Subdural haematoma (SDH)
A subdural haematoma is blood collecting in the potential space between the dura and the arachnoid mater. Most result from rupture of cortical bridging veins after head trauma; arterial bleeding can occur with high‑energy injuries. SDHs range from rapidly life‑threatening acute bleeds to slowly expanding chronic collections that may present weeks after minor or unrecognised trauma.
Pathophysiology
- Acceleration-deceleration shear forces tear bridging veins; blood accumulates in the subdural space producing a crescentic collection.
- Cerebral atrophy (age, alcohol use) increases the distance and tension on bridging veins and predisposes to SDH after minor trauma.
- Acute clotted blood may liquefy; organised outer membranes and fragile neovasculature in chronic SDH can produce recurrent bleeding and progressive enlargement.
- Expanding collections produce mass effect, raised intracranial pressure (ICP), focal deficits, decreased consciousness and risk of transtentorial herniation.
Epidemiology and risk factors
- Older age and cerebral atrophy.
- Recent head trauma (may be minor or unwitnessed); chronic SDH often has no clear history.
- Alcohol misuse (contributes to atrophy and coagulopathy).
- Anticoagulant and antiplatelet therapy.
- Thrombocytopenia and other bleeding disorders.
Classification and CT appearance
SDHs are commonly classified by age of the bleed, which correlates with density on non‑contrast CT.