What are the types of ischemic stroke?

Types of Ischemic Stroke

Ischemic stroke is classified into five main subtypes based on etiology: large-artery atherosclerosis, cardioembolism, small-vessel occlusion (lacunar), stroke of other determined etiology, and stroke of undetermined etiology (cryptogenic). 1

Main Classification System

The most widely used classification system for ischemic stroke is the TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification, which categorizes strokes based on their underlying mechanisms:

1. Large-Artery Atherosclerosis (LAA)

   • Characterized by cortical infarcts in the distribution of a large cerebral artery
   • Evidence of ≥50% stenosis or occlusion of a major brain artery or branch
   • Mechanism: artery-to-artery embolism or hemodynamic insufficiency
   • Often preceded by TIA in the same arterial distribution
   • Accounts for approximately 45% of non-lacunar strokes 1
   • Associated with highest long-term care needs 2

2. Cardioembolism

   • Cortical or large subcortical infarctions with identified high-risk cardiac source
   • Embolus originates from the heart or aorta
   • Evidence of previous TIA/stroke in multiple vascular territories supports this diagnosis
   • Requires exclusion of significant atherosclerotic narrowing
   • Accounts for approximately 35% of non-lacunar strokes 1
   • Associated with highest early mortality (30% at 1 year) 1

3. Small-Vessel Occlusion (Lacunar)

   • Subcortical infarct measuring <1.5 cm in diameter
   • Often presents with lacunar syndrome (e.g., pure motor hemiparesis)
   • Caused by occlusive arteriopathy of small perforating arteries
   • Strongly associated with hypertension and diabetes
   • Accounts for approximately 77% of all ischemic strokes 1
   • Has the best prognosis with lowest mortality (1.4% at 1 year) 1

4. Stroke of Other Determined Etiology

   • Caused by nonatherosclerotic vasculopathies, hypercoagulable states, or hematologic disorders
   • No restriction on size or location of infarct
   • Accounts for approximately 17% of non-lacunar strokes 1
   • Includes arterial dissections, vasculitis, genetic disorders, etc.

5. Stroke of Undetermined Etiology (Cryptogenic)

   • Stroke with unknown source despite thorough diagnostic assessment
   • Includes cases with two or more potential mechanisms identified
   • Also includes cases with incomplete evaluation
   • Accounts for approximately 3% of non-lacunar strokes when properly evaluated 1

Epidemiology and Risk Factors

The distribution of stroke subtypes varies by population, but generally:

• Small-vessel disease (lacunar) accounts for the majority (77%) of ischemic strokes 1
• Among non-lacunar strokes, large-artery atherosclerosis (45%) and cardioembolism (35%) are most common 1

Risk factor profiles differ between subtypes:

• Hypertension is a universal risk factor but particularly important in small-vessel disease
• High total cholesterol plays a more prominent role in small-vessel disease than in LAA 3
• Smoking and diabetes are significant risk factors for both LAA and small-vessel disease
• Atrial fibrillation is strongly associated with cardioembolic stroke

Clinical Implications

Understanding stroke subtype is crucial for:

1. Prognosis: Mortality varies significantly by subtype, with cardioembolic having the highest mortality (30% at 1 year) and small-vessel disease having the lowest (1.4% at 1 year) 1

2. Recurrence risk: LAA strokes have higher recurrence rates than small-vessel disease

3. Treatment decisions:

   • Cardioembolic strokes often require anticoagulation
   • LAA may benefit from carotid revascularization or intensive statin therapy
   • Small-vessel disease management focuses on blood pressure control

4. Cardiac risk assessment: Patients with LAA have significantly higher rates of asymptomatic coronary heart disease (50% abnormal stress tests) compared to other stroke subtypes (23%) 1

Special Considerations

• TIA (Transient Ischemic Attack): Episodes of focal neurological deficits resolving within 24 hours, typically within minutes to hours 1

• Retinal ischemia: Often shares mechanisms with cerebral ischemia and requires similar evaluation 1

• Cryptogenic stroke: Should be a diagnosis of exclusion only after comprehensive evaluation including extended cardiac monitoring and assessment for occult sources 4