A subdural hematoma is a collection of blood outside the brain. Subdural hematomas are usually caused by severe head injuries. The bleeding and increased pressure on the brain from a subdural hematoma can be life-threatening. Some subdural hematomas stop and resolve spontaneously; others require surgical drainage.
What Is a Subdural Hematoma?
In a subdural hematoma, blood collects between the layers of tissue that surround the brain. The outermost layer is called the dura. In a subdural hematoma, bleeding occurs between the dura and the next layer, the arachnoid.
The bleeding in a subdural hematoma is under the skull and outside the brain, not in the brain itself. As blood accumulates, however, pressure on the brain increases. The pressure on the brain causes a subdural hematoma's symptoms. If pressure inside the skull rises to very high level, a subdural hematoma can lead to unconsciousness and death.
Causes of Subdural Hematoma
Subdural hematoma is usually caused by a head injury, such as from a fall, motor vehicle collision, or an assault. The sudden blow to the head tears blood vessels that run along the surface of the brain. This is referred to as an acute subdural hematoma.
People with a bleeding disorder and people who take blood thinners are more likely to develop a subdural hematoma. A relatively minor head injury can cause subdural hematoma in people with a bleeding tendency.
In a chronic subdural hematoma, small veins on the outer surface of the brain may tear, causing bleeding in the subdural space. Symptoms may not be apparent for several days or weeks. Elderly people are at higher risk for chronic subdural hematoma because brain shrinkage causes these tiny veins to be more stretched and more vulnerable to tearing.
Symptoms of Subdural Hematoma
Symptoms of subdural hematoma depend mostly on the rate of bleeding:
- In head injuries with sudden, severe bleeding causing a subdural hematoma, a person may lose consciousness and become comatose immediately.
- A person may appear normal for days after a head injury, but slowly become confused and then unconscious several days later. This results from a slower rate of bleeding, causing a slowly enlarging subdural hematoma.
- In very slow-growing subdural hematomas, there may be no noticeable symptoms for more than two weeks after the bleeding starts.
Symptoms of subdural hematoma can include:
- Change in behavior
- Nausea and vomiting
- Lethargy or excessive drowsiness
People may vary widely in their symptoms of subdural hematoma. Besides the size of the subdural hematoma, a person's age and other medical conditions can affect the response to having a subdural hematoma.
Diagnosis of Subdural Hematoma
People who come to medical attention after a head injury often undergo head imaging, usually with computed tomography (CT scan) or magnetic resonance imaging (MRI scan). These tests create images of the interior of the skull, usually detecting any subdural hematoma present. MRI is slightly superior to CT in detecting subdural hematoma, but CT is faster and more readily available.
Rarely, angiography may be used to diagnose subdural hematoma. During angiography (angiogram), a catheter is inserted through an artery in the groin and threaded into the arteries of he neck and brain. Special dye is then injected, and an X-ray screen shows blood flow through the arteries and veins.
Treatment of Subdural Hematoma
Treatment of subdural hematomas depends on their severity. Treatment can range from watchful waiting to brain surgery.
In small subdural hematomas with mild symptoms, doctors may recommend no specific treatment other than observation. Repeated head imaging tests are often performed to monitor whether the subdural hematoma is improving.
More severe or dangerous subdural hematomas require surgery to reduce the pressure on the brain. Surgeons can use various techniques to treat subdural hematomas:
- Burr hole trephination. A hole is drilled in the skull over the area of the subdural hematoma, and the blood is suctioned out through the hole.
- Craniotomy. A larger section of the skull is removed, to allow better access to the subdural hematoma and reduce pressure. The removed skull is replaced shortly after the procedure.
- Craniectomy. A section of the skull is removed for an extended period of time, to allow the injured brain to expand and swell without permanent damage. Craniectomy is not often used to treat subdural hematoma.
People with severe subdural hematomas are often seriously ill, requiring machine-supported breathing and other forms of life support.
If a person has a bleeding problem or is taking blood thinners, measures should be taken to improve blood clotting. This may include giving medicines or blood products, and reversal of any blood thinners, when possible. Other medications to help reduce swelling or pressure in the brain or control seizures may also be used.