Synopsis
Distinguish traumatic acute subdural haematoma from chronic subdural haematoma, recognise their different time courses and CT patterns, and select urgent surgery, active observation and multidisciplinary recovery pathways appropriately.
- Acute SDH is usually traumatic fresh blood between dura and arachnoid, often with severe underlying brain injury; chronic SDH is an organised collection of fluid and blood products, commonly affecting older, frail and antithrombotic-exposed people.
- On CT, acute blood is usually a hyperdense crescent that can cross sutures but is limited by dural reflections; chronic collections are often hypodense or mixed-density and may be bilateral. Density alone does not date every component reliably.
- For acute traumatic SDH, BTF recommends evacuation when thickness exceeds 10 mm or midline shift exceeds 5 mm regardless of GCS, and also identifies deterioration, pupillary abnormality or ICP above 20 mmHg in selected comatose patients with smaller scans.
Key red flags
After major trauma, falling GCS, asymmetric pupils, new hemiparesis, posturing or seizure without recovery suggests acute SDH with mass effect and possible herniation.
In an older or frail person, days to weeks of worsening headache, falls, unsteadiness, confusion, speech change or one-sided weakness should prompt consideration of chronic SDH even without remembered trauma.
Sudden decline, a new focal deficit or reduced consciousness in known chronic SDH makes the situation urgent; the word chronic does not mean clinically stable.
Bilateral collections can produce little midline shift despite major brain compression, so apparent symmetry must not be read as low risk.
Exact anticoagulant or antiplatelet, indication, last dose, renal function and haemostatic results are consequential; “on blood thinners” is inadequate for reversal decisions.
An apparently incidental chronic collection does not explain every confusion syndrome: assess infection, metabolic disturbance, medication effects, stroke, seizure and the person’s cognitive baseline.
Reconstruct injury timing and energy, initial consciousness, subsequent GCS change, vomiting, seizure and extracranial bleeding. Acute SDH may coexist with skull fracture, contusions and diffuse axonal injury, making the neurological state worse than clot size alone predicts.
New anisocoria, impaired pupil response, unilateral weakness, posturing, a rapidly falling motor score or abnormal breathing requires immediate emergency treatment. This applies to acute SDH and to a chronic collection that rebleeds or expands.
Reasoning priorities
Differentiate an acute or chronic subdural collection, define mass effect and detect coexisting traumatic lesions.
Describe side, maximal thickness, density or layering, membranes when visible, midline shift, sulcal and cisternal effacement, ventricular compression, bilateral disease, contusions and fracture. Acute-on-chronic bleeding may be mixed density; bilateral mass effect may occur without large shift.
Worked reasoning
CT shows a subdural collection and the team must decide whether it is an acute traumatic emergency or chronic SDH care problem.
- First pair time course and physiology with imaging: treat high-energy trauma, fresh hyperdense blood, coma or rapid neurological decline as acute traumatic SDH; recognise days-to-weeks change, frailty and a hypodense or mixed organised collection as chronic SDH, while allowing acute-on-chronic bleeding.
- For either form, escalate falling consciousness, new pupil abnormality or progressive focal deficit immediately; stabilise ABC, involve neurosurgery, make images available and identify antithrombotic exposure without delaying source control.
- For acute traumatic SDH, evacuate lesions over 10 mm thick or with over 5 mm shift, and apply the additional comatose-patient criteria when smaller; if surgery is indicated, perform it as soon as possible.
- For chronic SDH, combine symptoms, mass effect, baseline function, frailty and patient goals; consider surgery for symptomatic disease or a large-volume collection with significant mass effect.
- Verify recovery through serial examination and cause-specific follow-up. Re-open the differential when cognition or focal signs do not improve as expected.
Neurosurgery determines that immediate surgery is unlikely to add benefit and the patient is clinically stable.