What is a Subarachnoid Hematoma?

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  • Written By: Synthia L. Rose
  • Edited By: Jenn Walker
  • Last Modified Date: 08 October 2019
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A subarachnoid hematoma is the pooling of blood beneath the second of three cerebral membranes. The brain’s innermost protective lining is called the pia mater, and the outermost lining is known as the dura mater. In between these membranes is the middle, or second, membrane known as the arachnoid. When bleeding occurs in the space under the arachnoid, the hemorrhage is formally referred to as a “subarachnoid hematoma.” This hematoma is considered extremely dangerous and possibly life threatening.

Several hazards can result from a subarachnoid hematoma. Strokes are often linked to these hemorrhages, as are seizures. Besides death, the greatest danger connected to a subarachnoid hematoma is long-term brain damage.

Bleeding beneath the arachnoid can arise from a many triggers. A physical accident that causes trauma to the brain, such as a fall or a car crash, for instance, can lead to a subarachnoid hematoma. This cause is particularly prevalent in vulnerable people, such as children or senior citizens.

The abnormal formation of blood veins in the brain during fetal development — a condition known as arteriovenous malformation — is another trigger. During this malformation, the arteries carrying blood to the brain directly link to veins without the aid of capillaries. This can result in a build up of pressure inside the veins and arteries that can cause them to burst.


Brain aneurysms and the use of medications that thin blood or prevent clotting can lead to subarachnoid hematomas as well. Blood disorders also can result in hematomas, and sometimes, spontaneous subarachnoid hemorrhages can appear with no discernible cause. These are referred to as idiopathic hematomas.

Some demographics are more susceptible to subarachnoid hematomas than others. Women, for example, have more hematomas in the subarachnoid space than men. In addition, those over age 20 and less than age 60 also tend to be more susceptible, according to medical studies. Other people at greater risk for having cerebral hematomas include those with hypertension, fibromuscular dysplasia, or a habit of smoking.

A subarachnoid hematoma doesn’t always have to lead to death. If symptoms are detected early, doctors can attempt to treat the condition. Symptoms include loss of mobility, the loss of consciousness, and nausea. Sometimes, mental confusion, photosensitivity, and sudden vision problems are clues that a hematoma might be present. Doctors say some people with hematomas also experience seizures.

CT scans, ultrasounds, and other neurological tests are used to identify a subarachnoid hematoma. After detection and location, surgeons can attempt to halt the bleeding and relieve cerebral pressure. Sometimes, doctors might need to make a circular incision in the brain and insert coils to repair aneurysms and prevent future bleeding.


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