Subdural haematoma

Introduction

A subdural haematoma, also known as a subdural haemorrhage, is defined as a collection of blood between the dura mater and arachnoid mater of the brain.¹

A subdural haematoma (SDH) can be acute (< 3 days), subacute (3-21 days) or chronic (>21 days).

Aetiology

Anatomy

The meningeal layers cover the brain and have a protective effect against intracerebral infections (Figure 1).

The dura mater is the outermost layer that is directly underneath the skull. It is tough, fibrous and inextensible.

Causes of a subdural haematoma

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

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

Risk factors

Risk factors for developing a subdural haematoma 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, DOACs)
• History of coagulopathy (e.g. haemophilia)
• History of loss of consciousness

Clinical features

History

Typical symptoms of subdural haematoma include:

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

Clinical examination

Patients with a traumatic head injury require a thorough neurological examination, including cranial nerves, upper limb and lower limb. In addition, an assessment of the patient’s level of consciousness using the Glasgow Coma Scale (GCS) should be performed.²

Clinical signs of SDH vary depending on the location and severity of bleeding. Clinical findings may include:

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

Investigations

Laboratory investigations

Relevant laboratory investigations include:

• FBC: to identify anaemia that 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 that may need correction
• LFTs: to provide a baseline and to assess the synthetic function of the liver which is important to produce 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

Imaging

CT head

A non-contrast CT head is required for all patients in which intracranial bleeding is suspected. This 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.

MRI

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

Differential diagnoses

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

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

For more information, see the Geeky Medics guide to CT head interpretation.

Management

Initial management

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. Local guidelines for anticoagulation should be followed, with input from haematology if required. 

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

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 to prevent brain stem herniation and death due to rising intracranial pressure.

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

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.

Reviewer

Mr Arif Zafar

Neurosurgery Registrar

Editor

Samantha Strickland

References

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. BMJ Best Practice. Grande AJ. Subdural Haematoma. Available from: [LINK]
4. Blausen.com staff. Scalp. Wikipedia. Published in 2018. Available from: [LINK]
5. Case courtesy of Dr Craig Hacking, Radiopaedia.org. Available from: [LINK]
6. Case courtesy of Dr Jeremy Jones, Radiopaedia.org.