A haemorrhage between the arachnoid and dura mater. It can be acute, chronic, or acute on chronic. Most cases are chronic, and occur in the elderly after mild trauma (e.g. a fall). Usually a venous bleed.
Epidemiology and aetiology
Vast majority due to trauma, but sometimes can be caused by ↑ICP and brain mets.
- The trauma may be so minor / so long ago that none can be recalled!
The bleed occurs due to damage to the bridging veins. These deliver blood from the brain, through the subdural region and then are attached to the inner surface of the skull. Deceleration/turning / jerking injury moves the brain relative to the skull, and puts pressure on these veins, and can cause them to tear.
- Elderly patients are particularly at risk due to shrinkage of the brain with age as a result of atherosclerosis
Signs and Symptoms
- Symptoms often fluctuate over time, e.g.:
- Personality change
- Other signs include:
- Late signs include focal neurological signs (e.g. unequal pupils, hemiparesis). Typical time from injury to onset of focal symptoms is 63 days!
- CT / MRI – typically a cresent of blood around the outer edge of the brain. Also look for midline shift of brain structures. In acute bleeds, blood will be hyperdense relative to brain tissue. In chronic bleeds, it will be hypodense. There is an intervening period where densities are similar, and visualising a bleed can be difficult.
- In acute-on-chronic bleeds, there may be a hypodense chronic bleed, as well as a hyperdense acute bleed
- Irrigation / evacuation / Burr hole craniostomy – via a burr twist drill – basically a hole is drilled into the skull
- Craniotomy – flap of bone is cut and temporarily left open to relieve high ICP. Used less often that burr hole.
- Try to find cause of trauma – e.g. cause of falls, cataracts etc