Subdural Haematoma

What are the meninges and the subdural space?

The meninges are the protective lining that surround and enclose the brain within the skull, and the spinal cord within the vertebral column. (The vertebral column is the name given to the backbone, the column of bony vertebrae in the back that sit one on top of the other to surround and protect the spinal cord.)

There are three layers of meninges:

• The outermost layer that lies next to the skull or the vertebral column is called the dura mater.
• The middle layer is called the arachnoid mater.
• The inner layer that is closest to the brain or the spinal cord is called the pia mater.

There are also three 'spaces' between the layers of meninges:

• The epidural space is the space between the vertebral column and the dura mater. (There is only a 'potential' epidural space in the skull.)
• The subdural space is the space between the dura mater and the arachnoid mater.
• The subarachnoid space is the space between the arachnoid mater and pia mater.

What is a subdural haematoma and what causes it?

A subdural haematoma is a collection of clotting blood that forms in the subdural space. It usually occurs because of an injury to the head. For example, someone falling and hitting their head, or being involved in an accident that causes a head injury. The head injury can damage and cause bleeding from one or more blood vessels near to or within the subdural space. The blood from the bleeding blood vessel(s) collects in the subdural space. The head injury may also cause injury to the brain tissue at the same time.

Sometimes a subdural haematoma can be due to spontaneous bleeding. That is, there is no injury that causes the bleeding. This can happen if you have a problem with the clotting of your blood. For example, if you take medication to 'thin the blood' (anticoagulation) or if your blood is ‘thinner’ for another reason (such as with haemophilia or thrombocytopenia). Another rare cause of a subdural haematoma is bleeding from an abnormal blood vessel within the brain called an aneurysm. An aneurysm is a balloon-like swelling in the wall of an artery. This makes the artery wall weaker and it can tear and cause bleeding.

A subdural haematoma may be:

• An acute subdural haematoma - the blood collects quickly after a head injury; symptoms can occur immediately or within hours.
• A chronic subdural haematoma - the blood collects more slowly after a head injury; symptoms can occur 2-3 weeks after the initial injury.

Who gets a subdural haematoma?

A subdural haematoma can occur at any age. However, there are certain groups of people who are more at risk of developing a subdural haematoma after a head injury.

• Elderly people. In people over the age of 60, some of the blood vessels around the brain can become a little weaker and more susceptible to injury and bleeding. As we get older, the brain can also 'shrink' a little inside the skull which can put extra 'strain' on these blood vessels and make them more likely to bleed after a head injury.
• People who misuse alcohol. Alcohol misuse can affect the clotting of the blood, making the blood 'thinner' and making bleeding more likely to occur. It can also cause a similar 'shrinking' of the brain that happens as we get older, putting an extra strain on blood vessels and making them more likely to bleed. People who misuse alcohol are also more likely to fall over and hit their head.
• People on anticoagulation treatment. Anticoagulation treatment to thin the blood (including treatment with aspirin or warfarin) can also make a subdural haematoma more likely after a head injury.
• Infants. In the infant brain, a subdural haematoma can be caused by tearing of veins in the subdural space. This may be caused by physical abuse to the child, the so-called 'shaken baby syndrome'. However, it should be noted that not all subdural haematomas in children are caused by physical abuse to the child and physical abuse should not be assumed. A subdural haematoma can also occur for other reasons in a child, for example, due to an accidental head injury.

How common is a subdural haematoma?

Head injuries are often minor and not serious. Most people with a minor head injury will not get a subdural haematoma. However, a subdural haematoma occurs in about one in three people with a severe head injury. For the reasons described above, it is more common with increasing age.

What are the symptoms of a subdural haematoma?

The brain, and the meninges covering it, fit tightly within the skull. If a subdural haematoma forms, the clotting blood that accumulates occupies space within the skull and pushes on (or squashes) the brain tissue. It also causes the pressure within the skull (the intracranial pressure) to increase. This increase in pressure can mean that the brain is not able to function normally and symptoms can start to develop. However, sometimes small subdural haematomas do not produce any symptoms.

Acute subdural haematoma

The symptoms of an acute subdural haematoma usually appear soon after a head injury (from minutes to within 24-48 hours). You may lose consciousness at the time of the head injury but this does not always happen. You may have a 'lucid interval' of a few hours after the head injury where you appear relatively well and normal but you can later deteriorate and lose consciousness as the haematoma forms. If you do not lose consciousness, you may experience drowsiness or a severe headache. You may also have nausea and/or vomiting. You may also become confused and may develop weakness of the limbs on one side of your body and speech difficulties. Sometimes a seizure (a fit) can occur.

Chronic subdural haematoma

The symptoms of a chronic subdural haematoma do not usually appear until about 2-3 weeks after the initial head injury (in some people it may be months). In fact, often the injury may be relatively trivial or forgotten. In particular, this may occur in an older person taking anticoagulant medication, or in someone who misuses alcohol.

The symptoms tend to progress gradually. There is often loss of appetite, nausea and/or vomiting. There is usually a headache that becomes progressively more severe. You (or others) may notice gradually worsening weakness of the limbs on one side of your body, speech difficulties or visual disturbance. There may also be increasing drowsiness and confusion or personality changes. Sometimes a seizure (a fit) can occur. A chronic subdural haematoma can be difficult to detect and can go unrecognised for some time.

What tests are needed for a suspected subdural haematoma?

Someone with a suspected subdural haematoma should be seen in a hospital. It is a serious condition and emergency treatment may be needed. The doctors and nurses will be able to perform a full examination to look for signs of a possible subdural haematoma and also signs of any other injury that you may have. They will be able to check your level of consciousness, look for any signs of limb weakness and also examine the back of your eyes to look for any signs of raised pressure within the skull.

Blood tests may be taken to look for other possible reasons for confusion and/or loss of consciousness. Blood tests may also show any problems with blood clotting/abnormally 'thin' blood. A CT scan of the head (or sometimes an MRI scan) is good at detecting a subdural haematoma. You may also need other scans or X-rays depending on whether any other injuries are suspected.

What is the treatment for a subdural haematoma?

The treatment will depend on whether the haematoma is acute or chronic, the size of the haematoma, and the symptoms that you may have.

If there is a small, acute subdural haematoma that is not producing any symptoms (or the symptoms are not severe), it can sometimes be treated just by careful monitoring and observation. The blood clot is left to re-absorb (clear) by itself. Repeated physical examinations are usually carried to assess your level of consciousness and look for any symptoms that may appear such as headache, limb weakness, etc. Repeated CT scanning may also be used to ensure that the haematoma is not getting any bigger. Surgery is usually needed to treat a subdural haematoma if symptoms start to appear and the person's condition deteriorates.

Surgery may be used at the outset if there is a large subdural haematoma, there are signs of raised pressure within the skull or there are problems such as limb weakness or speech disturbance. Surgery involves either making 'burr holes' in the skull or an operation called a craniotomy.

Burr holes are small holes that are drilled through the skull over the area where the subdural haematoma has formed. They allow the blood to be removed or 'sucked out' through the holes. Stitches or staples are then used to close the burr holes. A craniotomy is where a portion of the skull is removed so that the brain and meninges are exposed. It can relieve any raised pressure inside the skull and also means that the clotting blood in the subdural space can be removed. The section of skull that was removed is then replaced and fixed back in place.

What is the prognosis (outlook) for subdural haematoma?

This can depend on the severity of the initial head injury that caused the subdural haematoma. Many people with a small subdural haematoma can make a quick and full recovery. If there is no damage to underlying brain tissue, 4 out of 5 people with an acute subdural haematoma survive. If there is also damage to the brain tissue, the outlook is usually worse than if there is no brain tissue damage. Some people die as a result of the effects of a large haematoma on the brain.

Infection or meningitis can be a complication after surgery for subdural haematoma. Sometimes the pressure effects on the brain due to a subdural haematoma can lead to permanent damage such as weakness of the limbs, speech impairment or memory problems. If this is the case, rehabilitation and support from physiotherapists, occupational therapists and speech therapists may help to improve a person's function in the long term.

Can a subdural haematoma be prevented?

If you are taking anticoagulant medication such as warfarin, make sure that you attend for your regular blood tests to check that you are taking the correct dose and that your blood is not becoming too 'thin'. If your blood becomes too thin, you are more likely to experience a subdural haematoma if you fall over and hit your head.

Everyone should also take care to try to reduce the risk of falling and hitting your head. This may include simple measures around the home such as removing loose rugs and other obstacles. People who have problems with the amount of alcohol that they drink may also wish to seek help to cut down on their drinking.

If you or your children take part in sports such as cycling, roller-blading, skiing, boxing or skate-boarding, you should make sure that you wear a helmet/protective head-gear so as to reduce the risk of serious head injury.