Pathophysiology
Clinical meaning
A transient ischemic attack (TIA) is a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia WITHOUT acute infarction on imaging. The traditional '24-hour' definition has been replaced by a tissue-based definition โ if DWI MRI shows restricted diffusion, it is a stroke regardless of symptom duration (30-50% of 'TIAs' by the old definition have DWI lesions). TIAs represent a medical EMERGENCY because stroke risk after TIA is 10-15% within 90 days, with the highest risk in the first 48 hours. The ABCDยฒ score stratifies risk: Age โฅ60 (+1), BP โฅ140/90 (+1), Clinical features (unilateral weakness +2, speech disturbance +1), Duration (โฅ60 min +2, 10-59 min +1), Diabetes (+1). Scores 0-3 = low risk, 4-5 = moderate, 6-7 = high risk. However, ABCDยฒ alone is insufficient โ any TIA with identified LVO, significant carotid stenosis, or AF requires urgent intervention regardless of score. Pathophysiology mirrors ischemic stroke: embolic (cardiac, artery-to-artery), thrombotic (in-situ stenosis), or hemodynamic (watershed ischemia). The key difference is that in TIA, collateral circulation or spontaneous thrombolysis restores perfusion before irreversible infarction occurs....