemodynamic failure.
• Review of recent blood pressure, medicines and bleeding; echocardiography and rhythm monitoring.
• Blood tests: full blood count, haemoglobin, glucose, cardiac enzymes and renal function.

Differential diagnosis. Embolic stroke, hypoxic ischaemic brain injury, posterior reversible encephalopathy syndrome, hypoglycaemia, vasculitis, demyelination, tumour and moyamoya disease.

• Restore and maintain cerebral perfusion: lie flat early, avoid hypotension, stop or reduce blood pressure medicines, correct anaemia, bleeding and arrhythmia.
• Hypovolaemia: sodium chloride 0.9% 250 to 500 mL intravenously over 15 to 30 minutes, repeated depending on the response, to a maximum of about 30 mL/kg before reassessment. Monitor blood pressure, heart rate, urine output, oxygenation and electrolytes. Use smaller boluses with heart failure or renal impairment; no dose change in pregnancy.
• Aspirin 300 mg orally once as a loading dose (300 mg rectally if swallowing is impaired), then 75 mg orally once daily with food, long term. Maximum 300 mg daily. Monitor bleeding, dyspepsia and full blood count. Avoid in active peptic ulcer, bleeding disorders and in children under 16 years; use caution when eGFR is under 10.
• 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. Aim for LDL cholesterol under 1.8 mmol/L.
• Symptomatic carotid stenosis of 70 to 99%, and selected cases of 50 to 69%: carotid endarterectomy within 14 days, after protecting against perioperative hypotension and hyperperfusion.
• Occlusion with persistent haemodynamic failure: specialist review for revascularisation.
• Blood pressure: avoid aggressive lowering in the first days and with bilateral critical disease; long term target under 130/80 mmHg once stable.
• Smoking cessation, diabetes control and cardiac assessment for perioperative or low output states.

Monitoring. Blood pressure and neurological observations in the first days; repeat vascular imaging at 3 to 6 months; yearly review.

Referral and escalation. Vascular surgery for carotid disease; cardiology for low output or arrhythmia; stroke service for all patients.

Special groups. Older adults: avoid orthostatic hypotension from antihypertensive drugs and diuretics.