Subarachnoid Hemorrhage (SAH)

What happens in a subarachnoid hemorrhage

The brain is wrapped in three layers (the meninges). Between the middle layer (arachnoid) and the inner layer (pia) is the subarachnoid space, filled with cerebrospinal fluid and the large arteries at the base of the brain. When one of these arteries bursts, blood under arterial pressure floods this space.

Pressure inside the skull rises suddenly, which can briefly stop blood flow to the brain and cause collapse. Blood irritates the meninges, causing headache and neck stiffness. Over the following days, blood breakdown products can make arteries spasm and block the normal flow of spinal fluid.

Causes

• Ruptured cerebral aneurysm: a weak, balloon-like bulge in a brain artery, usually where vessels branch at the base of the brain. See brain aneurysm.
• Head injury: the most common cause of subarachnoid blood of any kind, usually managed differently from aneurysmal SAH.
• Perimesencephalic hemorrhage: a small bleed in front of the brainstem with no aneurysm found. It has an excellent outlook.
• Arteriovenous malformation (AVM): a tangle of abnormal blood vessels.
• Less common: arterial dissection, reversible cerebral vasoconstriction syndrome, blood-thinning medicines and bleeding disorders, cocaine or amphetamine use.

Risk factors

• Smoking
• High blood pressure
• Heavy alcohol use
• Cocaine and stimulant use
• Female sex and age 40 to 60
• Family history of aneurysms or SAH
• Polycystic kidney disease and some connective tissue disorders, such as Ehlers-Danlos syndrome type IV

Symptoms

• Thunderclap headache: sudden, explosive and severe, reaching peak intensity within seconds to a minute. It is often felt at the back of the head.
• Nausea and vomiting
• Stiff neck, usually developing over hours
• Sensitivity to light
• Brief loss of consciousness, or collapse
• Seizure
• Confusion, drowsiness or agitation
• Double vision, a drooping eyelid or a dilated pupil (pressure on the third cranial nerve, often from a posterior communicating artery aneurysm)
• Weakness or speech problems if there is bleeding into the brain tissue

Some people have a sentinel headache, a smaller warning leak, days to weeks before a major bleed. Any sudden, severe, unusual headache should be assessed urgently, even if it settles.

How it is diagnosed

1. CT scan of the head without contrast: detects nearly all SAHs if done within 6 hours of headache onset.
2. Lumbar puncture: if the CT is normal but suspicion remains, and the scan was done after 6 hours. Fluid is tested at least 12 hours after the headache for xanthochromia (yellow breakdown products of blood).
3. CT angiography: dye scan to find an aneurysm or other source.
4. Digital subtraction angiography: the most detailed test of the brain's arteries, often done during treatment.

Doctors grade severity using scales based on consciousness and neurological deficits (Hunt and Hess, WFNS) and the amount of blood on CT (modified Fisher scale). Higher grades predict worse outcomes and more vasospasm.

Treatment

Emergency care

• Protecting the airway and breathing, often in intensive care
• Controlling blood pressure to reduce the risk of rebleeding before the aneurysm is secured
• Reversing any blood thinners
• Pain relief and anti-nausea medicine
• Treating seizures

Securing the aneurysm

The risk of rebleeding is highest in the first hours to days, and a rebleed is often fatal. The aneurysm is treated as soon as possible, ideally within 24 hours:

• Endovascular coiling: a catheter is threaded from the groin or wrist to the aneurysm and filled with soft platinum coils, sometimes with a stent or flow diverter. It is preferred for many aneurysms.
• Surgical clipping: the skull is opened and a small metal clip is placed across the aneurysm's neck.

Preventing complications

• Nimodipine: a calcium channel blocker given by mouth for 21 days. It improves outcomes by reducing brain damage from delayed ischemia.
• Monitoring for vasospasm: frequent neurological checks and transcranial Doppler ultrasound. Treatment includes keeping fluid levels and blood pressure up, and angioplasty or medicines delivered directly into narrowed arteries.
• Drain for hydrocephalus: an external ventricular drain removes excess spinal fluid.
• Managing sodium and fluids, fever, blood sugar and blood clots.

Complications

• Rebleeding: most likely in the first 24 hours.
• Vasospasm and delayed cerebral ischemia: narrowing of brain arteries typically between days 3 and 14, causing stroke-like symptoms.
• Hydrocephalus: buildup of spinal fluid, which may need a long-term shunt.
• Seizures
• Low sodium (hyponatremia)
• Heart strain, abnormal heart rhythms and fluid in the lungs

Outlook and recovery

Aneurysmal SAH is serious: roughly a quarter to a third of people die, some before reaching the hospital. Of those who survive, many recover independence, but a large proportion have lasting problems such as fatigue, memory and concentration difficulties, mood changes, anxiety, headaches and changes in smell or vision. Recovery can continue for 12 to 18 months.

Rehabilitation with physical, occupational, speech and neuropsychological therapy helps. Follow-up scans check that the aneurysm remains sealed. Stopping smoking and controlling blood pressure reduce the risk of new aneurysms.

Frequently asked questions

What does a subarachnoid hemorrhage headache feel like?

Most people describe a sudden, explosive headache, the worst they have ever had, reaching full intensity within seconds to a minute. It is often felt at the back of the head and may come with vomiting, neck stiffness, light sensitivity or collapse.

What causes a subarachnoid hemorrhage?

Apart from head injuries, about 85% are caused by a burst brain aneurysm. Others come from a bleed around the brainstem without an aneurysm, arteriovenous malformations, artery tears, or drugs such as cocaine. Smoking and high blood pressure are the biggest risk factors.

What is the survival rate for subarachnoid hemorrhage?

Roughly two-thirds to three-quarters of people survive aneurysmal SAH, though about a third of survivors have lasting disabilities. Outcomes depend on the severity at arrival, age, rebleeding and vasospasm. SAH without an aneurysm, such as perimesencephalic hemorrhage, usually has an excellent outcome.

How long does it take to recover from a subarachnoid hemorrhage?

The hospital stay is usually 2 to 3 weeks or more. Physical recovery often continues for months, and cognitive and emotional recovery, such as memory, fatigue and mood, can take 12 to 18 months. Many people return to work, sometimes with adjustments.

Can a subarachnoid hemorrhage happen again?

Once an aneurysm is successfully coiled or clipped, the risk of it bleeding again is low. People can develop new aneurysms, especially if they smoke or have high blood pressure, so follow-up scans and risk factor control are recommended.