III. BRAIN TRAUMATIC LESIONS
- Concussion is a transient acute unconsciousness due to head injury.
It is of instantaneous onset and is manifested by neurological symptoms
without much evidence of structural cerebral injury.
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.
|| Contusions are present on the right frontal tip (left side of image) orbital
2. Location: In general the most common sites are orbital
surfaces, (inferior surface of frontal lobe) temporal lobes and occipital
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).
3. Pathology: In the most typical form of contusion, the
summit of a cerebral gyrus is smashed, and the lesion has a wedge shape
with its base toward the pia and the apex toward the white matter. All
layers of cortex are regularly affected. In its early stage the hemorrhage
remains bright red, and the surrounding brain tissue is edematous. When
the lesion is older it becomes brick-red and finally golden orange-brown
(due to deposition of hemosiderin), with a floor of glial tissue, covered
by leptomeningeal fibrosis. The most chronic stage is sometimes called
plaque jaune. Dura arachnoidal adhesions (meningocerebral cicatrix - scar
involving meninges & cerebral cortex) later form on the surface, and
frequently cause post-traumatic epilepsy.
C. Lacerations (rupture or tearing of brain tissue)
- This physical disruption of tissue, often accompanied by contusions,
is caused by a penetrating injury, e.g. by bony fragments or weapons. Meninges
and cortex are both involved. The pattern of pathologic changes differs
from that of contusion with respect to the increased amount of hemorrhage,
more disruptive effect and the more obvious fibroblastic proliferation
and scarring of meninges in lacerations.
D. Intracranial Hemorrhage
- Pure intracerebral hemorrhage is rare in trauma. Hemorrhage is usually
restricted to that associated with contusions or lacerations.
E. Diffuse Axonal Injury
- Diffuse axonal injury is a major cause of prolonged traumatic coma.
This type of lesion is present in 35% of head trauma deaths and is the
most common cause of poor neurological outcome.