Definition and WHO time-based concept

Summary

The World Health Organization (WHO) time-based concept defines a stroke as a neurological deficit of cerebrovascular cause that either persists beyond 24 hours or results in death within 24 hours. This 24-hour cutoff was intended to reflect the (then-assumed) reversibility of tissue damage and to distinguish stroke from related conditions based on symptom duration. Under this concept, if neurological symptoms resolve completely within 24 hours, the event is classified as a transient ischemic attack (TIA), often called a “mini-stroke.” Although this definition is historically important, modern practice increasingly emphasizes rapid treatment and urgency (e.g., “brain attack” or “acute ischemic cerebrovascular syndrome”) because early interventions can reduce stroke severity even when the original 24-hour framing is not the most practical guide for action.

Key Points

• 1

  WHO defines stroke using a time threshold: neurological deficit of cerebrovascular cause persisting beyond 24 hours or interrupted by death within 24 hours.

• 2

  The 24-hour limit separates stroke from transient ischemic attack (TIA), where symptoms resolve completely within 24 hours.

• 3

  The time-based definition was designed to reflect reversibility of tissue damage, but modern terminology and treatment priorities emphasize early action for better outcomes.