What Is a Subarachnoid Hemorrhage?

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A subarachnoid hemorrhage (SAH) is bleeding in the area surrounding the brain called the subarachnoid space. When this occurs, blood fills inside the subarachnoid space, between the brain and the skull, causing a buildup of pressure on the brain. A SAH is a life-threatening condition that requires immediate medical care.

This article provides an overview of subarachnoid hemorrhages, including symptoms, causes, diagnosis, and treatment.

Andriy Onufriyenko / Getty Images

Types

Strokes fall into two main categories: ischemic stroke, which is caused by a blood clot, and hemorrhagic stroke, which is caused by bleeding in the brain. A SAH is a type of hemorrhagic stroke.

Ischemic Stroke

An ischemic stroke occurs when arterial blood flow to the brain becomes blocked, such as by a blood clot or a buildup due to atherosclerosis, a hardening and narrowing of the arteries due to a collection of fats, cholesterol, and other substances in the walls of arteries.

About 87% of all strokes are ischemic strokes.

Hemorrhagic Stroke

Hemorrhagic strokes, such as a subarachnoid hemorrhage, are much less common than ischemic strokes.

This type of stroke most commonly occurs when a vessel bursts and bleeds due to too much pressure on the vessel. There is limited space within the skull and, eventually, the pressure damages brain cells.

The two types of hemorrhagic strokes are:

  • Intracerebral hemorrhage: The most common type of hemorrhagic stroke, caused by a burst blood vessel within the brain
  • Subarachnoid hemorrhage: Caused by bleeding in the subarachnoid space

Prevalence of SAH

SAHs cause 5%–10% of annual strokes in the United States, affecting 30,000 patients every year.

Symptoms

In 97% of cases, the most common symptom of SAH is sudden onset head pain that patients often describe as "the worst headache ever."

Other symptoms of a SAH include:

  • Nausea and vomiting
  • Fainting
  • Blurred or double vision
  • Loss of consciousness
  • Neck stiffness and back pain due to nerve irritation from blood circulating in the subarachnoid space
  • Sensitivity to light
  • Difficulty speaking
  • Seizures (abnormal electrical activity in the brain)

Causes

The most common reason for SAH (85% of cases) is a blood vessel rupture, also called an aneurysm. However, it can also result from other sources, such as a head injury or arteriovenous malformation (an abnormal tangle of blood vessels).

Other causes of a SAH include:

  • Extension of a parenchymal hemorrhage (a bleed from another part of the brain called the parenchyma)
  • A bleeding disorder, also known as coagulopathy

Factors that may put someone at higher risk of having a SAH include:

  • Smoking
  • Excessive alcohol consumption
  • High blood pressure, also called hypertension
  • Family history of aneurysms
  • Prior history of aneurysms
  • Drug use disorder, including of cocaine or methamphetamines
  • Genetics
  • Advanced age
  • Race

Sex is also a risk factor for strokes. They are more common in women than men.

Diagnosis

Patients with a subarachnoid hemorrhage may not have symptoms aside from a headache, and it is impossible to diagnose a SAH without further testing.

Diagnostic testing for SAH includes:

  • Computed tomography (CT) scan: A screening tool that uses X-rays and computers to create sliced (cross-sectional) images
  • Magnetic resonance imaging (MRI): A screening tool that uses radiofrequency and magnets to make images
  • Cerebral angiography: Dye is injected into a blood vessel of the brain to allow a CT scan to produce more detailed images
  • Lumbar puncture: Also known as a spinal tap, a needle is placed into the spinal canal to remove spinal fluid and test for the presence of blood. If a SAH doesn't appear on an imaging test, a lumbar puncture may help establish a diagnosis.

Treatment

A subarachnoid hemorrhage is a life-threatening condition and requires emergency treatment. If you or a loved one is experiencing symptoms, call 911 immediately. The faster a patient is treated, the greater the likelihood of survival and the lower the chances of having a permanent disability.

Treatment will depend on the cause of the SAH, but the goal of treatment is to stop the bleeding. Surgical treatment involves a craniotomy and may include using one of the following methods to control vessel bleeding:

Prognosis

A SAH is a life-threatening medical emergency.

Many SAH survivors will have some residual disability such as:

  • Speech and language deficits
  • Visual problems
  • Weakness or paralysis of the arms or legs
  • Seizures
  • Personality changes
  • Fatigue
  • Headaches
  • Short-term memory loss

Many stroke survivors have deficits that will eventually get better over time, though many will have some form of permanent disability.

Coping

Recovery from a SAH can be difficult, and it's important not to push yourself too hard. A SAH can significantly alter your regular way of life, including adapting to new ways of performing daily tasks.

You may also want to consider joining a support group or getting additional help from healthcare providers familiar with the difficulties that come with stroke recovery.

Avoid Substances

Avoiding tobacco and alcohol after a stroke can help prevent future strokes from occurring.

Summary

A subarachnoid hemorrhage is bleeding in the subarachnoid space of the brain. The bleeding leads to pressure on the brain, which can cause severe health issues or brain damage. The most common symptom is sudden onset head pain, but other symptoms include nausea, fainting, blurred vision, loss of consciousness, and seizures.

Most subarachnoid hemorrhages result from a blood vessel rupture, such as an aneurysm. Diagnosis requires diagnostic imaging and treatment involves stopping the bleeding as soon as possible through a surgical intervention.

A Word From Verywell

Having a subarachnoid hemorrhage is a frightening experience for everyone involved. If you or a loved one is experiencing symptoms of a subarachnoid hemorrhage or other neurological issues, call 911 immediately. Early diagnosis and treatment are key to improving prognosis.

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