What Is a Subdural Hematoma?
A subdural hematoma is a collection of blood outside the brain. It is usually caused by serious head injuries. The bleeding and added pressure on the brain from this condition can be life-threatening. While some may stop on their own and suddenly go away, others need surgical drainage. Sometimes, they are called intracranial hematomas or subdural hemorrhages.
In a subdural hematoma, blood collects between the layers of tissue that surround the brain. The outermost layer is called the dura. When bleeding occurs between the dura and the next layer, the arachnoid membrane, it's called a subdural hematoma.
This bleeding occurs under the skull and outside the brain, not in the brain itself. As blood pools, however, it puts more pressure on the brain causing symptoms. If pressure inside the skull rises to a very high level, a subdural hematoma can lead to unconsciousness and death.
Subdural vs. epidural hematoma
Like a subdural hematoma, an epidural hematoma occurs when blood pools in the cranial tissue outside the brain. But in an epidural hematoma, the blood collects outside the dura, the outermost layer of this tissue. It usually requires a more forceful blow to the head to create this type of injury. Epidural hematomas are less common than subdural hematomas and most often occur in young adults.
Epidural hematomas also tend to be more sudden than subdural bleeds. If you have an epidural hematoma, you will probably briefly lose consciousness. Other symptoms include headaches, drowsiness, vomiting and seizures. One of your pupils may also dilate, or become larger, a symptom known as a “blown pupil.” It is very important to get treatment for an epidural hematoma as quickly as possible, as the condition can become life-threatening or even fatal as it progresses.
Subdural Hematoma Symptoms
Symptoms of a subdural hematoma mostly depend on the rate of bleeding.
In head injuries with sudden, serious bleeding that causes a subdural hematoma, a person may pass out right away or even go into a coma.
But other times, a person may appear normal for days after a head injury, only to 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.
The general symptoms of a subdural hematoma include:
- Change in behavior
- Nausea and vomiting
- Lethargy or excessive drowsiness
- Unequal pupil size
- Loss of movement on the opposite side of your body as the head injury
- Enlarged head in babies
- Memory loss
- Slurred speech
- Vision changes
Worsening symptoms of subdural hematomas can include:
- Breathing problems
- Loss of consciousness
The symptoms and their severity will vary depending on your age, underlying medical conditions, how large the bleed is, and what type of subdural hematoma you have.
Acute subdural hematoma
Acute subdural hematomas are most often associated with head trauma. After a blow to the skull, veins below the dura matter might rupture, causing pressure on the brain. Symptoms such as confusion, dizziness, nausea, or loss of consciousness appear within hours or even minutes of the injury. People with acute subdural hematomas need medical attention as quickly as possible.
Subacute subdural hematoma
In people with subacute subdural hematomas, bleeding under the dura matter is more gradual. These bleeds are usually caused by a head injury, but the symptoms, such as vomiting and intense headaches, emerge over days or even weeks, rather than in the immediate aftermath. The condition is still dangerous and may require treatment, but it is not as deadly as an acute subdural hematoma.
Chronic subdural hematoma
Chronic subdural hematomas are most likely to occur in older adults who experience natural brain atrophy. As you age, your brain shrinks slightly, which can cause the blood vessels under the dura membrane to weaken. These delicate vessels might begin to leak slowly on their own, after a minor blow to the head, or as a side effect of taking certain medications.
Symptoms of chronic subdural hematomas usually develop slowly. They can be subtle and easily mistaken for other conditions, such as brain tumor, stroke, or dementia in older people. The symptoms include confusion, difficulty swallowing, trouble walking, drowsiness, and numbness in your arms, legs, or face. In some cases, you may not experience any symptoms at all.
If you think you might have a chronic subdural hematoma, you should have your doctor check for one, as the condition will not go away on its own and can be life-threatening if left untreated.
Some people who have a subdural hematoma may undergo a period of apparently normal functioning between the initial head injury and the onset of symptoms. During this time, blood continues to pool in the cranial tissue. This is known as the lucid interval, and it was once believed to only occur in cases of epidural hematoma. But now it's recognized as part of many people's subdural hematoma experience. Unlike the lucid interval in epidural hematomas, which typically lasts 4 hours or less, there is no upper limit to how long it can last in subdural hematoma cases.
Subdural Hematoma Causes
Subdural hematomas are usually caused by a head injury 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 who play contact sports, such as (American) football, boxing, or mixed martial arts (MMA) are especially at risk for this condition. Newborn infants are also at risk, as their skulls are still soft and pliable. They may experience subdural hematoma as a result of a traumatic birth or in cases of “shaken baby syndrome.”
People with a bleeding disorder or those who take blood thinners are also more likely to develop a subdural hematoma. A relatively minor head injury can cause the condition in people with a bleeding tendency. Finally, people with alcohol use disorder have a higher risk of developing a subdural hematoma, as alcohol can cause the brain to shrink, weakening the blood vessels in the tissues surrounding it.
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 show up for several days or weeks.
Elderly people are at a higher risk for chronic subdural hematoma because natural age-related brain shrinkage causes these tiny veins to stretch and become more vulnerable to tearing.
Subdural Hematoma Diagnosis
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 better than CT at 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. A special dye is then injected, and an X-ray screen shows blood flow through the arteries and veins.
Subdural Hematoma Treatment
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. They often perform repeated head imaging tests to monitor whether the subdural hematoma is improving.
People with severe subdural hematomas are often seriously ill, requiring machine-supported breathing and other forms of life support. More 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 to allow the injured brain to expand and swell without permanent damage. Craniectomy is not often used to treat subdural hematoma. Although they are often lifesaving, these decompression surgeries still carry risks. Some potential complications include blood clots, water on the brain (hydrocephalus), and an increased risk of cranial bleeding or infection, such as meningitis.
If a person has a bleeding problem or is taking blood thinners, doctors may take measures to improve blood clotting. This can include prescribing medicines or administering blood products, and the reversal of any blood thinners, when possible. They may also prescribe other medications to help reduce swelling or pressure in the brain or control seizures.
Can you survive a subdural hematoma without surgery?
The short answer is, yes. If you have a very small subdural hematoma, even an acute one, your doctor may recommend letting it heal on its own with careful observation. That's because any type of brain procedure carries risks, and in some cases, the risk of operating may be greater than allowing your body to mend itself. But you should always let an expert make this call.
Subdural Hematoma Complications
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.
Subdural Hematoma Outlook
Your health outlook after a 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.
The survival rate for subdural hematomas varies widely, depending on the type. Acute subdural hematomas tend to be the most dangerous, with average mortality rates somewhere around 66%. One study on life expectancy after subdural hematoma found that after a year, the mortality rate for chronic subdural hematoma was up to 32%. This could be due to other factors, such as age.
Your prognosis is best if your subdural hematoma is chronic, you deal with few symptoms, and you didn’t lose consciousness after your initial head injury.
Most of your recovery occurs within 3-6 months of injury. While some additional recovery is possible after that, you may never completely recover from a subdural hematoma, especially a severe acute one. Many people continue to experience neurologic symptoms and have a higher risk of seizures. However, going to occupational and physical therapy and joining a local support group can help you maintain a high quality of life.
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.
Subdural Hematoma Prevention
The best way to prevent a subdural hematoma is to prevent head injuries. This can mean taking some of the following steps:
- Wearing a helmet when riding a bike or motorcycle
- Wearing appropriate head protection when participating in contact sports, such as football or boxing
- Keeping your seatbelt buckled when riding in a car
- Avoiding and removing tripping hazards in your home
- Resting after a potential concussion
- Drinking responsibly
- Talking to your health care provider about whether your prescriptions put you at higher risk of getting a subdural hematoma
Subdural hematomas are potentially life-threatening and should be taken very seriously. If you experience a head injury, especially one that causes you to lose consciousness, seek medical evaluation right away. Continue to watch for symptoms for days or weeks after a blow to the head whether your doctor finds an initial bleed or not.
Subdural Hematoma FAQs
What is the survival rate of a subdural hematoma?
The survival rate for people who experience a subdural hematoma can vary depending on what type of bleed they have. If you have an acute subdural hematoma, your chances of survival are 10%-50%, depending on how soon you get treatment. You have a higher chance of surviving a chronic subdural hematoma, but this type of bleed comes with a higher chance of recurring.
What is the most common cause of a subdural hematoma?
Most subdural hematomas are caused by head injuries. The easiest ways to prevent them are to avoid high-impact sports and take appropriate safety measures when driving or riding a bike.