Aneurysmal subarachnoid hemorrhage (aSAH) is a sudden life-threatening bleeding occurring in the subarachnoid space (i.e. between two layers of the protective membranes that surround the brain). It is caused by the rupture of an aneurysm - a weak bulging spot on the wall of a brain artery which allows blood to escape and accumulate in the space around the brain. Surgical repair (endovascular coiling or microsurgical clipping) is required to prevent fatal rebleeding.

Aneurysmal SAH is estimated to affect 30,000 patients in the US each year. The mortality rate for patients suffering from aSAH is high, and among those who survive, long-term symptoms such as physical disabilities are common, making them entirely dependent upon relatives or caregivers.

In about one third of patients with aSAH, worsening of the neurological condition may occur due to delayed cerebral vasospasm (constriction of arteries in the brain). Cerebral vasospasm diminishes blood flow to the brain and may lead to cerebral infarction and poor long-term outcomes.

Currently, invasive, intra-arterial intervention is used to treat cerebral vasospasm. This therapy is associated with medical risk and often requires repeated procedures. No effective medication is available for the prevention or treatment of cerebral vasospasm.