Types of Stroke
Strokes are broadly classified into two main categories: ischemic (85% of cases) and hemorrhagic (15% of cases), with ischemic strokes further subdivided into five distinct subtypes based on their underlying mechanism. 1
Major Stroke Categories
Ischemic Stroke (85% of all strokes)
Ischemic strokes result from vascular occlusion leading to brain tissue infarction and are classified into five mechanistic subtypes using the TOAST classification system 2:
1. Large-Artery Atherosclerosis
- Occurs when there is ≥50% stenosis or occlusion of a major cerebral artery or branch cortical artery due to atherosclerotic disease 2, 3
- Presents with cortical infarcts in the distribution of large cerebral arteries 3
- Often preceded by transient ischemic attacks (TIAs) in the same arterial distribution 2, 3
- Mechanism involves either artery-to-artery embolism or hemodynamic insufficiency 2
- Associated with 8.1% mortality at 1 year 2
2. Cardioembolic Stroke
- Results from emboli originating from the heart or aorta, causing cortical or large subcortical infarctions 2, 3
- Requires identification of a high-risk cardiac source (such as atrial fibrillation) 3
- Carries the highest mortality among all ischemic stroke subtypes: 22.6% at 90 days and 45% survival at 2 years 2, 3
- Moderate-risk cardiac sources alone qualify for "possible cardioembolism" 2
3. Small-Artery (Lacunar) Stroke
- Small infarcts (<1.5 cm diameter) in deep brain structures or brainstem caused by occlusive arteriopathy of small penetrating arteries 3, 4
- Typically associated with diabetes or hypertension rather than large-vessel atherosclerosis 2
- Presents with classical lacunar syndromes including pure motor hemiparesis 4
- Has the best prognosis among all stroke subtypes: 85% survival at 2 years and only 3.3% mortality at 90 days 2, 3, 4
- Only 1.4% probability of death at 1 year 2
4. Stroke of Other Determined Cause
- Includes uncommon etiologies such as arterial dissection, hypercoagulable states, sickle cell disease, and other rare mechanisms 2, 3
- Particularly important to consider in younger patients (<50 years) 1
5. Stroke of Undetermined Cause
- Diagnosis made when adequate workup fails to identify a clear mechanism 2
- Reflects inadequacy or timing of diagnostic evaluation to visualize the occluded artery or localize the embolic source 2
Hemorrhagic Stroke (15% of all strokes)
Intracerebral hemorrhage accounts for approximately 15% of strokes worldwide and can be further categorized by location 1:
Deep (Basal Ganglia/Brainstem) Hemorrhages
- Usually result from deep perforator arteriopathy (hypertensive arteriolosclerosis) 1
Lobar Hemorrhages
- Mainly caused by cerebral amyloid angiopathy or arteriolosclerosis 1
Cerebellar Hemorrhages
- Distinct anatomic location with specific clinical implications 1
Secondary Hemorrhages (approximately 20% of intracerebral hemorrhages)
- Caused by macrovascular lesions including vascular malformations, aneurysms, cavernomas, or venous sinus thrombosis 1
- Particularly important to identify in younger patients 1
Clinical Significance of Stroke Subtype Classification
Determining the specific ischemic stroke subtype provides crucial prognostic information and guides treatment decisions 2:
- Stroke subtype is a strong predictor of long-term survival and mortality risk 2, 3
- Cardioembolic strokes carry the highest cardiac-related mortality risk 2, 3
- Small-vessel disease patients have significantly lower mortality rates compared to other subtypes 2
- Accurate classification requires comprehensive diagnostic testing including brain imaging and vascular studies 3
Transient Ischemic Attack (TIA)
TIA is now defined as a brief episode of neurological dysfunction caused by focal brain or retinal ischemia, typically lasting <1 hour, without evidence of infarction on imaging 2: