What is chronic subdural haematoma?
A chronic subdural haematoma (cSDH) is a collection of old (‘chronic’) blood (‘haematoma’) that forms between the skull and the surface of the brain (‘subdural space’).
It normally occurs in people over the age of 60, those who take medication to thin blood and/or those who have other significant health issues.
A cSDH is different to a ‘hygroma’, which is a collection of brain water (‘Cerebrospinal Fluid’) in the subdural space and different to an ‘Acute Subdural Haematoma’, which is a collection of fresh blood.
What problems can it cause and how is it diagnosed?
Most cSDH are small and do not cause any problems; when found they may be termed ‘incidental’ or ‘asymptomatic’.
If symptoms arise, they generally do so slowly, over days to weeks, as the haematoma slowly grows and exerts pressure. These are best thought of as a ‘slowly evolving stroke’ and include:
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Headache
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Worsening balance or mobility
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Weakness in the hands, arms and/or leg on one side of the body
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Nausea and/or Vomiting
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Difficulty speaking or communicating
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Confusion
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Drowsiness
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As cSDH mostly occur in older people (>60) with other health conditions, it may be some of these symptoms (e.g. difficulty walking or confusion) are present normally. The key feature to look for is the gradual worsening of these symptoms over days to weeks.
Occasionally, cSDH can cause sudden symptoms. This may be through a seizure (an abnormal discharge of electricity causing a fit).
Whilst ‘confusion’ is often a symptom that leads to a brain scan and the identification of a cSDH, if it occurs on its own without any other symptoms of a cSDH, it is unlikely the cSDH is the cause. In this case other tests may be needed to consider other causes, such as a chest or urine infection which more commonly cause confusion in the elderly. Symptoms such as arm or leg weakness, speech difficulties or headaches are a better indicator that the cSDH is causing a problem.
When suspected a cSDH is diagnosed with a brain scan. This is typically a CT scan, as they are more readily available and quicker to perform.
Why has it occurred?
We don’t fully understand why cSDH form.
A common idea is that an injury to the head has caused a bleed in the subdural space. The body has then failed to clear this blood and instead sealed it off within a membrane, which slowly draws in fluid.
It is thought that older people (>60) with other health conditions are more susceptible to developing a cSDH because naturally the brain gets smaller with age and/or other health conditions. This means the subdural space is larger (as the skull remains the same size) and the blood vessels that cross the gap become stretched. These blood vessels are then more prone to tearing with even minor injuries such as ‘banging the underside of a cupboard’. These groups are also more likely to suffer falls with head injuries, and/or have other conditions or medication that cause the blood to clot slowly.
However, it is unlikely this is a complete explanation: only 2 in 3 people can remember having any head injury prior to their cSDH and even amongst those who did, only 1 in 3 were found to have fresh blood (an Acute Subdural Haematoma) in their subdural space as a result.
How is it treated?
Some cSDH, particularly those without any symptoms (or perhaps very minor symptoms such as mild headaches) do not require treatment. This is because there is a chance that the cSDH can resolve without treatment.
For symptomatic cSDH, the most common treatment is an operation to remove the cSDH. This is generally well tolerated, even in those who are elderly or frail and can lead to significant improvement in symptoms.
In some hospitals a newer procedure to block off the blood vessels that supply the cSDH can be performed. This is known as a ‘middle meningeal artery embolization’. However, its role is less certain with much research ongoing. It is therefore not widely used currently.