imaging in acute thoracic trauma

Imaging in Acute Thoracic Trauma By Stuart E. Mirvis and Philip Templeton

T HE SUPINE anteroposterior portable chest radiograph serves as the principal screen-

ing test for the immediate assessment of the thorax following blunt chest trauma. Several significant abnormalities can be readily diagnosed or suggested including pneumothorax, with or without tension, hemothorax, pneumomediastinum or hemomediastinum, lung parenchymal contusion, atelectasis, pneumopericardium, chest wall, and hemidiaphragm injuries. The position of various internal catheters, lines, and tubes can be assessed. Although the admission chest radiograph serves as the initial and best overall screening test for thoracic injury following blunt trauma, the study is often com- promised by limited exposure capability, expira- tory views, poor or absent patient cooperation, suboptimal patient positioning, and magnifica- tion and distortion of the mediastinum on the supine chest radiograph.

Computed tomography (CT) scanning, although not an appropriate screening study for chest trauma, can overcome many of the limita- tions of chest radiography and can be useful to clarify suspected abnormalities seen on chest radiography1,2 and offers unique diagnostic capability for some injuries.

ECTOPIC LOCATIONS OF AIR IN THE THORAX

Pneumothorax

Pneumothorax may result from trauma or from an iatrogenic origin. The diagnosis is usually straightforward in the erect patient as

computed tomography; MRI, magnetic resonance imaging; TBR, tracheobronchial rupture

From the Thoracic Imaging Section, Department of Radiol- ogy, University of Maryland Medical Center, and the Universiry of Marylnnd Shock-Trauma Center, Baltimore, MD,

Address reprint requests to Stuart E. Mirvis, MD, Associate Professor of Radiology, Department of Radiology, University of Maryland Medical Center, Baltimore, MD 21201.

Copyright o 1992 by W B. Saunders Company 0037-198X192/2703-OOO5$5.OOlO

Fig 1. Pneumothorax in a supine patient. Note the hyperlucent left lung field and minimal mediastinal shift to the left indicating a component of tension pneumothorax. Both the anterior insertion (arrowheads) and the dome (open white arrow) of the left hemidiaphragm are shown as air outlines the anterior costophrenic recess. Contusion is observed in the right lung. (Reprinted with permission.13)

air ascends to the apical region of the hemithorax. Diagnosis requires visualization of the visceral pleura and absence of lung markings beyond this line. Confusion can be caused by

Fig 2. Pneumothorax shown by CT. This image shows a lucent area devoid of lung markings in the anterior left hemithorax (arrows) indicating a pneumothorax. This pneumothorax was not identified on the patient’s supine chest radiograph (not shown). There is subpleural atelectasis at the left posterior lung base.

184 Seminars in Roentgenology, Vol XXVII, No 3 (July), 1992: pp 184-210

IMAGING IN ACUTE THORACIC TRAUMA

Fig 3. Tension pneumothorax. This erect chest radiograph obtained in a 13-year-old blunt trauma victim shows collapse of the right lung (arrowheads), a hyperlucent right hemithorax, a deep costophrenic sulcus sign (curved arrow), spreading of the ipsilateral ribs, and mediastinal shift to the left. (Reprinted with permission.13)

skin folds, bandages, chest tube tracks, and emphysema. In the supine patient, air collects in the anterior-inferior pleural space producing a “deep” costophrenic sulcus, a “double-diaphragm” contour, hyperlucency in the lower thorax and upper abdomen, and sharp demarca- tion of the cardiac apex (Fig 1).3-7 The visceral pleura at the base of the lung may be outlined.

Fig 4. Distention of periportal lymphatics due to high venous pressure from tension pneumothorax. CT though the upper abdomen in the same patient shows marked distention of the inferior vena cava and a small aorta secondary to impaired venous return from a tension pneumothorax. The lateral right lobe of the liver is compressed by the tension pneumothorax. Also note distention of the periportal lymphatics in the hilum of the liver (arrowheads).

Fig 5. Pneumomediastinum. Supine chest radiograph shows a thin, radiodense line parallelling the left mediastinal border and terminating at the level of the mid left hemidiaphragm (white arrowheads). This line represents the parietal pleura and is seen as a result of air density in the mediastinum. (Reprinted with permission5*)

CT is much more sensitive to pneumothorax than chest radiography (Fig 2).H.y All abdominal CT scans should be initiated at the lung bases and viewed with lung window settings to detect subtle pneumothorax. All pneumothoraces have the potential to become larger and develop tension components. It is important to detect pneumothorax before surgery to provide prophy- lactic thoracostomy tube placement. Pneumo- thorax can appear in unusual locations includ-

MIRVIS AND TEMPLETON

ing the major and minor fissure, behind the inferior pulmonary ligament, and loculated by adhesions in the pleural space.lOJ1 Lobar collapse and/or consolidation can alter the typical distribution of a pneumothorax. These atypical sites of pneumothorax may be easier to detect using CT to guide optimal chest tube placement.

Tension pneumothorax is recognized by displacement of the ipsilateral diaphragm inferi- orly, shift of the mediastinum to the contralat- era1 side, flattening of the ipsilateral mediastinal contour, and spreading of the ipsilateral ribs (Fig 3). On CT, occasionally an enlarged inferior vena cava and renal veins are observed; also distention of periportal lymphatics in the liver

Fig 6. Pneumomediastinum with “continuous diaphragm” sign. This radiograph was obtained on an 18-year-old woman after a motorcycle accident. Her upper chest was struck by a metal bar she had tried to ride under. Note severe diffuse subcutaneous emphysema, right upper lobe atelectasis, and deep right costophrenic sulcus sign (arrow) indicating a right pneumothorax. Air outlines the central portion of the diaphragm beneath the heart (arrowheads) and is another manifestation of pneumomediastinum. The patient had a ruptured trachea and esophagus at surgery. (Reprinted with permission’3)

due to high central venous pressure may be seen (Fig 4).

Pneumomediastinum

Pneumomediastinum is a common sequelae of blunt chest trauma. The most common etiology is the “Macklin phenomenon,” disruption of the parenchyma and interstitial dissection of air due to sudden chest compression and re- expansion. Radiographically, pneumomediastinum is best detected by visualization of the parietal pleura along the left mediastinal border. The pleura is seen to parallel the mediastinum and descend below the mid hemidiaphragm (Fig 5). Linear streaks of gas frequently extend into the cervical soft tissues. Air in the

Fig 7. CT of pneumomediastinum. CT through the lower thorax shows air around the aorta and esophagus. The linear tissue stripe to the left of the aorta [arrow) represents the left parietal pleura. Mediastinal air density is also seen collecting in the retrosternal region (arrowheads). (Reprinted with permission.rs)

IMAGING IN ACUTE THORACIC TRAUMA 187

Fig 8. Right mainstem bronchus transection. (A) This admission radiograph in a 35-year-old woman, who sustained blunt chest trauma, shows collapse of the right lung intothe lower right hemithorax, a right pneumothorax, and mediastinal shift to the right. Thoracostomy tubes did not re-expand the right lung. The left parietal pleura indicates pneumomediastinum. (B) A sub- sequent study 3 weeks after injury shows the truncated branch of the right mainstem bronchus (arrow) at the point of transection. (Reprinted with permission’r)

mediastinum creates a sharply defined aorticopulmonary space, a sharp descending aorta that can be often be followed into the upper abdomen, and a “continuous diaphragm” sign under the cardiac shadow (Fig 6).‘* Pneumomediasti- num can dissect into the retroperitoneal or intraperitoneal spaces, as well as subcutane- ously.

CT is very sensitive in the detection of pneumomediastinum, which is best appreciated in the substernal region and around the aorta and esophagus (Fig 7).r3 Streaks of fat density may

be outlined by air in the substernal region and the parietal pleura can be distinguished as it is pushed away from the mediastinum. As noted above, the most common etiology of pneumomediastinum due to blunt thoracic trauma is the Macklin phenomenon. Pneumomediastinum from this mechanism is exacerbated by positive pressure ventilatory support. Tracheobronchial rupture (TBR) is a rare cause of pneumomediastinum occurring in about 1.5% of major blunt thoracic injuries. r4,1s Usually, 80% occur within 2.5 cm of carina, right-sided more frequent than

Fig 9. Traumatic perforation of the cervical esophagus. This lateral cervical radiograph was obtained in an elderly woman who had sustained a fracture-dislocation at the C5-C6 level. The cervical esophagus was perforated and contrast extravasation occurred into the precervical soft tissue and intervertebral disc. (Reprinted with permission.53)

left. Multiple proposed mechanisms include anteroposterior chest compression forcing bronchi outward, increased intraluminal pressure against a closed glottis, and traction shearing


forces. The hallmark of TBR is persistent; severe pneumomediastinum unrelieved by tube thoracostomy. TBR is associated in 90% of patients with fractures of the first through third ribs. Unusual findings on radiography of TBR include a “fallen lung,” a “bayonet” deformity of the bronchus, and ectopic endotracheat tube or balloon cuff position (Fig 8).14J5

Esophageal disruption is also very rarely caused by blunt chest trauma. Blunt and penetrating forces account for 10% of esophageal injuries, which are usually accompanied by other major thoracic damage.*2Jh Proposed mechanisms of injury caused by blunt trauma include crushing of the esophagus between the spine and trachea, traction from hyperextension, and direct penetration by cervical spine fracture fragments (Fig 9).13 In the acute trauma setting also consider iatrogenic causes such as esophageal intubation, traumatic nasogastric tube placement, and esophagoscopy as other possible etiologies. Manifestations of esophageal rupture include persistent severe pneumomediastinum or pneumothorax, left pleural effusion, or an abnormal mediastinal contour resulting from fluid extravasation or hemorrhage. Esoph- agoscopy and contrast esophagography are com- plimentary studies to diagnose this injury. CT can show pneumomediastinum, leakage of oral contrast from the disrupted esophagus into the mediastinum or pleural space, and mediastinitis secondary to delayed diagnosis of esophageal disruption.

Fig 10. Pneumopericardium developing on high positive ventilatory support. This radiograph obtained in an elderly woman who had been on prolonged high-pressure positive ventilatory support shows distension of the pericardium (arrows) and a small cardiac silhouette. The lungs show diffuse changes associated with chronic ARDS and there is a laceration in the right upper lobe (arrowheads). (Reprinted with permission.52)


Pneumopericardium

Pneumopericardium is usually the result of penetrating trauma but may result from blunt forces as well. Prolonged positive airway pressure in combination with parenchymal lung contusion may increase the development of this complication. Air can track along the adventitia of the pulmonary veins and enter the pericardial space. I7 Radiographically, air surrounds the heart but should not rise above the level of the pericardial reflection at the root of the great

Fig 11. Acute tension pneumopericardium. (A) This chest radiograph obtained soon after admission of a young male victim of a motor vehicle accident shows marked distention of the pericardium (white arrowheads) and compression of the heart. The cardiothoracic ratio was 0.36 and the patient had physiological signs of tamponade. (6) Temponade was relieved when a pericardial drain evacuated air under pressure from the pericardial space and the cardiac contour returned to normal (cardiothoracic ration 0.45. (Reprinted with permission.“)

vessels (Fig 10). Air in the pericardium will shift with change in patient position as apposed to pneumomediastinum. Pneumopericardium can appear acutely after blunt chest trauma or result from prolonged positive pressure ventila- tion. Rarely, air in the pericardium can com- press the heart and lead to the development of “tension” pneumopericardium.” Radiographi- tally this is manifest as a globally small cardiac silhouette accompanied by clinical signs of cardiac tamponade (Figs 10 and 11).

190 MIRVIS AND TEMPLETON

Fig 12. Hemothorax producing mediastinal shift. (A) This admission radiograph was obtained in a middle-aged woman with acute respiratory after a motor vehicle accident. The patient had undergone attempted right subclavian line placement at a referring institution. There is marked pleural and extrapleural fluid over the right hemithorax displacing the mediastinum to the left. Note that the density forms a border (arrowheads) suggesting an epipleural etiology. (6) A right subclavian arteriogram shows active hemorrhage from the internal mammary and subclavian artery suggesting an iatrogenic etiology (attempted line placements). (Reprintedwith permission.5z)

PLEURAL EFFUSIONS

Pleural effisions developing in the acute posttraumatic setting usually represent hemothorax. Venous bleeding resulting from laceration to the lung or pleura is low pressure, forms a typical meniscus, and is likely to be self- limited. A rapidly expanding pleural effusion in the setting of acute trauma is more likely of arterial origin such as an intercostal, internal mammary, or mediastinal great vessel source. Arterial bleeding may displace the mediastinum contralaterally (Fig 12). If the bleeding is extrapleural in origin, such as a subclavian arterial source, then the blood appears loculated and forms a convex bulge toward the lung, for example, an epipleural hematoma. CT can be helpful in distinguishing hematoma from other pleural collections suggested by high CT attenuation.*

Simple pleural effusions typically manifest a meniscus sign in the erect patient, widen the lateral pleural stripe, and blunt the lateral costophrenic sulcus. Fluid in the medial pleural space may form a triangular paraspinal mass. Fluid can track into the fissures producing typical patterns. In the erect patient, fluid may be subpulmonic in location, producing an appar- ently elevated hemidiaphragm, which peaks laterally and produces a sudden “cut-off’ of the lower lobe pulmonary vessels on radiography.‘*

Because pleural fluid is outside the lung, the bronchovascular markings are preserved. Unilat- eral effusions in the supine-positioned patient produce a uniform increase in density over the hemithorax. If bilateral and symmetric in size,

Fig 13. Pulmonary contusion. This radiograph obtained after blunt chest trauma in a young man shows a homoge- neous nonsegmental region of consolidation in the right mid and upper lung field. No air bronchograms are noted and the consolidation is predominantly peripheral in location suggesting contusion as the most likely diagnosis. (Reprinted with permission.13)


Fig 14. Pulmonary laceration and contusion. (A) Chest radiograph obtained in a 22-year-old man sustaining blunt chest trauma shows diffuse increased density in the left lung. There are scattered areas of ovoid radiolucency at the left base suggestive of lacerations within contused consolidated lung (arrows). (B) A CT scan through the lung bases shows left lower lobe consolidation and several lacerations within the consolidated lung. (Reprinted with permission.52)

pleural effusions may be difficult to identify radiographically. CT can best distinguish pleural fluid from other components causing radiographic density such as atelectasis, contusion, or infiltrate. CT can best show loculation of pleural fluid and better delineate complex pleuroparen- chymal opacities. Although very large effusions may produce mediastinal shift, this tendency is partially offset by compressive atelectasis which typically occurs with moderate to large effu-

sions. The presence of air within a pleural fluid collection may result from pneumothorax, infection, or tracheobronchial fistula.

TRAUMA TO THE LUNG PARENCHYMA

Pulmonary contusion occurs in 30% to 70% of blunt chest trauma victims and results from direct transmission of energy through the chest wall.‘” Radiologically, contusions appear as ho- mogeneous air-space-occupying processes that

Fig 15. CTof pulmonary laceration. CT scan in a patient with ARDS shows a lung laceration (traumatic pneumatocele) on the right. A thin “pseudomembrane” surrounds the laceration. (Re- printed with permission.13)


tend to be peripheral, nonsegmental and geo- graphic in distribution (Fig 13). There may or may not be associated adjacent rib fractures. Lesions can be unilateral, bilateral, focal, multi- focal, or diffuse. Air bronchograms are rarely seen because of blood in the small airways.

Contusions are usually evident at presenta- tion or within 6 hours. Initial clearing begins radiographically 48 to 72 hours after injury but may not appear for 5 to 7 days. Failure of the density to resolve suggests superimposed infection, atelectasis, aspiration, or adult respiratory distress syndrome (ARDS).*O Lacerations are frequently present in association with contusions but are poorly depicted by radiography.

Fig 16. CT of acute pulmonary hematomas. CT scan through the lung bases of a 16-year-old with hemoptysis injured in an explosion shows multiple parenchymal hematomas (HU 50 to 60). including some with cavitation (arrows), and lower lobe contusions. A chest tube is positioned in the minor fissure. (Re- printed with permission.‘)

Lacerations may be seen as the edema and hemorrhage associated with the contusion begins to resolve (Fig 14). CT is much more sensitive at detecting pulmonary lacerations than radiography. 21 Lacerations appear as ovoid radiolucencies with a 2- to 3-mm pseudomembrane (Fig 15). Hemorrhage into the cavity may produce an air-fluid level in the cavity, whereas air within the cavity may form a “crescent sign” if a hematoma forms within the cavity (Fig 16). Lacerations resolve slowly over 3 to 5 weeks and may leave a residual coin lesion for several months. Lacerations of the lung are generally benign, but can lead to complications such as bronchopleural fistula and/or infection (Fig

Fig 17. CT of infected pulmonary laceration. Mid-thoracic CT image in febrile 30-year-old man shows a large laceration posteriorly on the right with sur- rounding consolidated lung. There is a


Fig 18. Ruptured left hemidiaphragm with herniation. (A) This admission supine chest radiograph shows obscuration of the left hemidiaphragm, increased density at the left base, and mild mediastinal shift to the right. Findings are suggestive but non- diagnostic of a ruptured diaphragm. (8) A repeat radiograph several hours later shows pro- gressive mass effect with mediastinal shift and a large left pleural effusion. A ruptured diaphragm was surgically confirmed. (Reprinted with permission.5z)

17).22,2’ In our experience, infected lung lacerations are very resistent to successful management with antibiotics and postural drainage and may require surgical resection.

INJURY TO THE HEMIDIAPHRAGMS

Rupture of the hemidiaphragm is present in 3% to 5% of patients undergoing celiotomy after blunt abdominal trauma and occurs in 0.8% to 1.6% of major blunt thoracic trauma.24-28 Penetrating injury to the diaphragm is typically

not detected by diagnostic imaging but is found at surgical exploration. Injury to the diaphragm from blunt trauma is related to motor vehicle accidents in 90% of cases and the risk is three times greater from left lateral impact than from frontal impact, supporting a role for chest-wall deformation and shearing forces in producing this injury. Right hemidiaphragm injury occurs in 50% of patients after right lateral impact, but left hemidiaphragm rupture occurs in 91% of patients after left lateral impact. Left hemidia-


phragm injuries predominate (about 75%) probably as a result of the protective effect of the liver on the right side. Herniation of abdominal viscera occurs on the left side in 95% of cases leading to the predominant diagnosis of left diaphragm injury in imaging series. The diaphragm is typically torn in the area of the central tendon or musculotendinous junction but can be avulsed from its rib insertions or lacerated by a rib fracture fragment. A high percentage of patients with hemidiaphragm injury sustain other intra-abdominal(59% to 82%) or intrathoracic (45%) injuries.24 The clinical diagnosis of hemidiaphragm injury is difficult and is missed in 7% to 66% of patients.27 Diagnostic peritoneal lavage is falsely negative for the injury in up to 34% of patients.29

Radiological findings in ruptured hemidiaphragm are absent in at least 25% to 50% of cases initially but may develop on delayed radiographs. 24-29 Apparent elevation of the hemidiaphragm, obliteration or distortion of its contour, displacement of the mediastinum contralaterally, and left pleural effusions are suggestive but nonspecific findings (Figs 18 and 19). The demonstration of gas-containing viscera in the thorax, particularly with a focal constriction across air-containing bowel is pathognomonic of herniation (Figs 20 and 21). Ruptured diaphragm can be mimicked or masked by superimposed lung pathology including multiple traumatic lung cysts, atelectasis, pleural effusion,

Fig 19. Ruptured left hemidiaphragm. Chest radiograph shows marked apparent elevation of the left hemidiaphragm (left lung base) with left lower lobe increased density. Mild rightward mediastinal shift is observed and there is a sugges- tion of lucencv in the lower left hemithorax. Surgery revealed a rb-cm tear in the left hemidiaphragm and colonic herniation. (Reprinted with permission.3

Fig 20. Ruptured left hemidiaphragm with herniation. Chest radiograph in blunt trauma victim shows small bowel loops herniated into the lower left thorax with mediastinal displacement. (Reprinted with permission5*)

pulmonary contusion, aspiration pneumonia, total or partial eventration or the diaphragm, acute gastric distension, phrenic nerve palsy, subpulmonic fluid collections, loculated hemo- pneumothorax, and chronic esophageal or para- esophageal hernias (Fig 22).

In a retrospective review of 50 consecutive patients with surgically proven diaphragm ruptures seen at the Maryland Shock-Trauma Cen- ter, 44 were left-sided. Radiological findings were diagnostic in 20 (47%) and suspicious in another 8 patients .29 Delayed chest radiographs were diagnostic in an additional 5 patients (Fig 23). Only 2 of 6 patients with right hemidiaphragm rupture were diagnosed by chest radiography (Fig 24). Suspected herniation of liver through a right hemidiaphragm defect can be verified by technetium sulfur-colloid liver- spleen scintigraphy (Fig 25). Rarely, colon can herniate through a right hemidiaphragm laceration (Fig 26).

The authors have not found CT scanning to be particularly useful in confidently establishing this diagnosis. The diagnosis was prospectively suggested in only 1 of 7 (14%) of patients with surgically documented left diaphragm rupture using CT scanning in the study of Gelman et a1.29 CT diagnosis requires the visualization of fat or abdominal viscera posterior-lateral to the hemidiaphragm and a defect in the diaphragm contour (Figs 27 and 28).30

Magnetic resonance imaging (MRI) using T1-weighted coronal and sagittal images has


Fig 21. Ruptured left hemidiaphragm with herniation. Chest radiograph obtained in a young man after a motor vehicle accident with left-sided impact shows gas in the lower left chest with haustral markings. There is focal constriction of the bowel as it herniated through a tear in the diaphragm (arrows). The appearance is pathognomonic of ruptured diaphragm with bowel herniation. (Reprinted with parmission.5z)

been diagnostic for diaphragm rupture in two patients when all other studies were equivocal and excluded the diagnosis confidently in three other patients (Figs 29 and 30).31

INJURY TO THE CHEST WALL

Isolated fractures of the ribs, clavicle, or scapula seldom represent significant injuries in

Fig 22. Atelectasis mimicking diaphragmatic rupture. Re- peat chest radiograph 90 minutes after a normal admission study (not shown) shows elevation of the nasogastric tube to the level of the lower chest (arrowheads) and left lower lung field density. However, note that there is leftward mediastinal shift and no pleural effusion. The patient had exploratory surgery that revealed a normal left hemidiaphragm. The appearance is secondary to left lower lobe atelectasis. (Reprinted with permission.52)

and of themselves, but they do retlect the magnitude of force imparted, particularly in older patients with noncompliant chest walls. Fractures of the first three ribs in particular indicate significant energy transfer. Fractures to the upper ribs, clavicle, and upper sternum are significant in that they may be accompanied by brachial plexus or vascular injury in 3% to 1.55% of patients. ly Although subclavian vascular injury should be suspected with fractures of the first three ribs, clavicle, and scapula, such injuries are usually accompanied by significant fracture displacement, extrapleural hematoma, brachial plexus neuropathy, or radiological evidence of mediastinal hemorrhage. Angiography in the absence of these signs produces a low yield of significant vascular injuries and is probably not warranted on an emergency basis. Fractures of the lower ribs should increase suspicion of splenic, hepatic, or renal injury, confirmation of which should then be sought by appropriate diagnostic investigations such as CT.

Double fractures of three or more adjacent ribs or contiguous combined rib and sternal or costochondral fractures can produce a focal area of chest-wall instability. Paradoxical motion of a “flail” segment during the respiratory cycle can impair respiratory mechanics, pro- mote atelectasis, and impair pulmonary drainage. Although usually recognized by physical inspection, a flail segment involving the upper ribs may be hidden by the chest-wall musculature. Rib fractures are often accompanied by


Fig 23. Ruptured diaphragm diagnosed on delayed study. (A) Admission chest radiograph shows normal contour and position of left diaphragm. (B) Chest radiograph obtained 2.5 hours later shows a loss of the left hemidiaphragm contour, a large gas collection at the left lung base, and a left pleural effusion. The madiastinum is shifted to the right and pnaumoperitonaum has developed. Surgery showed an 8-cm rupture of the left hemidiaphragm with herniation of the gastric fundus. (Reprinted with parmission.*9)

extrapleural hematomas that present as focal hematomas over the apices may accompany lobulated areas of increased density on the fractures of the upper ribs or hemorrhage from chest radiograph. Due to their extrapIeura1 the subclavian vessels from blunt trauma or nature, such hematomas indent the parietal iatrogenic causes. Extrapleural hematomas will pleura focally and maintain a convex margin not change their configuration with changes in toward the lung. Development of extrapleural patient position as will fluid collections that are


Fig 24. Ruptured right hemidiaphragm. Chest radiograph shows elevated right lung base with shift of mediastinum to the left. There is a large left pleural effusion. Surgery showed a right diaphragmatic tear with herniation of liver into the right hemithorax. (Reprinted with permission.**)

free in the pleural space. Hemorrhage from lacerated intercostal arteries accompanying chest-wall trauma can lead to exsanguination. Both diagnosis and therapeutic embolization can be performed using angiographic tech- niques.

Rarely, a segment of lung may herniate through a defect in the chest wall created by a flail segment. Transthoracic lung herniation increases in likelihood with positive-pressure ventilatory support and with rupture of the internal thoracic fascia, parietal pleura, and pectoral and intercostal musculature. The diagnosis may be made by plain radiographs but is easier to detect by CT (Fig 31). Although entrapment and strangulation of the herniated portion of lung can occur, significant sequelae are generally rare with expectant management.

Fractures of the sternum are infrequent, occurring in 8% of major thoracic trauma admis-

Fig 25. Herniation of liver through the right hemidiaphragm. (A) Admission CT after blunt trauma shows abnormal contour to the right hemidiaphragm. (B) CT shows elevation of the liver but is not diagnostic for herniation. (C) Sulfur-colloid liver-spleen scan shows activity above level of right hemidiaphragm indicating herniation of liver parenchyma (arrow). (Reprinted with permission.Y)


Fig 26. Heriation of bowel through the right hemidiaphragm. Chest radiograph obtained in elderly man after a motor vehicle accident initially reveals lucency in the right upper lung field suggestive of colon (arrowhead). There is also increased soft tissue density at the right base. At surgery there was herniation of liver and colon through a torn right hemidiaphragm. (Reprinted with permission.52

sions at one institution. 32 Diagnosis may require both lateral and oblique sternal views. Concur- rent injury to the great vessels can result from sternal fracture and should be sought in the presence of radiographic evidence of an abnormal mediastinal contour. Laceration of the innominate artery secondary to a displaced fracture of the sternum has been reported but appears to be quite rare.33 Demonstration of a sternal fracture should always increase suspicion of myocardial contusion, which should be

evaluated by appropriate diagnostic studies. Most sternoclavicular dislocations are anterior and of no major clinical significance. Posterior dislocations of the clavicle relative to the manu- brium can damage the great vessels, superior mediastinal nerves, trachea, and esophagus. Although sternoclavicular dislocations are de- monstrable using angled chest radiographs (tube angled 35” cranially), they are more easily detected by CT (Fig 32).

Scapulothoracic dissociation is a rare injury characterized by a lateral displacement of the entire forequarter with intact overlying skin, complete acromioclavicular separation, and usually multiple fractures of the ipsilateral upper extremity. Avulsion injuries to the brachial plexus and subclavian nerves always accompany the injury (Fig 33).34

INJURY TO THE PERICARDIUM AND MYOCARDIUM

Hemopericardium may develop acutely as a direct consequence of blunt trauma to the anterior chest and severe crush injuries but more typically results from penetrating injury to the heart or severe blunt chest trauma producing cardiac rupture. A rapid accumulation of blood in the pericardial space often causes cardiac tamponade and severe hemodynamic compromise without altering the radiologic appearance of the cardiac silhouette but may be manifest as a nonspecific enlargement of the cardiopericardial contour. If time permits, bed- side sonographic evaluation of the heart can quickly and noninvasively detect even small

Fig 27. CT of left hemidiaphragm rupture. CT image through the upper abdomen shows interruption of the contour of the left hemidiaphragm (arrow) and fat on both sides of the diaphragm indicating disruption and herniation of fat. (Reprinted with permission.*g)


Fig 28. CT of left hemidiaphragm rupture. (A) CT image through the lung base shows a markedly displaced and de- pressed left posterior rib fracture that indents the pleura and lung. (6) A more caudal image shows fat density within atelectatic lung (arrowheads) suggesting fat herniation. (C)Still more caudal section shows sharp interruption of the left diaphragm (curved arrow) suggesting laceration. Left hemidiaphragm rupture with fat herniation was subsequently surgically verified. (Reprinted with permission.52)


quantities of pericardial fluid and is the study of choice. Simultaneously, cardiac function, chamber size, and valvular integrity can be assessed. CT is also very sensitive for detecting pericardial space fluid and may indicate pericardial hemorrhage as determined by the high CT attenuation of the fluid. Cardiac tamponade is reflected on CT by distention of the inferior

Fig 30. MRI of hemidiaphragm avulsion with herniation. Coro- nal T,-weighted image shows inferior-medial displacement of the lateral left hemidiaphragm indicating avulsion from the chest wall (arrow). Abdominal fat has herniated into the thorax and compressed the left lung. (Re- printed with permission.=)

Fig 29. MRI of hemidiaphragm rupture and herniation. Coronal T,-weighted MR image shows interruption of the left hemidiaphragm (arrow) with herniation of bowel and fat into the lower left hemithorax. The left upper lobe is atelectatic. (Reprinted with permission.J1)

vena cava, hepatic, and renal veins and by development of periportal vein edema within the liver (Fig 34). CT and sonography are also more sensitive than radiography in detection of chronically developing pericardial effusions as may occur with postpericardiotomy syndrome or pericardial empyema. Rarely mediastinal hematoma resulting from blunt chest trauma


Fig 31. Herniation of lung through the chest wall. CT shows lung herniating through the an- terolateral and posterolateral as- pects of the left chest wall in a patient who sustained multiple rib fractures. The patient was conservatively managed without difficulty. (Reprinted with permission.‘)

can cause compression of the right ventricle and extrapericardial tamponade.“”

Pericardial rupture represents a rare consequence of serious thoracic trauma and was diagnosed in only 22 (0.11%) of 20,000 admis- sions to the University of Maryland Shock- Trauma Center over a lo-year period.jh Rup- ture may involve the diaphragmatic pericardium and/or the pleuropericardium and the majority (64%) of tears involved the left pleuropericar-

dium. Typically, the diagnosis is established intraoperatively during resuscitation or surgery for associated injuries or at autopsy, but pericardial rupture can be indicated by chest radiograph with herniation of air-containing abdominal viscera into the pericardium accompanying diaphragmatic rupture (Fig 35). Pneumopericar- dium may appear in the presence of pneumothorax as air enters through the pericardial disruption. Finally, cardiac luxation into the pleural

I Fig 32. CT of posterior sterno-

i clavicular dislocation. CT image j obtained in 2O-year-old patient / /

struck by motor vehicle shows posterior dislocation of the proximal right clavicle.


Fig 33. Scapulothoracic dissociation. (A) Chest radiograph on admission of young motorcycle accident victim shows soft tissue swelling over the right clavicle, elevation, and lateral displacement of the right scapula compared with the left (arrows) and an inferior glenoid fracture (arrowhead). The patient had a pulseless anesthetic right arm, but the overlying skin of the shoulder was intact. (6) Digital subtraction arteriogram shows occlusion of the proximal right subclavian artery including the vertebral origin due to stretching of the vessel, intimal tearing, and thrombosis. (Reprinted with permissi0n.s’)

IMAGING IN ACUTE THORACIC TRAUMA

Fig 34. CT of cardiac tamponade. (A) CT through the lower chest shows fluid in the pericardium that mea- sured blood density (arrows). There are small bilateral pleural effusions and periaortic hemorrhage. (B) CT though the upper abdomen shows distention of the inferior vena cava and a small aorta due to pericardial tamponade and decreased cardiac output. There is also marked periportal lymphedema in the liver secondary to venous outflow obstruction (arrowheads). (Re- printed with permission.5S)

cavity (predominantly left) may occur after large pericardial tears and present as gross cardiac displacement (Fig 36).

CARDIAC CONTUSION/DYSFUNCTION

Cardiac contusion may result from blunt chest trauma in from 8% to 76% of patients, but functional cardiac abnormalities occur in less than 20% of patients.“‘Js Significant myocardial injury presents radiographically as a spectrum of findings related to the injury to the heart and chest. The cardiac findings may be similar to those occurring from acute myocardial infarc-

Fig 35. Traumatic herniation of bowel into the pericardium. Chest radiograph obtained after blunt torso trauma reveals hemiation of stomach, containing contrast and nasogastric tube, into the pericardium. Note lack of mediastinal displacement and pleural effusion.


Fig 36. Traumatic pericardial rupture and cardiac herniation. (A) Chest radiograph on admission of a man who fell 30 feet onto the left side shows gross displacement of the cardiac shadow into the right chest. There were numerous displaced left lower rib fractures. (B) A repeat radiograph 15 minutes later shows spontaneous return of the heart into the pericardial sac with improvement in cardiac output. Note the rounded contour of the right heart border (arrows) suggesting residual herniation of the right atrium through a pericardial defect. At surgery a 6-cm right pericardial tear was re- paired. (Reprinted with permission.j3)

tion, such as congestive heart failure, ventricular aneurysm, or massive cardiac enlargement. The presence of anterior rib fractures and sternal fractures should raise suspicion of myocardial injury, although there is no clear relation- ship between the extent of chest-wall injury and

the degree of underlying cardiac damage. Myo- cardial injury can range from mild cardiac contusion to severe transmural contusion. Patho- logically, blunt myocardial trauma produces a wide spectrum of injury, ranging from small, subepicardial, or subendocardial petechiae or


Fig 37. Comparison of supine and erect chest radiographs to evaluated mediastinum. (A) Ad- mission supine chest radiograph in this patient following blunt decelerating thoracic trauma shows marked widening of the mediastinum with loss of mediastinal contours. (B) Repeat erect chest radiograph of the same patient shows a normal mediastinal contour. No further workup of the chest was performed.

ecchymoses to full-thickness contusion. The right ventricle is most frequently injured as it comprises almost three times more exposed anterior surface of the heart than does the left ventricle.

Clinically, mild myocardial dysfunction can lead to diminished cardiac output and/or acute cardiac arrhythmias, whereas more severe injury can lead to congestive failure or cardiac rupture. Cardiac dysfunction after blunt chest

trauma is one of the most frequently missed or delayed diagnoses made after severe injury and is frequently masked by more obvious injuries.

At the Shock-Trauma Center, the diagnosis of cardiac contusion is made by radionuclide scintigraphy, using first-pass radionuclide ventriculography followed by gated equilibrium imaging for assessment of ventricular-wall motion. This is a simple, accurate, and reproduc- ible technique to assess right-ventricular ejec-


tion fraction. During an 8-month study at the Shock-Trauma Center, 26 (48%) of 54 patients with multisystem injury and blunt chest trauma had abnormalities of ventricular-wall motion confirmed by radionuclide ventriculography. Ab- normalities were confined to the right ventricle in 92% of cases and included right-ventricular dilatation, localized wall-motion abnormalities

Fig 39. Chest radiograph of unequivocal mediastinal hemorrhage. This erect chest radiograph shows obscuration of the aortic arch and aorticopulmonary window. The left paraspinal stripe is markedly widened and extends above the level of the aortic arch to the apical cap (arrowheads) that is distinctly abnormal. The patient had a rup tured thoracic aorta. [Reprinted with permisrion.r*)

Fig 38. Chest radiograph showing mediastinal hemorrhage. This radiograph obtained after motor vehicle trauma in 60- year-old man shows marked widening of the right peratracheal soft tissue (arrowheads), a thick- ened left paraspinal stripe (open arrow), increased soft tissue density lateral to the aortic arch (two- headed arrow), an obscured aortic arch, and aorticopulmonary window. The patient had a rupture proximal descending aorta on angiogram.

and diffuse hypokinesia. Patients with wall- motion abnormalities exhibited significantly lower right ventricular ejection fractions than those without. Follow-up nuclear scintigraphy was valuable in showing significant improvement in cardiac function by 3 weeks after injury.37 Radionuclide ventriculography allows identification of trauma victims who warrant the


Fig 40. Role of CT in evaluating mediastinal hemorrhage. (A) Admission supine chest radiograph (not shown) suggested mediastinal hemorrhage. An erect chest radiograph could not be obtained because of pelvic fractures, therefore a thoracic CT was performed to evaluate mediastinum. CT image through the aortic arch shows blood in mediastinum adjacent to the arch (arrowheads) and an intimal flap in the aorta (arrow) with a medial pseudoaneurysm (white arrow). (B) Scan through carina again shows anterior mediastinal hemorrhage (arrowheads) and an intimal flap in the aorta (arrow) with the pseudoaneurysm posterior(p).

most intensive monitoring for arrhythmias, guid- ance of fluid balance, and respiratory therapy for hypoxemia. Results of radionuclide ventriculography may influence the timing of surgery and the type of intraoperative monitoring and anesthesia used.

Two-dimensional echocardiography is useful for evaluating cardiac valve function, cardiac- wall function, cardiac chamber size, papillary muscle function, and the anatomy of the aortic valve and root. Cardiac sonography may be particularly useful in settings in which the cardiac silhouette remains unchanged radiographi- tally but clinical signs of severe hemodynamic embarrassment are present.

Direct injury to the coronary arteries follow-

ing blunt trauma to the chest can occur leading to pseudoaneurysm formation, intimal injury, and occlusion. In the presence of electrocardio- graphic changes of myocardial infarction, cardio- genie shock, or recurrent arrhythmias following blunt thoracic trauma, early catheterization to evaluate the coronary artery anatomy is indicated.

MEDIASTINAL HEMORRHAGE AND MAJOR ARTERIAL INJURY

The diagnosis of injury to the great arteries of the thorax constitutes one of the most controver- sial subjects in the field of trauma imaging.3”-J7 Well over 100 papers have appeared in the medical literature over the past two decades


Fig 40. (Cont’d) (C) Digital atteriogram confirms aortic rupture just distal to origin of the left subclavian artery.

discussing this topic. Many radiological signs and measurements have been applied to the chest radiograph in order to distinguish patients with and without major thoracic arterial injury. Some of these signs have enjoyed initial enthusi- astic support, only to be cast aside by larger or more carefully controlled studies. Some signs such as the apical pleural cap,48 a mediastinal width sign of greater than 8 cm,49 and first or second rib fracturesSo as indicators of great arterial injury have unfortunately “clung to life” despite extensive literature attesting to their limited predictive value for great vessel injury.

A great deal of attention has been paid to the role of imaging of the chest to assess for potential major arterial injury after blunt chest trauma at the Shock-Trauma Center over the past 20 years. Given over 2,000 patients admit- ted annually with an appropriate history to warrant consideration of this injury it has become an obsession. Based on an extensive experience in dealing with patients sustaining significant decelerating blunt chest trauma, the

following approach has emerged: (1) an erect chest radiograph (90° to 105” of elevation) permits a more accurate assessment of mediastinal anatomy than a supine or semi-erect study and should be obtained whenever clinically feasible (Fig 37); (2) a normal mediastinal contour on the true erect chest radiograph excludes the diagnosis of major arterial injury in our collective experience; (3) a chest radiograph demonstrating an unequivocally abnormal mediastinal contour mandates immediate thoracic arteriography (Figs 38 and 39); (4) dynamic, contrast-enhanced CT scan can serve as a valuable ancillary screening test to detect the presence of mediastinal hemorrhage and/or great vessel injury if the interpretation of the chest radiograph is equivocal or only technically poor radiographs can be obtained, including many patients in whom an erect chest radiograph is not possible (Fig 40); (5) CT should not be used as a screening test in all patients with an appropriate clinical history of decelerating chest trauma; (6) CT evidence of mediastinal hemorrhage without a clear etiology, such as paraspinal hematoma accompanying a thoracic spine fracture, should lead to arteriography, whereas CT examination showing no mediastinal hemorrhage and a normal aortic contour should pre- clude arteriography; (7) digital subtraction arteriography performed on a high-resolution system provides a completely reliable assessment of the aorta while saving time and contrast over cut- film arteriography; and (8) a very suggestive clinical history, such as very high-speed deceler- ation or clinical signs of great arterial injury, although of poor predictive value, should be considered in selecting the diagnostic pathway. Clinical evidence of acute coarctation syndrome or significant pressure differences in the upper extremities after blunt thoracic trauma should evoke immediate arteriography.41,43-45

Even the angiographic appearance of the great vessels, for example, the “gold-standard” of diagnosis can lead to confusion caused by a prominent ductus bump that may simulate an aortic pseudoaneurysm (see article by Pais else- where in this issue).51

CONCLUSION

Despite the rapidly growing high-technology environment of diagnostic imaging, the chest radiograph remains the principle imaging study


to rapidly assess patients sustaining blunt chest anticipated and warranted. CT scanning clearly trauma and can diagnose or suggest the pres- has a role in selected patients to more precisely ence or absence of most clinically significant delineate mediastinal anatomy, the pericardial intrathoracic injuries. Attaining optimal quality space, lung parenchymal injury, and complex of the admission chest radiography should be of pleural fluid collections among other indica- paramount importance. Computed radiography tions. Application of MRI in the acute trauma may provide some benefit over conventional victim has been limited technically, but has radiography by compensating for improper expo- proven of value in defining potential diaphragm sure technique and permitting “windowing” to injury. Further potential applications of MRI optimize visualization of the lung parenchyma, and magnetic resonance angiography in acute mediastinum, or bone anatomy from a single chest trauma are under consideration in our exposure. Further study of this technology is institution.

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imaging in acute thoracic trauma

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