What is a Subdural Haematoma

What is a haematoma?

When blood leaks from blood vessels following injury, this is a haematoma. We colloquially call this a bruise in other parts of the body. Imagine a subdural haematoma as a serious bruise occurring in the protective layers of the brain, right between the spiderweb arachnoid mater and the thicker dura mater underneath the skull. The problem is that the blood fills this small space and puts pressure on the brain, squashing it until the patient feels a severe headache. This can damage the brain and eventually be fatal.

The importance of understanding subdural haematoma

A subdural haematoma is a common result of severe head injury. It can also develop after milder injury: a recent study found that 20% of patients over 65 who experienced a mild head injury developed a subdural hematoma.¹

A subdural haematoma can occur at any age following head injury, including in children experiencing abuse and as a common consequence of ‘shaken baby syndrome’. Because this condition can result in death, it is important to be aware of the symptoms and risks, and get treatment quickly.

Symptoms 

Common symptoms of a subdural haematoma include:

• Worsening headache
• Feeling nauseous or vomiting
• Drowsiness
• Confusion
• Slurred speech
• Mood changes e.g. aggression
• Weakness or numbness of arms and legs
• Seizures (particularly with chronic subdural haematoma)²
• Low iron or anaemia (due to blood loss, with unnoticed chronic subdural haematoma)³
• Lethargy, breathing abnormalities and disturbed feeding in infants.⁴

Causes of subdural haematoma

Traumatic subdural haematoma 

Acute

In medicine, ‘acute’ means sudden and short-term. Usually, acute subdural haematoma occurs following severe head injury. The impact to the head damages blood vessels in the area between the dura and the arachnoid layers protecting the brain, which leak blood into this small gap. This blood puts pressure on the brain and eventually causes damage. The bleeding and consequent symptoms happen in a few hours.

Chronic

However, following minor head injuries the haematoma can form slowly. When the pooling of blood in the subdural area takes at least 4 days, this is ‘subacute’, and when the haematoma occurs 21 or more days after injury, this is ‘chronic’. Chronic subdural haematoma is more likely to go unnoticed and is more common in the elderly and patients with particular risk factors (as explained below). The patient might have experienced a trivial head impact, mild injury or occasionally severe injury with delayed bleeding. The incidence of chronic subdural haematoma is  1-5.3 cases per 100,000 population.⁵

Non-traumatic subdural haematoma

Rarely, a subdural haematoma can occur spontaneously, with no traumatic cause. For example, a seemingly healthy 31-year-old with no evidence of any head injury, nor any particular risk factors, spontaneously experienced a subdural haematoma on both sides of the head, causing severe headache. The blood was drained away and following treatment he was able to leave hospital in a few days and fully recover.⁶

Another example comes from a 22-year-old infected with Covid-19 who passed out after experiencing a severe headache and then required surgery to remove a subdural haematoma. She was able to leave hospital with no long-term effects once recovered from Covid-19.⁷

Intracranial hypotension (low pressure under the skull)

One possible cause of subdural haematoma is low pressure in the protective spaces inside the skull, called intracranial hypotension, which can be caused by a leakage of the cerebrospinal fluid that maintains and  protects the brain and spinal cord. This could happen spontaneously, due to a genetic defect, or the leak could be caused by treatments like lumbar puncture, spinal anaesthesia or back surgery.²

Risk factors

There are several factors which increase the risk of developing subdural haematoma:

• Previous head injuries
• Blood-thinning medication (anticoagulant or antiplatelet medication) e.g. warfarin which increases your risk of bleeding due to decreased blood clotting⁸
• Tangled or poorly-developed blood vessels - ‘arteriovenous malformation’ - which can weaken and burst to leak blood, causing haemorrhage or haematoma
• High blood pressure (hypertension) increases both the risk of developing a subdural haematoma and impeding recovery.
• Intracranial hypotension, low pressure under the skull, caused by leaking cerebrospinal fluid which could be due to an error after spinal surgery, or after a lumbar puncture 
• Older age significantly links to a higher risk of subdural haematoma and a worse outcome.⁹

Diagnosis

Recognising the signs

Some patients may quickly pass out and enter a coma if bleeding is severe following a serious head injury. However, others may seem normal and gradually present with symptoms such as confusion and headache. The symptoms can appear within hours, days or weeks, depending on how slowly the haematoma develops. It is therefore important to monitor someone’s well being for some time following a head injury.

Brain scans

Subdural haematoma is diagnosed via a brain scan to show the bleeding in the area between the dura mater and arachnoid membrane.

Computerised tomography (CT) scans are often used, which utilise X-rays to create a computerised image of the area of interest.

Alternatively magnetic resonance imaging (MRI) can be used; this produces better images for more accurate diagnosis, but MRI scanners are more expensive so less widely available. MRI uses a very strong magnet along with radio waves to create a detailed image.
Magnetic resonance venography (MRV) is similar to MRI but specifically examines the veins without the other tissues being clearly visible - an injection of a contrast dye makes the blood vessels clearly visible. MRV is effective at detecting blood clots, blood vessel abnormalities and bleeding. 

Treatment

Non-surgical management

A small acute subdural haematoma does not always need surgery. The patient should be closely monitored for symptoms and  ideally given regular scans to check for worsening haematoma. If they remain symptom-free it may resolve on its own, or with the use of medication to reduce the risk of the haematoma worsening.

Medication 

Low-dose statins such as atorvastatin may be prescribed for several weeks, e.g. 20mg per day for 8 weeks. This reduces the production of cholesterol in the body, reducing fatty build ups in arteries and therefore making strokes or burst blood vessels less likely. Corticosteroids such as dexamethasone may also be prescribed to reduce inflammation.

Angiotensin-converting enzyme inhibitors (ACE inhibitors) reduce the risk of subdural haematoma recurrence. These lower blood pressure by relaxing blood vessels and could reduce the risk for subdural haematoma happening in the first place.¹⁰

Surgery

Quicker surgery saves lives

Quickly removing the blood clot significantly helps patients’ survival. A study of over 1000 patients with severe head injury found that surgical clot removal within 4 hours led to only 30% mortality and 65% ‘functional survival’ (recovering to health without serious brain damage or disability), compared to the overall rates of 66% mortality and only 19% having functional recovery in the whole sample.¹¹

Craniotomy

Craniotomy is the main treatment for acute subdural haematoma after a severe head injury. The surgeon cuts into the skull and creates a flap to access the subdural space, then the pool of blood is drained with suction and washed out with water (irrigation). Craniotomy is necessary when the pool of blood is large or partly solidified. The removed bone is then replaced. Patients usually recover within 6-8 weeks.

Burr hole

Burr holes are the main treatment for subacute or chronic subdural haematoma, often after a minor injury. A small hole is drilled into the skull to allow access to the subdural space. A tube is inserted through the small burr hole, and the blood leakage is then drained to remove the pressure on the brain. Burr hole surgery is quicker and cheaper than craniotomy and leads to better patient recovery, so this treatment is preferred if it is sufficient to remove the haematoma.¹²

Rehabilitation

Following subdural haematoma, patients may experience brain damage resulting in speech problems, muscle weakness or other issues. Many patients may need rehabilitation to aid their recovery.

• Physiotherapists may help retrain patients to improve their coordination or strengthen weak muscles
• Speech therapists may be needed if the patient experiences any speech difficulties
• Occupational therapists help patients deal with everyday tasks such as cooking, cleaning or work-related activities
• Cognitive rehabilitation such as memory training or social skills therapy might help patients with cognitive issues after subdural haematoma.

Risk reduction

• Using seatbelts is a key preventative measure to reduce the risk of serious head injury from car  accidents
• Using helmets helps prevent head injury in high-risk environments or activities
• Avoiding risky sports or activities such as heading the ball 
• Regular health check-ups, including maintaining healthy blood pressure. 

FAQs

What is the main cause of subdural haematoma?

The most common cause of subdural haematoma is severe head injury e.g. head impact caused by a fall or car collision.

What happens if you have a subdural haematoma?

Patients experience severe headaches and other symptoms such as confusion, nausea or seizures. The increasing pressure on the brain can cause coma or death.

Can you fully recover from a subdural haematoma?

Some patients are able to fully recover from a subdural haematoma. Many factors affect recovery such as age, severity of head injury, speed of treatment to drain the haematoma, and blood pressure. Wilberger et al. (1991) studied over 1000 patients with acute subdural haematoma and found a 66% mortality rate, with 19% functional recovery.¹¹

How is a subdural haematoma fixed?

Usually a subdural haematoma is treated by draining the pool of blood via craniotomy (temporarily removing a flap of skull to then clean the affected area) or burr hole (drilling a small hole and inserting a tube to drain the blood). Patients are also given medication and rehabilitation.

Is a subdural haematoma a stroke?

A stroke involves a blockage in a blood vessel in the brain, cutting off the supply of blood and oxygen to a brain area, causing brain cells to die. On the other hand, subdural haematoma is leakage of blood just outside of the brain, which can damage the brain due to the pressure it causes. A subdural haematoma can sometimes lead to a stroke occurring.

Summary

A subdural haematoma is bleeding outside of the brain, in the space between the hard ‘dura mater’ protective layer and the thinner ‘arachnoid’ protective layer of the brain. The pooling of blood puts pressure on the brain which can cause brain damage. This may happen within hours of a severe head injury (acute subdural haematoma) or can take a few days (subacute) or more than three weeks (chronic subdural haematoma). The main symptoms are severe headache, confusion, slurring speech, vomiting or unconsciousness. This can be effectively treated by surgery to remove the haematoma from the subdural space.

Elena Dennis

MSc Neuroscience University of Sussex
BSc Neuroscience, University College London

Elena is a graduate of MSc Neuroscience and an experienced teacher. Her research has included a clinical project on postural control in dystonia, and research into cellular features of motor neuron disease. She is particularly interested in neurodegenerative diseases such as Alzheimer's, Parkinson's, and progressive movement disorders. She is also interested in autoimmune conditions such as eczema, and understanding the mechanisms and treatments for cancer.

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