Subdural Haemorrhage (SDH)
Summary
Subdural Haemorrhage (SDH) is a collection of blood in the subdural space (between the Dura Mater and the Arachnoid Mater). It is usually venous in origin, caused by the rupture of bridging veins that traverse this space. It has a characteristic Crescentic (Moon/Banana) shape on CT imaging. [1,2]
Key Facts
- Mechanism: The bridging veins drain blood from the cerebral cortex to the superior sagittal sinus. They are vulnerable to shearing forces, particularly in acceleration-deceleration injuries.
- Risk Groups:
- Elderly: Brain atrophy increases the distance the veins must travel, putting them under tension.
- Alcoholics: Atrophy + Coagulopathy + Frequent falls.
- Infants: Non-Accidental Injury (Shaken Baby Syndrome).
- Phases:
- Acute (less than 3 days): Fresh blood, Hyperdense (White).
- Subacute (3 days - 3 weeks): Clot lysis, Isodense (Grey). Dangerous as it can mimic normal brain tissue.
- Chronic (>3 weeks): Liquefied fluid (motor oil), Hypodense (Black).
Clinical Pearls
The Great Imitator: Chronic SDH often presents insidiously in the elderly with vague confusion, gait unsteadiness, or personality change. It is frequently misdiagnosed as dementia, depression, or a stroke. Always scan a confused elderly patient with a history of a "minor bump" weeks ago.
Extradural vs Subdural:
- Extradural: Arterial (Middle Meningeal). Lens shape (Lemon). Limited by suture lines. Lucid interval.
- Subdural: Venous (Bridging Veins). Crescent shape (Banana). Crosses sutures (but not midline/falx). Fluctuating course.
Isodense Phase: In the subacute phase, the clot becomes the same density as brain tissue. You might miss the clot itself, but look for the secondary signs: Effacement of sulci (smooth cortex) and Midline shift.
Incidence
- Acute SDH: 10-20% of traumatic brain injuries. High mortality (50-90%).
- Chronic SDH: Increasing incidence with aging population (~5 per 100,000).
The Bridging Vein Tear
- As the brain moves within the skull during trauma, the inertia causes a lag between the skull (which stops) and the brain (which keeps moving). This shears the delicate bridging veins.
- In Acute SDH, the bleeding is often associated with underlying cerebral contusions/lacerations.
- In Chronic SDH, a membrane forms around the clot. This membrane is fragile and re-bleeds repeatedly (micro-haemorrhages), causing the collection to expand slowly over time (osmotic gradient theory is now largely discarded).
Acute SDH
Chronic SDH
- GCS: Monitor trends.
- Pupils: Anisocoria suggests Uncal Herniation (compression of oculomotor nerve on the side of the clot).
- Limbs: Contralateral hemiparesis.
CT Head (Non-Contrast)
- Shape: Crescentic / Concave inner margin.
- Density:
- Acute: White.
- Chronic: Dark (like CSF).
- Acute-on-Chronic: Mixed density (fresh white blood within a dark chronic collection).
- Extension: Crosses suture lines. Does not cross midline (Falx cerebri).
Coagulation Screen
- Essential (INR, APTT, Platelets) as many patients are on Warfarin/DOACs.
Management Algorithm
SUBDURAL HAEMORRHAGE
↓
ABCDE / NEUROPROTECTION
- Optimize Oxygen / BP
- Reverse Anticoagulation (PCC/Vit K)
- Head up 30°
- Seizure prophylaxis (Keppra/Phenytoin)
↓
┌───────────┴───────────┐
ACUTE CHRONIC
(Trauma) (Insidious)
↓ ↓
SURGERY IF: SURGERY IF:
- Thickness >10mm - Symptomatic
- Shift >5mm - Shift >1cm
- GCS Drop - GCS Drop
↓ ↓
CRANIOTOMY BURR HOLE
(Large flap to (Drill holes to
evacuate clot) drain fluid)
1. Medical Management
- Reverse anticoagulants immediately (e.g., Octaplex for Warfarin, Idarucizumab for Dabigatran).
- Antiepileptics: Prophylactic for 7 days (high risk of cortical irritation).
- Conservative: Small (less than 10mm), asymptomatic acute SDHs may resorb over months.
2. Surgical Management
- Burr Hole Drainage: For Chronic SDH. Local anaesthetic. Drill 1 or 2 holes. Wash out the "motor oil" fluid. Insert drain.
- Craniotomy: For Acute SDH. The blood is solid clot and cannot be washed out through a small hole. A large bone flap is removed, dura opened, clot removed. Often the bone is left out (Craniectomy) if brain swelling is severe.
- Recurrence: 10-20% (especially Chronic SDH).
- Seizures: 10% risk.
- Subdural Empyema: Infection of the space.
- Tension Pneumocephalus: Air enters skull post-op.
- Acute SDH: Poor. Mortality 50-90% because of the associated underlying brain damage (contusions/DAI).
- Chronic SDH: Good. Most return to baseline function after drainage.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Head Injury | Brain Trauma Foundation | Operating criteria (Shift >5mm, Thickness >10mm). |
| Chronic SDH | SBNS (UK) | Burr hole drainage is superior to Twist drill. Drains reduce recurrence. |
Landmark Evidence
1. Santarius Trial (Lancet)
- RCT showed that placing a subdural drain after burr hole evacuation of chronic SDH significantly reduces recurrence and mortality. This is now standard of care.
What is a subdural?
It is a bleed on the surface of the brain, underneath the tough outer covering (dura). It presses on the brain.
Why did it happen so slowly?
In older people, the brain shrinks slightly, stretching the veins that connect it to the skull. A minor bump can tear these veins. Because it is a vein (low pressure), it bleeds very slowly, taking weeks to build up enough pressure to cause symptoms like confusion or unsteadiness.
How do you treat it?
For the chronic type, we drill a small hole (size of a 50p coin) in the skull and wash out the fluid, which looks like dark oil. The brain then expands back to fill the space. For an acute bleed (fresh clot), we need a larger operation.
Primary Sources
- Bullock MR, et al. Surgical management of acute subdural hematomas. Neurosurgery. 2006.
- Santarius T, et al. Use of drains versus no drains after burr-hole evacuation of chronic subdural haematoma: a randomised controlled trial. Lancet. 2009.
- Kolias AG, et al. Chronic subdural haematoma: modern management and emerging therapies. Nat Rev Neurol. 2014.
Common Exam Questions
- Radiology: "Shape on CT?"
- Answer: Crescentic / Banana.
- Anatomy: "Vessel involved?"
- Answer: Bridging Veins.
- Procedure: "Operation for Chronic SDH?"
- Answer: Burr Hole Evacuation.
- Risk Factor: "Why alcoholics?"
- Answer: Atrophy + Coagulopathy + Trauma.
Viva Points
- Uncal Herniation: What happens? The medial temporal lobe (Uncus) herniates through the tentorium cerebelli. It compresses:
- CN III: Dilated pupil (Parasympathetic fibres are on outside of nerve).
- Cerebral Peduncle: Contralateral hemiparesis.
- PCA: Occipital infarction.
- Kernohan's Notch: False localising sign. Herniation pushes the opposite cerebral peduncle against the skull edge, causing ipsilateral hemiparesis.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.