Life-threatening head injuries are generally associated with significant trauma, but blood vessels on the inside of the skull can be torn after relatively minor knocks or falls. The consequent bleeding – an extradural haemorrhage – can lead to a pool of blood forming inside the skull that compresses the blancmange-like brain with catastrophic consequences unless dealt with promptly.

An extradural bleed is one of a handful of emergencies where minutes really do matter and where prompt diagnosis and surgery to open the skull, relieve the pressure and evacuate the clot can mean the difference between a full recovery and irreversible brain damage.

The classic presentation is a person who has developed an increasingly severe headache after apparently recovering from a blow to the head. It is only when the growing pool of blood starts to raise the pressure within the skull and impinge on the brain that the patient starts to take a turn for the worse.

It is a condition that all doctors dread as it easy to miss in the early stages. A falsely reassured concussed rugby player leaves A&E to drown his sorrows with his mates but, unbeknown to him and his doctor, the leaking blood vessel in his skull will soon threaten his life. He goes to bed drunk and is found dead in his room in the morning.

Extradural haemorrhages are the reason that doctors admit people who have been knocked out, even if they are fully conscious on admission. Telltale signs of trouble – worsening headache, vomiting, drowsiness, a rise in blood pressure, a falling pulse and dilation of the pupils – should prompt an urgent CT scan. Small bleeds can be treated conservatively, with the patient being watched. Larger bleeds require evacuation through a hole drilled in the skull.

Patients who are conscious on admission usually recover, but about four out of ten who are in a coma on arrival will die.

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