Subdural haematoma

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A subdural haematoma (SDH; also known as a subdural haemorrhage), is defined as a collection of blood between the dura mater and arachnoid mater of the brain.3

SDH may be acute (< 3 days), subacute (3-21 days) or chronic (>21 days).

A cross-section of the layers covering the brain. The layers can be remembered using the mnemonic SCALP - Skin, Connective Tissue, Epicranial Aponeurosis, Loose Connective Tissue and Periosteum.
Figure 1. Layers covering the brain. 4


The most common cause of subdural haematoma is trauma, typically a blow to the temporal side of the head, rupturing the bridging cranial veins.

Other causes of SDH include: ³

  • Trauma
  • Rupture of a cerebral aneurysm
  • Rupture of an arteriovenous malformation (AVM)
  • Cerebral hypotension
  • Malignancy (rare)

Risk factors

When taking a history from a patient whom you suspect has a subdural haematoma (if you are able), it is important to identify risk factors that make the diagnosis more likely. Examples of risk factors include:2,3

  • History of trauma (e.g. a fall, road traffic accident, blow to the head)
  • Co-morbidities that make a patient vulnerable to falls (e.g. dementia and delirium)
  • Age greater than 65
  • Anticoagulant use (e.g. warfarin, NOACs)
  • History of coagulopathy (e.g. haemophilia)
  • History of loss of consciousness

Clinical features


Typical symptoms of subdural haematoma include:

  • Headache
  • Nausea/vomiting
  • Confusion
  • Drowsiness
  • Poor balance
  • Weakness
  • Paraesthesia or numbness

Clinical examination

Clinical signs of SDH vary depending on the location and severity of bleeding. Some examples of potential clinical findings include:

  • Limb weakness or sensory disturbance
  • Cranial nerve abnormalities (e.g. facial weakness, visual field defect)
  • Ataxia
  • Seizures
  • Reduced level of consciousness

A complete neurological examination of the upper and lower limbs should be performed, along with a cranial nerve examination. In addition, an on-the-spot assessment of the patient’s level of consciousness using the Glasgow Coma Scale (GCS) should be performed.²


Blood tests

Routine blood tests should be performed in all patients presenting with SDH including:

  • FBC: to identify anaemia which may need correction and/or a raised WCC which may indicate the presence of an underlying infection.
  • U&Es: to assess renal function pre-operatively and to identify electrolyte abnormalities which may need correction.
  • LFTs: to provide a baseline and to assess the synthetic function of the liver which is important for the production of vitamin K dependent clotting factors.
  • Coagulation studies: to identify coagulopathy which may need correction to reduce haematoma extension and to allow for surgical intervention.
  • Group and save: to allow crossmatching of blood in case blood products are required.


CT head

A non-contrast CT head is required for all patients in which intracranial bleeding is suspected (it is the gold-standard investigation).

Typical appearances of SDH include a crescent-shaped collection of blood overlying one of the cerebral hemispheres (see images below).

The CT appearances of SDH vary depending on whether the bleed is acute or chronic:

  • Acute SDH typically has a hyperdense appearance (bright white). The hyperdense appearance of acute SDH represents recently coagulated blood.
  • Chronic SDH typically has a hypodense appearance (black/dark grey). The hypodense appearance of chronic SDH represents the dissolution of cellular elements into liquified blood.

Make sure to check out our guide to CT head interpretation for more details.


An MRI is not usually required in the acute setting, however, it may be used to identify certain underlying causes of bleeding (e.g. malignancy, stroke).2

Differentiating types of intracranial bleeding

Sub-types of intracranial haemorrhage differ in their clinical presentation and radiological appearance.

Types of intracranial bleeding

The table below provides a brief summary of the different types of intracranial haemorrhage including their typical clinical features and appearance on CT.

Table 1. Types of intracranial bleeding

Radiological appearances of different types of intracranial bleeds

The images below demonstrate how radiological appearances differ between different types of intracranial haemorrhage.



Initial management

Stabilising the patient

Initial management of a patient with a suspected subdural haematoma should follow an ABCDE approach to ensure the patient is stable before considering further management options.2 

Correction of coagulation studies

All patients on anticoagulation will require reversal agents to prevent further bleeding and extension of the subdural haematoma. If a patient is anticoagulated with warfarin, Beriplex is commonly used to quickly replace vitamin-K dependent clotting factors and normalise the INR. Haematology typically guides the anticoagulation reversal.

Patients who are found to have a coagulopathy (e.g. prolonged PT, thrombocytopenia) need to be discussed with haematology for advice on appropriate treatments (e.g. fresh-frozen plasma, platelet transfusion).

Anticonvulsant medication

Patients presenting with acute SDH are at an increased risk of developing seizures and therefore may be temporarily commenced on anticonvulsant medication to prevent seizures (e.g. levetiracetam, phenytoin). 

Definitive management

The choice of definitive management differs depending on the location, age, size and clinical features of the bleed.

Conservative management

Conservative management may be appropriate if the bleed is small with minimal mass effect (i.e. midline shift or ventricular obstruction).

Trauma craniotomy

A trauma craniotomy is typically used in the context of acute SDH with significant mass effect to both evacuate blood and reduce intracranial pressure.


If there is a large bleed and/or a lot of associated cerebral oedema a hemicraniectomy (also known as a decompressive craniectomy) may be performed in an attempt to prevent brain stem herniation and death due to rising intracranial pressure.

Burr hole craniotomy

Burr hole craniotomy is typically reserved for the management of chronic SDH. This procedure involves the removal of a small disc-shaped fragment of the skull overlying the SDH to allow the evacuation of the liquified blood. A drain may also be placed for a day or two after to reduce the risk of re-accumulation.


Complications of subdural haematoma include:2,3  

  • Permanent neurological deficits
  • Coma
  • Seizures
  • Intracranial infection
  • Recurrent subdural haematoma
  • Death

Key points

  • A subdural haematoma is defined as a collection of blood between the dura mater and arachnoid mater of the brain.
  • The most common cause of SDH is trauma, however other causes include rupture of an arteriovenous malformation and malignancy.
  • Patients with a suspected SDH should undergo a full neurological examination and have consciousness level assessed using the Glasgow Coma Scale (GCS).
  • Clinical features of SDH can include headache, nausea, vomiting, signs of raised intracranial pressure and/or focal neurological deficits.
  • The gold standard investigation for suspected SDH is a non-contrast CT head.
  • Typical appearances of SDH include a crescent-shaped collection of blood overlying one of the cerebral hemispheres.
  • Conservative management may be appropriate if the bleed is small and with minimal mass effect (i.e. midline shift or ventricular obstruction).
  • A trauma craniotomy is used to manage acute SDH with significant mass effect to both evacuate blood and reduce intracranial pressure.
  • Hemicraniectomy may be required for large acute SDH to reduce intracranial pressure.
  • Burr hole craniotomy is typically reserved for the management of chronic SDH.
  • Complications of SDH include seizures, persistent neurological deficits, recurrent haemorrhage and infection.


Mr Arif Zafar

Neurosurgery Registrar


Samantha Strickland


  1. Brain Injury Group. Brain Injury- The Facts. The BIG Network Ltd. Published in 2018. Available from: [LINK]
  2. NICE Clinical Knowledge Summaries. Head Injury: Assessment and early management. Available from: [LINK]
  3. MJ Best Practice. Grande AJ. Subdural Haematoma. Available from: [LINK]
  4. staff (2014). Scalp. Wikipedia. Published in 2018. Available from: [LINK]
  5. Case courtesy of Dr Craig Hacking, Available from: [LINK]
  6. Case courtesy of Dr Jeremy Jones, Available from: [LINK]
  7. Radiology Masterclass. SDH acute v. chronic. Published in 2018.
  8. Case courtesy of Dr Sandeep Bhuta, Available from: [LINK]
  9. Case courtesy of Dr David Cuete, Available from: [LINK]
  10. Case courtesy of Dr Farzad Pirzad,  Available from: [LINK]
  11. Lewis A, Sen R, Hill TC, James H, Lin J, Bhamra H, et al. Antibiotic prophylaxis for subdural and subgaleal drains. J Neurosurg. 2017;126(3):908–12. Available from: [LINK]


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