What Causes a Subarachnoid Hemorrhage?

Medically Reviewed on 11/2/2022
Subarachnoid Hemorrhage
Sudden bleeding into the subarachnoid space in the brain is known as a subarachnoid hemorrhage.

The most common cause of a subarachnoid hemorrhage is the rupture of a blood vessel commonly caused by spontaneous rupture of a brain aneurysm and an injury. A brain aneurysm is a blood vessel in the brain that bulges due to the weakening of the vessel wall particularly at the branching point. Motor vehicle accidents and increased incidence of falls in older people also cause subarachnoid hemorrhage. 

Other causes of a subarachnoid hemorrhage include:

Other factors that increase the risk of a subarachnoid hemorrhage include:

What is a subarachnoid hemorrhage?

Sudden bleeding into the subarachnoid space, the space between the arachnoid and pia mater (two of the three tissue layers that surround the brain), is known as a subarachnoid hemorrhage. As an aneurysm close to the arachnoid matter ruptures, the blood accumulates in the subarachnoid space. 

In 85 percent of cases, a congenital cerebral saccular or berry aneurysm ruptures, causing subarachnoid hemorrhage. Although aneurysmal hemorrhage can occur at any age, the average range is from 40 to 65 years.

A subarachnoid hemorrhage also results in complications such as:

  • Secondary vasospasm
    • Refers to the narrowing of the blood vessels, which further reduces the flow of blood to various areas of the brain and causes ischemia.
    • About 25 percent of people experience symptoms of a transient ischemic attack or an ischemic stroke because of secondary vasospasm, which further results in focal brain ischemia.
    • Incidence of infarction (tissue death due to reduced blood supply) is at its highest between 72 hours and 10 days.
    • The incidence of cerebral vasospasm increases between 1 and 28 days following the first hemorrhage.
  • Meningismus
    • Refers to neck stiffness in association with meningeal irritation.
    • The accumulated blood in the subarachnoid space can cause chemical meningitis and increase intracranial pressure that persists for a few days to weeks.
  • Hydrocephalus
    • Causes persistent headache and loss or impairment of consciousness.
    • Abnormal swelling of the ventricles (brain cavities).
    • Caused by accumulation of the cerebrospinal fluid (CSF). 
    • Blood from the initial bleed or associated surgery can interfere with CSF absorption or flow.
  • Rebleed
    • Possible until the injured vessel is fixed. 
    • Often occurs 24 to 48 hours after the initial bleeding. If left untreated, the risk of additional complications, including death, increases.
    • Without proper medical care, the risk of secondary bleeding is highest in the first two weeks following the first hemorrhage. 
  • Cerebral edema
    • Often known as brain swelling and is a common side effect of any traumatic event that involves brain tissue. 
    • Caused by the shortage of oxygen to brain tissue.


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What are the symptoms of a subarachnoid hemorrhage?

Symptoms of a subarachnoid hemorrhage include:

How to diagnose a subarachnoid hemorrhage

An MRI scan and angiography (MRA) or a CT scan and angiography (CTA) are performed to identify brain aneurysms.

  • The use of CT in the early detection of bleeding in or near the brain is very beneficial. Blood vessel images from CTA are used to identify aneurysms.
  • An MRI is useful for detecting a subarachnoid hemorrhage. 
  • An MRA is a noninvasive study like a CTA that looks at the blood vessels.
  • A lumbar puncture is an invasive procedure to check for blood in the cerebrospinal fluid by inserting a hollow needle into the subarachnoid space of the spinal canal.
  • The gold standard blood vessel test is diagnostic cerebral angiography. It resembles cardiac angiography. In this technique, a catheter is placed into the femoral artery in the leg and then advanced internally into the blood vessels of the neck. Contrast dye is injected after the catheter is positioned, and X-ray images are then captured.

What are the treatment options for a subarachnoid hemorrhage?

The goal of a subarachnoid hemorrhage treatment is to stop bleeding and its recurrence and preserve brain function. 

Surgical treatment

  • Embolization
    • Your aneurysm can be treated with embolization so that it is no longer in danger of bleeding. 
    • Aneurysms are packed with specially crafted platinum coils to stop them from bleeding.
  • Surgical clipping
    • A surgical clip may be used to repair aneurysms that are not suited for coiling or other comparable forms of therapy. 
    • To perform this neurosurgical procedure, the skull is opened (craniotomy), and a metal clip is inserted at the aneurysm's base.

Medical treatment

Physical therapy

  • Subarachnoid hemorrhage often causes neurologic damage, such as weakness or difficulty speaking.
  • Therapists can teach you techniques to help you regain as much physical and mental strength including walking and speaking. 

Lifestyle modifications

  • Stop smoking
  • Eliminate the use of cocaine or other drugs of abuse
  • Limit alcohol consumption
  • Perform regular exercise
  • Consume a healthy diet
  • Maintain a healthy weight
  • Manage underlying health conditions such as hypertension and diabetes
Medically Reviewed on 11/2/2022
Image Source: iStock image

Subarachnoid Hemorrhage: https://www.uclahealth.org/medical-services/neurosurgery/conditions-treated/subarachnoid-hemorrhage

Subarachnoid Hemorrhage: https://www.cedars-sinai.org/health-library/diseases-and-conditions/s/subarachnoid-hemorrhage.html