Stroke Definition
A stroke is defined as an acute episode of focal or global neurological dysfunction caused by brain, spinal cord, or retinal vascular injury (infarction or hemorrhage), with symptoms lasting ≥24 hours, OR <24 hours if neuroimaging documents a new hemorrhage or infarct, OR the neurological deficit results in death 1.
Core Diagnostic Criteria
The diagnosis requires an acute episode of focal or global neurological deficit with at least one of the following clinical features 1:
- Change in level of consciousness
- Hemiplegia or hemiparesis
- Numbness or sensory loss affecting one side of the body
- Dysphasia or aphasia
- Hemianopia
- Amaurosis fugax
- Other neurological signs or symptoms consistent with stroke
Critically, other readily identifiable non-stroke causes must be excluded (brain tumor, trauma, infection, hypoglycemia, peripheral lesion, pharmacological influences) 1.
Stroke Classification
By Mechanism
Ischemic stroke (85% of all strokes): An acute episode of focal cerebral, spinal, or retinal dysfunction caused by infarction of central nervous system tissue 1, 2.
Hemorrhagic stroke (15% of all strokes): An acute episode of focal or global cerebral or spinal dysfunction caused by intraparenchymal, intraventricular, or subarachnoid hemorrhage 1, 2.
Undetermined: When insufficient information exists to categorize as ischemic or hemorrhagic 1.
Modern Neuroimaging-Based Definition
A critical evolution in stroke definition involves neuroimaging findings: Patients with symptoms lasting up to 24 hours who have diffusion-weighted imaging-positive lesions on MRI are now classified as ischemic strokes, not transient ischemic attacks 3. This tissue-based definition supersedes the traditional time-based definition and is widely accepted in contemporary practice.
Confirmation of Diagnosis
The diagnosis should be confirmed by at least one of the following 1:
- Neurologist or neurosurgical specialist evaluation
- Neuroimaging procedure (CT scan or brain MRI)
- Note: Stroke may be diagnosed on clinical grounds alone when imaging is unavailable 1
Distinction from Transient Ischemic Attack (TIA)
TIA is defined as: Duration of focal or global neurological deficit <24 hours AND neuroimaging does not demonstrate a new hemorrhage or infarct 1. The modern definition emphasizes that TIA represents "brief neurological dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than 1 hour, and without evidence of infarction" 4.
Severity Classification
Strokes are further classified by disability impact 1:
Disabling stroke: Modified Rankin Scale (mRS) score ≥2 at 90 days AND an increase of ≥1 mRS category from prestroke baseline
Nondisabling stroke: mRS score <2 at 90 days OR no increase in ≥1 mRS category from prestroke baseline
Clinical Context
Stroke represents a medical emergency requiring immediate evaluation and treatment 5. It is the second leading cause of death and disability worldwide 2, the fifth leading cause of death in the United States 6, and the most common cause of adult-onset disability 6. The definition emphasizes that stroke is not a single disease but rather a clinically defined syndrome with multiple potential causes and mechanisms 2.
The most recent guidelines 7, 8 maintain these core definitional elements while emphasizing the importance of rapid diagnosis and treatment to minimize morbidity and mortality.