Yes, subarachnoid hemorrhage (SAH) is a stroke. The American Heart Association and American Stroke Association explicitly classify it as one, defining it as a stroke because it is a bleeding event in the central nervous system with a vascular cause that commonly results in permanent neurological injury. SAH accounts for 6 to 8% of all strokes, making it relatively uncommon but disproportionately dangerous.
Where SAH Fits Among Stroke Types
Strokes fall into two broad categories: those caused by a blockage cutting off blood flow (ischemic strokes) and those caused by bleeding (hemorrhagic strokes). Ischemic strokes make up roughly 85% of cases. Hemorrhagic strokes include two subtypes: bleeding directly into the brain tissue (intracerebral hemorrhage) and bleeding into the space surrounding the brain (subarachnoid hemorrhage).
The subarachnoid space is a fluid-filled gap between two layers of membrane that cover the brain. When blood leaks into this space, it irritates the brain’s surface, raises pressure inside the skull, and can damage brain tissue both immediately and over the following days. The formal definition requires that the bleeding not be caused by trauma, so a head injury that causes bleeding in the same area is categorized differently.
What Causes It
The most common cause is the rupture of a brain aneurysm, a weak, balloon-like bulge in an artery wall. When an aneurysm bursts, blood rushes into the subarachnoid space under arterial pressure. Less commonly, SAH results from abnormal blood vessel formations or bleeding disorders, though in some cases no clear source is ever identified.
SAH most commonly strikes between ages 40 and 60. The two biggest modifiable risk factors are smoking and high blood pressure. A 2024 study published in the AHA’s journal Stroke found that for women, every 10 mmHg increase in systolic blood pressure was linked to SAH occurring nearly 4 years earlier in life. Women with a high genetic susceptibility to hypertension developed SAH almost 5 years sooner than those without it.
The Hallmark Symptom
The defining feature of SAH is a thunderclap headache: a sudden, explosive headache that reaches maximum intensity within 60 seconds. People often describe it as the worst headache of their life. It can occur during exertion, but it can also strike at rest. Other symptoms may include a stiff neck, nausea, vomiting, sensitivity to light, brief loss of consciousness, or seizures.
Not everyone experiences the full picture. Some people have a less dramatic “sentinel headache” days or weeks before a major bleed, caused by a small warning leak from an aneurysm. These are frequently mistaken for migraines or tension headaches, which makes the sudden, severe onset the most important red flag to recognize.
How It’s Diagnosed
A non-contrast CT scan of the head is the first-line diagnostic tool. When performed within six hours of headache onset, CT scanning is remarkably accurate. A prospective study published in The BMJ found 100% sensitivity in detecting SAH when the scan was done within that six-hour window. After six hours, sensitivity drops to about 86%, meaning roughly one in seven cases can be missed on CT alone. When the scan is negative but suspicion remains high, a lumbar puncture (spinal tap) or specialized imaging of the blood vessels is typically the next step.
Treatment After a Bleed
If a ruptured aneurysm is found, the immediate priority is preventing it from bleeding again. Two main procedures accomplish this. Microsurgical clipping involves opening the skull and placing a small metal clip at the base of the aneurysm to seal it off. Endovascular coiling is less invasive: a catheter is threaded through a blood vessel in the groin up to the aneurysm, where tiny platinum coils are packed inside it to block blood flow.
The choice between the two depends on the aneurysm’s location, size, and shape, along with the patient’s age and overall health. Neither approach is universally better. Some aneurysms are easier to reach surgically, while others are better suited to the catheter-based approach.
Complications in the Days After
Surviving the initial bleed is only the first hurdle. One of the most feared complications is delayed cerebral ischemia, a secondary injury where parts of the brain lose adequate blood flow days after the original hemorrhage. This process typically begins 3 to 4 days after the bleed and peaks around days 7 to 8. It is closely related to vasospasm, a narrowing of blood vessels near the bleeding site that occurs in up to 70% of patients within 4 to 12 days.
Because of this risk, patients who survive the initial event are closely monitored in an intensive care unit for roughly two weeks. During this period, doctors watch for new neurological symptoms like confusion, weakness, or difficulty speaking that would signal the brain isn’t getting enough blood.
Long-Term Outlook
SAH carries a high mortality rate compared to other stroke types. A significant number of patients die before reaching the hospital or within the first few days. Among those who survive, many face lasting cognitive difficulties including problems with memory, concentration, and executive function, even when they appear physically recovered. Fatigue, mood changes, and difficulty returning to work are common and can persist for months or years.
Recovery timelines vary widely. Some people return to their normal lives within a few months, while others require extended rehabilitation. The severity of the initial bleed, whether complications like vasospasm developed, and the patient’s age and baseline health all influence outcomes. Neuropsychological testing months after the event often reveals subtle deficits that standard neurological exams miss, which is why follow-up care that addresses cognitive and emotional recovery matters as much as the physical side.