The most severe type of craniocerebral injury is brain injury, which is categorized into primary and secondary injuries. Primary brain injuries include cerebral concussion, cerebral contusion, and diffuse axonal injury (DAI). Secondary brain injuries encompass cerebral edema, cerebral swelling, and intracranial hematomas.
Mechanisms of Injury
Understanding the mechanisms and patterns of craniocerebral injury, combined with the location and direction of force applied to the head, holds significant clinical importance for diagnosing and determining the nature and site of brain injury. The mechanisms underlying brain injury are complex, with three primary contributing factors:
- Direct cranial deformation or fracture: Brain injury caused by indentation, rebound, or fracture of the skull at the site of impact.
- Relative motion between the brain and skull: Injury resulting from the brain’s movement relative to the skull immediately after impact, which may occur at the site of impact or on the opposite side of the brain (contrecoup injury).
- Compression, deformation, or torsion of brain tissue: Injury caused by the brain’s physical distortion under external force.
The roles of these factors differ between acceleration and deceleration injuries. In acceleration injuries, the first factor predominates. In deceleration injuries, all three factors are involved, with injuries from relative brain-skull motion being more frequent and severe. Due to the smooth inner surface of the occipital bone and tentorium cerebelli compared to the uneven surfaces of the anterior and middle cranial fossae, deceleration injuries—whether impacting the occipital or frontal region—commonly affect the frontal and temporal lobes, particularly their anterior and basal regions.
Figure 1 Impact sites and corresponding brain injury locations in deceleration injuries
Classification
Brain injuries are classified temporally and mechanistically into:
- Primary brain injury: Immediate damage caused by direct force to the head.
- Secondary brain injury: Delayed damage developing hours to days after the initial trauma.
Based on communication with the external environment, brain injuries are categorized as:
- Closed brain injury: No communication between brain tissue and the external environment.
- Open brain injury: Communication exists between brain tissue and the external environment.
To be continued