General Principles

I. GENERAL PRINCIPLES

A. Classification of traumatic injuries.

1. Trauma may produce closed or open head injuries

2. Injuries may be penetrating or blunt

3. Skull fractures may be depressed or non-depressed

B. Mechanisms of damage in closed-head injury

1. Linear acceleration or deceleration of head

a) coup lesions (directly beneath impact),

b) contrecoup lesions (directly opposite the site of impact),

c) intermediary coup lesions.

2. Rotation of brain within cranial cavity

a) shearing of bridging veins producing subdural hemorrhage

b) shearing of small vessels producing petechial intracranial hemorrhages or subarachnoid hemorrhage

c) shearing stresses in brain causing rupture or stretching of axons

d) contusions: the orbital surfaces may be damaged by contact with the floor of the anterior fossa; the temporal lobe tips may be damaged by edges of the sphenoid ridge; the corpus callosum may be damaged by the falx cerebri; the superior surface of the cerebellum or brainstem may be injured by contact with the tentorium cerebelli.

3. Secondary damage may be produced by the space-occupying effects of edema and/or hematoma (see chapter on Increased Intracranial Pressure ).

C. Additional mechanisms of damage involved in open-head injuries

1. Direct inoculation of bacteria

2. Laceration by bony fragments

D. Brain swelling

Increased intracranial pressure and herniation can be a lethal complication in head trauma. The two major factors which contribute to brain swelling are edema and increased cerebral blood volume. Secondary damage may be produced (see chapter on Increased Intracranial Pressure).

E. Delayed sequelae of CNS trauma

1. Post-traumatic epilepsy, due to seizure activity initiated at sites of meningocerebral cicatrix (scar tissue)

2. White matter degeneration (pathogenesis not clear, may be related to stretching or shearing of axons during trauma)

3. Delayed intracerebral hemorrhage - may occur days or months later (probably due to partial tearing of vessels during trauma with subsequent rupture)

4. Psychological deficits (post-traumatic syndrome) -symptoms include headache, dizziness, anxiety, poor concentration; morphogical substrate unknown