Subdural Haemorrhage (SDH)
Subdural haemorrhage (SDH) is an extra-axial intracranial haemorrhage occurring between the dura and arachnoid mater.
This updated UKMLA guide to SDH covers acute subdural haemorrhage, chronic subdural haemorrhage, causes, risk factors, symptoms, diagnosis, and management.
Definition and Anatomy
Intracranial haemorrhage is a broad term referring to any bleeding within the skull (cranial vault). It can be categorised into:
| Extra-axial haemorrhage = bleeding outside the brain parenchyma | Intra-axial haemorrhage = bleeding within the brain parenchyma |
Which includes:
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Which includes:
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Overview of Intracranial Extra-Axial Haemorrhage
The 3 main extra-axial haemorrhages:
| Haemorrhage type | Location | Typical cause / source | Classic CT appearance | High-yield clinical presentation |
|---|---|---|---|---|
| Extradural haemorrhage (EDH) | Between the skull and dura | Middle meningeal artery | Biconvex / lens-shaped hyperdense mass | Head injury followed by a possible lucid interval, then rapid deterioration |
| Subdural haemorrhage (SDH) | Between the dura and arachnoid | Bridging veins | Crescent-shaped mass (hyperdense in acute; hypodense in chronic) | Confusion, focal neurology, reduced GCS, esp. in elderly, alcohol excess, anticoagulation use |
| Subarachnoid haemorrhage (SAH) | Between the arachnoid and pia | Ruptured aneurysm | Hyperdense signal in the sulci, fissures, or basal cisterns | Thunderclap headache, meningism, reduced GCS |
Causes and Risk Factors
There are 2 types of SDH, with different pathophysiology, causes and risk factors: [Ref1][Ref2]
| Feature | Acute subdural haemorrhage | Chronic subdural haemorrhage |
|---|---|---|
| Description | Acute bleeding into the subdural space, usually occurring immediately after head injury | A delayed collection of fluid and blood that can present weeks, months, or even years after an initial event |
| Pathophysiology | Tearing / rupture of bridging veins due to mechanical or shearing forces | Currently understood as a complex cerebrovascular disease.
A minor dural injury triggers an inflammatory cascade, recruiting fibroblasts and angiogenic growth factors. This grows a leaky, incompetent “neovasculature” that continuously exudes blood and fluid. |
| Causes |
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| Risk factors |
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Clinical Features
Patients with repeated trauma / underlying coagulopathy are more likely to develop chronic SDH or acute-on-chronic SDH.
Acute Subdural Haemorrhage
Acute SDH usually presents shortly after head trauma, and has a wide spectrum of presentation: [Ref]
- Asymptomatic
- Headache
- Confusion, agitation or drowsiness
- Focal neurological deficits
- Seizures
- Reduced GCS
Acute SDH can rapidly expand in the subdural space and can cause raised ICP and can lead to uncal herniation: [Ref]
- Cushing reflex – triad of ↑ BP (or wide pulse pressure) + bradycardia + irregular breathing (Cheyne-Stokes breathing)
- Ipsilateral fixed, dilated pupil or asymmetrical pupils (due to CN III compression)
- Contralateral upper motor neuron lesion signs
Chronic Subdural Haemorrhage
A chronic SDH often undergoes a “latent stage” that can last for weeks, months, or even years after a minor initial injury. [Ref]
Once the accumulation of fluid and blood grows large enough, the patient enters the “clinical stage” and manifests clinically, ranging from: [Ref]
- Cognitive decline
- Altered mental status
- Headaches
- Focal neurological deficits
- Aphasia
- Seizures
- New or recurrent signs of raised ICP
Assessment and Management
Shared Investigation and Diagnosis
1st line investigation: non-contrast CT head
| Classic CT finding |
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| Other radiographic features |
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| Acute vs chronic SDH |
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Acute Subdural Haemorrhage Approach
Since most acute SDHs result from blunt head trauma / traumatic brain injury, initial assessment and management should follow a standard TBI approach.
Imaging should be performed urgently once the primary survey is complete, and the patient is stable enough for imaging.
Primary Survey (Initial Management)
A-E primary survey and management (to be started pre-hospitally and continued in the hospital):
| Component | Assessment and investigations | Management |
|---|---|---|
| A & B – Airway and breathing |
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| C – Circulation |
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| D – Disability |
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| E – Exposure |
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Indications for Urgent CT Head
Perform a non-contrast CT head within 1 hour if ANY of the following are present (based on NICE NG232):
- GCS ≤12 on initial assessment
- GCS <15 at 2 hours after injury
- Suspected open / depressed skull fracture
- Post-traumatic seizure
- >1 vomiting episode
See the Head Injury in Adults article for other indications of CT.
Acute SDH-Specific Management
Indications for neurosurgical intervention (ANY of the following): [Ref]
- >10 mm thickness
- Midline shift >5 mm
- GCS ≤8 PLUS decline in GCS ≥2 points OR asymmetric / non-reactive pupils
Standard procedure (in comatose patients): craniotomy with haematoma evacuation
Complication / other management: [Ref]
| Clinical aspect / complication | Management |
|---|---|
| ICP monitoring | Insertion of an ICP monitor is indicated with ANY of the following:
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| Raised | If monitored, ICP >22 mmHg requires prompt treatment:
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| Seizure prophylaxis | Cortical irritation from the blood increases the risk of seizures.
Levetiracetam is the preferred medication |
Do NOT routinely perform or give the following:
- Corticosteroids
- Prophylactic hypothermia
- Prophylactic hyperventilation (in the absence of signs of raised ICP and brain herniation)
Chronic Subdural Haemorrhage Approach
Assessment and Work-Up
1st line: non-contrast CT head
Management
Observation and non-surgical management are often recommended for patients who are asymptomatic or only mildly symptomatic, particularly those who are at surgical risk [Ref]
Conservative management usually involves: [Ref]
- Reviewing anticoagulant and antiplatelet use, balancing the risks and benefits of continuing vs withholding treatment
- Serial follow-up CT scans to monitor for stability, resolution or recurrence
- Close neurological monitoring and safety-netting for worsening symptoms
Neurosurgical intervention is typically considered if: [Ref]
- Thickness >10 mm, or
- Midline shift >5 mm