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I. Evidence-based Neuroimaging for Traumatic Brain Injury.
II. Authors
Karen A. Tong, M.D.a
Udo Oyoyo b
Barbara A. Holshouser, Ph.D.a
Stephen Ashwal, M.D.c
a Department of Radiology, Loma Linda University Medical Center, Loma Linda, CA
b School of Public Health, Loma Linda University, Loma Linda, CA
c Department of Pediatrics, Loma Linda University Medical Center, Loma Linda, CA
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KEY POINTS
Issues
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Which patients with head injury should undergo imaging in the acute setting?
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What is the sensitivity and specificity of imaging for injury requiring immediate treatment/surgery?
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What is the sensitivity and specificity of imaging for all brain injury?
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Can imaging help predict outcome after traumatic (TBI)?
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Is the approach to imaging of children different?
IV. Key points
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Head injury is not a homogeneous phenomenon and has a complex clinical course. There are different
mechanisms, varying severity, diversity of injuries, secondary injuries, and effects of age or underlying disease.
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Classifications of injury and outcomes are inconsistent. Differences in diagnostic procedures and practice
patterns prevent direct comparison of population-based studies.
•
There are a variety of imaging methods that measure different aspects of injury (Table 1), but there is not one
all-encompassing imaging method.
•
Plain films have limited use for evaluating TBI (moderate evidence).
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Computed tomography (CT) is an important part of the initial evaluation and currently is the imaging modality
of choice for screening of life-threatening lesions requiring surgical intervention. It is probably more useful for
predicting short-term/crude (survival versus mortality) outcomes (moderate evidence).
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Magnetic resonance imaging (MRI) techniques are more sensitive than CT and are useful for secondary
evaluation. It is more useful for predicting long-term outcome; although utility remains controversial (moderate
evidence). Functional MR imaging holds promise for predicting neuropsychological outcomes (limited
evidence).
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Accurate prognostic information is important for determining management, but there are different needs for
different populations. In severe TBI, information is important for acute patient management, long-term
rehabilitation, and family counseling. In mild or moderate TBI, patients with subtle impairments may benefit
from counseling and education.
.
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X. Discussion of Issues
Issue: Which patients with head injury should undergo imaging in the acute setting?
Summary of Evidence
The need for acute imaging is generally based on the severity of injury. It is agreed that severe TBI (based
on GCS score), indicates the need for urgent CT imaging to determine the presence of lesions that may require
surgical intervention (strong evidence). There is greater variability concerning recommendations for imaging of
patients with mild or moderate TBI, although there are several recent guidelines (strong evidence) summarized in
take home tables 3 and 4.
Issue: What is the sensitivity and specificity of imaging for injury requiring immediate treatment/surgery?
Summary of Evidence
CT is the mainstay of imaging in the acute period. The majority of evidence relates to the use of CT for
detecting injuries that may require immediate treatment or surgery. Speed, availability, and lesser expense of CT
studies remain important factors for using this modality in the acute setting. Sensitivity of detection also increases
with repeat scans in the acute period (strong evidence).
Issue: What is the sensitivity and specificity of imaging for all brain injuries?
Summary of Evidence
The sensitivity and specificity of MRI for brain injury is generally superior to CT, although most studies
have been retrospective and very few head-to-head comparisons have been performed in the recent decade. CT is
clearly superior to MRI for the detection of fractures. MRI outperforms CT in detection of most other lesions
(limited to moderate evidence), particularly diffuse axonal injury (DAI). However, MRI is expensive and not widely
available, which also hinders research. Because different sequences vary in ability to detect certain lesions, it is
often difficult to compare results. MRI allows more detailed analysis of injuries, including metabolic and
physiologic measures, but further evidence-based research is needed.
Issue: Can imaging help predict outcome after TBI?
Summary of Evidence
The study of outcome prediction after TBI is complex. Predictor variables may not be as accurate if
measured too early, but may be less useful if measured too late. Evaluation of prognostic variables has ranged from
studying individual measures to comprehensive multimodal evaluations. Many clinical predictors have been studied
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including age, gender, GCS, pupillary reactivity, intracranial pressure (ICP), coagulopathy, hypothermia, hypoxia,
hypotension, hyperglycemia, electrolyte imbalance, in addition to imaging findings. Thatcher and colleagues
(moderate evidence) studied 162 patients and showed that combined measures are more reliable and accurate than
any single measure. There have been relatively few comprehensive studies of long-term prognostic indices
compared to acute prognostic indices (e.g. death versus survival).
Analysis of CT predictors of outcome have yielded variable results in the literature. CT abnormalities have
been analyzed individually, collectively (in various combinations) or combined with clinical prognostic variables.
Various studies have shown improvement in outcome prediction after severe TBI when adding CT information to
clinical variables (moderate evidence). CT has been studied more extensively than other imaging modalities,
although it is likely that MRI and other imaging methods will have greater value for predicting long term outcome.
Unfortunately, available evidence is sparse.
Issue: Is the approach to imaging of children with TBI different from adults?
Summary of Evidence
Pediatric TBI patients are known to have different biophysical features, risks, mechanisms, and outcomes
after injury. There are also differences between infants and older children, although this remains controversial.
Categorization of pediatric age groups are variable and measures of injury or outcomes are inconsistent. The GCS
and GOS have been used for pediatric studies, sometimes with modifications, or with variable dichotomization. For
infants and toddlers, some investigators have used a Children’s Coma Scale (CCS). There are several pediatric
adaptations of the GOS, such as the King’s Outcome Scale for Childhood Head Injury (KOSCHI), the Pediatric
Cerebral Performance Category (PCPC) or the Pediatric Overall Performance Category (POPC). Management
guidelines are controversial. There are few pediatric studies regarding the use of imaging and outcome predictions.
Guidelines in children are summarized in take home table 5.
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Table 1: Current imaging methods of traumatic brain injury
Modality
Principle & advantages/limitations
Use in TBI
CT
Xenon CT
Perfusion
MRI
MRI FLAIR
Based on x-rays, measures tissue
density; rapid, inexpensive,
widespread
Inhalation of stable xenon gas which
acts as a freely diffusible tracer;
requires additional equipment and
software that is available only in a few
centers
Uses RF pulses in magnetic field to
distinguish tissues, employs many
different techniques; currently has
highest spatial resolution; complex
and expensive
Suppresses CSF signal
Detects hemorrhage and
‘surgical lesions’
Detects disturbances in CBF due
to injury, edema or infarction
Detection of various injuries,
sensitivity varies with different
techniques
Long term outcome –
global or
neuropsychological
Detection of edematous lesions,
particularly near ventricles and
cortex; as well as extra-axial
blood
Detection of small parenchymal
hemorrhages
Long term outcome –
global or
neuropsychological
MRI - T2*
GRE
Accentuates blooming effect, such as
blood products
MRI - DWI
Distinguishes water mobility in tissue
Detection of recent tissue
infarction or traumatic cell death
MRI - DTI
Based on DWI, maps degree and
direction of major fiber bundles;
requires special software
Suppression of “background” brain
tissue containing protein-bound H20,
enhances contrast between water and
lipid-containing tissue
Analyzes chemical composition of
brain tissue; requires special software
Detects impaired connectivity of
white matter tracts, even in
normal-appearing tissue
May detect microscopic
neuronal dysfunction, even in
normal-appearing tissue
MRI - MT
MRI - MRS
MR
volumetry
fMRI
MR
Perfusion
(global, non
fMRI)
SPECT
PET
Measure volumes of various brain
structures or regions; time-consuming,
requires special software
Measures small changes in blood flow
related to brain activation; requires
cooperative patients
Measures tissue perfusion using
contrast or non-contrast methods;
better temporal resolution than PET,
SPECT; not as well studied
Photon emitting radioisotopes used to
measure CBF
Positron emitting radioisotopes act as
freely diffusible tracers, used to
measure CBF, metabolic rate (glucose
Potential Correlation
with Outcome
Short term outcome –
mortality versus
survival
Long term outcome –
global or
neuropsychological
Metabolite patterns indicate
neuronal dysfunction or axonal
injury, even in normal-appearing
tissue
Detects atrophy of injured
tissue, can quantitate
progression over time
Detects impairment or
redistribution of areas of brain
activation
Detects disturbances in CBF due
to injury, edema or infarction
Detects disturbances in CBF due
to injury, edema or infarction
Detects disturbances in CBF due
to injury, edema or infarction
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
Long term outcome –
global or
neuropsychological
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metabolism or oxygen consumption)
or response to cognitive tasks;
available only in a few centers
Abbreviations: CT-computed tomography; MRI-magnetic resonance imaging; FLAIR-fluid attenuated inversion
recovery; GRE-gradient recalled echo; DWI-diffusion weighted imaging; DTI-diffusion tensor imaging; MTmagnetization transfer; MRS-magnetic resonance spectroscopy; fMRI-functional magnetic resonance imaging;
SPECT-single photon emission computed tomography; PET-positron emission tomography; CBF-cerebral blood
flow.
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Table 3: Suggested guidelines for acute neuroimaging in adult patients with mild TBI (GCS 1315), modified from the Canadian Head CT Rule20, EAST guidelines2, and the Neurotraumatology
Committee of the World Federation of Neurosurgical Societies1
If GCS 13-15, CT recommended if have any one of the following:
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High risk
o GCS remains < 15 at 2 hours after injury
o Suspected open or depressed skull fracture
o Any clinical sign of basal skull fracture
o Two or more episodes of vomiting
o Aged 65 years or older
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Medium risk
o Possible loss of consciousness
o Amnesia for period before impact, of at least 30 minute time span
o Dangerous mechanism (pedestrian versus motor vehicle, ejected from motor
vehicle, fall from greater than 3 feet or five stairs)
o Any transient neurologic deficit
o Headache, vomiting
If GCS of 15, patient can be discharged home without CT scan if:
• Low risk
o GCS remains 15
o No loss of consciousness or amnesia
o No neurologic/cognitive abnormalities
o No headache, vomiting
Abbreviations: CT-computed tomography, TBI-traumatic brain injury, GCS-Glasgow coma scale.
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Table 4: Suggested guidelines for acute neuroimaging in adult patients with severe TBI (GCS 38)
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•
•
•
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CT scan all patients with severe TBI as soon as possible to determine if require surgical
intervention
If initial scan is normal, but have neurologic deterioration, repeat CT scan or consider
MRI as soon as possible
If initial scan is abnormal, but patient status is unchanged, repeat CT scan within 24-36
hours to determine possible progressive hemorrhage or edema requiring surgical
intervention, particularly if initial scan showed:
o Any intracranial hemorrhage
o Any evidence of diffuse brain injury
If initial scan is abnormal, repeat CT scan or consider MRI as soon as possible if GCS
worsens
Consider MRI within first few days if:
o Suspect secondary injury such as focal infarction, diffuse hypoxic-ischemic
injury or infection
Abbreviations: TBI-traumatic brain injury, CT-computed tomography, MRI-magnetic resonance imaging, GCSGlasgow coma scale.
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Table 5: Suggested guidelines for acute neuroimaging in pediatric patients with mild TBI (GCS
13-15) – and no suspicion of non-accidental trauma or comorbid injuries, modified from AAP
guidelines116 and the Cincinnati Children’s Hospital117
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CT scan if:
o History of loss of consciousness
o Disoriented
o Any neurologic dysfunction
o Possible depressed or basal skull fracture
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Observe or discharge home if:
o No loss of consciousness
o Oriented, neurologically intact
Abbreviations: TBI-traumatic brain injury, CT-computed tomography.
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