Advanced Trauma Life Support ATLS Student Course Manual 2018

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CHAPTER 6 n Head Trauma
fibrous membrane that adheres firmly to the internal
surface of the skull. At specific sites, the dura splits
into two “leaves” that enclose the large venous
sinuses, which provide the major venous drainage
from the brain. The midline superior sagittal sinus
drains into the bilateral transverse and sigmoid
sinuses, which are usually larger on the right side.
Laceration of these venous sinuses can result in
massive hemorrhage.
Meningeal arteries lie between the dura and the
internal surface of the skull in the epidural space.
Overlying skull fractures can lacerate these arteries
and cause an epidural hematoma. The most commonly
injured meningeal vessel is the middle meningeal
artery, which is located over the temporal fossa. An
expanding hematoma from arterial injury in this
location can lead to rapid deterioration and death.
Epidural hematomas can also result from injury to
the dural sinuses and from skull fractures, which
tend to expand slowly and put less pressure on
the underlying brain. However, most epidural
hematomas constitute life-threatening emergencies
that must be evaluated by a neurosurgeon as soon
as possible.
Beneath the dura is a second meningeal layer:
the thin, transparent arachnoid mater. Because the
dura is not attached to the underlying arachnoid
membrane, a potential space between these layers
exists (the subdural space), into which hemorrhage
can occur. In brain injury, bridging veins that travel
from the surface of the brain to the venous sinuses
within the dura may tear, leading to the formation of a
subdural hematoma.
The third layer, the pia mater, is firmly attached
to the surface of the brain. Cerebrospinal fluid (CSF)
fills the space between the watertight arachnoid
mater and the pia mater (the subarachnoid space),
cushioning the brain and spinal cord. Hemorrhage
into this fluid-filled space (subarachnoid hemorrhage)
frequently accompanies brain contusion
and injuries to major blood vessels at the base of
the brain.
Brain
The brain consists of the cerebrum, brainstem, and
cerebellum. The cerebrum is composed of the right
and left hemispheres, which are separated by the falx
cerebri. The left hemisphere contains the language
centers in virtually all right-handed people and in
more than 85% of left-handed people. The frontal lobe
controls executive function, emotions, motor function,
and, on the dominant side, expression of speech (motor
speech areas). The parietal lobe directs sensory function
and spatial orientation, the temporal lobe regulates
certain memory functions, and the occipital lobe is
responsible for vision.
The brainstem is composed of the midbrain, pons,
and medulla. The midbrain and upper pons contain
the reticular activating system, which is responsible
for the state of alertness. Vital cardiorespiratory
centers reside in the medulla, which extends downward
to connect with the spinal cord. Even small
lesions in the brainstem can be associated with severe
neurological deficits.
The cerebellum, responsible mainly for coordination
and balance, projects posteriorly in the posterior
fossa and connects to the spinal cord, brainstem, and
cerebral hemispheres.
Ventricular System
The ventricles are a system of CSF-filled spaces and
aqueducts within the brain. CSF is constantly produced
within the ventricles and absorbed over the surface of
the brain. The presence of blood in the CSF can impair
its reabsorption, resulting in increased intracranial
pressure. Edema and mass lesions (e.g., hematomas)
can cause effacement or shifting of the normally
symmetric ventricles, which can readily be identified
on brain CT scans.
Intracranial Compartments
Tough meningeal partitions separate the brain
into regions. The tentorium cerebelli divides the
intracranial cavity into the supratentorial and
infratentorial compartments. The midbrain passes
through an opening called the tentorial hiatus
or notch. The oculomotor nerve (cranial nerve III)
runs along the edge of the tentorium and may
become compressed against it during temporal lobe
herniation. Parasympathetic fibers that constrict the
pupils lie on the surface of the third cranial nerve;
compression of these superficial fibers during
herniation causes pupillary dilation due to unopposed
sympathetic activity, often referred to as a
“blown” pupil (n FIGURE 6-3).
The part of the brain that usually herniates through
the tentorial notch is the medial part of the temporal
lobe, known as the uncus (n FIGURE 6-4). Uncal herniation
also causes compression of the corticospinal
(pyramidal) tract in the midbrain. The motor tract
crosses to the opposite side at the foramen magnum,
so compression at the level of the midbrain results
in weakness of the opposite side of the body (contralateral
hemiparesis). Ipsilateral pupillary dilat-
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