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rocognitive outcome, validated the assump-tion that MRI is superior for lesion detection[3]. CT and MRI were used to evaluate 36patients with isolated relatively mild headinjury and a Glasgow Coma Scale (GCS)score of 1315 [3]. All patients had loss ofconsciousness for fewer than 30 minutes andhad posttraumatic amnesia. Not surprisingly,MRI was substantially more sensitive thanCT for detection of parenchymal lesions,which were detected in 50% of patients onCT and 75% of patients on MRI. The rateof detection of nonhemorrhagic diffuse ax-onal injury (DAI) was 0% by CT and 11% byMRI. Similarly, the rate of hemorrhagic DAIdetection was 22% by CT and 47% by MRIand that for detection of contusion was 36%by CT and 57% by MRI.

Diffusion-Weighted Imaging andDiffusion Tensor Imaging

The use of diffusion-weighted imaging(DWI) and diffusion tensor imaging (DTI)in assessment of patients with traumatic braininjury is widely gaining acceptance. DWI can

detect changes in the rate of microscopic wa-ter motion, which is measured by the appar-ent diffusion coefcient (ADC). On the otherhand, DTI is based on the fact that microscop-ic water diffusion in white matter tracts tendsto occur in one direction rather than random-ly, a phenomenon termed anisotropy. Thedegree of aniso tropy in a white matter regioncan be viewed as a reection of the degreeof the structural integrity of white matter. Anumber of different measures of anisotropy

Imaging of Traumatic Brain Injury:A Review of the Recent MedicalLiterature

James M. Provenzale 1,2

Provenzale JM

1

Department of Radiology, Duke University MedicalCenter, Box 3808, Durham, NC 27710 . Addresscorrespondence to J. M. Provenzale.

2Departments of Radiology, Oncology, and BiomedicalEngineering, Emory University School of Medicine,Atlanta, GA.

N e u r o r a d i o l o g y / H e a d a n d N e c k I m a g i n g R e v i ew

AJR 2010; 194:1619

0361803X/10/194116

American Roentgen Ray Society

In recent years, many researchershave emphasized the role of vari-ous forms of brain injury in pro-ducing neurocognitive decits

and neurobehavioral abnormalities. As a re-sult, increased attention has turned to imagingevaluation of the head trauma patient. This re-view will examine some of the more impor-tant articles on the topic of imaging of headtrauma in recent years. Specically, articlespublished in the past 5 years (20052009) thatcontain information of interest to the radiolo-gist interpreting CT and MR ndings of headtrauma patients will be discussed. Space limi-tations allow review of only a small number ofarticles. Clearly, a number of excellent articlescontaining important information have notbeen included in this review.

Comparison of CT and MRI forLesion Detection

CT is standardly the rst imaging test per-formed in the emergency department settingfor evaluation of head trauma. The goal ofemergency imaging is to depict lesions that

need emergent neurosurgical treatment orin other ways alter therapy. In many institu-tions, MRI is reserved for showing lesionsthat could explain clinical symptoms andsigns that are not explained by pr ior CT or tohelp better dene abnormalities seen on CT.The increased sensitivity of MRI relative toCT for detection of many forms of brain in-

jury has been well-documented [1, 2]. A re-cent study, which was primarily designed tocompare CT and MRI for prediction of neu-

Keywords: brain, diffuse axonal injury, diffusion tensorimaging, diffusion-weighted imaging, MRI, susceptibility, trauma

DOI:10.2214/AJR.09.3687

Received September 27, 2009; accepted without revisionSeptember 29, 200 9.

F O C U S O N :

OBJECTIVE. This article provides a summary of some of the important articles pub-lished during the period 20052009 on the topic of imaging ndings in head trauma. The in-tent is to provide the latest information regarding the diagnosis of important abnormalitiesand new insights into their clinical signicance.

CONCLUSION. With the growing realization that even mild head injury can lead tovarious types of neurocognitive decits, medical imaging of brain injury has assumed even

greater importance than previously.

ProvenzaleImaging of Traumatic Brain Injury

Neuroradiology/Head and Neck ImagingReview


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can be used; one of the more commonly usedis fractional anisotropy (FA).

Regions of acute DAI can be depictedas bright lesions on DWI and dark regionson ADC maps because of restricted diffu-sion caused by acute cell death. In the past5 years, many studies have shown that thesetechniques can detect regions of DAI thatare subtle or undetected on T2-weighted andFLAIR images as well as provide a quantita-tive assessment of DAI for large areas of thebrain [4, 5]. A large number of articles havebeen published on this topic, and it is possi-ble to provide only some examples here rath-er than an exhaustive review.

ADC values can be measured in specif-ic regions or in the whole brain. In one arti-cle, investigators measured ADC values us-ing both methods and compared ndings in37 children with various degrees of brain inju-ry (measured by GCS scores) and neurologicoutcomes (measured by the Pediatric CerebralPerformance Category Scale [PCPCS]) and10 normal control subjects [4]. The authorsmeasured ADC values in normal-appearingbrain in the following regions: deep gray mat-ter, peripheral gray matter, deep white matter,peripheral white matter, posterior fossa, andwhole brain. The major goal of the study wasto determine whether ADC values in variousregions or in the whole brain could predictoutcome. The mean ADC value in peripher-al white matter was able to predict outcomein children with severe traumatic brain in-

jury. Overall, mean ADC in the whole brainwas the best predictor of outcome among alldegrees of traumatic brain injury. One of themore interesting aspects of this study is thatthe authors assessed only normal-appear-ing white matterthat is, the study showedthat important prognostic information can begleaned from abnormalities that are not ap-parent on conventional MR images.

DTI and another advanced MR tech-nique, MR spectroscopy, were recently com-pared for their ability to predict outcome ina group of 43 traumatic brain injury patientswho were imaged, on average, approximate-ly 3 weeks after trauma [6]. FA values weremeasured at 16 sites within the supratentorialand infratentorial white matter or brainstem.The metabolite N -acetyl aspartate (NAA), amarker of neuronal integrity, was measuredand compared with the stable metabolite cre-atine (Cr) at ve locations on an axial im-age through the level of the lentiform nucleusand expressed as the NAA:Cr ratio. Patientswere divided into either a favorable outcome

group ( n = 24) or an unfavorable outcomegroup ( n = 19) depending on scores on theGlasgow Outcome Scale performed at 1-yearfollow-up after trauma. In 15 of the 16 brainregions studied, FA values were signicant-ly reduced in the unfavorable outcome groupcompared with both the favorable outcomegroup and normal control subjects. In all ofthese regions, FA values were signicantlydecreased in the favorable outcome groupcompared with normal control subjects. Theauthors attributed decreased FA to disrup-tion of axonal membranes and the cytoskel-etal network. With regard to MR spectros-copy ndings, in all ve regions in whichthe NAA:Cr ratio was measured, statisticallysignicant differences were found betweenthe unfavorable outcome group and the oth-er groups and between the favorable outcomegroup and normal control subjects. The au-thors attributed these ndings to axonal lossor decreased metabolism.

Detection of MicrohemorrhagesA type of lesion termed the cerebral micro-

hemorrhage has gained importance amongmany researchers because such hemorrhagesfrequently accompany DAI. For some inves-tigators, such lesions serve as a biomarker ofDAI [7]. Interest in t raumatic brain lesions ofall types, but especially DAI, in professionaland amateur athletes alike has increased be-cause it is apparent that concussion and otherforms of head injury may have both acute and

long-lasting effects on neurocognitive func-tion [8, 9]. Detection of microhemorrhagesdepends on a fairly large number of factors,such as pulse sequence, TE, slice thickness,spatial resolution, and possibly imaging plane,which have recently been explained in a de-tailed review article [10]. For instance, thesusceptibility effect induced by gradient-re-called echo and susceptibility-weighted im-aging (SWI) sequences causes microhemor-rhages to appear more conspicuous relative toother pulse sequences. The term SWI refersto a high-resolution MR technique in whichimages containing the phase information, andnot solely images containing the magnitudeimages, are provided [11]. The phase imagesare sensitive for depiction of regions of localalteration of the magnetic eld (i.e., suscepti-bility) caused by various substances, such ashemorrhage and iron and other metals. Thus,SWI would be expected to be a sensitivemeans to show microhemorrhages.

As mentioned earlier, the capacity of var-ious forms of head trauma (in some cases,

even head trauma that is generally consid-ered to be relatively mild) to produce im-paired cognitive and memory function hasbeen increasingly recognized. As a result, thestudy of brains of amateur and professionalathletes has assumed greater importance. Asan example, in one recent study, researchersstudied the prevalence of cerebral microhe-morrhages in amateur boxers [12]. Forty-twomale amateur boxers underwent imaging on a3-T scanner using an axial spin-echo MRI se-quence, a 3D sagittal magnetization-preparedrapid acquisition of gradient-echo sequence,a coronal T2*-weighted sequence, and an ax-ial time-of-ight MR angiography sequence.Findings were correlated with a number ofboxer characteristics (total numbers of ghtsand knockouts, weight division, and durationof boxing) and with MR ndings in 37 nor-mal, nonboxing male volunteers. The studyshowed more microhemorrhages in amateurboxers (three of 42 individuals with micro-hemorrhages) than in the normal population(none of 37), but the difference was not statis-tically signicant, which the authors believepossibly to have been caused by the small pa-tient sample.

A comparison of various MRI pulse se-quences for detection of microhemorrhageshas been the subject of a number of studies.Two such articles are briey reviewed here. Inone report, researchers compared the sensitiv-ities of MRI using a T2*-weighted gradient-echo sequence at two eld strengths, 1.5 T and

3 T [7]. The study population consisted of 14adult patients who experienced head traumain road accidents. On average, approximatelytwice as many microhemorrhages were seenin each patient at 3 T compared with 1.5 T.However, in only one patient were microhem-orrhages seen solely at 3 T. The authors con-cluded that scanners with a eld strength of1.5 T appear to be sufcient for detecting mi-crohemorrhages and that the increased sensi-tivity offered by 3-T scanners may not provideadditional clinical information.

In another study, the sensitivities of SWIand 2D gradient-echo T2*-weighted imaging,

another hemorrhage-sensitive sequence, fordetection of microhemorrhages were com-pared recently in a small group of patientswith suspected brain injury [13]. The studypopulation consisted of 15 pediatric and adultpatients with GCS scores varying across awide range. The report found that SWI detect-ed approximately four times as many hemor-rhagic foci as T2*-weighted imaging. Theauthors report that the difference between


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Provenzale

the two techniques was especially evident fordetecting lesions in the corpus callosum.

Notably, those studies solely addressed theissue of the sensitivity of various imagingtechniques for detecting microhemorrhages;the important topics of how the detection ofsuch lesions inuences patient care and theimpact of such lesions on patient outcomewere not addressed. However, such topics areaddressed in other articles in the PredictiveModels section of this article.

Predictive Models for Uses of Imagingin Head Trauma

It is clear that simply knowing which im-aging technique is superior for lesion detec-tion does not allow us to fully assess the mer-its of various techniques. For instance, onetechnique might be twice as sensitive as an-other for detecting regions of DAI, but theincreased sensitivity might not alter decisionmaking or translate into changes in clinicaloutcome for patients. The elds of decisionanalysis and outcomes research as applied toradiology deal with the issues of how physi-cians use data that imaging studies provide[14, 15]. For example, studies have been per-formed that examine how emergency de-partment physicians make decisions aboutordering CT for patients with subarach-noid hemorrhage [16]. However, little hasbeen written about the ways in which spe-cic types of imaging guide the decisions ofphysicians in treating head trauma patients

or the ways in which imaging studies benetpatients by producing improved clinical out-comes. Nonetheless, a number of articles ex-amining how well imaging techniques pre-dict (rather than change) patient outcomehave been written in the past 5 years; someof those articles are reviewed next.

CT for Prediction of Mortality inHead Trauma Patients

Because almost all head trauma patientsundergo CT as the rst imaging test, re-searchers have attempted to develop meth-ods to use early CT ndings for determiningprognosis. For instance, in 1991, Marshallet al. [17] proposed a scoring scale for de-termining prognosis in head trauma patientsbased on CT criteria. The scale categoriz-es patients on the basis of the presence of aspace-occupying lesion (or recent evacuationof such a lesion, e.g., a subdural hematoma),intracranial abnormalities, and ndings ofincreased intracranial pressure (e.g., obliter-ation of basal cisterns or brain shift). Mul-

tiple studies have validated this scale and ithas gained widespread acceptance.

In a recent article, investigators used imag-ing ndings of patients from a previously pub-lished multicenter trial to rene the Marshallclassication [18]. The subjects were betweenthe ages of 15 and 65 years, had recent closedhead trauma, and were classied as having ei-ther moderate (GCS score of 912) or severe(GCS score of 38) injury. Outcome predic-tion was based on CT ndings within 4 hoursof injury. The researchers rened the Mar-shall classication scheme in two ways. First,they provided a more detailed analysis of twoparameters: presence of mass lesions and sta-tus of the basal cisterns (as a reection of in-tracranial pressure). In addition, they addedtwo CT parameters that were not includedin the Marshall classication: traumatic in-traventricular hemorrhage and subarachnoidhemorrhage. Next, the investigators comparedthe ability of this rened scheme to forecastoutcome against alternative predictive modelsthat the authors developed. Using this meth-od, the authors conrmed the predictive valueof the Marshall classication. However, theyfound that better discrimination was possibleusing individual components of the classica-tion scheme (rather than the entire scheme)and adding the new hemorrhage parameterspreviously outlined. Based on these results,the authors devised a simple prognostic CTscoring scale for probability of mortality inpatients with moderate or severe traumatic

brain injury.In a discussion section published at the

end of the article, reviewers noted some studylimitations [18]. Among other items, they cit-ed that the study does not assess patients withmild traumatic brain injury; some imagingcriteria (e.g., assessment of size of basal cis-terns) are quite subjective and might be opento substantial interobserver variability be-tween readers having different levels of train-ing; and unlike some other scoring scales, thestudy assessed CT scans very early in the clin-ical course whereas CT ndings often pro-gressively worsen after that initial per iod.

Comparison of CT and MRI for Prediction ofNeurocognitive Outcome

In the study cited earlier that comparedsensitivity of CT and MRI for detection oftraumatic lesions [3], 28 patients also under-went neurocognitive testing at three time in-tervals after head trauma: within 2 weeks, at1 month, and at 1 year. Two blinded read-ers assessed CT scans and MR images us-

ing a large number of ndings associatedwith head trauma (e.g., extraaxial uid col-lections, midline shift, etc.). MRI ndingsand neurocognitive scores were comparedwith those of 18 healthy control subjectsmatched to patients for various characteris-tics. The control subjects underwent MRI butnot CT. Signicant differences were found inneurocognitive scores between patients withabnormal imaging ndings, normal imagingndings, and control subjects. However, neu-rocognitive scores did not signicantly differbetween patients with normal imaging nd-ings and those with abnormal imaging nd-ings. In fact, neither CT nor MRI ndingspredicted neurocognitive decits soon afterinjury or at 1-year follow-up. Thus, early im-aging ndings were not found to have predic-tive value for clinical outcome.

Although CT ndings were not found to bepredictive of neurocognitive outcome in thestudy just described, in another, larger study,early CT ndings were predictive of neurologicoutcome [19]. In that study, investigators exam-ined the predictive value of CT for functionaloutcome in a large group of patients with mi-nor head injury (dened as GCS score of 13).CT was assessed for many different forms ofparenchymal injury and various types of skullfractures. The clinical outcomes measured in-cluded the Glasgow Outcome Scale, modiedRankin Scale, and Barthel Index. Parenchymalinjury (i.e., contusions and DAI) was predic-tive of a poor clinical outcome in a statistically

meaningful way.Finally, in yet another study, the researchers

compared CT and various MRI techniques forpredicting neurologic outcome at 612 monthsin 40 children with traumatic brain injury [20].All children underwent CT within 24 hoursof injury and MRI was performed using T2-weighted, FLAIR, and SWI pulse sequencesat an average of 7 days after trauma. Regionsof parenchymal hemorrhage and edema wereanalyzed using a computer software programthat semiautomatically counted and tracedlesion outlines. Imaging ndings were com-pared with outcomes determined using the

PCPCS. Patients were assigned to one ofthe following outcome categories based onPCPCS score: normal, mild disability, orpoor outcome (i.e., moderate or severe dis-ability or vegetative state). CT scores did notdiscriminate between any of the three out-come groups. Furthermore, within the pooroutcome group, 40% of children had normalCT ndings. However, all MRI sequencesdiscriminated between outcome groups in a


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statistically signicant manner by differenc-es in both lesion counts and lesion volumes.SWI showed substantially more lesions com-pared with the T2-weighted and FLAIRpulse sequences; on the other hand, lesionvolumes measured on either T2-weighted orFLAIR pulse sequences were substantiallygreater than those measured on SWI.

SummaryThis review has outlined a variety of as-

pects of head trauma imaging in the recentmedical literature. It is worth summarizingboth the imaging advances and some issuesthat remain to be addressed. First, it is clearthat MRI is much more sensitive than CT fordetection of small trauma-related brain ab-normalities [3]. Furthermore, some MRI se-quences are particularly sensitive to detectionof specic forms of brain injury. However,the actual clinical relevance of this increasedsensitivity is relatively unclear. Although ar-ticles reporting correlation of imaging nd-ings and clinical outcome have some value,more information is needed regarding howthe increased sensitivity of MRI techniquesaffects physician decision making.

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