36ournal of Neurology, Neurosurgery, and Psychiatry 1996;60:362-369

NEUROEPIDEMIOLOGY

Epidemiology of head injury

Bryan Jennett

In western countries injuries are the leadingcause of death under the age of 45 years, and inseveral Third World countries that applies alsofor ages 5-45 years. Because many injury vic-tims are young, more years of life are lost inmales below the age of 65 from trauma thanfrom cardiac and cerebrovascular disease, or

from cancer, in the United States, Japan, andseveral European countries.' Up to half oftrauma deaths are due to head injuries butthese account for most cases of permanent dis-ability after injury.2 Recognition that headinjury is a major health problem has led to sev-

eral studies over the past decade to produceepidemiological data in order to devise effec-tive preventive measures, and to plan the mostappropriate health care provision both foracute care and the rehabilitation of disabledsurvivors.

Limitations of available dataReliable statistics are difficult to discover fromroutinely collected data. International compar-

isons of deaths from injury do not identifyhead injuries, although their incidence reflectsgeographical differences and trends over timein the frequency of trauma deaths as a whole.There are wide differences between countriesin how many deaths are attributed to injuries,and how many injury deaths are due to motor

Professor emeritus ofneurosurgery, Instituteof NeurologicalSciences, University ofGlasgowB Jennett

Table 1 Deaths from injury in different countries in 19853

Motor vehicleInjuries as % as % of injuryof all deaths deaths

France 7 30Australia 5 51United States 5 48Canada 5 42Japan 4 42The Netherlands 3 41Scotland 3 30England 2 36

Table 2 Road deaths per 100 000 population41980 1985 1993

France 21 20 17Australia 24 18USA 23 19 16Canada 23 16 -

Japan 10 10 11The Netherlands 13 11 8Great Britain 11 9 7

vehicle or road deaths (table 1). The best timetrend data are for road deaths and these havebeen falling for some years in many developedcountries (table 2). This is believed to bemainly due to preventive measures such as

seat belts, motorcycle helmets, enforcing lawson alcohol limits for drivers, speed limits, andimproved car and road design. For example, inGreat Britain the number of motorists testedfor alcohol level in 1994 was 80% higher thanthe average for 1981-5, whereas the absolutenumber testing positive was halved; fatalitiesassociated with drink driving were reduced by70%. Rates for road deaths are much higherin developing countries where such measures

have not been taken (table 3), and are believedto be rising in such countries as vehiclesbecome more common. In Taiwan deaths dueto vehicle accidents rose from 31 per 100 000population in 1977 to 37 per 100 000 in19877-higher than in any of the countries intable 2.

Data on hospital discharges and on deathsat national or local level do allow head injuriesto be identified by the codes of theInternational Classification of Diseases (ICD)that specify location of injury. However, thereare several difficulties in using these that limitthe accuracy of data not only in routine statis-tics but also in research surveys that rely on

ICD coding alone for case ascertainment. Inthe current (9th) edition of these codes8 headinjuries are covered by no less than 10 rubrics(table 4); moreover these are based on patho-logical rather than clinical criteria, and theyare not mutually exclusive. For example,intracranial haematoma, the commonest treat-able complication causing death and disability,is associated with skull fracture in 75% ofcases, yet it is classified by a rubric that seems

to exclude skull fracture. Severity of injury isalso difficult to identify reliably from ICDcodes. In particular the three digit codes make

Table 3 Road deaths per 1000 million vehicle km

19856 J9934

United States 15 9United Kingdom 18 5Japan 22 15South Korea 540Cameroons 530Kenya (1984) 390 -

S Africa (1984) 180

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Epidemiology ofhead injuty

Table 4 International Classification ofDiseases8

Three digit categories:Fracture of skull, spine, and trunk (N800-N09)N800 Fracture of vault of skullN801 Fracture of base of skullN802 Fracture of face bonesN803 Other and unqualified skull fracturesN804 Multiple fractures involving skull or face with other bones

Intracranial injury (excluding those with skull fracture):N850 ConcussionN851 Cerebral laceration and contusionN852 Subarachnoid, subdural, and extradural haemorrhage after injury (without mention

of cerebral laceration or contusion)N853 Other and unspecified intracranial haemorrhage after injury (without mention of

cerebral laceration or contusion)N854 Intracranial injury of other and unspecified nature

no reference to the duration or degree ofimpaired consciousness, the universally recog-nised clinical criterion of severity. Morerecently an expanded five digit clinical modifi-cation (ICD 9-CM) has been introducedwhich deals with the anomalies of fracturesand haematomas and in a fifth digit registersduration of unconsciousness,9 and this is nowused in some United States hospitals. Anotherproblem is the variation in the use of codesbetween hospitals when recording similarinjuries, as well as simple coding errors. In one

United States survey nearly two thirds of headinjuries selected by ICD codes were excludedwhen the medical records were reviewed.'0Therefore higher incidence rates will bereported from surveys based on routine codingthan when case records are reviewed. Forexample, Lyle et al" have suggested that therate of 392 admissions per 100 000 populationin New South Wales reported by Selecki et al "2should be reduced to 266, to take account ofthe experience of Klauber et al in San Diego."3Incidence rates based on admissions (or dis-charges) may also be inflated by the doublecounting of patients transferred between acutehospitals (for example, from primary surgicalwards to neurosurgical units and perhaps thenback to primary surgical wards), and also bythe inclusion of late admissions with delayedcomplications. Each of these has been esti-mated to account for 2% of recorded admis-sions for head injury.

Reports about head injuries from cliniciansare of limited value. The several different spe-cialists who are responsible for head injuries ofdifferent severities, together with varyingadmission and transfer policies in differentplaces, make it difficult to put these reportsinto an epidemiological setting. The catch-ment population is often unknown, and thefactors affecting the selection for treatment by a

particular clinical unit are unlikely to be recog-

nised, unless there are explicit policies. Mosthead injuries admitted to hospital are mild,but many clinical reports are from neurosur-geons who focus only on the 5%-10% ofsevere or complicated injuries that are trans-ferred to them. Two large sets of data aboutsevere injuries prospectively collected accord-ing to strict protocols from several centres are,

however, now available. The internationalstudy of severe injuries that began in theInstitute of Neurological Sciences in Glasgowin 1970 accumulated data from the Institutethere and from centres in The Netherlands

and California.14 15 The United States NationalComa Data Bank began 10 years later, collect-ing from four centres.'617 These two studiesprovide invaluable information about theminority of head injuries that are severe, butlittle about the population of head injuriesfrom which they were selected or about thecatchment populations. Reports from patholo-gists likewise focus on selected injuries, thosefrom forensic laboratories including many vic-tims who died instantaneously or very soonafter injury. Such deaths that occur beforeadmission to hospital account for two thirds ormore of deaths from head injury in the UnitedStates and Australia and 45% of those in theUnited Kingdom. Reports from neuropatholo-gists, by contrast, deal mostly with cases thatsurvived long enough to be referred to special-ist clinical centres, with very early deathsunderrepresented.

Definition ofhead injury: grading severityHead injury covers a wide range of severityfrom patients who die before admission tohospital to those with head injuries so mildthat they do not even attend hospital. Inbetween are those in coma, either initially or asa result of complications, those who are lessserious but are admitted to hospital, and themuch larger number who attend hospital butare sent home. Much of the difficulty in com-paring different reports about the features andfrequency of head injury stems from differingcriteria for the minimum degree of severityrequired for classification as a head injury.Most reports depend on administrative cate-

gories based on management or process,rather than on clinical criteria or outcome.The assumption is that cases admitted to hos-pital were more severe than those sent home,and that those transferred to a neurosurgicalunit were more severe again. However, man-agement policies, whether implicit or explicit,vary so much that the case mix of severity canvary widely from place to place. Policies caninfluence not only whether or not patients areadmitted to hospital but also when they aredischarged, so that duration of stay can bemisleading as a measure of severity. Associatedextracranial injuries can also distort the databy determining the admission, and prolongingthe stay, of some patients. Social factors mayhave a similar influence-for example, forelderly patients and those who are injured farfrom home.

Clinical evidence of damage to the head isthe most reliable way to recognise that a headinjury has occurred, but all definitions excludeinjuries confined to the face and foreign bodiesin the nose or ears. Scalp, skull, or brain mayeach be injured independent of the other. Only2% of attenders at Scottish accident depart-ments for recent head injury have a skull frac-ture, but 15%-20% of severe and fatal injurieshave no fracture.'8 Almost half of all attenderswith head injuries in Scotland have a scalp lac-eration, but few have any evidence of braindamage by the time they arrive in hospital.'920This applied to both adults and children and

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similar proportions have recently been foundfor a series of children in an American emer-gency room (personal communication). Somepatients who are fully alert and oriented do,however, have a period of amnesia for someminutes after the injury. Most of the patientswith head injuries admitted to hospital inBritain and the United States are only mildlyinjured. But a small minority of these patientsdevelop complications-brain swelling orintracranial haematoma or infection. More-over CT and MRI have recently confirmedwhat clinicians and psychologists have longsuspected, that there is structural brain dam-age in some patients whose injuries seem tohave been mild and who have not developedclinical complications.2'

It has been suggested that patients who donot have either altered consciousness of a cer-tain degree or duration, or neurological signs,should be excluded from estimates of inci-dence because they do not have brain injury.22In the light of the above clinical and imagingevidence the concept of "non-neurological"head injury seems to be unjustified on logicalgrounds, whereas it is certainly unwise fromthe standpoint of clinical management, asFife23 has also pointed out. These mild injuriesare so frequent that they make considerabledemands on the healthcare system, and theycause concern because of the small proportionwho develop serious early complications,and the larger number who develop post-concussional symptoms. They are importantalso when exploring the pattern of causation ofhead injuries as a basis for devising strategiesfor prevention because most mild injuriesmight well have been more severe, given onlyslightly different circumstances.When milder injuries are included, as they

are in most surveys, the incidence rates basedon admissions are considerably higher thanwhen only those with actual as distinct frompotential brain damage are counted. ThusKraus et al22 recorded only 180 cases of trau-matic brain injury per 100 000 population inSan Diego in 1981 compared with an estimateof 295 in 1978 in a study that included mildercases.'3 Similarly, Lyle et al, applying the sameexclusions to data from New South Wales,reduced the incidence from 266 to 180-200per 100 000 population."Trauma centres now commonly use the

abbreviated injury score (AIS) to define severityfor trauma in general.24 A conversion pro-gramme for deriving the AIS from the ICD 9-CM codes has been devised giving 5 severities:1/2 minor, 3 moderate, 4 serious, 5 severe.23However, it proved much more difficult toconvert the 519 possible combinations of headinjury codes reliably to the five AIS categoriesthan it did for injuries in other locations. Themost common severity classification is by theGlasgow coma scale,26 considering a score of13-15 as mild, 9-12 as moderate, and 3-8 assevere. Others have used duration of uncon-sciousness or post-traumatic amnesia, but aspost-traumatic amnesia is commonly as muchas four times as long as the duration of comathese alternative definitions allow a wide lati-

tude of severity. So also do the durations ofaltered consciousness used by differentauthors to distinguish mild from severeinjuries. Durations of less than 15 or 30 min-utes or 24 hours can count as mild, with severedefined as more than six or 24 hours of alteredconsciousness or evidence of brain contusionor intracranial haematoma. Classificationsbased on CT or MRI findings are suited onlyfor the more severe injuries admitted to neuro-surgeons.

Population based surveys in variouscountriesUNITED KINGDOMData for all deaths and for a 10% sample ofadmissions by ICD codes, and duration ofinpatient stay have been published annuallyfor many years in Britain, and these data forhead injuries in England and Wales up to1972 have been reviewed.27 More detailed datafor a stratified sample of injuries of all severi-ties in Scotland in 1974 and 1985 have beenanalysed by an epidemiological team inGlasgow.'92028 30 These studies includeddeaths before reaching hospital and attendersat emergency rooms sent home, as well asadmissions to general hospitals and to neuro-surgical units. The admissions included manypatients without definite evidence of braindamage.

UNITED STATESData on admissions for head injury are notroutinely collected on a national basis in theUnited States, but discharges after head andspinal cord injury were reported from a sampleof hospitals throughout the country during1970-4.3' Some local surveys have beenreported since then and these have beenreviewed by Jennett and Frankowski32 and byKraus.2 A report of head injuries in OlmstedCounty, Minnesota from 1935-74 includeddeaths, admissions, and attenders but onlythose with loss of consciousness, amnesia, orneurological signs.33 A survey in Bronx Countyin 1980 included admissions within 24 hoursof an injury associated with unconsciousnessof at least 10 minutes or skull fracture, neuro-logical signs, or seizure.34 Two surveys in SanDiego identified cases by different criteria for19781' and 1981.22 The second was based onadmissions with medically confirmed concus-sion or contusion and haemorrhage or lacera-tion of the brain, and included prehospitaldeaths. A Chicago study compared twosocioeconomically distinct communities: innercity and suburban; it included admissionswithin seven days of a blow to the head and alldeaths were included.35 A study of residentsadmitted to Rhode Island hospitals excludedearly fatal injuries,36 and the same went for astatewide study in Maryland.37 Almost allthese studies included cases of skull fracturewithout evidence of brain damage. A review ofroutinely collected mortality data from1979-86 in the United States as a whole bythe Centre for Disease Control identifieddeaths associated with head injury related to

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Table S Head injury admissions and deaths

Year CasePlace and of Admissionsl Deathsl fatalityreference study 100 000 100 000 rate (%)

USA National3' 1970-4 200 25 12-5Olmsted33 1935-74 193 22 11-3Bronx34 1981 249 28 10-8San Diego'3 1978 295 22 7-5San Diego22 1981 180 30 16-6Chicago35 1980

City black 403 32 7 9Suburban black 394 19 4-8Suburban white 196 11 5-6

Australia'2 1977 392 25 6-3Australia" 1977 180-200 25 14-15-6England27 1972 270 10 3-7Scotland20 1974-6 313 10 3-2Johannesburg46 1986 316 81 25-6France43 1986 281 22 7-8Spain44 1988 91 20 21-9Northern Sweden42 1984 249 17 6-8

age, sex, race, cause, and region,38 butacknowledged that these might have beenunderestimated by as much as 23%-44%-again indicating the limitation of routine sta-tistics.

OTHER COUNTRIESThe epidemiology of neurotrauma (head,spine, and peripheral nerves) was studied inNew South Wales, South Australia, and theCapital Territory of Australia in 1977 basedon admissions and death records.'2 39 InNorway admissions after head injury to aregional hospital in 1979-80 have beenreported40 and also to a county hospital nearOslo for 1974-5.4' A study in northernSweden was limited to persons aged 16-60years who had impaired brain function; itincluded early deaths.42 In the region ofAquitaine in France all admissions and deathsafter head injury were surveyed for the year1986.43 A study in Cantabria, Spain for 1988was limited to admissions with loss of con-sciousness, skull fracture, or neurologicalsigns, but excluded early deaths, whichaccounted for 92% of all deaths.44 A study inJohannesburg was limited to admitted patientsaged 15 years or over who had altered con-sciousness or evidence of contusion or lacera-tion of the brain, excluding prehospitaldeaths.45 46

Variations in frequency ofhead injuriesCalculations of incidence vary according towhether the numerator is deaths, admissions,or attenders. They also depend on how welldefined is the population denominator.Patients who were not local residents wereexcluded from some studies, but other reportssuggested that they be included on the basisthat they would be balanced by injuries sus-tained by local residents who were injuredelsewhere during the same period.

DEATHSIn several United States locations and inAustralia, France, and Spain death rates fromhead injury are two to three times those inBritain (table 5). That for adults inJohannesburg is eight times greater than inBritain for all ages. The only reported rate thatapproached the low British level is that from a

small sample of white patients in suburbanChicago.35 In Britain the death rate from headinjury has been falling since 196820 and wasestimated to be only seven per 100 000 in1994; a similar trend is reported from theUnited States.38 Age specific mortality graphsare similar in Britain and one United Statesstudy (fig 1), but set at a higher level in theUnited States.22 As in most countries for ages15-60 years male rates are about twice thosefor females; the peak incidence is in males inthe 15-30 age group.The case fatality rates for those studies with

population based rates for both admissionsand deaths vary between 25-6% forJohannesburg to 3-2% for Scotland. They arehigher when admissions are limited to caseswith definite brain damage, when early deathis excluded from incident rates based onadmission, and when a large proportion of alldeaths occur before hospital admission.Because many deaths occur before admissionthe in hospital case fatality rates are muchlower (1%-6%) and are available for somestudies that do not have population basedmortality rates (table 6). The case fatality ratesin clinical series of more severe injuries aremuch higher-14% for a regional neurosurgi-cal unit in Virginia,48 15% for Scottish neuro-surgical units,30 and 33%17 and 50%'5 foradmissions in coma.

ADMISSIONS TO HOSPITALAdmission to hospital is a less reliable indica-tor of the incidence of head injuries becausepolicies for admission vary widely even withinone country, but they are an important indica-

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Age (y)Figure 1 Age specific mortality rates for head injury. (A)San Diego 198122 (with permission); (B) England andWales 1985.47 Note the similarity in age distribution, withpeaks in young adults and elderly people. The rates for SanDiego are much higher at all ages than in England andWales.

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Table 6 In hospital case fatality rates (CFRs)

AdmissionPlace Study rate perand reference year 100 000 CFR (%)

San Diego'355 1978 295 < 31981 180 6

Maryland37 1986 132 4Rhode Island36 1980 152 4 9Norway4" 40 1974-5 236 1-3

1979-80 200 2-8Sweden42 1984 249 1-3France43 1986 281 2Spain44 1988 91 1-7Scotland28 1974 313 1-0

tor of the impact of local injuries on hospitalresources. The age specific admission rates arevery similar in Britain and the United States(fig 2) with a less dramatic rise in elderly peoplethan in the mortality rates (fig 1). In Britainthe regional range is 210-404 per 100 000 andfor other countries 91-403 per 100 000 (table5). However, most estimates are in the rangeof 200-300 per 100 000 despite differences inthe criteria of severity used for case ascertain-ment, and the much wider variations in deathrates. Moreover, despite these differencessome 80% of admissions for head injury inmost places are categorised as mild and only5%-10% as severe. The mild cases are patientswho were presumably admitted as a precau-tion against the development of serious com-plications. Thus two thirds of admissions toprimary surgical wards in Scotland in 1974had no skull fracture or evidence of braindamage and did not have an extracranialinjury to account for admission. About 60%-70% of all admissions in United Kingdomhospitals were discharged within 48 hours.Publication of guidelines for admission triagein Britain50 51 has led to some reduction in theproportion of attenders at accident and emer-gency departments that are admitted.'9 Thatfewer patients are admitted in the UnitedStates despite higher population mortalityrates may be accounted for by there beingaccess to neurosurgical advice in many morehospitals, giving other clinicians the confi-

Figure 2 Age specificincidence rates (admis-sions) for head injury. (A)Various USA studies2(with permission); (B)Scotland.49 The agedistribution is similar inthe two countries, and therates are less different thanfor mortality.

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A San Diego 1981)O A o San Diego 1978

)O_/ \ ~~xBronx 1980-10 0 Virginia 1978)OR- + Maryland 1986

" Rhode Island 1979-80

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10 20 30 40 50 60 70 80

Table 7 Attenders at accidentlemergency departmentsafter head injury: age specific rates per 100 000 populationperyear (Scotland 1985)'9

Children Adults All

All causes:All 4011 1473 1967Males 5340 2180 2832Females 2613 831 1158

Falls:All 2280 459 813Males 2924 544 1035Females 1603 381 605

Assaults:All 230 399 366Males 350 677 610Females 99 147 138

Road traffic accident:All 364 222 249Males 486 306 343Females 235 144 161

dence to send mildly injured patients home.

PATIENTS WITH HEAD INJURIES NOT ADMITTEDTO HOSPITALMany patients with mild injuries either seek nomedical attention or they attend hospital andare sent home after assessment. Data aboutsuch cases depend on specific surveys becauseno country keeps routine records of thesecases. In 1974 about 20% of attenders withhead injury in Scotland were admitted,29somewhat less than that a decade later. '9 This isvery similar to a report of 20 years ago fromVancouver,52 and recent findings for RhodeIsland.21 This last study estimated that duringthe years 1977-81 only 1 1%-22% (95% confi-dence interval) of head injured persons whowere medically attended, or who reported atleast one day of disability due to acute injury,were admitted to hospital. This indicated thatcases not admitted to hospital accounted for82% of all medically attended patients withhead injuries in the United States, and forabout half of all disability days due to headinjury.Some patients with minor head injuries may

deliberately minimise or conceal their injuries.Sportsmen may worry that doctors will adviseprolonged rest from their sport, and injuriesassociated with assault carry the risk of policeinvestigation if a hospital becomes involved.Local geography and ease of access to medicalcare also influence whether or not mildlyinjured patients seek attention. These various

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Figure 3 Age specificAge (y)

Figure 3 Age specific attendance rates for head injuies atScotish accident and emergency departments for 1985'9

F-, (with permission). About half the attenders are under 1575 + years, hence the earlier age for the peak of incidence rates

than for deaths or admissions.

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Epidemiology of head injury

Table 8 Attenders with evidence of brain damage*: agespecific rates per 100 000 peryear (Scotland 1985)19

Children Adults All

All causes:All 290 341 331Males 395 537 508Females 180 163 166

Falls:All 130 118 120Males 165 168 167Females 94 73 77

Assaults:All 6 147 78Males 8 171 137Females 4 26 22

Road traffic accident:All 99 70 76Males 141 77 112Females 55 39 42

*Brain damage = any evidence of altered consciousness eitherbefore or after reaching hospital, or neurological signs.

Table 9 Distribution (%o) of causes in different places(based on admission ± early deaths)

Place and Road trafficreference accidents Falls Assault

USA' 49 28 NIOlmsted Co"3 47 29 4Bronx34 31 29 33Sand Diego" 48 21 12Rhode Island36 39 35 9Chicago35

City black 31 29 40Suburban black 32 21 26Suburban white 39 31 10

Maryland37 49 26 11Australia'" 53 28 NIScotland 24 39 20France43 60 32 1Spain" 60 24 NITaiwan7 90 5 NIJohannesburg46 M 35 4 45

F39 3 38

NI = no information.

factors combine to limit the accuracy of esti-mates of the incidence of head injuries as awhole. Indeed they can only be reliablycounted when they impinge on the hospitalsystem, or on the coroner or medical exam-iner. The number of patients who present athospital after injury is, however, probably thebest guide to the incidence, because this isleast likely to be influenced by differencesbetween health care systems, or local admis-sion policies.

Incidence rates for attenders in Scotland in1985 have been calculated on the basis of acountrywide survey (table 7). About half theattenders were children (under 15 years) giv-ing an earlier peak incidence than for deaths oradmissions (fig 3). Only about 20% of adultsand 9% of children had any evidence of braindamage-either impairment of consciousnesson arrival, or a history of brief post-traumaticamnesia or witnessed impairment of con-sciousness. In both adults and children 40%

Table 10 Main causes ofhead injury according to severity

A and E PSW NSU NSUattenders admissions transfers severe Deaths

Year 1985 1985 1985 1984-6 1985n 5242 1130 572 391 4100

Falls (%) 41 39 37 27 25Assaults (%) 20 20 15 12 2Road accidents (%) 13 24 32 50 58Pedestrians

as % of road traffic accidents (%) 29 39 46 50

A and E = Accident and emergency department (Scotland); PSW = Primary surgical ward(Scotland); NSU = neurosurgical unit (Glasgow); Severe = coma > 6 hours (Glasgow).Deaths includes deaths at scene (England and Wales).

had a scalp laceration, which is more oftenfound in those without brain damage.Incidence rates for those with brain damagewere naturally much lower than for all atten-ders (table 8).

DISABILITY AND PREVALENCEA significant proportion of survivors of headinjury are left with disability which may beboth considerable and prolonged and it is ofsome importance to estimate the incidenceand prevalence of such cases. Kraus2 empha-sises that even patients with mild injuries maybe left with some disability for some months,and he calculated that the number of newcases of disability from head injury per year inthe United States varies from 33-45 per 100000 according to whether 10% or 18% ofpatients with mild injuries are estimated ashaving some disability. Lyle et al II estimate onthe basis of the San Diego study22 that thereare two per 100 000 new cases of severe dis-ability and four per 100 000 of moderate dis-ability per year there; he made a similarestimate for New South Wales. Because dis-ability can persist for years the prevalence ratesare much higher-one estimate for the UnitedStates was 439 per 100 000.3" However,Moscato et al53 in a household survey inCanada estimated 54 per 100 000 having atleast six months of disability as a prevalencerate. The disability had lasted for more thanfive years in 65% of respondents and for morethan 10 years in 45%. In a similar householdsurvey in Scotland Bryden54 found a preva-lence rate of 100 per 100 000 for considerabledisability, compared with an incidence rate oftwo per 100 000 of such newly disabled sur-vivors.

Causes ofhead injuryAll reports show that the main causes of headinjury are road accidents, falls, and assaults.There is, however, considerable variation fromplace to place, with the proportion of admis-sions due to road accidents ranging from 24%in Scotland to 90% in Taiwan (table 9).Similarly the proportion due to assault rangesfrom 1% of males in France to 45% of malesin Johannesburg; in the United States therange is from 40% for inner city black personsin Chicago to 4% in Olmsted. The distribu-tion of causes also varies greatly with theseverity of injury, with road accidents thedominant cause only for severe and fatalinjuries (table 10). Within a given severitythere is also a pronounced difference in thedistribution of causes according to age and sex(tables 7, 8, and 11).Among those with fatal head injuries from

road accidents in the United States two thirdsare vehicle occupants compared with only40% in Britain, where pedestrians are oftenthe victims. Pedestrians are apt to be moreseverely injured than occupants and injuries topedestrians are particularly common in youngchildren and elderly people. In Taiwan 62% ofadmissions with head injury from road acci-dents were motor cyclists, 33% were pedestri-

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Table 11 Causes of head injury in admissions according to age and sex (Scotland 1985)

< 15y 15-64y > 65y Males Females All

n 351 653 117 785 336 1121Falls (%) 55 27 40 35 49 39Assaults (%) 5 32 3 34 12 20Road accidents (%) 23 24 23 24 23 24Pedestrians

as % of road traffic accidents (%) 63 24 52 34 49 39

ans, and only 5% were vehicle occupants.Clearly recommendations for preventive mea-sures must take account of local conditions.There is increasing awareness of the impor-tance of bicycle accidents, which are particu-larly common in children.55 57 Most of thechildhood accidents result from falls ratherthan collisions, and are often sustained off theroad. It is often unclear whether they areincluded in road accident statistics or comeunder recreational activities.

Falls are a significant cause of head injury,particularly in young children and elderly peo-ple. Many falls in adults are related to alcoholand others result from assault, so that falls arelikely to be underreported and the details areoften inaccurate.

Assault is a common cause of head injury insome places, particularly in economicallydepressed and densely populated urban areas.In the Bronx34 and inner Chicago35 assault wasthe leading cause of head injury, but overall inthe United States it accounted for only 10%.Within Rhode Island36 and San Diego58 ratesof admission to hospital for head injury due toassault varied fivefold with deciles of medianincome. The frequency of gunshot wounds ofthe head in the United States is unique to thatcountry, but there are wide regional variationsthere. There were 31 764 firearms relateddeaths in the United States in 1986, half ofwhich were suicides and a third homicides; insome places gunshot wounds of the headaccount for half of all suicides and homi-cides.59 Only 3%-6% of all admissions forhead injury in the United States were due tofirearms; they accounted for 20%-40% of alldeaths from head injury in some local studiesbut for only 14% in the national deathsreview.38

Alcohol is an important contributory causeof injury and its influence is best documentedfor road accidents, and especially for drivers.However, studies in New York city60 andGlasgow6' both showed that pedestrian victimsof head injury were more often intoxicatedthan injured drivers. In San Diego over halfthe brain injured cyclists over the age of 15were intoxicated.55 Alcohol is also a commonfeature of victims of assaults, of falls, and ofsuicides. In admissions for head injury inScotland alcohol featured four times moreoften after falls and assaults than after roadaccidents; in the latter pedestrians wereaffected twice as often as vehicle occupants.

Almost any sport or recreational activity canresult in head injury. It is seldom clear fromreports whether injuries ascribed to sport werelimited to organised games, or also includedinformal recreational play. However, theimportance of informal play as a cause of head

injury in the young is highlighted in a recentreport of 58 000 such injuries in United Statesemergency rooms.62 Playground equipmentand childrens' vehicles (excluding bicycles)were the main causes. In various United Statesstudies some 10% of admissions for headinjury were related to sport or recreationalactivities; in the Scottish survey 12% of newhead injuries coming to emergency depart-ments were attributed to sport.

Practical value of epidemiological dataProgrammes directed towards reducing thenumber of head injuries, and minimising thedamage to the brain when an accident doesoccur, have already had some impact. A strat-egy of prevention is, however, unlikely torealise its full potential unless there are reliabledata about the incidence, demography, andgeography of injuries in different places.Neither can the provision of medical servicesbe planned appropriately without this knowl-edge. There is evidence that mortality can bereduced if there is a coherent scheme for thecare of head injuries of all severities, but thatmost impact is made on less severe injuries.63Because mild injuries are so much more com-mon, and among them are some patients whowill develop serious but remediable complica-tions, it is essential to have guidelines for thevarious specialties involved, to ensure thatappropriate triage is carried out.64 This is allthe more essential in those countries whereCT and neurosurgical services are provided ona regional basis. In those places secondaryreferral of serious injuries, and of mild injuriesat risk of complications, is an essential compo-nent of good care for the community as awhole. Monitoring or audit of the carereceived and of the outcome depends on havingreliable denominators. With increasingemphasis in all countries on the quality of careand on cost effectiveness it is important toensure that reliable data are routinely collectedabout head injuries of all severities, theircauses, and their outcomes.

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7 Lee S-T, Louis T-N, Chang C-N, Lang D-J, HeimbergerRF, Fai H-D. Features of head injury in a developingcountry-Taiwan (1977-1987). J Trauma 1990;30:194-99.

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