What are the primary classifications of stroke, including ischemic and hemorrhagic subtypes?

Stroke Classification

Strokes are classified into two major categories: ischemic strokes (accounting for 80-87% of cases) and hemorrhagic strokes (13-20% of cases), with ischemic strokes further subdivided into five mechanistic subtypes using the TOAST classification system. 1, 2

Primary Classification: Ischemic vs Hemorrhagic

Brain imaging with CT or MRI is mandatory to distinguish between ischemic and hemorrhagic stroke, as this distinction is critical for treatment decisions—particularly for thrombolytic eligibility. 3 CT should be completed within 25 minutes of emergency department arrival for potential thrombolytic candidates. 3

• Ischemic strokes represent 85% of all strokes and result from arterial occlusion causing brain tissue infarction. 2
• Hemorrhagic strokes represent 15% of all strokes and result from ruptured blood vessels causing bleeding into or around the brain. 2

Ischemic Stroke Subtypes (TOAST Classification)

The American Heart Association endorses the TOAST classification system, which divides ischemic strokes into five etiologic categories: 4, 1, 5

1. Large-Artery Atherosclerosis (20% of ischemic strokes)

• Defined by ≥50% stenosis or occlusion of a major cerebral artery (carotid, vertebral, or major intracranial vessels) due to atherosclerotic plaque. 4, 1
• Presents with cortical infarcts in the distribution of a large cerebral artery. 4
• Often preceded by TIAs in the same arterial distribution. 4
• Mechanism involves artery-to-artery embolism or hemodynamic insufficiency. 4
• Requires vascular imaging (CT angiography, MR angiography, carotid duplex, or transcranial Doppler) to confirm stenosis. 3

2. Cardioembolic Stroke (20% of ischemic strokes)

• Results from emboli originating from the heart or aorta, most commonly from atrial fibrillation. 1, 6
• Presents as cortical or large subcortical infarctions with an identifiable high-risk cardiac source. 4, 1
• Carries the highest mortality rate among all ischemic stroke subtypes (22.6% at 90 days, 55% survival at 2 years). 4
• Requires 12-lead ECG and continuous cardiac rhythm monitoring to detect atrial fibrillation. 3
• Echocardiography may be needed to identify structural cardiac sources. 3

3. Small-Vessel (Lacunar) Stroke (25% of ischemic strokes)

• Characterized by small infarcts (<1.5 cm diameter) in deep brain structures (basal ganglia, internal capsule, thalamus) or brainstem. 1, 6
• Caused by occlusive arteriopathy of small penetrating arteries. 4, 1
• Strongly associated with diabetes and hypertension rather than large-vessel atherosclerosis. 4, 1
• Has the best prognosis among ischemic stroke subtypes (1.4% mortality at 1 year, 85% survival at 2 years). 4, 1
• Requires exclusion of large-artery stenosis and cardiac embolic sources for diagnosis. 3

4. Stroke of Other Determined Etiology

• Includes uncommon causes such as cervical artery dissection, vasculitis, moyamoya disease, hypercoagulable states, and drug-related causes. 4, 1
• Particularly important to identify in younger patients (<50 years). 2
• Requires targeted testing based on clinical suspicion (prothrombotic screening, inflammatory markers, toxicology). 3

5. Stroke of Undetermined Etiology

• Assigned when no clear cause is identified despite adequate diagnostic workup, or when multiple potential causes are present. 4, 5
• Includes embolic stroke of undetermined source (ESUS), which accounts for 58% of recurrent strokes after initial ESUS. 7
• Should not be used as a default category—requires comprehensive evaluation including brain imaging, vascular studies, and cardiac workup. 4, 6

Hemorrhagic Stroke Subtypes

Hemorrhagic strokes must be separated into two distinct categories: intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH). 4, 3

Intracerebral Hemorrhage (ICH)

ICH should be classified by anatomic location: 4, 3

• Deep (basal ganglia): Usually results from hypertensive arteriopathy. 4, 2
• Lobar: Mainly caused by cerebral amyloid angiopathy or arteriolosclerosis. 2
• Brainstem: Associated with hypertensive arteriopathy. 4, 2
• Cerebellar: Can result from hypertension or vascular malformations. 4, 2
• Primary intraventricular hemorrhage (IVH): Bleeding primarily into the ventricular system. 4
• Multiple ICH: Suggests underlying coagulopathy or amyloid angiopathy. 4

Severity assessment: Use Glasgow Coma Scale (minimum requirement) or ICH score/FUNC score (preferred). 4, 3 Measure ICH size using the ABC/2 method and document presence/absence of IVH. 4

Exclude: Traumatic ICH, subdural hematomas, hemorrhage from cerebral venous thrombosis, and neoplasm-related hemorrhage. 4, 3

Subarachnoid Hemorrhage (SAH) (3% of all strokes)

SAH should be classified etiologically: 4, 1

• Aneurysmal SAH (aSAH): Berry or fusiform aneurysm rupture—the most common cause. 4, 1
• Intracranial dissection: Arterial wall tear causing bleeding. 4
• Perimesencephalic SAH: Without identified aneurysm, typically benign course. 4
• Cortical SAH: Without structural cause, may indicate amyloid angiopathy. 4

Severity assessment: Use Hunt and Hess scale or World Federation of Neurosurgical Societies (WFNS) grading scale. 4 Classify hemorrhage volume using Fisher or Hijdra scales. 4

Transient Ischemic Attack (TIA)

• Defined as brief neurological dysfunction caused by focal brain or retinal ischemia with symptoms typically lasting <1 hour and no evidence of infarction on imaging. 1, 6
• Carries significant stroke risk: Up to 10.5% at 90 days. 1
• Shares the same pathogenetic mechanisms as ischemic strokes and should be classified using the same etiologic categories. 1, 6
• Critical pitfall: Up to one-third of patients with symptoms lasting <24 hours show evidence of infarction on MRI—these are strokes, not TIAs. 6, 3
• Requires stroke physician adjudication and imaging (MRI strongly preferred) to exclude acute infarct and non-vascular mimics. 4, 6

Severity Assessment for Ischemic Stroke

Use the National Institutes of Health Stroke Scale (NIHSS) to capture initial stroke severity, as this allows determination of genetic associations with outcomes and enables adjustment for severity in analyses. 4, 3 The Modified Rankin Scale (mRS) at 30 days is the standard outcome measure, with mRS <3 indicating significant functional independence. 3

Clinical Significance and Prognostic Implications

Stroke subtype classification is critical because it strongly predicts long-term survival, guides treatment approaches, and determines secondary prevention strategies. 1, 6

• Cardioembolic strokes have the highest mortality (22.6% at 90 days). 4
• Small-vessel strokes have the lowest mortality (3.3% at 90 days, 85% survival at 2 years). 4, 1
• Large-artery atherosclerosis has intermediate mortality (8.1% at 1 year). 4
• Patients with large-artery atherosclerosis or intracranial stenosis have 50% rate of abnormal cardiac stress testing, compared to 23% for other stroke causes. 4

Common Pitfalls to Avoid

• Do not rely solely on clinical features without imaging for accurate stroke classification—brain imaging is mandatory. 3
• Do not combine TIA and stroke cases in classification systems—TIA requires symptom resolution within 24 hours and imaging to exclude acute infarct. 4, 3
• Do not assign "undetermined" category without comprehensive workup—requires brain imaging, vascular imaging, cardiac evaluation, and appropriate laboratory testing. 4, 6, 3
• Do not perform lumbar puncture routinely—it is only indicated when infectious etiology is suspected and brain imaging is negative. 3
• Do not delay thrombolytic therapy while awaiting coagulation studies unless there is clinical suspicion of bleeding disorder or known anticoagulant use. 3