Subdural haematomas generally occur following trauma to the head. The rate of volume increase of the subdural haematoma will determine its timing of presentation as follows:
Acute: presentation within 24 hours of injury. These haematomas always comprise clotted blood and have high density on CT.
Subacute: presentation from 24 hours to 10 days from injury. The original clotted haematoma undergoes lysis over this period of 10-14 days with an increase in liquid and a decrease in the clotted component. There is therefore a reducing radiodensity, often with mixed densities on CT.
Chronic: presenting after 10 days from head injury. As clot lysis continues these become progressively more liquid as time proceeds and the appearances on CT are of reducing radiodensity to hypodense, often with low density/higher density "fluid level". The average duration from head injury to a patient presenting with a chronic subdural haematoma is generally 4-6 weeks. In approximately one third of patients with chronic subdural haematomas, no definite history of head injury/trauma can be elicited.
A high index of suspicion is the key to diagnosis, especially in the elderly, in chronic alcoholics, and patients on anticoagulants.
A preceding history of trauma is not necessary for the diagnosis to be considered.
Consider a subdural haematoma if there is a:
History of headache plus progressive clouding of consciousness, with or without, localizing signs.
Clinical picture of headache, intellectual change, alteration in alertness, and signs of bilateral hemisphere dysfunction.
It is uncommon for marked unilateral focal signs to be present e.g., a dense hemiplegia in an alert patient is unlikely to be due to a subdural haematoma.
Diagnostic errors are common. Most frequent misdiagnosis is stroke.
Younger patients tend to present with raised intracranial pressure/headaches and clouding of consciousness, whereas older patients tend to present with a progressive neurological deficit e.g., hemiparesis rather than raised intracranial pressure.
Although some small haematomas with only mild clinical signs can be treated 'medically', all patients must be referred for neurosurgical opinion.