SAH: What is the Most Common Cause of a Subarachnoid Hemorrhage?
A subarachnoid hemorrhage (SAH) is bleeding into the space around the brain that can be life-threatening. The most common cause of spontaneous SAH is rupture of a brain aneurysm - accounting for about 80–85% of non-traumatic cases. Early recognition and urgent specialist care are essential.
What Is a Subarachnoid Hemorrhage and What Is the Most Common Cause?
A subarachnoid hemorrhage (SAH) is a serious type of bleeding in the brain that occurs when blood leaks into the subarachnoid space - the area between the brain and the thin membranes that cover it. This space normally contains cerebrospinal fluid, which cushions the brain. When blood enters this area, it increases pressure on the brain and disrupts normal brain function, making SAH a medical emergency.
Because SAH can happen suddenly and without warning, understanding what it is and what most often causes it can help people recognize warning signs and seek urgent care sooner. This article is part of our guide to understanding brain aneurysms. For a complete overview, visit, Brain Aneurysm: What You Should Know.
What Happens in a Subarachnoid Hemorrhage?
In a subarachnoid hemorrhage, bleeding occurs in the space surrounding the brain rather than within the brain tissue itself. This causes a rapid rise in pressure inside the skull and irritates sensitive brain tissues. The classic symptom is a sudden, severe headache often described by patients as “the worst headache of my life.” Other symptoms can include nausea, vomiting, neck stiffness, light sensitivity, confusion, or loss of consciousness.
Because the bleeding is abrupt and severe, SAH requires immediate medical attention to prevent complications such as stroke, loss of consciousness, or life-threatening consequences.
The Most Common Cause: Brain Aneurysm Rupture
The most common cause of spontaneous (non-traumatic) subarachnoid hemorrhage is the rupture of a brain aneurysm.
A brain aneurysm is a weak or thin spot on a blood vessel in the brain that bulges outward like a balloon. These aneurysms most often occur at branching points of arteries in the brain’s blood supply, where mechanical stress on the vessel wall is higher.
When an aneurysm ruptures, blood leaks rapidly into the subarachnoid space, causing SAH. According to medical literature, ruptured aneurysms are responsible for about 80–85% of all non-traumatic subarachnoid hemorrhages.
This makes aneurysm rupture by far the most common cause of spontaneous SAH.
Making Sense of the Statistics
When we talk about SAH causes, there are two broad categories:
Traumatic SAH: Resulting from head injuries such as a fall, accident, or blow to the head.
Spontaneous (non-traumatic) SAH: Occurring without external injury.
In spontaneous SAH, aneurysm rupture accounts for the vast majority - about 80–85% of cases. The remaining 15–20% may result from other vascular abnormalities or rare causes.
Why Brain Aneurysms Rupture
A brain aneurysm may remain silent for years and never cause symptoms. However, certain risk factors make rupture more likely:
High blood pressure (hypertension)
Smoking
Genetic predisposition
Age-related changes in blood vessels
Certain connective tissue disorders
These factors contribute to weakening of the vessel wall. When the pressure inside the vessel becomes too high or the wall becomes too fragile, the aneurysm can rupture.
Other Causes of Subarachnoid Hemorrhage
While aneurysm rupture is the most common cause of spontaneous SAH, other less frequent causes include:
Arteriovenous malformations (AVMs) – Abnormal tangles of blood vessels that can bleed
Intracranial dissection – A tear in a blood vessel wall
Perimesencephalic SAH – A benign type of bleeding around the brainstem without an aneurysm
Bleeding disorders or anticoagulant medications
These other causes account for a small minority of non-traumatic SAH cases.
How Is SAH Different From Other Brain Bleeds?
Unlike other forms of brain bleeding that occur within the brain tissue (such as intracerebral hemorrhage), SAH occurs in the space around the brain. This can lead to sudden pressure effects and irritation of nerves and vessels critical for brain function.
Because SAH often affects previously healthy arteries due to aneurysm rupture, it can come as a complete surprise and progress rapidly.
Why Immediate Care Matters
Subarachnoid hemorrhage is a medical emergency. Without prompt treatment, increased pressure on the brain and blood vessel complications can lead to severe disability or death.
Emergency doctors use imaging tests such as CT scans, MRI, or specialized angiography to confirm SAH and identify the cause. If a ruptured aneurysm is detected, neurointerventional or endovascular treatments may be necessary to stop further bleeding.
The Bigger Picture
Aneurysm-related SAH is a particularly serious form of stroke. Although it represents a smaller proportion of all strokes, its sudden onset and rapid progression make education, prevention, and rapid response crucial.
By understanding that ruptured aneurysms are the most common cause of SAH, patients and families can better appreciate the importance of risk factor management (like controlling blood pressure and avoiding smoking) and the need for urgent action when symptoms occur.
When to See a Brain Aneurysm Specialist in Singapore
If you or a loved one experiences a sudden, severe headache, unexplained neurological symptoms, or has risk factors such as high blood pressure or a family history of brain aneurysms, early evaluation can be life-saving.
At the Supreme Vascular & Interventional Clinic, our compassionate specialist, Dr. Manish Taneja, provides vigiligant imaging, accurate diagnosis, and comprehensive care for brain aneurysms and subarachnoid hemorrhage. Whether you need urgent assessment, ongoing monitoring, or expert guidance, our team is here to help. Schedule a consultation with him today to protect your brain health and gain peace of mind.
Consult a Stroke Specialist in Singapore
Dr. Manish Taneja, is an expert in endovascular and image guided neurointerventional procedures of brain and spine. It's important to find a stroke specialist and doctor you can trust in Singapore. He has special interest in treatment of brain aneurysms, stroke and vascular malformations. Come in for a further evaluation. Arrange an appointment with Dr. Manish Taneja, our neurointervention specialist.
Stroke Resources
Benefits and Differences Between Stroke MRI and CT Scans
To determine if you have suffered from a stroke or have the potential to undergo another one, MRI and CT scans are two types of tests that you can get to see what the status may be.
We've Got You Covered for Specialized Stroke Screening, Prevention, and Management
Imagine heart attacks where the blood flow to your heart is blocked. Similarly, a stroke occurs when the blood flow to your brain is interrupted becoming a “brain attack”, affecting a blood vessel and surrounding brain function. When blood supply does not reach a certain part, brain cells begin to die. Different types of stroke include ischemic strokes or a mini stroke, a TIA (transient ischemic attack). Common risk factors include high blood pressure, which increases strain on the blood vessel and raises the likelihood of a stroke. Symptoms can vary, but may include difficulty in speaking and other changes depending on how blood flow is affected. Understanding risk factors and acting early can make a difference. It’s important to work closely with a specialist to monitor your health and reduce stroke risk.
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Brain Aneurysm Resources
Explore our brain aneurysm resources. Understanding a brain aneurysm often involves learning across several areas.
Put Brain Aneurysm on Your Health Radar
Did you experience the worst headache of your life? Thoughts could be racing through your mind. A brain aneurysm is a weak spot in a blood vessel in the brain that can change over time. The key concern is when an aneurysm ruptures, which can disrupt blood flow, affect brain tissue, and lead to serious brain damage. Controllable conditions like high blood pressure can increase this risk and treatment options can depend on the condition. Surgical clipping is one option that prevents blood from entering the weakened area. In many cases, minimally invasive treatments can also be used to restore normal blood flow and reduce risk. We have created structured guides to help you explore each stage in more detail:
A simple (computed tomography) CT scan could be just what the doctor ordered and the first step in early detection and prevention of a brain aneurysm. Come in for an easy consultation with our brain aneurysm specialist in Singapore to be on your health radar.
Other Health Conditions
The Supreme Vascular and Interventional Clinic is your “go-to” facility for various neurological conditions and treatments. To arrange an appointment with Dr. Manish Taneja, our neurointervention specialist, contact us. You can also call us at (+65) 6904 8084 for a consultation.