III. Brain Traumatic Lesions
Concussion is a transient neurologic dysfunction, which may include loss of consciousness, temporary respiratory arrest, and loss of reflexes, due to head injury. It is of instantaneous onset and is manifested by neurological symptoms without evidence of structural cerebral injury. A change in momentum of the head is thought to be a critical factor in producing concussion.
B. Contusions (areas of hemorrhagic necrosis)
1. Pathogenesis: Following head injury, the brain strikes supporting structures (tentorium and falx cerebri), and bony projections of skull, producing superficial bruising of gyral crests.
2. Location: In general the most common sites are frontal lobe orbital surfaces and temporal lobes. Contusions can be produced by rotation of the brain or by linear forces through the site of impact. The exact location may depend on conditions of the trauma. Contusions may be coup lesions (directly adjacent to the site of impact) or contrecoup lesions (on the opposite side of the brain from the impact). In the case of linear acceleration or deceleration injuries (i.e. a single blow to the unsupported head), contrecoup lesions are a common sequelae. A blow to the well-supported head results in severe skull fractures, often with absence of coup and contre-coup lesions (the head does not accelerate or decelerate and the skull absorbs much of the force).