diagnostic imaging of acute thoracic injury

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Diagnostic Imaging of Acute Thoracic Injury

Stuart E. Mirvis, MD, FACR

n recent years, the advent of multidetector CT (MDCT) has begun to change the imaging approach to patients

ustaining blunt or penetrating thoracic injury. The ability to directly detect some injuries that are often occult on

hest radiography, such as pericardial hemorrhage, major thoracic vascular injury, small pneumothorax, and

iaphragm tears, as well as the ability to better define the extent of other injuries, such as lung contusion and

aceration, account for this transition. This article reviews current concepts of diagnostic imaging in acute chest

rauma from both blunt force and penetrating mechanisms, emphasizing the spectrum of diagnostic imaging

ndings for various injuries, primarily based on multidetector MDCT.

2004 Elsevier Inc. All rights reserved.

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HE INITIAL CHEST radiograph provides in-formation regarding immediately life-threat-

ning conditions, such as tension pneumothorax orotentially life-threatening conditions, includingemothorax and pneumothorax. Other conditions,uch as diaphragm rupture, flail chest, pulmonaryontusion, pneumopericardium, and pneumo- andemomediastinum, are often diagnosed or sug-ested by initial plain radiographic findings. Inost centers, the chest radiograph remains an in-

egral part of the immediate imaging assessment ofhe hemodynamically stable trauma patient. Thebility of CT, particularly MDCT, to detect manyypes of pathology that are not usually diagnosedadiographically has increased use of this modalitys an additional or substitute screening study forhest trauma victims. The utility of CT studies isost advantageous for direct diagnosis of major

ascular, airway and diaphragm injury, pericardialffusion, the course of penetrating trauma, andubtle pneumothorax, or pleural effusions, amongthers. The extent of lung parenchymal and chestalls injuries is also more accurately assessed withT than radiographs. It is rare today for major

rauma patients not to undergo CT of one or moreody parts. The inclusion of the thoracic CT, andften other body areas without direct clinical find-ngs, is becoming increasingly common, given therequent “clinical silence” of some life-threateningntra-thoracic injuries. The degree of reliance onelical or MDCT in chest injury diagnoses must be

From the Department of Diagnostic Radiology, University ofaryland Medical Center, Baltimore, Maryland.Address reprint requests to Stuart E. Mirvis, MD, FACR,

epartment of Diagnostic Radiology, University of Marylandedical Center, 22 South Greene Street, Baltimore, MD 21201;

-mail: [email protected]© 2004 Elsevier Inc. All rights reserved.0887-2171/04/2502-0007$30.00/0
doi:10.1053/j.sult.2004.02.001
56 Seminars in Ult

onsidered in the total context of the emergencyare environment of the given medical institution,nd its use may vary appropriately among emer-ency departments.

CHEST WALL

Isolated fractures of the ribs, clavicle, or scapulaeldom represent significant injuries, but reflect theagnitude of force imparted, particularly in older

atients with noncompliant chest walls. The moreompliant chest walls of children and youngerdults may allow transmission of significant en-rgy into the thorax without fracturing, so severehest trauma can be present in the absence of rib orther thoracic skeletal injury.1 Fractures of the firsthree ribs, in particular, indicate significant energyransfer. Fractures involving the thoracic outlet,pper ribs, upper sternum, and clavicle may beccompanied by brachial plexus or vascular injuryn 3.0% to 15.0% of patients.2-6

Single rib fractures are usually of limited clini-al consequence and precise localization and quan-ification of such fractures is of dubious clinicaltility. Double fractures in three or more adjacentibs, or adjacent combined rib and sternal or cos-ochondral fractures, can produce a focal area ofhest-wall instability (Fig 1). Paradoxical move-ent of this “flail” segment during the respiratory

ycle can impair respiratory mechanics, promotetelectasis, and impair pulmonary drainage. Al-hough usually recognized by physical inspection,

flail segment involving the upper ribs may beidden by the chest-wall musculature.7 Fracturedibs accompanied by lacerations of intercostal ar-eries can cause major intrapleural hemorrhage,ften requiring angiographic identification and em-olization. The irregular edges of fractured andisplaced ribs can lacerate the pleura, lung, andbdominal organs directly.

Rib fractures are often accompanied by ex-

rasound, CT, and MRI, Vol 25, No 2 (April), 2004: pp 156-179

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157MDCT ACUTE THORACIC INJURY

rapleural hematomas that present as focal, lobu-ated areas of increased density on the chest radio-raph. Due to their extrapleural nature, suchematomas indent the parietal pleura focally andaintain a convex margin toward the lung. Devel-

pment of extrapleural hematomas over the apicesay accompany fractures of the upper ribs or

emorrhage from the subclavian vessels from bluntrauma or iatrogenic causes. Extrapleural hemato-as will not change configuration with changes in

atient position, as will free pleural space fluidollections.8 On CT, the localization of a hema-oma to the pleural or extrapleural space is usuallytraightforward due to the shape of the collection,ut may be uncertain on occasion. Incorrect local-zation may lead to extrapleural chest tube place-ent. EPH produces medial displacement of a fat

ayer that is just external to the parietal pleura andeep to the endothoracic fascia and inner intercos-al muscles. This medial fat layer displacementids in localization of hematoma to the extrapleuralegion.9

Fractures of the sternum are infrequent, occur-ing in 1.5% to 4% of blunt chest trauma cases.10

he diagnosis may be made by clinical inspectionr chest wall palpation, but typically is establishedy imaging. While a lateral chest radiograph willetect sternal fractures with reasonably high sen-itivity,11 this view is seldom obtained in the acute

Fig 1. Flail chest. Multiple comminuted, displaced right-

ided rib fractures are observed. There is diffuse increase in

he density of the right lung due to contusion. Soft tissue air

s superimposed over the right chest. A small pneumothorax

s also present (arrowhead).

rauma assessment. The frontal view misses all 2

ternal fractures unless associated with significantransverse displacement.12 CT should permit de-ection of most sternal fractures unless they areondisplaced and occur in the horizontal plane.ften sternal fractures occur in the coronal orien-

ation, or have a component in that axis, allowingasy CT recognition. While sternal fractures haveeen associated with major injuries to the heart andreat vessels, this appears to be quite uncommon,articularly with isolated, nondisplaced, and non-epressed patterns.13,14 Cardiac injury arising as airect result of sternal fracture has been reported inrom 1.5% to 6% of patients.10 Laceration of thennominate artery secondary to a displaced fracturef the sternum has been reported, but appears to beuite rare.15 Crestanello et al10 noted that fracturesf the manubrium, rather than the sternal body,equire high force and are likely to be associatedith more severe associated injuries. They de-

cribed sternal fractures occurring as a result ofirect impact, but also arising indirectly from flex-on associated with thoracic spine wedge compres-ion fractures. They also noted a 3-fold increase inhe incidence of the injury with use of the shoul-er-lap belt restraint system.Most sternoclavicular dislocations are anterior

nd have no major clinical significance. However,osterior dislocations of the clavicle, relative to the

Fig 2. Deep costophrenic sulcus sign. The right lateral

ostophrenic sulcus is filled with air in this supine patient,

reating a lucent and atypical deep appearing sulcus (arrow-

ead). A visceral pleural line is not reliably demonstrated

Mirvis, SE: Diagnostic imaging of thoracic trauma, in Mirvis

E, Shanmuganathan K (eds.): Imaging in trauma and critical

are, 2nd edition. Philadelphia, PA, W.B. Saunders, 2003, pp.

97-367, with permission).

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158 STUART E. MIRVIS

anubrium, can damage the great vessels, superiorediastinal nerves, trachea, and esophagus. Al-

hough sternoclavicular dislocations are demon-trable using angled chest radiographs (tube angled5o cranially), they are most easily diagnosed us-ng axial CT. Posterior dislocation can result from

posterior and laterally directed force applied tohe shoulder, moving the lateral end of the clavicleorward and pivoting the medial end posteriorly.horacic angiography and esophagography arearranted to exclude injury to the aorta, greatessels, and esophagus.Isolated fractures of the scapular are frequently

verlooked in interpretation of both chest radio-raphs and thoracic CT.16 These injuries indicatehe likelihood of significant chest wall impact andre important for that reason, as well as to recog-ize a cause for pain and limitation of shoulderirdle motion. Scapulothoracic dissociation is aare and serious injury characterized by a lateralisplacement of the entire forequarter with intactverlying skin, complete acromioclavicular sepa-ation, and usually multiple ipsilateral upper ex-remity fractures.17 Avulsion injuries to the bra-hial plexus and subclavian nerves alwaysccompany the injury. Vascular injuries are alsoommon and should be sought even in the presencef a normal distal pulse, which may be maintained
y collateral flow. Usually there is a large hema- i
oma over the involved shoulder and the injury islinically apparent. The diagnosis may be sug-ested on chest radiography or CT initially. Bothodalities typically demonstrate lateral displace-

Fig 3. Active bleeding into the chest.

CT image of blunt trauma victim shows

a “jet” of active arterial contrast extrav-

asation (arrow) into the pleural space.

The air-blood level results from a con-

current tension pneumothorax displac-

ing the heart and mediastinum to the

left.

Fig 4. Radiograph of lung contusions. Admission supine

hest radiograph demonstrates areas of increased density,

rimarily involving both upper lobes. There is a peripheral

istribution of density on the left. No air-bronchograms are

een. This is a typical presenting appearance of lung contu-

ion. Note also that no rib fractures are seen, which is not

nconsistent with the diagnosis of lung contusion, particularly

n children and young adults.

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ent and often an abnormal orientation of thenvolved scapula.18

Fractures of the thoracic spine may be easilyverlooked when interpreting the frontal chest ra-iograph in acute blunt trauma patients. Theselms are often underexposed and are frequentlyompromised by patient motion, overlying supportines and tubes, and scatter radiation. More overtndings can easily distract a reader from a carefuleview of the radiograph for evidence of paraspinalematoma and gross abnormalities of spinal align-ent. A substantial percentage of thoracic injuries

re fracture dislocations that present with profound

Fig 5. CT of lung contusion lacera-

ions. CT image in a blunt trauma pa-

ient shows a consolidated area within

he left lower lobe. There are numerous

ucent areas from lung lacerations, as

ell as small rounded foci of hema-

oma.

eurologic deficits, but many others are amenableo reduction and stabilization before the onset orxacerbation of neurologic dysfunction. Similarly,eview of thoracic CT images for bone detail, inddition to the traditional lung and soft tissueindow surveys, can often detect unsuspected tho-

acic spine injuries. The presence of diffuse medi-stinal hemorrhage associated with lower cervical,horacic, or upper lumber spine fractures shouldot be assumed to arise strictly from the skeletalnjury, and concurrent major vascular injury shouldlso be excluded. However, if a paraspinal hema-oma surrounds a spine fracture more or less sym-

Fig 6. CT of lung lacerations. CT im-

age shows two ovoid hypodense areas

in the left lower lobe with some sur-

rounding density. Note the thin

“pseudomembrane” (arrowhead) caused

by laceration. There is a hemorrhage-air

level in the more dependent laceration.

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etrically and displaces the aorta, but the aorta andreat vessels appear normal on high quality intra-enous contrast enhanced thoracic CT, aortogra-hy is not required.19,20

PLEURAL SPACE

Most chest radiographs in polytrauma patients,r those with penetrating thoracic injury, are ob-

Fig 8. Lung herniation. A

arge segment of the anterior

ight upper lobe herniates

hrough the disrupted anterior

hest wall. A large portion of the

ight anterior chest wall soft tis-

ues is avulsed. There is pneu-

omediastinum and soft tissue

ir, as well as a focal right upper

obe contusion.

ained with the patient in the supine position. Inhis position, pneumothorax tends to accumulate inhe anteroinferior aspect of the pleural space po-entially producing basal hyperlucency, a deepenedateral costophrenic sulcus, or a “double-dia-hragm” appearance21 (Fig 2). It is important tocrutinize the lung bases and upper abdomen care-ully to avoid missing this diagnosis. In uncertain

Fig 7. Complicated lung laceration.

A left upper lobe traumatic pneumato-

cele has enlarged over time to com-

press the adjacent normal lung. As the

cyst expands, ventilatory dead space

increases, compromising respiratory

function.

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ases, or for follow-up after chest tube removal, anrect expiratory radiograph offers the highest sen-itivity for detection of small pneumothoraces.everal studies have documented much higher sen-itivity of CT for pneumothorax as compared withupine chest radiographs, one of many reasons forncreasing reliance on CT screening in thoracicrauma.22-24 Atypical locations of pleural space air

Fig 9. Penetrating injury to

he hemidiaphragm. A sagittal

eformatted CT study of a stab

ound victim shows a defect in

he anterior left hemidiaphragm

econdary to penetration by the

nife (arrowhead). L, liver; H,

eart; S, stomach.

Fig 10. Herniation of stomach. A coronal volumetric image

emonstrates the bulk of the contrast-filled stomach above

he level of the left hemidiaphragm. The stomach tapers as it

asses through the defect in the diaphragm (arrowhead). e

Fig 11. “Hourglass sign.” A sagittal multiplanar reforma-

ion from MDCT of a blunt trauma patient demonstrates

onstriction of the liver at the point of the torn diaphragm

dge (arrow).

Fig 12. Effect of negative intrapleu-

ral pressure on transdiaphragmatic her-

niation. A. Pre-intubation chest radio-

graph clearly shows herniated bowel

above the diaphragm (arrow). B. Post-

intubation chest radiograph shows the

effect of positive intrapleural pressure,

depressing the bowel toward the dia-

phragm (arrow), where herniation is far

less evident. (Mirvis, SE: Diagnostic im-

aging of thoracic trauma, in Mirvis SE,

Shanmuganathan K (eds.): Imaging in

trauma and critical care, 2nd edition.

Philadelphia, PA, W.B. Saunders, 2003,

pp. 297-367, with permission).

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nclude infrapulmonic, behind the pulmonary lig-ment, loculated by pleural adhesions, or confinedo the medial pleural space. Skin folds, tape,owns, vascular lines, and the medial scapularorder create shadows that mimic pneumothorax.he complete absence of vascular shadows beyond

he apparent visceral pleural line is a key support-ng finding. Occasionally, decubitus views, withhe side of pneumothorax suspicion nondependent,an help secure the diagnosis, but a high-qualityecubitus view is often difficult to obtain withortable equipment.

Tension Pneumothorax

A tension pneumothorax produces high intratho-acic pressure reducing cardiac filling, compress-ng the ipsilateral lung, and usually displacing theediastinum contralaterally. In addition, high in-

rapleural pressure can depress the ipsilateral hemi-iaphragm and widen the interspaces between ip-ilateral ribs. A hyperlucent appearance of theffected hemithorax is usually observed, with vari-

Fig 13. Right hemidiaphragm tear.

he “bump” and “band” signs. Coronal

eformation from 16 row-MDCT shows

bump-like herniation of liver paren-

hymal into the right hemithorax. Note

he band of lucency at the base of the

erniated portion (arrow), possibly indi-

ating the site of decrease perfusion at

he indentation of diaphragm into liver.

ble degrees of lung collapse. When a tension d

neumothorax persists despite adequate chest tubelacement, there should be concern for a majorirway injury. The increase in intrathoracic pres-ure is usually secondary to one-way movement ofir from the lung, airway, or mediastinum into theleural space. Recognition of this entity requiresrgent relief by thoracostomy.

Hemothorax

Hemothorax of some extent is present in 50% ofajor trauma patients. On supine radiography, liq-

id blood layers posteriorly, producing uniformncreased density over the hemithorax and possibly

stripe of higher density along the lateral pleuralpace (depending on quantity of blood present). Inhe semi-erect or erect view, the liquid blood cre-tes a meniscus with increased density confined tohe lower hemithorax. If a hemothorax is underressure (arterial bleeding), the mediastinum canhift contralaterally. Lung markings are generallyisible and intact, as seen through the pleural-ased density. Clotted blood may cause lobulated
ensity along the pleural surface, but this is un-

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ommon in acute trauma, and blood is usually in aiquefied state. One may see air-fluid level(s) in theemi-erect or erect position when an associatedneumothorax is present. Rarely, blood or otheruid collects in the subpulmonic space in theemi-erect patient, within fissures, or behind pleu-al adhesions. On CT, hemorrhage can be diag-osed by virtue of its density of 30-45 HU, de-ending on the hematocrit, admixture of otherypes of fluid, and the state of clot formation.igher attenuation clot is brighter than surrounded

iquid clot (45-70 HU). Rarely, active extravasa-ion of contrast-enhanced blood into the pleuralpace (Fig 3) can be detected on admission CT,rompting urgent surgical or arteriographic inter-ention. The management of intrapleural hemor-hage depends on its initial quantity, rate of bleed-ng, and overall patient condition.

In the setting of acute chest trauma, otherources of pleural effusion can also occur. Simple

Fig 14. Direct finding of diaphragm tear on 16 row-MDC

emarcates the retracted edges of the torn left hemidiaphragm

hrough the chest wall. (Shanmuganathan K, Mirvis SE: Triple

adiol 32:11-18, 2003, with permission).

erous effusions result from impaired pulmonary t

ynamics and decreased resorption of fluid by theleura, and are commonly associated with atelec-asis or ipsilateral chest wall injury that limitsespiratory excursions. Rarely, bilo-pleural fistulasan occur from simultaneous injury to the liver andight diaphragm.25 Chylous effusions result fromraumatic disruption of the major thoracic lym-hatic channels.26

LUNG PARENCHYMA

Pulmonary Contusions and Lacerations

Pulmonary contusions result from direct impacto the chest wall and often reflect the shape andocation of the impact site. Rib fractures associatedith contusion are less common in children andoung adults since they have more compliant ribs.ontusions appear radiodense and are usually pe-

ipheral, nonsegmental, and nonlobar in distribu-ion. Contusions are also commonly seen adjacent

l CT image at the level of the left hemidiaphragm clearly

s). Retroperitoneal fat is herniated above the diaphragm and

t helical CT imaging of penetrating trauma to the torso. Appl

T. Axia

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Fig 15. The “dependent viscera” sign. The herniated stomach falls into direct contact with the posterior thoracic wall (arrow),

ince there is no intact diaphragm to hold it up against gravity. Normally, the posterior aspect of the lung and diaphragm is

nterposed between the stomach and posterior chest wall.

Fig 16. MRI of diaphragm rupture.

oronal T1-weighted MR image nicely

hows a defect in the left hemidia-

hragm (arrow), with fat and the stom-

ch herniated into the chest. There is

telectasis in the left lower lobe.

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ung into the rigid spine, or from shearing effectsrom rapid deceleration. The increased lung den-ity is due to alveolar and distal bronchial hemor-hage and edema. Since the peripheral airwayssually fill with blood, air-bronchograms are un-

Fig 17

blunt tr

ing trac

visualiz

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ommon (Fig 4). Pulmonary lacerations very fre- d

uently accompany pulmonary contusions27 andre much better seen with CT than radiograph.24,27

ften, there are numerous small lacerations withinreas of contused lung, producing a “Swiss cheese”ppearance. In addition, variable-sized, uniformly

tle mediastinal hemorrhage. A. Supine chest radiograph of a

atient shows subtle signs of mediastinal hemorrhage, includ-

row) and nasogastric tube deviation to the right, and a poorly

ic arch and descending aorta. The width of the mediastinum

rrow. B. Aortography confirms pseudoaneurysm of the prox-

g thoracic aorta (arrow).

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ense, rounded areas of hematoma are present

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ithin contused regions (Fig 5). Pulmonary lacer-tions become more apparent radiographically ashe edema and hemorrhage associated with contu-ions begins to resolve within a few days afternjury. On CT, pulmonary lacerations appear asvoid or elliptical air spaces surrounded by a 2- to-mm-thick pseudomembrane (Fig 6). They mayontain a central hematoma or air-hemorrhageevel (Fig 6). In general, lung lacerations are be-ign, but complications can occur and are besthown by CT. Complications include infection,ronchopleural fistula formation, enlargement withompression of adjacent normal lung, and hemor-hage28 (Fig 7). Lung hematomas slowly contractver time, but can present as a pulmonary “softissue nodule” if the recent history of chest traumas not revealed. Most pulmonary contusions begino resolve radiologically within a few days ofnjury. Failure to resolve, or increasing lung den-ity, suggests superimposed pneumonia, or ARDS.

Lung Herniation

Rarely, a segment of lung may herniate throughdefect in the chest wall created by the flail

egment. Transthoracic lung herniation increasesn likelihood with positive-pressure ventilatoryupport and with rupture of the internal thoracic

Fig 18. Mediastinal hemorrhage with aortic injury. A. Sup

oft tissue density, tracheal (T) deviation to the right, and a wid

ematoma. B. Corresponding CT image shows a pseudoaneur

ediastinal hemorrhage (M) displaces the carina (C) to the ri

ascia, parietal pleura, and pectoral and intercostal o

usculature. The diagnosis may be made withadiographs, but lung herniation is easier to detectith CT (Fig 8). Although entrapment and stran-ulation of the herniated portion of lung can occur,n my experience, significant sequelae generally doot occur with expectant management. Large her-iated lung segments that restrict respiratoryovement are typically reduced and the overlying

hest wall repaired.

ACUTE DIAPHRAGM TEARS

Injury to the diaphragm occurs in 0.8% to 5.8%f major blunt abdominal trauma cases undergoingaparotomy.29 Penetrating trauma is a far moreommon cause and is usually diagnosed directly aturgery. However, recent studies using MDCTith oral and intravenous contrast enhancement,

ugmented by multiplanar reconstruction, havehown promise in documenting or excluding dia-hragm injury from penetrating trauma30 (Fig 9).iagnostic supine radiographic signs of blunt trau-atic injury to the left hemidiaphragm are present

n about 50% of patients with such injury (rangingrom 27% to 60%).31 The definitive radiographiciagnosis requires herniation of abdominal viscera,ypically the stomach, above the hemidiaphragmFig 10). A nasogastric tube, perhaps with injection

ission chest radiograph shows increased right paratracheal

araspinal stripe that is contiguous with an apical extrapleural

) arising anteriorly at the level of the left mainstem bronchus.

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he gastric fundus and its relationship to the hemi-iaphragm. Focal constriction of the stomach orther herniating viscus at the level of the diaphrag-atic tear may produce a “collar or hourglass

ign,” which is pathognomonic of diaphragm rup-ure (Fig 11). Injury to the left hemidiaphragm isore commonly diagnosed radiographically, since

Table 1. CT Signs of Traumatic Aortic Injury

ortic pseudoaneurysm—very commoneriaortic hemorrhage—very commonisplacement of the trachea and esophagus to the right byhematoma—commonn irregular shape of the aortic lumen—very common

ntimal flaps projecting within the lumen—commonuminal clot at sites of intimal disruption—uncommonudden change in caliber of the aorta without interveningbranch vessels [coarctation]—uncommonsmall aortic caliber in the lower chest andabdomen—uncommon

eridiphragmatic hemorrhage—commonransection of the aorta (very rare)ctive bleeding from the aorta into the mediastinum orpleural cavity (very rare)
p
erniation of abdominal contents is more likely toccur than on the right side, where they arelocked by the liver. Other radiographic signs thatre suggestive, but nondiagnostic of diaphragmupture, are present in another 18% of patients andnclude a poorly defined or apparently elevatediaphragm, especially with mass effect on the heartnd mediastinum and air-fluid levels at the leftung base.31 It is important to obtain chest radio-raphs in blunt trauma patients after they are re-oved from positive pressure airway support,

ince positive intrathoracic pressure delays or pre-ents transdiaphragmatic herniation; whereas typ-cal negative intrathoracic pressure promotes itFig 12). In such cases, follow-up radiography maye of value, since a delayed presentation of herni-tion is not uncommon. Ruptures of the rightemidiaphragm are strongly suggested in bluntrauma patients by both elevation of the apparentight hemiphragm or a mass-like “bump” project-ng above the diaphragm (Fig 13). The torn dia-

Fig 19. MDCT of traumatic aortic in-

jury. Axial CT image shows a typical

pseudoaneurysm (arrow) arising from

the antero-medial portion of the proxi-

mal descending aorta at the level of the

left main (L) pulmonary artery. There is

mediastinal hemorrhage around the

aorta and carina, left hemothorax, and

posterior rib fractures.

hragm may appear completely normal radio-

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Fig 20. Reformatted 16 detector-MDCT of an ascending aortic pseudoaneurysm. A. Axial CT image shows a pseudoaneurysm

Ps) arising between the ascending aorta (A) and the pulmonary artery (P). B. Coronal reformation shows the pseudoaneurysm

rising from the proximal ascending aorta (arrow). This injury is usually fatal, but this patient survived to have surgical repair.

Fig 21. Subtle traumatic aortic injury. A. Axial CT image of a blunt trauma patient shows a very subtle intimal flap (arrow)

emarcating an anterior pseudoaneurysm at the level of the left main pulmonary artery. B. A volumetric image of the aorta shows

roximal and distal intimal flaps marking the extent of the pseudoaneurysm.

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raphically or may be associated only withpsilateral atelectasis or pleural fluid. MDCT mayhow a line of relatively decreased density withinhe liver parenchyma that is adjacent to the torniaphragm edges. This line may represent focallyecreased perfusion due to compression of theiver at the margin of the torn diaphragm (unpub-ished data).

Etiologies of falsely positive radiographic diag-osis of diaphragm tear include lacerations at theung bases, with air-fluid levels mimicking herni-ted bowel, phrenic nerve injury, diaphragm paral-sis, and eventration of the hemidiaphragm. Falseegative radiologic diagnoses are usually due toears without associated herniation, or may occurhen an acute injury is mistaken for a remote or

ongenital abnormality. Again, acute injury is usu-lly associated with mediastinal and cardiac dis-lacement away from the herniated viscera andpsilateral pleural effusion (hemothorax).

If the radiologic diagnosis is suspected but de-nitive diagnosis is required, CT scan, preferably

Fig 22. Traumatic aortic injury in volume rendering. A. Axia

rising from the anterior aspect of proximal descending aorta

lightly displaced to the right by hemorrhage. B. Volume

seudoaneurysm (arrow) and the relationship to the adjac

lanning. (Color version of figure is available online.)

sing MDCT technology, is an appropriate second- t

ry study that is often obtained routinely in bluntolytrauma victims. MDCT can often directlyemonstrate the edges of the torn diaphragm andhe site of herniation, if present (Figs 9 and 14).hin section CT imaging of the diaphragm, such asverlapping 1-mm reconstruction, provides excel-ent reformation in the sagittal and coronal planes,ptimizing diagnostic accuracy.29 In our practice, Iave found these high-resolution multiplanar re-onstruction studies particularly useful for diagno-is or exclusion of right-sided diaphragm injuryhen herniation is less common. Other useful CT

igns of potential diaphragm injury include theollowing: (1) the “dependent viscera sign,” inhich an abdominal visceral structure contacts theosterior abdominal wall without intervening lungarenchyma or diaphragm (Fig 15); (2) thickeningf the diaphragm, focally or diffusely; or (3) seg-ental nonvisualization of the diaphragm.32

If MDCT remains equivocal for diaphragm in-ury, then MRI can be used as a third line study.

RI will usually depict direct diaphragm discon-

age from 4 detector-MDCT shows a typical pseudoaneurysm

is minimal mediastinal hemorrhage. The nasogastric tube is

ed oblique image of the aorta shows the length of the

t subclavian artery (LSA), information needed for surgical

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inuity and visceral herniation with only T1-

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eighted sagittal and coronal images.33 MRI isery useful to confirm an intact diaphragm in bluntrauma patients with apparent diaphragm elevationy radiography33 (Fig 16).Usually, penetrating injury to the diaphragm is

iagnosed at surgical exploration performed due toroximity to the lower thorax or upper abdomen.DCT can be useful to clarify the course or

rajectory of a penetrating injury and determine itselationship to the diaphragms. Obviously, an ob-ect that crosses between the chest and abdomenas injured the diaphragm. Careful inspection ofT axial images in such cases may directly show

he location and extent of such injuries.30 Whileost penetrating injuries to the left hemidiaphragm

re repaired surgically or thorascopically, minorears on the right side may be observed clinically,ithout repair, due to the protective presence of the

iver. The demonstration of blood around the dia-hragm, a thickened diaphragm, or a wound tractn close proximity to the diaphragm should beonsidered evidence of direct injury, and of theeed for careful follow-up, if there is no directvidence of herniation, particularly on the left side.

Fig 23. Ruptured bronchus on radiograph. A tension pneu-

othorax persists despite adequate thoracostomy tube

lacement, suggesting a large air leak into the pleural space.

n this case, the right mainstem bronchus was ruptured.

Mason AC, Mirvis SE, Templeton PA: Imaging of acute tra-

heobronchial injury: Review of the literature. Emerg Radiol

:250-260, 1994, with permission).

he typical lacerations created by penetrating in- 2

ury are short (�2 cm) and unlikely to be associ-ted with herniation, but delayed herniation is stillossible. High-energy ballistic wounds may createvidence of injury on both sides of the diaphragm,ue to shock wave energy, without necessarilyrossing the diaphragm. Since isolated ballisticnjury to the right upper quadrant is increasinglyeing managed nonoperatively, recognition of thisact is important.34,35 Laparoscopic assessmentay be prudent to evaluate the integrity of hemi-

iaphragm before open exploration in such cases.36

MEDIASTINAL HEMORRHAGE ANDTHORACIC VASCULAR INJURY

The presence of mediastinal hemorrhage is anmportant clue to potential major thoracic vascularnjury, most commonly involving the proximalescending thoracic aorta. Chest radiography pro-ides the initial assessment of the mediastinalontour. While several articles have described ap-arently reliable radiographic signs of hemomedi-stinum37-39 and potential aortic injury, subsequenteports of larger series have shown many of theseigns to be less accurate then originally indi-

Fig 24. Ruptured trachea. An overdistended endotracheal

ube balloon (arrows) indicates rupture of the tracheal wall,

ith subsequent failure to resist the expansion of the balloon

s more air is added in an attempt to obtain airway seal.

Mirvis, SE: Diagnostic imaging of thoracic trauma, in Mirvis

E, Shanmuganathan K (eds.): Imaging in trauma and critical

are, 2nd edition. Philadelphia, PA, W.B. Saunders, 2003, pp.

97-367, with permission)

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ated.40-42 While it is true that most patients withemomediastinum display a “widened mediasti-um” on chest radiography, this finding is by noeans accurate at indicating the presence or ab-

ence of vascular injury. Indeed, patients with veryarrow mediastinal widths, or mediastinal-to-car-iac width ratios, can certainly have traumaticortic injury (Fig 17). Patients with mediastinalemorrhage have no more than a 20% probabilityf major thoracic vascular injury.43 It is the precisenalysis of the mediastinal contour that offers theest chance of diagnosing or excluding mediastinalemorrhage. Radiologic signs that serve as mark-rs for mediastinal hematoma associated with trau-atic aortic injury include:1. Obscured or absent aortic arch and descend-

ing aorta shadow (Fig 18)2. Right paratracheal soft tissue density (Fig 18)3. Rightward displacement of the esophagus

and trachea in a nonrotated patient (Fig 18)4. Widened left paraspinal stripe or extension of

the stripe above the aortic arch (Fig 18).Unfortunately, radiographic evaluation is often

Fig 25. CT of tracheal air leak. CT image shows a direct c

arrow). Injury at this site was confirmed with bronchoscop

racheal rupture. AJR Am J Roentgenol 176:1273-1280, 2001,

alsely positive for evidence of mediastinal blood t

nd therefore for potential great vessel injury.ome causes of falsely positive diagnoses include:1. Radiographs in supine patient that widen and

distort the mediastinal contour2. Atelectasis, pleural effusions, lung contu-

sions, and lung hematoma that obscure themediastinal margins

3. Limited technical quality of studies, motionartifacts, and overlying support tubes andlines

4. Mediastinal lipomatosis5. Acquired and congenital vascular anomalies,

marked thoracic scoliosis6. Mediastinal hemorrhage without vascular in-

jury (common)Unless the mediastinal contours can be clearly

nd unequivocally defined, mediastinal hemor-hage cannot be excluded. Given that aortic andther major thoracic arterial injuries have a highncidence of vascular rupture and mortality withinours to days of admission, the injury must bexcluded definitely and quickly.44 Generally, ante-iography has provided the diagnostic standard for

ion between the trachea at the carina and the mediastinum

n JD, Shanmuganathan K, Mirvis SE: Using CT to diagnose

rmission)

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ime-consuming, and may significantly delay otheriagnostic or therapeutic procedures. Few centersrovide immediate diagnostic arteriography on a4-hour basis. Furthermore, in some cases, theesults of arteriography are atypical and nondiag-ostic.45

In recent years, the Maryland Shock Traumaenter has virtually abandoned thoracic angiogra-hy in favor of MDCT when there is possibleediastinal hematoma. While the radiologists still

clear” many adequate chest radiographs on supiner erect views, our threshold for proceeding toDCT is quite low in any questionable case, sinceT is often requested anyway in blunt polytraumaatients. Using bolus tracking with a threshold of50 HU in the proximal aorta, we perform a 16 �.5-mm scan of the entire chest and reconstructata at 5 mm. If needed, in questionable cases, wean have the original data reconstructed at 2-mmntervals with 1 mm overlap. This thin sectioneconstruction data set is utilized for all multipla-ar reformations (MPRs), maximum intensity pro-ections (MIPs), and volumetric reformations.

Most patients with traumatic aortic injury havelear evidence shown by pseudoaneurysm, typi-

Fig 26. Penetrating tracheal injury. An endotracheal balloo

reated by a bullet wound through the superior mediastinum

hanmuganathan K (eds.): Imaging in trauma and critical care,

ermission).

ally located in the anterior aspect of the proximal t

escending aorta at the level of the left mainulmonary artery and left mainstem bronchus, theite of the embryonic ductus arteriosus (Fig 19).he pseudoaneurysm is an incomplete tear in theall in which the arterial blood is contained by the

dventia of the artery alone. Therefore, it is quitenstable. Other typical CT findings of traumaticortic injury include one or more of the featuresisted in Table 1.

In all cases, a search must be made for concur-ent or atypical sites of aortic injury, such as thescending aorta (Fig 20), the aortic arch, the per-diaphragmatic aorta, and the great vessel origins.n some cases, the aortic injury may be quite subtleFig 21) consisting of a small intimal tear andossible thrombus. The use of MPR, MIP, andolumetric images can help convey the importantnatomy of the aortic injury to the vascular or chesturgeon (Fig 22). Once an aortic injury is diag-osed on CT, it is rarely necessary to performngiography, as this procedure will introduce annnecessary delay in treatment when time is of thessence.46 Only if the CT study is equivocal, de-pite the use of thin-slice collimation, a well opac-fied lumen, and use of image reformations, should

ates through a focal defect in the trachea (arrow), which was

is, SE: Diagnostic imaging of thoracic trauma, in Mirvis SE,

ition. Philadelphia, PA, W.B. Saunders, 2003, pp. 297-367, with

n herni

. (Mirv

2nd ed

horacic angiography or transesophageal sonogra-

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hy be performed.46 Information described in pos-tive cases of traumatic aortic injury should includehe location and length of the injury, its proximityo the nearest major branch vessel, any anomaliesf thoracic anatomy (particularly vessel branchingatterns), the size and orientation of the pseudoan-urysm, and the presence of adherent thrombus.vidence of active bleeding from the aorta consti-

utes a hyper-emergency finding requiring imme-iate notification of the responsible clinical ser-ice.

TRACHEAL INJURY

Tracheal injury occurs in from 0.35% to 1.5% ofajor blunt trauma cases.47 The cervical trachea

an be injured by a direct blow, such as a karateick, impaction against a fixed object (i.e., steeringheel), “clothesline”-type crushing against a fixedorizontal barrier (i.e., snowmobile and tree limb),r rarely from cervical spine injuries. If the tear isomplete, the major manifestation is marked cer-ical soft tissue gas. Rarely, tracheal disruption canllow the larynx to elevate, permitting the hyoid toscend above the top of C3, which normally neverccurs. Cervical tracheal injuries are most com-
only located between the cricoid and thyroid d
artilage and below the 4th tracheal cartilage. In-uries to the larynx, esophagus, and recurrent la-yngeal nerve are commonly associated from eitherlunt or penetrating force.Intrathoracic tracheal injury occurs as a result of

ompression of the trachea against the spine, shear-ng forces, or possibly by sudden increased intralu-inal pressure. Most injuries occur within 2.5 cm

f the carina (76%) and favor the right mainstemronchus.47 The hallmark of the injury is persis-ent, progressive, and severe pneumomediastinum,nrelieved by tube thoracostomy. Fractures of ribs-3 are also very commonly associated with tra-heal injuries (90%), reflecting the massive bluntmpacts required to produce the injury.48 Otheradiologic signs of airway disruption include inter-titial air in the tracheal or mainstem bronchialall, persistent pneumothorax despite chest tuberainage, the “fallen lung” sign, consisting of aependent position of a collapsed lung, ectopicocation of an endotracheal (ET) tube, and over-istension of the ET tube cuff (Figs 23 and 24).he ET tube balloon should not appear wider than.5 cm in men and 2.1 cm in women. Distention ofhe ET tube �2.8 cm implies tracheal rupture. The

Fig 27. Esophageal tear from blunt

trauma. CT image demonstrates con-

trast (arrowheads) and pneumomedias-

tinum arising from the mid esophagus.

(Mirvis, SE: Diagnostic imaging of tho-

racic trauma, in Mirvis SE, Shanmuga-

nathan K (eds.): Imaging in trauma and

critical care, 2nd edition. Philadelphia,

PA, W.B. Saunders, 2003, pp. 297-367,

with permission.)

iagnosis of tracheal or mainstem bronchial injury

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s confirmed by bronchoscopy. On occasion, thedventia of the airway may remain intact, despiteomplete disruption, masking the typical radio-ogic findings caused by air leak. The mainstemronchi can rarely rupture into the pericardium,eading to pneumopericardium and potentiallyamponade. The presence of air directly outlininghe outside of the trachea or mainstem bronchi, aseen by radiography or CT, is statistically associ-ted with injury to these structures, as opposed toediastinal air in general, and should increase

uspicion for airway disruption.49

With the advent of MDCT, direct tears of therachea can often be detected with demonstrationf a direct communication between the airwayumen and the mediastinum49 (Fig 25). Such anding should be carefully sought in all patientsith radiographic and clinical signs of a severe androgressive airway leak. Penetrating injuries to theirway can also be suggested by the path of pene-rating objects (particularly bullets) as indicated byT, or by direct evidence of airway injury such aserniation of a part of the endotracheal tube bal-oon cuff through the tracheal wall defect (Fig

49

Fig 28. Tension pneumopericardium. A chest radiograph

hows the outline of the pericardium (arrowheads) on either

ide of heart. The increased pressure in the pericardial space

ompresses the cardiac shadow, producing the “small heart”

ign. (Mirvis, SE: Diagnostic imaging of thoracic trauma, in

irvis SE, Shanmuganathan K (eds.): Imaging in trauma and

ritical care, 2nd edition. Philadelphia, PA, W.B. Saunders,

003, pp. 297-367, with permission.)

6).

ESOPHAGEAL DISRUPTION

Esophageal disruption is very rarely caused byrauma, with both blunt and penetrating forcesccounting for less than 10% of such injuries.50

enetrating injury predominantly involves the tho-acic esophagus. Again, injury to the esophagus isften accompanied by injury to adjacent structures,ncluding the trachea and vascular structures. Thesophagus can be injured from compression be-ween the sternum and spine, traction from cervicalyperextension, direct penetration by bone frag-ents from spine fractures, and of course, direct

enetration by foreign bodies both from within andithout. In the setting of acute trauma, one need

lso consider iatrogenic injury from traumatic at-empts at intubation, forced nasogastric tube place-ent, esophagoscopy, and potentially from trans-

sophageal sonography. In the emergencyepartment setting, a history of impacted foreignody should be sought. Recently reports have alsoppeared describing “airblast” injuries from ex-loding tires or inner tubes as a cause of esopha-eal injury.Imaging manifestations of esophageal injury in-

lude pneumomediastinum, usually more limitedhan from airway injury, pleural effusion, and con-our change in the mediastinum that may be pro-ressive with superimposed inflammation. Mostften, in blunt trauma cases, esophageal injury isot suspected unless there is also injury to therachea, or unless infection (mediastinitis/abscess)ntervenes. The demonstration of an air column inhe esophagus or gas bubbles in the nasogastricube suggests a tracheo-esophageal communica-ion.

When the diagnosis of injury to the esophagus isuspected or considered, both contrast esophagog-aphy and endoscopy can be used. Most studiesuggest that both have diagnostic limitations andogether offer the highest level of sensitivity. Gen-rally, water-soluble esophagography is performedith fluoroscopic guidance and, if negative, bar-

um esophagography follows. CT may also be ofalue by demonstrating bubbles of air or fluidccumulation adjacent to the esophagus. CT mighte warranted to detect subtle leaks even if esopha-ography is initially negative (Fig 27). The diag-ostic accuracy of CT contrast esophagography inhe trauma setting is not established.

Since there is lower intraluminal pressure in the

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sophagus than the trachea, air leaked from thesophagus into the mediastinum is likely to remainlose to the site of the injury, rather than progressistantly. Small air bubbles within the mediasti-um should be sought. In my experience, the veryare esophageal injuries that result from blunt forcerauma are typically in the distal esophagus. Leak-ge of fluid into the left pleural space is most
ommon. Due to its rarity and lack of major im- e
ging findings, the diagnosis of esophageal perfo-ation after blunt trauma is often missed untilnfection such as mediastinitis or empyema devel-ps.

CARDIAC/PERICARDIAL INJURY

The heart and pericardium are also subject tooth penetrating and blunt force injury, with pen-

Fig 29. CT of pericardial tamponade.

A. An axial image through the mid-

heart shows a moderate hemopericar-

dium (P). There is some mediastinal

hemorrhage as well. B. A CT image

through the liver shows marked disten-

sion of the inferior vena cava due to

high central venous return pressure

from tamponade. The periportal lym-

phatics are also distended due to im-

paired drainage. The aorta is small in

caliber due to decreased cardiac output.

(Goldstein L, Mirvis SE, Kostrubiak IS,

et al: AJR Am J Roentgenol 152:739-

741, 1989, with permission).

trating injury predominating. Cardiac contusions

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re typically not diagnosed by imaging in the acuteeriod and will not be considered. Pericardial tam-onade can occur secondary to air or blood accu-ulating in the pericardial sac. Tension pneumo-

ericardium occurs when air dissects along theulmonary adventitia into the pericardial space andannot egress (1-way valve effect). I have notedhis most commonly in patients with a combinationf severe lung contusions and high airway pres-ures. The pericardium becomes distended and theardiac shadow grows progressively smaller.51 Theadiographic and CT findings are usually quitepparent (Fig 28). Air within the pericardial spaceutlines the heart and is confined superiorly by theericardial reflections at the root of the great ves-els (Fig 28). With tamponade, CT shows disten-ion of venous return vessels (IVC, hepatic veins;VC, renal veins) and periportal lymphedema (Fig9).52 These findings demand immediate pericar-iotomy for tube decompression. Detection of he-opericardium is most difficult radiographically,

Fig 30. CT of myocardium perfora-

ion. CT image shows contrast material

eaking from the apex of left ventricle

hrough a myocardial tear (arrow).

here patient was bleeding directly into

he left pleural space. The tear was

aused by a displaced rib fracture. The

atient did not survive the injury.

Killeen KL, Poletti PA, Shanmuga-

athan K: CT diagnosis of cardiac and

ericardial injuries. Emerg Radiol 6:339-

44, 1999, with permission).

ince only a small amount of blood can tamponade d

ardiac motion acutely without changing the car-iac shadow significantly. CT is very reliable foretecting pericardial hemorrhage and will alsohow evidence of tamponade, as described above.edside sonography is also very useful to quicklyonfirm or exclude pericardial fluid after trauma.

Pericardial rupture can occur from blunt or pen-trating trauma. The rent in the pericardium canllow herniation of part or all of the heart, usuallyeading to tamponade. Occasionally, herniation oftructures into the pericardium can occur, such asccurs with diaphragmatic-pericardial rupture andowel herniation. At the Shock Trauma Center inaryland, pericardial rupture occurred in only 22

f 20,000 admission (0.11%).53 The majority ofears involve the left pericardium (64%).53

Injury to the myocardium, such as from pene-rating trauma, is usually made at surgery. How-ver, direct evidence of disruption of the myocar-ium can be established rarely on CT (Fig 30).raumatic communication between the pericar-
ium and the airway or esophagus can also occur.

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CONCLUSION

Diagnostic imaging quickly provides accuratenformation on the nature and extent of thoracicnjury from blunt and penetrating forces. Given thencreasing utilization of MDCT in the trauma set-ing, it has become increasingly useful to add CT tohe screening assessment of the thorax, in order toetect injuries that are not likely to be apparent
rom clinical assessment or radiographic studies, i
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19. Mirvis SE, Shanmuganathan K, Buell J: Use of spiral

ct

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ut may still be life-threatening. Bedside sonogra-hy can be used, in well-trained hands, to assesshe pericardium and pleural spaces, but falls wellhort of CT when considering the full spectrum ofajor thoracic injuries that must be excluded.hile the admission chest radiograph will proba-

ly remain the “first look” at the traumatized chest,DCT will come to serve as the definitive screen-

ng study in most major trauma patients.

ES

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diagnostic imaging of acute thoracic injury

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