Subdural Hematoma

Medically Reviewed by Carol DerSarkissian, MD on November 02, 2022

A subdural hematoma is a collection of blood outside the brain. They’re usually caused by serious head injuries. Bleeding and added pressure on the brain from a subdural hematoma can be life-threatening. Some stop and go away suddenly; others need surgical drainage.

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 is under the skull and outside the brain, not in the brain itself. As blood pools, however, it puts more pressure on the brain. The pressure on the brain causes symptoms. If pressure inside the skull rises to a very high level, a subdural hematoma can lead to unconsciousness and death.

Symptoms of subdural hematoma depend mostly on the rate of bleeding:

  • In head injuries with sudden, serious bleeding causing a subdural hematoma, a person may pass out right away or even go into a coma.
  • A person may appear normal for days after a head injury, but slowly become confused and then pass out 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 2 weeks after the bleeding starts. 

Symptoms of subdural hematoma include:

The symptoms you have depends on a few things. Besides the size of the subdural hematoma, your age and other medical conditions can affect how your body responds to. Slow-growing subdural hematomas are more common in older people. They can bring on subtle personality changes and apathy.

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 a 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.

People who get 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 the neck and brain. Special dye is then injected, and an X-ray screen shows blood flow through the arteries and veins.

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.

Some subdural hematomas can bring on serious complications, including coma or even death. This can happen if the hematoma is not treated, or even sometimes after treatment. Possible complications include:

  • Brain herniation. Pressure in your brain can move tissue away from where it’s supposed to be. This can lead to death.
  • More bleeding events. If you’re older, you’re at a high risk of another hemorrhage as you recover from the first one, especially if you have a head injury.
  • Seizures. You may have seizures, even if you’ve treated your hematoma.

Your health outlook after your subdural hematoma depends on how old you are, how severe your head injury was, and how quickly you got treatment. The younger you are, the higher your chance of survival. 

Your prognosis is best if your subdural hematomas are chronic, you deal with few symptoms, and you didn’t lose consciousness after your head injury. 

Older adults are at the highest risk of another brain bleed after a subdural hematoma. Older brains don’t expand and fill the space left after a hematoma. With more space between the brain and skull, your chance of bleeding goes up, even with a minor injury to the head.  

Show Sources


Aminoff, M. Neurology and General Medicine, Churchill Livingstone, 2008.

eMedicine:  "Subdural Hematoma."

Cleveland Clinic: “Subdural Hematoma.”

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