Pathology - Head Injury

I. Epidemiology & Severity

• Incidence: Approximately 50,000 severe head injuries occur annually in the UK.
• Mortality: Accounts for roughly 20% of deaths in young adults (5-45 years).
• Disability: Significant disability is common among survivors.

II. Types of Head Injuries

A. Skull Fracture:

• Mechanism: Occurs at the impact site in severe head injuries.
• Significance: Indicates serious injury and increases the risk of intracranial damage (contusions, hematomas).
• Base of Skull Fractures: Can lead to cranial nerve palsies or cerebrospinal fluid (CSF) leakage from the nose or ear.

B. Cerebral Contusions:

• Mechanism: Brain bruising caused by sudden movement within the skull, resulting in impact against the skull.
• Location: Typically occurs at the impact site ("coup" lesion) and opposite ("contrecoup" lesion).
• Consequences: Bleeding into brain tissue (parenchyma) and cerebral edema increase intracranial pressure.

C. Extradural Hematoma (Epidural Hematoma):

• Mechanism: Bleeding between the dura mater and the skull.
• Cause: Often due to middle meningeal artery rupture from temporal bone fracture.
• Progression: Slow initial blood accumulation due to the dura's adherence to the skull. Patients may initially appear well, then rapidly deteriorate as the hematoma expands.

D. Subdural Hematoma:

• Mechanism: Bleeding between the dura and arachnoid mater.
• Cause: Tearing of bridging veins draining into the cerebral venous sinuses.
• Spread: Blood spreads widely, enveloping the affected hemisphere.
• Clinical Presentation: Common in the elderly after minor trauma; may present with confusion.

E. Traumatic Axonal Injury (TAI):

• Mechanism: Typically caused by sudden acceleration-deceleration forces.
• Diffuse Axonal Injury (DAI): The most severe form, leading to immediate unconsciousness and high mortality.
• Histology: Shows widespread axonal swelling, increased microglia, and eventual fiber tract degeneration.

III. Key Differences & Summary Table

ICP: Intracranial Pressure