Introduction to Subarachnoid Hemorrhage

An Introduction

Let me give you a scenario that is seen all too often in hospital emergency rooms and intensive care units. A 55-year-old woman comes in to the emergency room with nausea, vomiting, a stiff neck and "the worse headache of her life." This headache started suddenly as a thunderclap, and is worsened by bright light and loud noise. As time passes, she becomes more confused, eventually becoming unresponsive.

What is Subarachnoid Hemorrhage?

The brain is surrounded by three layers of tissue: the pia mater, the arachnoid mater, and the dura mater. Together, these tissues are known as the meninges. The pia is closest to the brain, and the dura furthest from the brain. While there isn't much space between the dura mater and arachnoid mater, there's much more room between the arachnoid mater and the pia mater. This space, known as the subarachnoid space, is usually filled with cerebrospinal fluid that surrounds and protects the brain.

In subarachnoid hemorrhage (SAH), ruptured vessels lead to bleeding into the subarachnoid space. The blood mixes with the cerebrospinal fluid, and can be irritating to the meninges. Women are more likely than men to suffer subarachnoid hemorrhage. The average age is about 55 years old.

Signs and Symptoms of Subarachnoid Hemorrhage

The phrase "the worst headache of my life" fires off alarm bells for physicians.

While it's true that many things can make the head hurt, and while in fact everyone will at some point have a headache that will be their personal worst, these words warn us that our patient could be suffering from a subarachnoid hemorrhage. This is especially true if the headache comes on all of a sudden.

There are other things about our fictional patient that are concerning for subarachnoid hemorrhage. Her nausea and vomiting are due to increasing pressure in her skull as blood builds up. Her stiff neck is due to her meninges being irritated by something, in this case blood.

Causes of Subarachnoid Hemorrhage

The most common cause of subarachnoid hemorrhage is trauma. Fortunately, this is usually easy to identify just based off someone's immediate history. As a result, the subarachnoid hemorrhage can be recognized and treated as soon as possible.

Excluding trauma, about 80% of SAH is due to the rupture of an aneurysm in the brain. Other possibilities include arteriovenous malformation (AVM) and rare causes like fibromuscular dysplasia, amyloid angiopathy, neoplasms, and moyamoya.

What is an Aneurysm?

An aneurysm is an outpouching of a blood vessel. This usually results in the tissue of the blood vessel being relatively weak in that spot. Aneurysms come in many shapes and sizes, but one of the more common is a berry aneurysm, so named because of their characteristic round shape.

People with connective tissue disorders like Ehler-Danlos syndrome, fibromuscular dysplasia or even polycystic kidney disease have an increased risk of having aneurysms, but it's possible to have an aneurysm without any such risks. Many people have aneurysms that have been with them their entire life, not causing any trouble.

A subarachnoid hemorrhage occurs when an aneurysm ruptures, allowing blood to pour into the subarachnoid space. Berry aneurysms are more likely to rupture if the patient is a smoker, cocaine user, or has high blood pressure. Larger aneurysms are more likely to rupture than smaller aneurysms. The location of the aneurysm is also important. An aneurysm closer to the back of the brain is more likely to rupture than an aneurysm closer to the front. However, the most common locations for aneurysms are in the front of the brain, so bleeds there are actually more common overall.

Prognosis in Subarachnoid Hemorrhage

How someone does after suffering from a subarachnoid hemorrhage depends on several different factors, including how severe the symptoms were initially and the size of the hemorrhage on a CT scan. Overall, the prognosis is very serious. About 51% of patients die. Of those who survive, SAH leads to cognitive impairment about 46% of the time. About one third to one half of surviving patients can return to work in a year, but mood problems, cognitive problems and other subtle deficits can persist.

The serious complications from a subarachnoid hemorrhage make it important that someone be seen as soon as possible. Once in the hospital, they will likely be admitted to an intensive care unit, and may require neurosurgery either immediately or in the near future. For this reason, someone who has a new, sudden and severe headache should go to the nearest emergency department immediately. If there is any diminished consciousness or other neurological impairment, an ambulance should be called.


Ropper AH, Samuels MA. Adams and Victor's Principles of Neurology, 9th ed: The McGraw-Hill Companies, Inc., 2009. McCabe MP, O'Connor EJ.

Braunwald E, Fauci ES, et al. Harrison's Principles of Internal Medicine. 16th ed. 2005.

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