- Defined as neurological deterioration related to ischaemia 1 (unrelated to treatment of the aneurysm) that persists for one hour 1 and has no other cause
- The clinical syndrome is of focal neurologic deficits
- Approximately 25% of patients develop clinical evidence of delayed ischaemia/infarction; of these 25% die as a result. About 10% of the survivors remain permanently disabled
