A subdural haematoma is a collection of blood deep to the dural layer of the meninges. The blood is not within the substance of the brain and is therefore called an ‘extra-axial’ or ‘extrinsic’ lesion. They can be unilateral or bilateral.


Subdural haematomas can be classified in terms of their age:
  • Acute
  • Subacute
  • Chronic

Although the collection of blood is within the same anatomical compartment, acute and chronic subdurals have important differences in terms of their mechanisms, associated clinical features and management.


  • Incidence: 3.00 cases per 100,000 person-years
  • Peak incidence: 70+ years
  • Sex ratio: more common in males 2:1
Condition Relative
Subdural haemorrhage1
Central venous thrombosis0.28
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Clinical features

Acute subdural haematoma

An acute subdural haematoma is a collection of fresh blood within the subdural space and is most commonly caused by high-impact trauma. Since it is associated with high-impact injuries, there is often other brain underlying brain injuries.

There is a spectrum of severity of symptoms and presentation depending on the size of the compressive acute subdural haematoma and the associated injuries. Presentation ranges from an incidental finding in trauma to severe coma and coning due to herniation.

Chronic subdural haematoma

A chronic subdural haematoma is a collection of blood within the subdural space that has been present for weeks to months.

Rupture of the small bridging veins within the subdural space rupture and cause slow bleeding. Elderly and alcoholic patients are particularly at risk of subdural haematomas since they have brain atrophy and therefore fragile or taught bridging veins.

Presentation is typically a several week to month progressive history of either confusion, reduced consciousness or neurological deficit.

Infants also have fragile bridging veins and can rupture in shaken baby syndrome.


Acute subdural haematoma

CT imaging is the first-line investigation and will show a crescentic collection, not limited by suture lines. They will appear hyperdense (bright) in comparison to the brain. Large acute subdural haematomas will push on the brain (‘mass effect’) and cause midline shift or herniation.

Chronic subdural haematoma

On CT imaging they similarly are crescentic in shape, not restricted by suture lines and compress the brain (‘mass effect’). In contrast to acute subdurals, chronic subdurals are hypodense (dark) compared to the substance of the brain.


Acute subdural haematoma

Small or incidental acute subdurals can be observed conservatively. Surgical options include monitoring of intracranial pressure and decompressive craniectomy.

Chronic subdural haematoma

If the chronic subdural is an incidental finding or if it is small in size with no associated neurological deficit then it can be managed conservatively with the hope that it will dissolve with time. If the patient is confused, has an associated neurological deficit or has severe imaging findings then surgical decompression with burr holes is required.