TIA: neurologic symptoms of ischemic origin that last less than 24 hours; most 1 to 60 minutes.

Transient occlusion: intermittent occlusion by fragment of thrombotic plaque; distal branch occlusion (embolus which then breaks into smaller fragments).

Hemodynamic insufficiency: e.g., arrhythmia; subclavian steal syndrome (arm exercise diverts blood away from vertebrae).

Other: intraparenchymal vascular disease, anemia, polycythemia.