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U N I T 1 0
Nervous System
Because the brain floats freely in the CSF within
the rigid confines of the skull, blunt force to the head
causes the brain to accelerate within the skull, and
then decelerate abruptly upon hitting the inner skull
surfaces.
7,10–12
As the brain strikes the rough surface
of the cranial vault, brain tissue, blood vessels, nerve
tracts, and other structures are bruised and torn,
resulting in contusions and hematomas (Fig. 37-6).
A special type of acceleration-deceleration motion is
angular rotation.
7,12
It involves the rotational motion
of the cerebral hemispheres in the anterior-posterior
plane around the fixed-in-place brain stem, caus-
ing disruption of electrical and subcellular activities
of neurons in the reticular activating system (RAS),
which extends through the central core of the brain
stem (Fig. 37-6).
There are two main stages in the development of
brain damage after brain injury: primary and second-
ary. Primary injuries, which represent the immediate
response to the initial injury, include focal lesions (con-
tusions and hemorrhage) and diffuse injuries (concus-
sion and diffuse axonal injuries).
1,4
Secondary injures
involve complicating processes resulting from the ini-
tial injury, including brain swelling, and infection.
7,9–12
Ischemia is considered the most common cause of sec-
ondary brain injury. It can result from the hypoxia and
hypotension that occur during the resuscitation process
or from the impairment of regulatory mechanisms that
control cerebrovascular responses that maintain blood
flow and oxygen supply.
Contusions
Contusions represent a bruising on the brain surface or
a lacerations or tearing of brain tissue.
1,4
Contusions
can result from direct force, a depressed skull frac-
ture, or a closed acceleration-deceleration injury.
Closed injury contusions are often distributed along
the rough, irregular inner surface of the brain and are
more likely to occur in the frontal or temporal lobes,
resulting in cognitive and motor deficits. The clinical
effects of a contusion depend on its size and related
cerebral edema. Small, unilateral, frontal lesions may
be asymptomatic; whereas larger lesions may result
in neurological defects. They can cause secondary
mass effects from edema resulting in an increased ICF,
and possible herniation syndromes. Persons suffering
from cerebral contusions are usually managed medi-
cally with emphasis toward prevention of secondary
injuries.
Hematomas
Hematomas result from vascular injury and bleeding.
Depending on the anatomic position of the ruptured
vessel, bleeding can occur in any of several compart-
ments, including the epidural, subdural, and sub-
arachnoid spaces, or into the brain itself (intracerebral
hematoma).
Epidural Hematoma.
An epidural hematoma is one
that develops between the inner side of the skull and
the dura
1,4,7
(Fig. 37-7). It usually results from a tear
in an artery, most often the middle meningeal, usu-
ally in association with a head injury in which the
skull is fractured.
1,5,17
Because bleeding is arterial in
origin, rapid expansion of the hematoma compresses
the brain. Epidural hematoma is more common in a
young person because the dura is less firmly attached
to the skull surface than in an older person; as a con-
sequence, the dura can be easily separated from the
inner surface of the skull, allowing the hematoma to
grow.
Typically, a person with an epidural hematoma pres-
ents with a history of head injury and a brief period
of unconsciousness followed by a lucid period in which
consciousness is regained. There is then a rapid pro-
gression to unconsciousness. The lucid interval does
not always occur, but when it does, it is of great diag-
nostic value. With rapidly developing unconsciousness,
Rotational injury
Midbrain
Front and back injury
B
A
FIGURE 37-6.
Mechanism of brain
injury
(A)
acceleration–deceleration
and
(B)
acceleration–decelerations
with rotational motion of the cerebral
hemispheres around the fixed-in-place
brainstem that affects neurons in
reticular activating system (RAS), which
extends through the central core of the
brainstem. (Adapted from Hickey JV.
The Clinical Practice of Neurological
and Neurosurgical Nursing. 6th ed.
Philadelphia, PA: Wolters Kluwer
Health | Lippincott Williams &Wilkins;
2009:372.)
