1998 Plenary Session: Imaging Symposium

Transcription

1 1998 Pleary Sessio: Imagig Symposium LEARNING OBJECTIVE Uderstad basic woud ballistics ad their radiographic implicatios. Gushot Ijuries: What Does a Radiologist Need to Kow? 1 Athoy J. Wilso, MB, ChB INTRODUCTION Ay discussio of gushot ijuries teds to evoke emotioal reactios from citizes o both sides of the political issues. The simple fact remais that gushot ijuries are a major cause of morbidity ad mortality i cities i the Uited States. The age group most affected is years (1,2). The icidece is greatest amog black males ad lowest amog white females. I several states, mortality rates from gushot wouds already exceed mortality rates from motor vehicle accidets (1 3). If curret atioal treds cotiue, mortality rates from gushot wouds could exceed mortality rates from motor vehicle accidets for the etire coutry i less tha 5 years (1). Util their icidece decreases substatially, gushot ijuries will cotiue to be commo i urba emergecy departmets. It is therefore essetial for radiologists who service these emergecy departmets to have a clear uderstadig of gushot ijuries ad their imagig. I this article, firearms ad their projectiles, mechaisms of gushot ijuries, ad imagig of gushot ijuries are discussed. FIREARMS AND THEIR PROJECTILES To uderstad the mechaisms of gushot ijuries, it is importat to uderstad the ature of firearms ad their projectiles. Ballistics is defied as the scietific study of projectile motio (4,5) ad is divided ito three categories: iteral, exteral, ad termial ballistics. Iteral ballistics has to do with the projectile withi the firearm. Exteral ballistics has to do with the projectile i the air. Termial ballistics has to do with what Figure 1. Sectioal diagram of a hadgu bullet. happes whe the projectile hits its target. Woud ballistics is a subset of termial ballistics ad is the most importat aspect of ballistics for physicias to uderstad (5,6). However, a basic uderstadig of all aspects of ballistics is helpful i uderstadig the woudig process. Hadgus, rifles, ad shotgus are the major types of firearms ecoutered i the Uited States. The woudig potetial of each is differet from that of the other two (4,6,7), ad it is importat to be aware of these differeces. The same weapo ca ofte fire several differet types of projectiles. The costructio of these projectiles also has a effect o woudig potetial (8). However, the ature ad severity of gushot ijuries deped o more tha just the type of weapo ad projectile. Local tissue factors ad the distace (rage) betwee the weapo ad the victim both have a major effect o these ijuries. It is therefore importat to be aware ot oly of the way projectiles behave before ad after impact but also of the maer i which various tissues respod to gushot ijuries. Idex terms: Foreig bodies Gushot ijuries, ** Trauma RadioGraphics 1999; 19: From the Departmet of Radiology, Harborview Medical Ceter, 325 Nith Ave, Seattle, WA From the Pleary Sessio, Friday Imagig Symposium: Acute Radiology Where Miutes Cout, at the 1998 RSNA scietific assembly. Received April 19, 1999; revisio requested May 4 ad received Jue 7; accepted Jue 9. Address reprit requests to the author. 2 **. Multiple body systems RSNA, Imagig Symposium Volume 19 Number 5

2 Table 1 Ballistic Data for Four Hadgus Bullet Muzzle Kietic Caliber Weight Velocity Eergy (iches) Weapo Type (grais) (ft/sec) (ft-lbs) automatic mm Luger 115 1, magum 158 1, magum 240 1,470 1,150 Table 2 Ballistic Data for Four Rifles Bullet Muzzle Kietic Caliber Weight Velocity Eergy (iches) Weapo Type (grais) (ft/sec) (ft-lbs) 0.22 Remigto , M ,200 1, Wichester 150 2,900 2, ,910 2,820 Hadgus ad rifles fire bullets. Before firig, the lead bullet is held firmly i the ed of a brass cartridge case. This cartridge case cotais a flammable propellat, kow as the charge, ad has a primer at its base (Fig 1). Whe the firig pi of the gu strikes the primer, the primer is detoated, which igites the charge withi the cartridge case. The burig gases expad ad propel the bullet from the cartridge case ad alog the barrel of the gu. Spiral grooves withi the barrel of the gu, kow as riflig, grip the bullet ad cause it to spi aroud its log axis. This spiig creates a gyroscopic effect, which gives the bullet directioal stability i the air, eablig it to travel straighter ad be more accurate tha a ospiig projectile (4,7). The loger the barrel, the more time the bullet has to accelerate ad the faster it will be goig whe it leaves the gu. Because rifles have loger barrels tha hadgus, rifle bullets leave the gu with much higher velocities tha hadgu bullets (Tables 1, 2). Because the kietic eergy of the bullet is equal to half its mass multiplied by the square of its velocity, high-velocity bullets have much higher kietic eergy tha low-velocity bullets. This higher kietic eergy gives the rifle bullet greater woudig potetial tha the hadgu bullet (4,5,7). However, woudig potetial is oly part of the equatio (5 7). Although rifle bullets have greater eergy available for woudig tha hadgu bullets, the woudig mechaisms of the two are similar i may respects (5). Whe the bullet strikes its target, it ceases spiig. Havig lost its directioal stability, it is ow able to tumble (rotate aroud its short axis). A odeformed bullet will usually be tapered at its distal ed ad hece have more mass cocetrated at its proximal ed. The bullet will thus ted to tumble through 180 ad cotiue through the target with its proximal ed leadig (7). This tedecy meas that bullets see o radiographs frequetly do ot poit toward their directio of travel ad will ofte poit toward their etry wouds. If the bullet is deformed by impact with the target (Figs 2, 3), this tedecy to tumble will be September-October 1999 Wilso RadioGraphics 1359

3 Figures 2, 3. (2) Radiograph of expeded bullets. The bullets were imaged o a step spoge at various distaces from the film. Thus, each has a differet magificatio ad its caliber caot be accurately measured. All of these bullets were fired ito a water bath. Several show deformities characteristic of their costructio. They are as follows: 1, soft-poit 0.44 magum bullet; 2 ad 3, hollow-poit 0.38 special bullet; 4 ad 5, hollow-poit semijacketed 9-mm bullet; 6, solid-poit fully jacketed 9-mm bullet; 7, 7.62-mm fully jacketed rifle bullet; 8, jacket fragmet of soft-poit rifle bullet; 9, lead fragmet of soft-poit rifle bullet; 10, solid-poit ojacketed 0.22 bullet; ad 11, hollow-poit ojacketed 0.22 bullet. (3) Bullet deformatio patters. Solid straight arrows = live rouds, ope arrows = empty cartridge cases, arrowheads = spet bullets. All of the spet bullets were fired ito a water bath. (The radiograph i Fig 2 icludes all of the spet bullets show here.) (a) Photograph of fully jacketed 9-mm hadgu rouds shows lack of deformatio of the bullet ad the spiral riflig marks (curved arrow) o the sides of the bullet. (b) Photograph of hollow-poit semijacketed 9-mm hadgu rouds shows the characteristic mushroomig of the bullets. The bullet o the right has a metal post withi its hollow ose, but this post has little effect o the overall patter of deformity. (c) Photograph of soft-poit caliber rifle bullet shows oly two of the multitude of bullet fragmets from the water bath. The left fragmet is a piece of lead, ad the right is a piece of copper jacket modified ad may eve be elimiated completely (7,8). Bullets are usually classified by caliber (Fig 2), which is a measuremet of the diameter of the bullet, most commoly i decimals of a ich (eg, 0.308) or i millimeters (eg, 9 mm). The measuremet of caliber does ot address the weight of the bullet or the size of the charge, which are importat factors i determiig kietic eergy (Tables 1, 2). Bullet costructio also has a effect o woudig. Most bullets are made of lead. I may low-velocity weapos, the bullet is made etirely of lead. I medium- ad high-velocity weapos, bullets usually have a metal jacket surroudig the lead to protect them from deformity while they are i the gu barrel. A copper jacket is most commo, but occasioally other metals are used. If the bullet is etirely ecased, it is said to have a full metal jacket (Fig 3); if the bullet is partially ecased, it is said to be semijacketed. Semijacketed bullets typically 3c. have exposed lead at the tip ad are desiged to deform o impact (Fig 3). Some bullets have a ope cavity i their tips ad are referred to as hollow-poit bullets. Hollow-poit bullets are also desiged to deform o impact, which typically trasforms them ito a mushroom shape (Figs 2, 3) (8). Whe bullets deform o impact, 1360 Imagig Symposium Volume 19 Number 5

4 Figures 4, 5. (4) Hadgu bullet ijury to the head. Axial computed tomographic (CT) image of the head (boe widow) shows craial etry ad exit wouds with medial bevelig of the former ad lateral bevelig of the latter. The bullet was travelig from left to right. Note also how boe ad bullet fragmets from the etry woud are propelled ito the brai, whereas fragmets from the exit woud are propelled ito the scalp. (5) Hadgu bullet ijury to the leg. Ateroposterior radiograph shows that the bullet traveled from lateral to medial. Most of the boe ad bullet fragmets are see medial to the tibi Note the bevelig of the boe medially toward the directio of travel they decelerate faster, deliverig more of their eergy to a smaller volume of tissue. This desig is iteded to icrease tissue damage, makig the bullets more effective at woudig tha odeformig bullets (4,7,8). MECHANISMS OF GUNSHOT INJURIES Bullet ijuries are most severe i friable solid orgas (eg, the liver ad brai) (4), where damage may be caused by temporary cavitatio remote from the actual bullet track. Dese tissues (eg, boe) ad loose tissues (eg, subcutaeous fat) are more resistat to bullet ijury (4,5). Boes modify the behavior of bullets markedly, alterig their course, slowig them dow, ad icreasig their deformity ad fragmetatio. Evaluatio of boe ijuries ad the distributio of boe ad bullet fragmets o radiographs ca be helpful i determiig the directio of travel, which is importat ot oly for cliical assessmet but also for foresic evaluatio of the icidet (5,9). Although radiography ca frequetly demostrate the directio of travel accurately, it has bee show that trauma physicias are uable to reliably distiguish exit wouds from etry wouds (10). Boe ad bullet fragmets are usually distributed alog the bullet track withi the soft tissues, beyod the defect i the boe (Figs 4, 5). Careful examiatio of the images should reveal bevelig of the boe (4,11,12) toward the directio of travel (Figs 4, 5). The degree of bullet fragmetatio is also affected by bullet costructio. The presece of a full or partial metal jacket has a major effect o deformity (4,8). Bullets with full metal jackets ofte remai i oe piece ad usually do ot September-October 1999 Wilso RadioGraphics 1361

5 Figure 6. Gushot ijury to the eck. (a) Lateral radiograph of the eck shows a fracture of the madible with adjacet bullet fragmets (arrow) ad a sigle large bullet fragmet i frot of the cervical spie. (b, c) Axial CT images obtaied through the madible (b) ad just below the madible (c) show that these are two separate ijuries. The distributio of boe ad bullet fragmets (arrows i b) shows that the bullet that caused the madibular fracture traveled from left to right. Vertebral fractures ad lead i the spial caal (straight arrow i c) idicate that the bullet (curved arrow i c) traveled through the spial caal ad vertebral body. The patiet was itubated ad pharmaceutically paralyzed whe he arrived i the emergecy departmet, ad his quadriplegia was ot suspected util these images were obtaied. deform much (Figs 2, 3). These projectiles typically do ot leave a trail of lead fragmets alog their path. O the other had, semijacketed, hollow-poit, ojacketed, ad soft-poit bullets ted to deform o impact or break apart (4,8), leavig a telltale trail of metal fragmets through the soft tissues (Figs 4 6) (9,12). Hollow-poit hadgu bullets usually deform by simply mushroomig with miimal fragmetatio (Figs 2, 3), whereas high-velocity soft-poit rifle bullets usually udergo marked fragmetatio (Figs 2, 7). This fragmetatio of high-velocity bullets creates a lead sowstorm appearace o radiographs (4,12) (Fig 7). The area over which the lead sowstorm fragmets are deposited i the soft tissues wides as the distace from the etry site icreases. Thus, a coical distributio of lead fragmets is see o radiographs, with the apex of the coe poitig toward the etry site Imagig Symposium c. Low-velocity weapos (eg, air gus ad smallcaliber hadgus) have much lower woudig potetial tha high-velocity weapos (4). Whereas close-rage ijuries with low-velocity bullets ca be fatal, medium- ad log-rage ijuries are ofte superficial. The subcutaeous tissue offers a path of least resistace for low-velocity projectiles. These bullets ad pellets ofte travel log distaces through the subcutaeous tissue but fail to peetrate the fascia (Fig 8). This pheomeo is most commo at medium to log rage ad whe the etry woud is at a shallow agle to the ski surface. If these projectiles are a log distace from the etry site, they may ot be icluded i the field of view of the iitial radiographs. If a low-velocity projectile is ot foud o iitial radiographs ad there is o exit woud, additioal radiographs over a wider field of view should be obtaied. Volume 19 Number 5

6 Figure 7. High-velocity rifle ijury to the hip. Ateroposterior (a) ad lateral (b) radiographs of the left hip show the typical lead sowstorm appearace of a high-velocity soft-poit rifle bullet. The bullet was travelig from frot to back. O the ateroposterior view (a), the lead fragmets are distributed i a circular patter. O the lateral view (b), the fragmets show a coical distributio, with the apex of the coe at the femoral fracture site ad the base of the coe posterior. This distributio of lead cofirms the directio of travel. The severe commiutio of the fracture from this high-eergy ijury makes it difficult to use bevelig of the boe to help determie the directio of travel. Figure 8. Low-velocity bullet ijury to the thigh. Ateroposterior (a) ad lateral (b) radiographs of the thigh show a bullet (curved arrow) that is itact ad remote from the etry woud (straight arrow). The bullet etered the ski at a steep agle ad did ot peetrate the fasci Istead, it traveled distally through the subcutaeous fat util it ra out of eergy adjacet to the patella ad stopped. Note that the bullet tumbled 180 as it traveled, ad its distal ed ow poits toward the etry woud. (Reprited, with permissio, from referece 13.) September-October 1999 Wilso RadioGraphics 1363

7 Figures 9, 10. (9) Sectioal diagram of a shotgu cartridge. The shotgu shell is ecased i a plastic cylider with a brass cap at its base. The distal ed of the cartridge cotais the pellets (shot), which are separated from the charge by plastic or paper waddig. As with bullet cartridges, the firig pi of the gu detoates the primer, which i tur igites the charge. The expadig gases from the burig charge expel the pellets from the cartridge ad alog the barrel of the gu. (10) Shotgu pellets. Photograph shows four groups of pellets. The left three groups are differet sizes of birdshot. The right group is size 00 buckshot. The pellets i this photograph are all made of lead. Figure 11. Shotgu ijury to the head. Ateroposterior radiograph of a self-iflicted ijury from a 12- gauge shotgu shows the devastatig ijury that a cotact woud from a shotgu ca produce. Shotgu ijuries differ substatially from rifle ad hadgu wouds (4,12,14). Rifles ad hadgus usually fire a sigle bullet with each shot (Figs 1 3), whereas shotgu shells usually cotai multiple metal pellets, also kow as shot (Figs 9, 10). Shotgus do ot have rifled barrels, ad their pellets do ot spi. The size of shotgu cartridges is ot measured i caliber but i gauge. The higher the gauge, the smaller the diameter (4). Shotgu pellets spread apart after leavig the barrel of the gu, ad their velocity rapidly decreases (4). As the pellets spread with icreasig rage, their area of distributio icreases ad the eergy i each pellet decreases. Thus, rage differeces affect the woudig potetial of shotgu pellets far more tha they affect the woudig potetial of bullets. At close rage, shotgu ijuries are usually far more severe tha bullet ijuries because the total eergy available is much greater (4,14). The combied mass of multiple pellets spread over a small area ca produce massive destructio of soft tissue ad boe (Fig 11). I cotact ijuries, ot oly the mass of the pellets but also most of the combustio gases eter the victim, causig devastatig ijuries (Fig 11). At log rage, the wider spread ad lower velocity of the pellets produce multiple, widely separated, superficial ijuries that are ofte paiful but rarely life threateig. At itermediate rage, shotgu ijuries are less predictable, with severity beig maily a fuctio of aatomic locatio ad pellet desity (Fig 12) (14). Pellets come i may sizes (Fig 10), but each idividual cartridge usually cotais oly oe size. Larger pellets are kow as buckshot, ad smaller pellets are called birdshot (4). Most ijuries ecoutered i cliical practice ivolve birdshot. As with bullet ijuries, the severity of shotgu ijuries varies with tissue type ad local aatomy. Vascular ijuries are of particular cocer because they ca result i pellet embolizatio (Fig 13) (15). Such emboli ca result i tissue ifarctio. I the past, all shotgu pellets were made of lead. However, recet wildlife 1364 Imagig Symposium Volume 19 Number 5

8 Figure 12. Shotgu ijury to the shoulder. (a) Ateroposterior radiograph of the shoulder shows a tight patter of birdshot. Some of the pellets are o loger roud, ad there are tiy scattered pieces of metal. This deformity ad fragmetatio cofirm that the pellets are made of lead. Because the regio of ijury icluded the axillary vessels, agiography was performed. (b) Agiogram shows itravascular pellets (arrows). Figure 13. Pellet embolizatio to the lugs. (a) Ateroposterior radiograph of the chest shows two well-separated shotgu pellets projected over the right lug (arrows). (b) Lateral radiograph shows that at least oe of the pellets is cetrally located withi the chest (arrow). These pellets were emboli from a close-rage ijury to the lower back with ijury to the iferior vea cav (Reprited, with permissio, from referece 13.) regulatios require shotgu pellets used o waterfowl to be made of steel. Steel pellets are ferromagetic ad ca move if the patiet is exposed to a strog magetic field, thus causig additioal damage. Therefore, magetic reso- September-October 1999 ace (MR) imagig may be cotraidicated i such patiets. Fortuately, steel ad lead pellets ca usually be distiguished from oe aother Wilso RadioGraphics 1365

9 Figure 14. Gushot ijury to the foot. Ateroposterior (a) ad lateral (b) radiographs of the foot show a fully jacketed 9-mm bullet i the soft tissues of the sole of the foot with a commiuted third metatarsal fracture superior ad posterior to the bullet. The relatioship of the bullet ad the fracture idicate that the projectile came from above ad behid, cofirmig that this patiet literally shot himself i the foot. Figure 15. Gushot ijury to the face. Ateroposterior (a) ad lateral (b) radiographs of the face show a madibular fracture with scattered boe ad bullet fragmets posterior to the madible. This appearace cofirms that the assailat was stadig i frot of the victim ad did ot shoot from behid, as the victim (who was also armed) had claimed. at radiography. Lead pellets ted to be deformed ad fragmeted by impact with soft tissues ad boe (Fig 12), whereas steel shot usually remais roud. Simple aalysis of a radiograph is all that 1366 Imagig Symposium is eeded to determie if a patiet with a shotgu ijury ca be safely placed i the MR imagig maget. Ufortuately, the same is ot true for jacketed bullets because the type of metal used for the jacket caot be determied from radiographs. Because bullet jackets are occasio- Volume 19 Number 5

10 c. Figure 16. Gushot ijury i a youg ma who preseted to the emergecy departmet with a sigle bullet hole i the posterior thorax. (a, b) Ateroposterior (a) ad lateral (b) chest radiographs show at least three separate clumps of lead (arrow ad arrowheads), which could ot possibly have come from a sigle bullet. (c) A old ateroposterior radiograph from the files shows that two of the clumps of lead predated the curret ijury. The rather superficial complete bullet (arrow i a ad b) is ot preset o the old radiograph ad was the oly acute ijury. ally made of steel, it may ot be safe to place a bullet woud victim ito a MR imager whe the ature of the bullet costructio is ukow. IMAGING OF GUNSHOT INJURIES The primary objectives of imagig are to determie the path of the projectile or projectiles, assess which tissues have bee ijured, estimate the severity of ijury, ad determie what additioal studies are eeded (9,11,12). The iitial work-up should always iclude covetioal radiography. To determie the course of the projectile or projectiles ad to begi to assess potetial tissue damage, two perpedicular views are essetial (12) (Figs 14, 15). CT ca be helpful for preoperative plaig i the head, eck, ad truk (Figs 4, 6) but is rarely ecessary i extremity ijuries. Agiography is essetial wheever vascular ijury is suspected (11,12) (Fig 12), ad vascular ijury must be suspected wheever the bullet travels close to major vessels. Palpable distal pulses are ot eough to exclude vascular ijury. I cases of recurret ijury, access to images from previous visits is ivaluable i determiig which of the bullet fragmets are ew (Fig 16). Careful evaluatio of radiographs ad CT images is geerally more reliable tha cliical evaluatio for determiig the directio of projectile travel ad the tissue or tissues ijured (9,10). Rapid acquisitio of adequate images is essetial i all patiets. I hemodyamically ustable patiets, there may be eough time for oly covetioal radiography before the patiet must be take to the operatig room (12). A rapid ad accurate assessmet of the path of the projectile ad its directio of travel makes plaig of surgical maagemet ad further imagig more efficiet. Placemet of ski markers prior to radiography is essetial to reliably locate the surface wouds o the images. September-October 1999 Wilso RadioGraphics 1367

11 CONCLUSIONS A radiologist who is familiar with the basic priciples of gushot ijuries ad who is available whe the patiet arrives ca have a major effect o imagig ad maagemet. Prompt ad accurate assessmet of the ijuries is essetial, both cliically ad radiographically. Although may patiets with gushot ijuries will be take directly to the operatig room, further imagig is eeded i some cases. Appropriate plaig of additioal imagig ad the surgical approach depeds o the acquisitio of appropriate iitial radiographs ad accurate determiatio of the paths of the projectiles. Two perpedicular projectios of the ijured area are essetial. With good imagig data, the orgas at risk ca be determied ad the best possible actio pla ca be made. REFERENCES 1. From the Ceters for Disease Cotrol ad Prevetio: deaths resultig from firearm- ad motor-vehicle-related ijuries Uited States, JAMA 1994; 271: Ceters for Disease Cotrol ad Prevetio Woder Web site. Available at: woder.cdc.gov. Accessed Jauary From the Ceters for Disease Cotrol: firearmrelated deaths Louisiaa ad Texas, JAMA 1992; 267: Dimaio VJM. Gushot wouds: practical aspects of firearms, ballistics, ad foresic techiques. Boca Rato, Fla: CRC Press, 1985; , Swa KG, Swa RC. Priciples of ballistics applicable to the treatmet of gushot wouds. Surg Cli North Am 1991; 71: Adams DB. Woud ballistics: a review. Mil Med 1982; 147: Hollerma JJ, Fackler ML, Coldwell DM, Be- Meachem Y. Gushot wouds. I. Bullets, ballistics, ad mechaisms of ijury. AJR 1990; 155: Padra JC, Baroe JE, Reed DM, Wheeler G. Expadig hadgu bullets. J Trauma 1997; 43: Choi CH, Pritchard J, Richard J. Path of bullet ad ijuries determied by radiography. Am J Foresic Med Pathol 1990; 11: Collis KA, Latz PE. Iterpretatio of fatal, multiple, ad exitig gushot wouds by trauma specialists. J Foresic Sci 1994; 39: Hollerma JJ, Fackler ML, Coldwell DM, et al. Gushot wouds. II. Radiology. AJR 1990; 155: Phillips CD. Emerget radiologic evaluatio of the gushot woud victim. Radiol Cli North Am 1992; 30: Ster EJ. Trauma radiology compaio. Philadelphia, Pa: Lippicott-Rave, Glezer JA, Miar G, Croce MA, Fabia TC, Kudsk KA. Shotgu wouds to the abdome. Am Surg 1993; 59: Yoshioka H, Seibel RW, Pillai K, Luchette FA. Shotgu wouds ad pellet emboli: case reports ad review of the literature. J Trauma 1995; 39: Imagig Symposium Volume 19 Number 5