Pure subdural haematoma (occurring without detectable subarachnoid haemorrhage) caused by intracranial aneurysm rupture is uncommon and is usually associated with delayed diagnosis and treatment. We describe the case of a 43-year-old man who presented with ongoing headache. Computed tomography and magnetic resonance imaging of the brain revealed subdural haematoma in the left fronto-temporo-parietal region, without subarachnoid haemorrhage. Digital subtraction angiography showed an aneurysm measuring 5 mm in diameter, arising from the distal region of the left middle cerebral artery. During hospitalization, an acute change in mental status accompanied by slurred speech and narcolepsy prompted an emergency CT scan. This revealed an enlargement of the subdural haematoma. The patient underwent an emergency craniotomy, during which a large amount of bloody fluid was evacuated, and the aneurysm was coagulated and resected. The patient had a good outcome without neurological deficit. The incidence, mechanisms and treatment of this condition are discussed.

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