Acute Subdural Hematoma

An acute subdural hematoma is a collection of blood in the subdural space, between the dura mater and the arachnoid, that develops within hours to a few days of head trauma. Usually caused by tearing of bridging veins or by bleeding from an underlying brain contusion, it is often accompanied by significant primary brain injury, which makes its outcome typically worse than that of an epidural hematoma.

Definition

An acute subdural hematoma is an accumulation of blood in the subdural space arising within hours to days of trauma, most commonly from rupture of cortical bridging veins or from haemorrhage of an underlying cerebral contusion.

Scope

This entry covers the acute subdural hematoma as a traumatic surgical lesion: its venous and parenchymal sources, the crescent-shaped CT appearance that crosses suture lines, the frequent association with underlying brain injury, and the principles of surgical evacuation and decompression. It is a reference overview rather than treatment guidance.

Core questions

• What vascular and parenchymal sources produce an acute subdural hematoma?
• Why is its prognosis often worse than that of an epidural hematoma?
• How does its CT appearance differ from an epidural hematoma?
• What principles guide surgical evacuation and decompression?

Key concepts

• Bridging vein rupture
• Crescent (concave) CT appearance
• Spread across suture lines
• Association with underlying brain injury
• Mass effect and midline shift
• Craniotomy and decompressive craniectomy
• Worse prognosis than epidural hematoma

Mechanisms

Acceleration-deceleration forces stretch and tear the bridging veins that cross from the cortical surface to the dural sinuses, or a cerebral contusion bleeds into the subdural space. Blood spreads over the convexity in a crescentic layer that, unlike an epidural collection, is not constrained by suture lines. Because the same forces frequently injure the underlying brain, mass effect from the clot is compounded by parenchymal damage and swelling, raising intracranial pressure and worsening prognosis.

Clinical relevance

The acute subdural hematoma illustrates how a surgical mass lesion and diffuse primary brain injury often coexist, which is why its outcomes differ from the more favourable epidural hematoma. The entry explains these concepts to support critical reading of the literature; it is descriptive and not a guide to individual care.

Epidemiology

Acute subdural hematoma is among the more common significant traumatic intracranial lesions and is associated with high-energy mechanisms in younger patients and with falls in older adults, in whom cortical atrophy stretches the bridging veins; coexisting brain injury contributes to its substantial morbidity and mortality (Greenberg, 2020).

Evidence & guidelines

The Brain Trauma Foundation/AANS surgical management guideline for acute subdural hematomas (Bullock et al., 2006) summarises the clot-thickness, midline-shift, and clinical thresholds discussed for operative decision-making, and craniectomy trials such as RESCUEicp (Hutchinson et al., 2016) inform the role of decompression. These are cited to map the evidence, not as directives.

History

Surgical evacuation of traumatic subdural collections is long established, but recognition that coexisting primary brain injury drives outcome reframed the lesion as more than a simple clot. The 2006 surgical management guideline codified contemporary operative criteria, and later craniectomy trials clarified the role of decompression in refractory swelling.

Debates

When should evacuation be combined with decompressive craniectomy?

In acute subdural hematoma with substantial brain swelling, surgeons debate whether to replace the bone flap (craniotomy) or leave it out (decompressive craniectomy); trial evidence on last-tier decompression informs but does not settle the choice for individual cases.

Key figures

• Ross Bullock
• Mark Greenberg
• Peter Hutchinson
• Angelos Kolias

Seminal works

• bullock-2006-subdural
• hutchinson-2016

Frequently asked questions

Why does an acute subdural hematoma often have a worse outcome than an epidural hematoma?

An acute subdural hematoma is usually caused by forces that also injure the brain itself, so the underlying brain damage adds to the harm from the clot, whereas in an epidural hematoma the brain beneath is often relatively spared.

How does a subdural hematoma look on a CT scan?

It typically appears as a crescent-shaped (concave) collection over the surface of the brain that can extend across skull suture lines, in contrast to the lens-shaped epidural hematoma.