Makindo Medical Notes

Related Subjects: |Neurological History taking |Causes of Stroke |Ischaemic Stroke |Hypertension |Small Vessel Disease |CADASIL |CARASIL

Introduction

Watershed infarcts occur in regions of the brain that lie between two or more arterial territories. These border zones are particularly vulnerable to hypoperfusion, especially when systemic blood pressure falls, leading to reduced perfusion in these areas.

About

• Watershed infarcts comprise approximately 10% of all ischemic strokes.
• They are localized to the border zones between major cerebral arteries.
• Watershed infarcts can be classified as cortical border-zone (CBZ) infarcts or internal border-zone (IBZ) infarcts.

Aetiology

• Result from decreased cerebral perfusion due to systemic hypotension or arterial stenosis.
• Embolic phenomena can also contribute, particularly in cortical watershed infarcts.
• Commonly associated with severe carotid artery disease or episodes of systemic hypoperfusion.

Cortical Border-Zone Infarcts

• Located at the junctions of distal branches of the anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA).
• Often present as wedge-shaped areas of infarction in the frontal or parieto-occipital regions.
• Frequently unilateral and may be related to microemboli or hypoperfusion.

Internal Border-Zone Infarcts

• Occur at the junctions of the cortical vessels and deep perforating arteries (e.g., lenticulostriate arteries, artery of Heubner, anterior choroidal artery).
• Typically associated with profound hypotension or severe stenosis/occlusion of the internal carotid or middle cerebral arteries.
• Infarcts may appear as linear or band-shaped lesions parallel to the lateral ventricles and can be bilateral.

Risk Factors

• Severe hypertension with rapid reduction in blood pressure.
• Perioperative hypotension or significant fluctuations in blood pressure during surgery.
• Episodes of systemic shock (e.g., cardiac arrest, severe dehydration).
• Severe carotid artery stenosis or occlusion.
• Conditions leading to decreased cardiac output.

Clinical Presentation

• Symptoms depend on the affected cortical or subcortical regions.
• Common manifestations include:
• Weakness or paralysis (motor deficits).
• Sensory disturbances.
• Visual field defects.
• Language difficulties if dominant hemisphere is involved.
• "Man-in-the-barrel" syndrome: proximal muscle weakness affecting the shoulders and hips more than distal muscles.

Investigations

• Laboratory Tests:
• Full Blood Count (FBC).
• Urea and Electrolytes (U&E).
• Liver Function Tests (LFTs).
• Blood glucose levels.
• Cardiac enzymes (e.g., Troponin).
• Lactate levels to assess for hypoperfusion.
• Imaging Studies:
• Magnetic Resonance Imaging (MRI) with diffusion-weighted imaging (DWI) to identify acute infarcts.
• Computed Tomography (CT) scan if MRI is unavailable or contraindicated.
• Magnetic Resonance Angiography (MRA) or Computed Tomography Angiography (CTA) to assess vascular structures.
• Carotid duplex ultrasound to evaluate carotid artery stenosis.
• Echocardiogram to detect cardiac sources of emboli.
• Other Assessments:
• Electrocardiogram (ECG) to identify arrhythmias.
• Continuous cardiac monitoring if indicated.

Management

• Ensure Adequate Cerebral Perfusion:
• Maintain optimal blood pressure to prevent further hypoperfusion.
• Avoid rapid fluctuations in blood pressure.
• Correct dehydration or hypovolemia with appropriate fluid therapy.
• Address Underlying Causes:
• Treat significant carotid artery stenosis (medical management or consider revascularization procedures).
• Manage cardiac conditions contributing to decreased output.
• Secondary Prevention:
• Antiplatelet therapy (e.g., aspirin) unless contraindicated.
• Lipid-lowering agents (statins) to manage dyslipidemia.
• Blood pressure control according to guidelines.
• Lifestyle modifications: smoking cessation, diet, and exercise.
• Stroke Rehabilitation:
• Multidisciplinary approach involving physiotherapy, occupational therapy, speech and language therapy.
• Early mobilization and functional recovery interventions.
• Patient Education:
• Inform about warning signs of stroke and importance of timely medical attention.
• Discuss risk factor modification and adherence to medications.

Prognosis

• Prognosis varies depending on the extent of the infarct and timely restoration of adequate cerebral perfusion.
• Early intervention and rehabilitation can improve functional outcomes.

References

• Caplan LR, Hennerici M. Impaired clearance of emboli (washout) is an important link between hypoperfusion, embolism, and ischemic stroke. Arch Neurol. 1998;55(11):1475-1482.
• Derdeyn CP, Powers WJ. Stroke: Pathophysiology, Diagnosis, and Management. In: Barnett's Stroke, 5th ed. Elsevier Saunders; 2011.
• Bladin CF, Chambers BR. Clinical features, pathogenesis, and computed tomographic characteristics of internal watershed infarction. Stroke. 1993;24(12):1925-1932.