Trauma is the leading cause of death in
patients younger than 45 years. Cranial trauma accounts for a substantial
proportion of morbidity and mortality in all age groups and is the leading cause
of death in patients younger than 30 years. Accurate, rapid, noninvasive
assessment of people with cranial trauma is required for appropriate triage
and management. Computed tomography (CT) is the diagnostic procedure of
choice for acute injury, while magnetic resonance imaging (MRI) has great
value for evaluation in the subacute and long-term.
Closed head injury and penetrating
trauma account for the majority of cerebral trauma, although other processes,
such as acute cerebral infarction or subarachnoid
hemorrhage due to rupture of intracranial aneurysms, may mimic a traumatic
injury on presentation. Acute cranial trauma affects all ages
and both sexes, with incidence of 0.25% annually. Penetrating injuries affect
young males disproportionately. The male-to-female ratio is 4:1 for fatal
injuries, predominantly penetrating trauma and assaults. Nonaccidental
trauma in children, ie, child abuse, accounts for
over 1 million cases annually. The mortality from cranial injury alone
is 20% overall. Approximately 20% of survivors have permanent damage and
disability.
History
Physical
Acute stroke |
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Computed tomography scanning CT is the imaging procedure of choice
in evaluation of acutely injured patients or patients with acute neurologic deficit. Quick, easy, reliable, and routinely available,
CT is valuable in making a firm diagnosis, as well as in excluding
alternative diagnoses or the sequelae of other
pathology, even in uncooperative patients. Patient monitoring is simple and
safe, and CT is compatible with patient stabilization devices. Identification
and localization of calvarial fractures and
bony/metallic fragments are easily achieved. Assessment for acute hemorrhage
and mass effect is optimal. The routine cranial CT protocol should
include contiguous sections, 5-10 mm thick, from the skull base through the
vertex, displayed at 3 window/level settings, as follows:
Contrast infusion is rarely indicated
in the search for mass lesions or vascular pathology, except in patients with
a history of human immunodeficiency virus infection and neurological
examination abnormalities. Magnetic resource imaging MRI is valuable in the subacute setting following initial resuscitation (eg, child abuse, shearing injuries), as well as for
identifying subtle abnormalities (eg, posterior fossa and brainstem injury, cortical contusions, shearing
injury) and as a method to date the injury (eg,
child abuse, parenchymal hemorrhage). Appropriate
patient monitoring, however, is difficult and unreliable due to strong
magnetic fields, time-varying magnetic gradients, and restricted access to
the patient. Patient motion, due to the extended imaging time, reduces the
chances of obtaining studies adequate to achieve final diagnosis. Faster
machines and sequences, as well as MRI units that are more open and
comfortable for unstable or acutely injured patients, are expected to improve
the imaging process in the future. The routine MRI protocol varies
considerably based on strength of the unit's field, machine capabilities, and
suspected diagnosis. Most centers perform sagittal
T1-weighted and axial T1- and T2-weighted sequences of the brain routinely,
with the addition of specific additional sequences depending on the clinical
indications. T2-weighted gradient echo sequences are more sensitive for subacute/chronic parenchymal
hemorrhage/shearing injuries, while fluid-attenuated inversion recovery
(FLAIR) sequences have been shown to be more sensitive for subtle subarachnoid blood. Magnetic resonance angiography and venography, diffusion and perfusion imaging, and
spectroscopy may all be valuable in selected circumstances. Conventional catheter angiography Depending on practice patterns at
individual centers, consider conventional catheter angiography in patients
with penetrating trauma, subarachnoid and parenchymal hemorrhage, or stroke, both as a diagnostic
test and as a treatment option. Conventional radiography Conventional radiography has no role in
the evaluation of the patient with acute head injury. In any case where skull
radiographs may be requested, keep in mind that CT is significantly more
sensitive for soft tissue injury and is superior for spatial localization and
assessment of bony alterations.
Epidural hematoma The dura
mater is composed of 2 layers closely invested with each other: the visceral
or meningeal layer, which lines the intracranial
space; and the parietal layer, which functions as the periosteum
of the calvarium. The dura,
therefore, adheres tightly to the cranial sutures. A skull fracture that crosses an
arterial branch may bleed into the closed space between the calvarium and the periosteal
layer, forming a homogeneously high-density lens-shaped or biconvex
collection, termed epidural hematoma (see Images 1-2).
Because of the transmitted arterial pressure, epidural hematomas
tend to continue to enlarge, with resultant increasing mass effect (ie, lucent interval). Since the dura
splits to encase the major venous sinuses and form the falx
cerebri and tentorium cerebelli, inward displacement of the superior sagittal or transverse sinus indicates an epidural
process. Venous epidural hematomas occur when the
fracture disrupts one of the sinuses and occur more commonly in the posterior
fossa (see Images 3-4).
Subdural hematoma The subdural
space is bound externally by the meningeal layer of
the dura and internally by the arachnoid
mater. Hematomas are confined by the reflected dura of the tentorium and falx but easily spread into the intervening potential
space to form crescentic or convex-out/concave-in
collections called subdural hematomas
(see Image
5). Tearing of the bridging cortical veins that traverse this space
accounts for most subdural hematomas,
usually from abrupt acceleration/deceleration injury. This is more likely to
occur in elderly patients and other patients with atrophy, where the subdural space is enlarged. Acute hemorrhage is dense on the brain
windows, assuming normal hematocrit. As blood ages,
it becomes less dense, so that by about 7-10 days, it approximates the same
density as adjacent brain tissue. At this stage, the isodense
subdural hematoma (see Image 6)
is described. Careful inspection of the subdural or
intermediate windows usually shows inward displacement of the cortical
gray/white matter junction and mass effect, otherwise unexplained by the
imaging findings. Contrast enhancement of the bridging veins may define the
collection (see Image 7).
Homogeneous density within a subdural collection
generally represents interval hemorrhage into a preexisting chronic subdural hematoma. Subarachnoid hemorrhage The subarachnoid
space extends between the subdural space and the
cortical/pia mater surface of the brain. Hemorrhage
into this space interdigitates with the sulci and gyri of the brain
(see Image
8). Focal dense clot often signifies the location of hemorrhage,
particularly in patients with aneurysm rupture. More subtle or diffuse
bleeding is often due to cortical contusion, dilution from a focal
collection, or intraventricular hemorrhage due to
delayed presentation. Catheter angiography is usually indicated on an
emergency basis to identify cerebral aneurysms and define their anatomy prior
to surgical intervention (see Image 9).
Parenchymal lesions Focal cortical hemorrhage is common as
a sequela of head trauma and may be multifocal, as in coup and contrecoup
injuries, or diffuse. Focally dense gyri with
subjacent edema, particularly those adjacent to the inner calvarial
structures (ie, orbit roof-frontal pole, petrous
ridge, and sphenoid wing-temporal pole) represent contusions (see Images
10-11). Diffuse axonal injury, caused by
shearing of the white matter, is due to the differing density or fixation
between two structures and the differing response to rotation and
deceleration. The lobar white matter, brainstem, and corpus callosum are most often affected, with focal ovoid or
elongated regions of decreased density. Cerebral edema may result from loss of
normal autoregulation and hyperemia or diffuse
edema from other causes. Diffuse loss of normal sulci
and cisterns with small ventricles is noted (see Image
12-13). MRI is more sensitive than CT scanning for subtle injuries of
these types, especially in the subacute or chronic
phases. Children are most commonly affected; they have a 50% mortality rate,
3 times that of adults. Parenchymal hemorrhage Focal parenchymal
hematomas occurring in regions of end-arteries,
such as the basal ganglia, thalamus, brainstem, and cerebellar hemispheres, occur most frequently in
patients with chronic hypertension or hypertensive crisis, probably due to
spontaneous rupture of these tiny vessels. Less than 1% of such patients have
a radiographically definable lesion; thus,
angiography is rarely indicated. (See Image 14.)
Focal lobar parenchymal
hematomas, by contrast, are far more likely to be
secondary to a structural lesion, often an arteriovenous
malformation (AVM), vasculitis, or mass lesion (see
Image
15). If an appropriate clinical history has been obtained, angiography
(AVM) or contrast-enhanced MRI is the diagnostic procedure of choice prior to
surgical intervention, unless secondary mass effect is life threatening and
patient management decisions dictate otherwise (see Image 16).
Stroke Patients with strokes in the emergency
setting may present a different course for decision-making. Acute occlusion of one or more large vessels results in focal,
wedge-shaped peripheral areas of loss of grey/white matter differentiation
involving the cortex and contiguous white matter, or simply as a focal mass
effect (see Image 17).
Anoxia or hypotension results in diffuse loss of gyral/cortical
markings and diffuse mass effect (see Image 18).
Such changes are exceedingly difficult
to appreciate on CT studies obtained acutely (<6-12 h from ictus). One
exception is the dense middle cerebral artery (MCA) sign, which represents
acute clot within the horizontal portion of the middle cerebral artery (see Image 19).
Patients with resolved neurologic deficits (ie,
transient ischemic attacks) rarely demonstrate acute pathology on CT
examinations without having sustained acute trauma. New MRI techniques allow
rapid identification and diagnosis in as little as 30 minutes from initial
insult. Recent brain injury protocols have shown excellent results in
treating such patients with intravenous or intraarterial
thrombolytic agents. Child abuse Child abuse merits specific mention
because of the severe morbidity and mortality of cranial injuries inflicted
in abusive settings and because of the possibility of intervention to spare
other household members further trauma. The key to diagnosis of child abuse
is repeated injury, which is present in the majority of victims. Presence of
hemorrhages of various ages and locations is pathognomonic
(see Images
20-22). Retinal hemorrhages, rib and long bone fractures, burns, and
other skin lesions are common. MRI is ideal for the evaluation of such
patients because of its superior sensitivity and ability to date the injuries
with accuracy. It further offers the benefit of not using ionizing radiation.
Penetrating trauma CT is the diagnostic procedure of
choice for patients with gunshot wounds and other penetrating trauma. The
course of the projectile may be identified, and location of foreign bodies
can be noted. Hematomas and mass effect are easily
assessed. (See Images
23-27.)
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