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Imaging of Blunt Thoracic Trauma
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Imaging of Blunt Thoracic Trauma Sreevathsan Sridhar M.D., Constantine Raptis M.D., Sanjeev Bhalla M.D.
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S0037-198X(15)00062-0 http://dx.doi.org/10.1053/j.ro.2015.12.002 YSROE50527
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Seminar in Roentgenology
Cite this article as: Sreevathsan Sridhar M.D., Constantine Raptis M.D., Sanjeev Bhalla M. D., Imaging of Blunt Thoracic Trauma, Seminar in Roentgenology, http://dx.doi.org/ 10.1053/j.ro.2015.12.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Imaging of Blunt Thoracic Trauma
Sreevathsan Sridhar1 M.D., Constantine Raptis2 M.D., Sanjeev Bhalla3 M.D. From Mallinckrodt Institute of Radiology, Washington University in St. Louis
1
Cardiothoracic Imaging Fellow, Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO 2
Assistant Professor of Radiology, Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO
3
Professor of Radiology, Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO
No grant support was used for this work.
Contact: [email protected] or [email protected], 314-362-2927 510 S Kingshighway Blvd, Box 8131 Saint Louis, MO 63112
Introduction Greater than 60% of blunt traumatic injuries are related to fall or motor vehicle collision. Of all anatomic regions, injuries to the thorax represent the third most common type of injury (behind head and extremities) with a mortality rate close to 10%, compared to overall mortality in trauma of 4.3%.1 Given the relatively higher rate of mortality compared to other anatomic injuries and the association between chest trauma and greater severity of overall injury2, recognition of injuries to the thorax is of great importance in approaching the patient with blunt thoracic trauma. Portable chest radiography is typically the first imaging study performed on patients in the emergency department after blunt trauma. The primary goals of chest radiography are to confirm support device placement and evaluate for immediately life-threatening findings, such as tension pneumothorax.3 Previous comparisons have indicated that a majority of thoracic injuries found on CT (and in particular multi-detector CT) may be missed on chest radiography. Up to 20% of these injuries may significantly
influence subsequent management.4 MDCT, therefore, has been established as a critical portion of the initial evaluation of patients in blunt thoracic trauma.5 In this article, we will discuss typical and atypical findings on chest radiography and CT for non-vascular thoracic injuries in blunt trauma. We will follow an “outside-in” approach to discussing the anatomic regions involved, beginning with the chest wall, proceeding to the pleura and lungs, and following with the central structures including the airways, esophagus, and heart/pericardium. When applicable direct and indirect signs of injury will be described to help the reader build their confidence in describing traumatic findings. The common and uncommon findings of injury to each of these structures are summarized in Table 1. The table is intended to help the reader develop a search pattern in the setting of trauma.
Table 1. Summary of common and uncommon findings of blunt thoracic injury on radiography and CT. Anatomic Category
Chest wall
Structure or Pathology
Lungs
Computed Tomography
Common
Uncommon
Common
Uncommon
Ribs
Involvement of middle ribs, displaced fracture
First or second rib fractures, flail chest
Angulation or displacement of fragments, associated soft tissue injuries
Costal cartilage fractures
Sternum
Not commonly identified on radiography
Displaced fracture on lateral radiograph
Transversely oriented fracture (use MPR to identify), mediastinal hematoma
Sternoclavicular joint dislocation: Anterior – usually isolated Posterior - look for associated injuries
Scapula
Scapular body fractures, difficult to assess extent
Isolated scapula fracture – usually associated with thoracic or additional arm injury
Transverse orientation inferior to glenoid
Articular involvement (3D reconstructions helpful)
Elevation of the ipsilateral hemidiaphragm
“Cottage bread” sign, NG tube coursing into thorax
Visceral herniation through a diaphragmatic defect, “dependent viscera” sign, elevation of abdominal organs
Distinct defect in diaphragm, “band” and “collar” signs
Pneumothorax
“visceral-pleural line” sign, mediastinal shift (with tension)
“deep sulcus” and “double diaphragm” signs, unilateral hyperlucent lung, widening of intercostal spaces (with tension)
Direct visualization of gas in the pleural space, anteromedial location of pneumothorax, associated pneumomediastinum
Dissection through diaphragmatic channels to cause pneumoperitoneum
Hemothorax
Blunting of costophrenic angles, posteriorly layering effusion
Subpulmonic effusion, signs of tension – inverted diaphragm, mediastinal shift
Hyperattenuating pleural fluid (30-45 HU when acute)
Signs of tension – mediastinal shift, inversion of the diaphragm, compression of vasculature
Pulmonary Contusion
Airspace consolidation or ground glass, develops in 6 hours
Prolonged airspace opacification beyond 5-7 days – indicates alternate pathology
Patchy airspace consolidation or ground glass crossing fissures
Diffuse bilateral lung involvement, prolonged
Diaphragm
Pleura
Chest Radiograph
Pulmonary Laceration
Intraparenchymal cavity, filled with air, fluid, or both
Airspace consolidation
Radiolucent cavity (pneumatocele)
Trachea and Bronchi
Pneumomediastinum Pneumothorax Subcutaneous emphysema
Postobstructive pneumonia or atelectasis from airway hemorrhage
Esophagus
Rare in blunt trauma
Pneumomediastinum Hydropneumothorax
Heart
Pericardial effusion, pulmonary edema
Acute cardiomegaly (from heart failure)
Hemopericardium, pulmonary edema
Wall irregularities, myocardial hypoattenuation, extravasation of contrast into pericardial space
Pericardium
Pericardial effusion, pneumopericardium
Abnormal cardiac contour
Hemopericardium, pneumopericardium
Cardiac herniation through pericardial defect
Defect in tracheal or bronchial wall, pneumomediastinum, pneumothorax, subcutaneous emphysema Same as chest radiography – difficult to identify site of injury (Signs of aspiration almost always present)
Laceration due to shearing in the setting of fibrosis
“Fallen lung” sign (in bronchial avulsion)
Mediastinitis (delayed complication which may be suggested on initial imaging)
Chest wall Ribs Rib fractures are the most common injury in blunt thoracic trauma and reflect a broad range of clinical significance. When they occur, the rib fracture fragments can transform a blunt injury mechanism into a local penetrating injury. Consideration should be given to adjacent soft tissue structures and how the fracture fragments may cause associated injury, such as lacerations to the adjacent pleura or lung. Fractures of the lower ribs can be associated with injury to abdominal organs, while upper rib fractures, while rare, may be associated with injuries to adjacent vessels or the brachial plexus.3 The primary consequence of rib fractures without adjacent organ injury is pain. Specifically in the setting of multiple rib fractures, flail chest can be a cause of significant morbidity as the patient may not be able to maintain full inspiration due to severe pain.6 A flail chest can occur when there are 3 adjacent segmental rib fractures3 and represents paradoxical motion of the fractured ribs with respect to the remaining chest wall during inspiration. (Figure 1) Identification of these injuries is important as a severe flail chest injury may be an indication for epidural catheter placement to administer anesthesia.7 Chest radiography Posterior rib fractures are usually readily detected on chest radiography, as are displaced fractures. However, the sensitivity of chest radiography for non-displaced fractures is limited. Focused radiography of the ribs is often more effective at identifying rib fractures but is still somewhat limited.3
Computed tomography CT is the preferred imaging modality for diagnosis of rib fractures.8 Careful examination of each rib along its course is necessary and documentation of multiple fractures should be performed to allow prompt clinical evaluation for flail chest. In additional to standard axial evaluation, coronal reformatted images are helpful to clarify equivocal findings. Two different typical morphologies have been described for rib fractures – buckling of the cortex and an actual fracture gap. Special attention should be given to buckle fractures, which are frequently missed.8 Additionally, CT allows for evaluation of the costal cartilage, where fractures are commonly missed radiographically.9 (Figure 2) Three dimensional reconstructions using surface rendering may be helpful to evaluate the cartilage. Sonography and bone scintigraphy can be useful adjuncts to further evaluate the costal cartilage.
Sternum Fractures of the sternum are often secondary to direct trauma or deceleration injuries.3,10 These are an indication of high-energy trauma and often associated with other soft tissue injuries. Cardiac injuries in particular are a major concern, as the right ventricular free wall typically lies immediately posterior to the sternum. Mediastinal hematoma is almost always seen with sternal fractures. Sternal fractures are rarely apparent on frontal chest radiography. Lateral radiographs improve the ability to detect sternal fractures, but still provide limited sensitivity.3 Axial CT offers another pitfall in identifying sternal fractures, as the orientation of the injury is typically transverse to the long axis of the sternum. Multiplanar reconstructions are essential to fully evaluate the sternum.10 (Figure 10 c and d)
Sternoclavicular Joint and Clavicle Although a rare occurrence in blunt thoracic trauma, the sternoclavicular joint may dislocate anteriorly or posteriorly, with different implications on morbidity and management. Anterior dislocations are typically managed conservatively with closed reduction (of varying success), and less likely to cause any secondary injuries.11 Posterior dislocations, however, carry a greater risk of injury to adjacent organs such as the lung, esophagus, or neurovascular structures.12 While closed reduction may be attempted, the risk of associated complications may necessitate surgical intervention. Clavicle fractures on the other hand are very common in blunt thoracic trauma, and often of little clinical significance.3 Non-operative management is preferred, but open reduction and internal fixation may be indicated depending on the location and degree of angulation of the fragments.13
Chest Radiography The sternoclavicular joint is very poorly evaluated on traditional chest radiography, but clavicle fractures are readily identified. One exception to this is a distal clavicle fracture that may be excluded in an overly collimated image. Angled radiography may allow identification of sternoclavicular joint dislocations3 but is rarely performed. Computed tomography The use of axial CT with multiplanar reformations allows for distinguishing between anterior and posterior dislocations of the sternoclavicular joint. Of greater importance, however, is the ability to recognize associated soft tissue injuries from posterior dislocation.10,14 With left sided dislocations, the left brachiocephalic vein is particularly at risk of injury due to its course immediately behind the clavicular head. On the right, the innominate artery is at risk because of its course.
Scapula Scapula fractures are an uncommon injury seen in very high energy trauma. The direction of force is often from lateral to medial and downward into the shoulder and these are almost always associated with additional thoracic or upper extremity injuries.15 Chest radiography can identify the presence of a scapular fracture as well as associated injuries to the thorax or arm, but has limited utility in precise characterization of the extent of the fracture and specific involvement of the different parts of the scapula. CT with three dimensional reconstructions is often performed to delineate fracture orientation and articular involvement for treatment planning. The majority of fractures extend inferior to the glenoid with a lateral to medial orientation, while a minority of scapular fractures will involve the glenoid.15 (Figure 3)
Diaphragm Although more common in penetrating trauma, traumatic diaphragmatic injury is an important entity in blunt thoracic trauma. If missed, a diaphragmatic defect may enlarge and allow progressive herniation of abdominal contents through the defect with potential strangulation or obstruction.16,17 Blunt diaphragmatic injury is almost always associated with other injuries.16 (Figure 4) Chest Radiography Radiographic signs of blunt diaphragmatic injury are nonspecific and must be correlated to CT findings. Potential radiographic signs include elevation of the hemidiaphragm in question, the “cottage bread” sign of herniation of abdominal organs through the diaphragmatic defect3, or frank extension of abdominal viscera into the ipsilateral hemithorax. In the “cottage bread” sign, the abdominal contents
take on the appearance of a brioche as they herniate through the diaphragmatic defect. Abnormal course of a nasogastric tube above the hemidiaphragm is also a finding suggestive of diaphragmatic injury.18 Computed tomography Many CT signs of diaphragmatic rupture have been described and these have been classified into direct (i.e. defect in diaphragm is visualized) and indirect signs (i.e. sequela of diaphragmatic injury are seen).16 These provide varying degrees of confidence in the presence of diaphragmatic injury. The most convincing are the direct signs, where either a partial or complete defect in the diaphragm is visualized. Indirect signs of diaphragmatic injury which indicate high likelihood of diaphragmatic injury include visceral herniation (through a defect), the dependent viscera sign (where the viscera directly abut the ribs in the thorax), and elevation of abdominal organs above the contralateral hemidiaphragm.17 The band and collar signs, both created by constriction of an organ herniated through a diaphragmatic defect, are less common and less reliable signs of diaphragmatic injury. Common pitfalls of CT in diaphragmatic injury include distinguishing true diaphragmatic injuries from common congenital hernias (i.e. Bochdalek and Morgagni), diaphragmatic eventration, and acquired defects such as a very large hiatal hernia.16 Right sided diaphragmatic injuries are harder to see and are more commonly missed than those on the left.17 We have found the collar sign to be useful in making the diagnosis of a right-sided defect. In this sign a constricting band (corresponding to the diaphragm) can be seen at the level of the defect. Less commonly, the band sign can be seen where the herniated liver is edematous from venous congestion and lower in attenuation.
Pleura Pneumothorax A collection of air in the pleural space, pneumothorax, is common in blunt thoracic trauma. Early recognition is critical due to the risk of progression to tension pneumothorax, which can be exacerbated by positive pressure ventilation.
Chest Radiography: Most commonly, the “visceral pleural line sign” indicating separation of the visceral and parietal pleura is used to identify a pneumothorax radiographically.3 (Figure 5) More subtle findings of pneumothorax on supine radiography include the “deep sulcus sign” of a hyperlucent and deepened costophrenic sulcus, hyperlucency in the lung bases, and the “double diaphragm sign” where the anterior and posterior hemidiaphragm are outlined by gas in the pleural space.3,10,19 An additional uncommon finding of pneumothorax is unilateral hyperlucent lung where the air collects anteriorly and there is no identifiable pleural separation in the supine position.
Radiographic findings of tension pneumothorax include mediastinal shift, which may be most evident by the tracheal position, widened intercostal spaces, and depression of the diaphragm.3 Depression of the diaphragm may be seen before mediastinal shift in the setting of positive end expiratory pressure ventilation (PEEP).
Computed tomography: In the supine position, pleural gas often moves anteromedially10, limiting the sensitivity of radiography. Up to 55% of pneumothoraces identified on CT may be radiographically occult.20 (Figure 6) The use of lung parenchymal windows readily allows the differentiation of lung from pneumothorax on CT, including allowing the identification of those pneumothoraces which are either too small or in a position where they cannot be identified by radiography. The additional advantage of CT in evaluation of pneumothorax is to help identify the cause. In blunt trauma, a pneumothorax may be cause by an “outside-in” mechanism whereby the parietal pleural is lacerated by fragments from an adjacent rib fracture. Alternatively, an “inside-out” mechanism may be responsible where compression of the chest causes increase in intrathoracic pressure which results in alveolar rupture.21 The “inside-out” mechanism may cause either pneumomediastinum or pneumothorax, depending on the direction in which air dissects through the interstitium. Uncommonly, congenital or developmental defects in the diaphragm may allow air to dissect into the peritoneal cavity and cause pneumoperitoneum in the absence of abdominal hollow viscus injury. Subcutaneous dissection into the abdominal wall or retroperitoneal space can also present a potential mimic of true pneumoperitoneum.22
Hemothorax Similar to a pneumothorax, the accumulation of blood in the pleural space, i.e. hemothorax, is a common occurrence in the setting of blunt thoracic trauma, and can be associated with early and late morbidity. Drainage with a thoracostomy tube is considered for all hemothoraces, although smaller collections often resolve spontaneously.3 In the case of massive hemothorax with greater than 1500 ml output and clinical signs of hemodynamic compromise, surgical management may be required.23 Early recognition and management are important to prevent clotting, which increases the difficulty of drainage and resultant fibrothorax.
Chest radiography The identification of pleural effusion on chest radiography in the setting of blunt trauma should raise concern for hemothorax. The common findings include blunting of the costophrenic angles and opacification of the lower hemithorax from posteriorly layering fluid. Uncommonly, a massive
hemothorax may result in complete opacification of the hemithorax.3 Inversion of the ipsilateral hemidiaphragm and mediastinal shift3,24 can be suggestive of tension with a pleural effusion as well as hemothorax. Often, a hemothorax will present with a concomitant pneumothorax. The radiographic finding will often consist of a pleural effusion that is more lucent than usual.
Computed tomography In addition to identifying the presence of fluid in the pleural space, CT allows further characterization by measuring the Hounsfield units. While simple fluid in the pleural space typically has attenuation less than 15 HU, blood in the acute setting will measure 30-45 HU.19 (Figure 8c) As time progresses, evolution of blood products including clotting will further increase the attenuation to up to 90 HU.25 CT also allows the added advantage of identifying any contrast blush. This blush may be indicative of active extravasation or pseudoaneurysm formation. The presence of a blush will often prompt either surgical or interventional radiology management and can direct the intervention to the site of active bleeding.
Lung Injuries There are two types of parenchymal injury to the lungs seen in blunt thoracic trauma – pulmonary contusion and pulmonary laceration. Pathologically, the distinguishing feature of these entities is the absence (contusion) or presence (laceration) of alveolar disruption.
Pulmonary contusion Pulmonary contusions are more common than pulmonary lacerations. They are frequently seen on imaging in blunt thoracic trauma patients with multiple injuries, where they have been reported to occur in 17-70% of patients.26,27 (Figure 7) Chest Radiography Contusions can be seen as geographic areas of airspace opacification versus a ground-glass appearance. They typically are evident at 6 hours after injury and resolve in 5-7 days.3 The time course of findings may help distinguish contusion from non-traumatic pulmonary diseases such as aspiration or pneumonia10, and chest radiography is particularly useful in establishing a time course as it is routinely performed at regular intervals. Computed Tomography CT may be able to identify contusions at an earlier stage. Findings include patchy airspace consolidation which is not limited by segmental anatomy, as well as possible subpleural sparing.10 Minor contusions may simply present with geographic areas of ground glass. The extent can be quite variable – contusions
may be uni- or bilateral, focal or multifocal, or diffuse.28 They may be adjacent to the site of injury (coup) or opposite (contre coup).
Pulmonary Laceration The mechanical disruption of alveoli from blunt trauma, as seen in pulmonary laceration, is an indication of a more severe injury.3 These frequently coexist with pulmonary contusions.27 Typically, the elastic recoil of lung tissue after alveolar disruption causes the lacerated lung to retract and create a cavity.10 The resulting cavity may be seen as an air (traumatic pneumatocele) or blood (traumatic hematocele) filled structure. More frequently, a combination of the two entities is formed (traumatic hemopneumatocele). Pulmonary lacerations can take weeks to months to resolve.3 When the laceration extends through the visceral pleura (including the fissures), a pneumothorax may be formed.27 (Figure 8) Chest radiography Lacerations most commonly present radiographically as airspace opacification when the cavity fills with blood. When a traumatic pneumatocele is formed, the loculated air collection may be identified on chest radiography.3 Rarely, the laceration will simulate a pulmonary nodule. Computed tomography Identification of the cavity as either an air-filled, blood-filled, or a combination of the two is typically seen on CT. The presence of an air fluid level within the cavity of a traumatic hemopneumatocele is the most common identifying feature of a pulmonary laceration. Pulmonary lacerations have been classified into 4 types27, which help correlate the mechanism of injury and location of the laceration, as follow: Type 1: Sudden compression to the chest wall causes rupture of air containing lung. This is the most common type and typically occurs in the deep/central lung. These occur more commonly in younger people, especially children, who have a more flexible chest wall. Type 2: Compression of the lower lobes results in a shearing injury across the spine. This injury occurs in the lower lobes and is seen in the paravertebral lung. The compressive force is directed side-to-side. Type 3: A fractured rib causes a direct laceration of the adjacent lung. This type of laceration is seen in the peripheral lung and is generally also associated with pneumothorax. Type 4: Tearing of the lung due to altered biomechanics in the setting of previously formed pleuropulmonary adhesions. CT may not be able to distinguish this type of mechanism but prior examinations or prior surgical history may help clarify this injury. CT with contrast will also allow for identification of any contrast blush within the parenchyma. As with the hemothorax, these may be indicative of a pseudoaneurysm or active extravasation. Their presence often prompts further treatment (either percutaneous embolization or surgery).
Airways Injuries to the airways are uncommonly seen on imaging in blunt thoracic trauma as the majority of these are fatal prior to arrival in the hospital.10,19,29 The typical setting of injury to the airways is a motor vehicle collision with high-speed deceleration; crush injuries represent an additional possible mechanism. When they occur, lacerations to the trachea or bronchi may be caused by compression against osseous structures, shearing at fixation points, or elevation in intrathoracic pressure against a closed glottis.10 Transverse tears can occur in the trachea and bronchi between cartilaginous rings, while longitudinal tears can occur in the trachea along the posterior membrane at its junction with the cartilaginous rings.3,10 Bronchial injuries occur more commonly than tracheal injuries and are more common on the right than on the left.29 Almost all tracheobronchial injuries occur within 2 cm of the carina. (Figure 9) Chest Radiography The identification of airway injuries on chest radiography is limited to recognizing sequela of the injury. Typical manifestations of tracheal injury which can be identified radiographically are extensive pneumomediastinum leading to subcutaneous emphysema, and pneumothorax which does not resolve despite thoracostomy tube placement.25 Hemorrhage into the airways may lead to postobstructive pneumonia or atelectasis. Computed tomography In a majority of cases, CT is able to identify the site of tracheal or bronchial injury10 as a defect in the wall, oriented either transverse to the cartilage rings or in the trachea along the posterior membrane. This may represent the site of the greatest amount of extraluminal air. An indirect sign which may be seen in a complete bronchial laceration is the “fallen lung” sign, where the now unattached and collapsed lung is able to fall to the dependent aspect of the ipsilateral hemithorax.3,19
Esophagus Blunt traumatic injury to the esophagus is a rare occurrence. When it does occur, the injury is more likely to occur in the cervical esophagus from trauma to the neck. Thoracic esophageal injuries are less common due to the central location and protection by adjacent tissues.10,30 However, traumatic injury to the esophagus has been reported from a high-level fall.30 Chest radiography and CT may be able to identify the sequela of esophageal perforation, i.e. pneumomediastinum and hydropneumothorax, but even CT is usually unable to identify a specific site of injury. Thus, the diagnosis is difficult to make on conventional imaging, and a water-soluble contrast swallow study is the preferred method of imaging. Early diagnosis can help avoid the major complication of missed esophageal injury, which is mediastinitis.3,10,30 Almost all esophageal injuries will have some concomitant aspiration pneumonia.
Heart When they occur, myocardial injuries may be among the most fatal traumatic injuries in the chest.10,19,31 In blunt trauma, myocardial injury may occur from direct impact, rapid deceleration, or the most common method which is compression of the heart between the sternum and the spine.31,32 The right ventricular free wall, based on its location immediately subjacent to the sternum, is the most susceptible cardiac chamber to blunt trauma. (Figure 10) However among valves, the aortic valve, followed by the mitral valve, is the most susceptible to traumatic injury due to increased left heart pressures. 31 Less commonly, the interventricular septum or papillary muscles may be injured.3 Cardiac dysfunction can occur as a result of blunt trauma with no identifiable injury. The term “myocardial concussion” is used to describe cardiac injury with no proven anatomic or histologic disruption, while “myocardial contusion” indicates anatomic injury or cellular disruption identified by elevated cardiac enzymes.33,34 Increasingly, the term “blunt cardiac injury” is being used to describe both entities. Although chest pain is the most common manifestation of cardiac injury, it is ubiquitous to all forms of thoracic trauma and thus nonspecific. Less common clinical findings such as pulmonary edema, cardiogenic shock, or a new murmur should lead to careful examination for cardiac injury.34 Chest Radiography Although it is usually normal, acute enlargement of the cardiac silhouette may be the only finding of cardiac injury on radiography. Most cardiac injuries are associated with hemopericardium10, although myocardial injury may cause myocardial dysfunction and subsequent cardiomegaly.31 Additionally, the presence of myocardial dysfunction can lead to acute congestive heart failure, and thus pulmonary edema is an additional manifestation of cardiac injury.3 Computed tomography The same findings identified on chest radiography can be seen on CT to a greater degree of sensitivity – identification of hemopericardium and pulmonary edema. Additional injuries in the trajectory between the sternum and spine, which is the most common mechanism of cardiac injury, may also be identified on CT. Extravasation of intravenous contrast into the pericardial space or mediastinum may also be seen in the setting of cardiac injury with chamber perforation.10 Decreased attenuation of the injured myocardium after contrast administration is another infrequently seen finding. Magnetic Resonance Imaging Although not useful in the emergent setting, magnetic resonance imaging may be helpful to assess the extent of myocardial injury as focal wall motion abnormalities or abnormally enhancing myocardium.35
Pericardium Traumatic pericardial laceration is often associated with other injuries (particularly cardiac), although it has been reported as an isolated finding.36 The majority of these occur on the left at the junction between the pleura and pericardium37, but injuries can also occur at the pericardial-diaphragmatic interface with associated diaphragmatic injury.38 Injuries to the pericardium may result in pericardial effusion, which can be hemopericardium, transudative fluid, or pneumopericardium.3 (Figure 11) Emergent pericardiocentesis is indicated if there is physiologic evidence of cardiac tamponade. Another potential consequence of pericardial laceration is herniation of portions of the heart through the acquired defect.36,37 Chest Radiograph Although nonspecific, the presence of pericardial effusion or pneumopericardium is the most likely radiographic manifestation. Radiographic signs of pericardial effusion include global enlargement of the cardiac silhouette, or the “water bottle” sign, and separation of pericardial and epicardial fat pads, or the “Oreo cookie” sign.3 Pneumopericardium is often more readily identifiable radiographically, as increased lucency outlining the heart. Air may also be seen in the transverse pericardial sinus on erect radiographs or in the retrosternal space on lateral radiographs. Rarely, an abnormal contour of the heart may be seen, indicating herniation through a pericardial defect.3 Computed tomography As with radiography, the most likely evidence of pericardial injury on CT is the presence of hemopericardium or pneumopericardium. However, CT may allow better detection of the rare cardiac herniation through a pericardial defect. When the heart herniates through a left sided pericardial defect, it often attains a more transverse orientation secondary to clockwise rotation. (Figure 12)
Conclusions Thoracic injury is a common occurrence in patients arriving to the hospital with blunt trauma, and both chest radiography and CT provide valuable information to direct clinical management. Recognition of the common and uncommon manifestations of injury to superficial and visceral structures is of critical importance in initial evaluation. Using a systematic approach, such as the “outside-in” sequence presented here, helps facilitate comprehensive evaluation of all potential injuries.
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Smith JA, Albarghuthy B, Khosla R. Inversion of the hemidiaphragm due to pleural effusion. Annals of the American Thoracic Society. Oct 2014;11(8):1323-1326. Sangster GP, Gonzalez-Beicos A, Carbo AI, et al. Blunt traumatic injuries of the lung parenchyma, pleura, thoracic wall, and intrathoracic airways: multidetector computer tomography imaging findings. Emergency radiology. Oct 2007;14(5):297-310. Cohn SM. Pulmonary contusion: review of the clinical entity. The Journal of trauma. May 1997;42(5):973-979. Wagner RB, Crawford WO, Jr., Schimpf PP. Classification of parenchymal injuries of the lung. Radiology. Apr 1988;167(1):77-82. Miller LA. Chest wall, lung, and pleural space trauma. Radiologic clinics of North America. Mar 2006;44(2):213-224, viii. Kiser AC, O'Brien SM, Detterbeck FC. Blunt tracheobronchial injuries: treatment and outcomes. The Annals of thoracic surgery. Jun 2001;71(6):2059-2065. Strauss DC, Tandon R, Mason RC. Distal thoracic oesophageal perforation secondary to blunt trauma: case report. World journal of emergency surgery : WJES. 2007;2:8. Tenzer ML. The spectrum of myocardial contusion: a review. The Journal of trauma. Jul 1985;25(7):620-627. Orliaguet G, Ferjani M, Riou B. The heart in blunt trauma. Anesthesiology. Aug 2001;95(2):544548. Mattox KL, Flint LM, Carrico CJ, et al. Blunt cardiac injury. The Journal of trauma. Nov 1992;33(5):649-650. Restrepo CS, Gutierrez FR, Marmol-Velez JA, Ocazionez D, Martinez-Jimenez S. Imaging patients with cardiac trauma. Radiographics : a review publication of the Radiological Society of North America, Inc. May-Jun 2012;32(3):633-649. Co SJ, Yong-Hing CJ, Galea-Soler S, et al. Role of imaging in penetrating and blunt traumatic injury to the heart. Radiographics : a review publication of the Radiological Society of North America, Inc. Jul-Aug 2011;31(4):E101-115. Verkroost MW, Hensens AG. Isolated pericardial rupture with left-sided haematothorax after blunt chest trauma. European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery. Nov 1998;14(5):517-519. Fulda G, Brathwaite CE, Rodriguez A, Turney SZ, Dunham CM, Cowley RA. Blunt traumatic rupture of the heart and pericardium: a ten-year experience (1979-1989). The Journal of trauma. Feb 1991;31(2):167-172; discussion 172-163. Borrie J, Lichter I. Pericardial rupture from blunt chest trauma. Thorax. May 1974;29(3):329-337.
Figures: Imaging of Blunt Thoracic Trauma. To The Journal Editors: Please use the separately provided image files, and not the images included in this file to aid in editing.
Figure 1. Flail Chest. Volumetric reconstruction demonstrates segmental fractures of the right fourth through eighth ribs in a patient with flail chest after crush injury. Post-processing techniques such as volumetric reconstructions can elucidate osseous injuries.
Figure 2. Costal Cartilage Fractures. Oblique axial CT image (A) shows a displaced fracture of the cartilaginous right seventh rib with surrounding gas and hemorrhage. Volume-rendered image (B) from
the same examination depicts cartilage fractures of the right sixth and seventh ribs (white arrows) as well as osseous right fifth and sixth rib fractures.
Figure 3. Scapula Fracture. Chest radiograph (A) shows a fracture of the left scapula (white arrow) which appears to enter the glenoid, although it is difficult to follow the full extent. Also note presence of left clavicle fracture. Volumetric reconstruction (B) performed from subsequent CT examination more clearly defines the fracture orientation through the scapular body with involvement of the glenoid fossa.
Figure 4. Diaphragmatic Injury. Chest radiograph (A) shows elevation of the left hemidiaphragm with gas-filled viscus (stomach) in the left hemithorax. Multiplanar CT images (B, C, D) confirm rupture of the left hemidiaphragm. Black arrow (B) indicates the “dependent viscera” sign and white arrows (C and D) delineate the site of left hemidiaphragm defect.
Figure 5. Pneumothorax. Chest radiograph (A) depicts a right pneumothorax indicated by the “visceral pleural line sign”. The pneumothorax is more evident on subsequent right shoulder radiograph (B) where it is indicated by white arrows. Black arrows show right second and third rib fractures and right acromioclavicular joint dislocation, which were more difficult to identify on the chest radiograph.
Figure 6. Pneumothorax. Chest radiograph (A) shows no definite pneumothorax, although in retrospect the black arrow likely represents basilar lucency from pneumothorax. Axial CT image (B) shows a moderate-sized left pneumothorax with associated left third rib fracture (black arrow). An apparent pneumatocele (white arrow) actually represents pneumothorax extending into the major fissure.
Figure 7. Pulmonary Contusions. Chest radiograph (A) shows non-specific upper lobe airspace consolidation. Axial CT image (B) shows bilateral lower lobe and right upper lobe pulmonary contusion. Consolidation crossing the right major fissure (black arrows) distinguishes contusion from aspiration.
Figure 8. Pulmonary Lacerations and Hemothorax. Chest radiograph (A) shows increased attenuation of the left hemithorax and bilateral rib fractures. Oblique axial CT image at lung window (B) shows a type 3 pulmonary laceration in the left lower lobe adjacent to a left eighth rib fracture (black arrows) and a type 2 laceration in the medial right lower lobe adjacent to the T7 vertebral body (white arrow). CT image at soft tissue window (C) demonstrates the left pleural fluid to be greater attenuation than simple fluid (in this case approximately 50 HU), consistent with hemothorax.
Figure 9. Bronchial Avulsion. Chest radiograph (A) shows a collapsed right lung with large pneumothorax despite thoracostomy tube placement, along with subcutaneous emphysema, pneumomediastinum, and mediastinal shift to the left. Axial CT image (B) shows the “fallen lung” sign where collapsed lung falls into the medial and dependent ipsilateral hemithorax, in this case rotated counterclockwise. The site of bronchial injury was not seen on CT due to motion artifact but confirmed intraoperatively.
Figure 10. Myocardial Injury. Chest radiograph (A) shows enlargement of the cardiac silhouette, corresponding to hemopericardium. Reformatted CT image along the long axis of the heart (B) shows contrast extravasation through a defect in the right ventricular free wall, as well as hemopneumopericardium corresponding to radiographic findings. Axial and sagittal CT images at bone window (C and D) show a transversely-oriented fracture of the sternum, a finding which can be seen in association with cardiac injury.
Figure 11. Pericardial injury. Chest radiograph (A) shows lucency along the right heart border, indicating pneumopericardium. Axial CT image (B) confirms the presence of pneumopericardium with a defect in the pericardium indicated by the black arrow. Bilateral pulmonary contusions and right pneumothorax are also noted.
Figure 12. Pericardial Injury. Chest radiographs obtained immediately after (A) a motor vehicle collision and 6 hours later (B) show interval displacement of the heart into the left hemithorax. Left basilar pneumothorax is also seen on the delayed examination after thoracostomy tube placement. CT images obtained at soft tissue (C) and lung (D) window show clockwise rotation of the heart, indicating herniation through an acquired defect in the left pericardium, along with bilateral pneumothoraces and pneumopericardium.
Imaging of Blunt Thoracic Trauma Sreevathsan Sridhar M.D., Constantine Raptis M.D., Sanjeev Bhalla M.D.
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S0037-198X(15)00062-0 http://dx.doi.org/10.1053/j.ro.2015.12.002 YSROE50527
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Seminar in Roentgenology
Cite this article as: Sreevathsan Sridhar M.D., Constantine Raptis M.D., Sanjeev Bhalla M. D., Imaging of Blunt Thoracic Trauma, Seminar in Roentgenology, http://dx.doi.org/ 10.1053/j.ro.2015.12.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Imaging of Blunt Thoracic Trauma
Sreevathsan Sridhar1 M.D., Constantine Raptis2 M.D., Sanjeev Bhalla3 M.D. From Mallinckrodt Institute of Radiology, Washington University in St. Louis
1
Cardiothoracic Imaging Fellow, Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO 2
Assistant Professor of Radiology, Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO
3
Professor of Radiology, Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, MO
No grant support was used for this work.
Contact: [email protected] or [email protected], 314-362-2927 510 S Kingshighway Blvd, Box 8131 Saint Louis, MO 63112
Introduction Greater than 60% of blunt traumatic injuries are related to fall or motor vehicle collision. Of all anatomic regions, injuries to the thorax represent the third most common type of injury (behind head and extremities) with a mortality rate close to 10%, compared to overall mortality in trauma of 4.3%.1 Given the relatively higher rate of mortality compared to other anatomic injuries and the association between chest trauma and greater severity of overall injury2, recognition of injuries to the thorax is of great importance in approaching the patient with blunt thoracic trauma. Portable chest radiography is typically the first imaging study performed on patients in the emergency department after blunt trauma. The primary goals of chest radiography are to confirm support device placement and evaluate for immediately life-threatening findings, such as tension pneumothorax.3 Previous comparisons have indicated that a majority of thoracic injuries found on CT (and in particular multi-detector CT) may be missed on chest radiography. Up to 20% of these injuries may significantly
influence subsequent management.4 MDCT, therefore, has been established as a critical portion of the initial evaluation of patients in blunt thoracic trauma.5 In this article, we will discuss typical and atypical findings on chest radiography and CT for non-vascular thoracic injuries in blunt trauma. We will follow an “outside-in” approach to discussing the anatomic regions involved, beginning with the chest wall, proceeding to the pleura and lungs, and following with the central structures including the airways, esophagus, and heart/pericardium. When applicable direct and indirect signs of injury will be described to help the reader build their confidence in describing traumatic findings. The common and uncommon findings of injury to each of these structures are summarized in Table 1. The table is intended to help the reader develop a search pattern in the setting of trauma.
Table 1. Summary of common and uncommon findings of blunt thoracic injury on radiography and CT. Anatomic Category
Chest wall
Structure or Pathology
Lungs
Computed Tomography
Common
Uncommon
Common
Uncommon
Ribs
Involvement of middle ribs, displaced fracture
First or second rib fractures, flail chest
Angulation or displacement of fragments, associated soft tissue injuries
Costal cartilage fractures
Sternum
Not commonly identified on radiography
Displaced fracture on lateral radiograph
Transversely oriented fracture (use MPR to identify), mediastinal hematoma
Sternoclavicular joint dislocation: Anterior – usually isolated Posterior - look for associated injuries
Scapula
Scapular body fractures, difficult to assess extent
Isolated scapula fracture – usually associated with thoracic or additional arm injury
Transverse orientation inferior to glenoid
Articular involvement (3D reconstructions helpful)
Elevation of the ipsilateral hemidiaphragm
“Cottage bread” sign, NG tube coursing into thorax
Visceral herniation through a diaphragmatic defect, “dependent viscera” sign, elevation of abdominal organs
Distinct defect in diaphragm, “band” and “collar” signs
Pneumothorax
“visceral-pleural line” sign, mediastinal shift (with tension)
“deep sulcus” and “double diaphragm” signs, unilateral hyperlucent lung, widening of intercostal spaces (with tension)
Direct visualization of gas in the pleural space, anteromedial location of pneumothorax, associated pneumomediastinum
Dissection through diaphragmatic channels to cause pneumoperitoneum
Hemothorax
Blunting of costophrenic angles, posteriorly layering effusion
Subpulmonic effusion, signs of tension – inverted diaphragm, mediastinal shift
Hyperattenuating pleural fluid (30-45 HU when acute)
Signs of tension – mediastinal shift, inversion of the diaphragm, compression of vasculature
Pulmonary Contusion
Airspace consolidation or ground glass, develops in 6 hours
Prolonged airspace opacification beyond 5-7 days – indicates alternate pathology
Patchy airspace consolidation or ground glass crossing fissures
Diffuse bilateral lung involvement, prolonged
Diaphragm
Pleura
Chest Radiograph
Pulmonary Laceration
Intraparenchymal cavity, filled with air, fluid, or both
Airspace consolidation
Radiolucent cavity (pneumatocele)
Trachea and Bronchi
Pneumomediastinum Pneumothorax Subcutaneous emphysema
Postobstructive pneumonia or atelectasis from airway hemorrhage
Esophagus
Rare in blunt trauma
Pneumomediastinum Hydropneumothorax
Heart
Pericardial effusion, pulmonary edema
Acute cardiomegaly (from heart failure)
Hemopericardium, pulmonary edema
Wall irregularities, myocardial hypoattenuation, extravasation of contrast into pericardial space
Pericardium
Pericardial effusion, pneumopericardium
Abnormal cardiac contour
Hemopericardium, pneumopericardium
Cardiac herniation through pericardial defect
Defect in tracheal or bronchial wall, pneumomediastinum, pneumothorax, subcutaneous emphysema Same as chest radiography – difficult to identify site of injury (Signs of aspiration almost always present)
Laceration due to shearing in the setting of fibrosis
“Fallen lung” sign (in bronchial avulsion)
Mediastinitis (delayed complication which may be suggested on initial imaging)
Chest wall Ribs Rib fractures are the most common injury in blunt thoracic trauma and reflect a broad range of clinical significance. When they occur, the rib fracture fragments can transform a blunt injury mechanism into a local penetrating injury. Consideration should be given to adjacent soft tissue structures and how the fracture fragments may cause associated injury, such as lacerations to the adjacent pleura or lung. Fractures of the lower ribs can be associated with injury to abdominal organs, while upper rib fractures, while rare, may be associated with injuries to adjacent vessels or the brachial plexus.3 The primary consequence of rib fractures without adjacent organ injury is pain. Specifically in the setting of multiple rib fractures, flail chest can be a cause of significant morbidity as the patient may not be able to maintain full inspiration due to severe pain.6 A flail chest can occur when there are 3 adjacent segmental rib fractures3 and represents paradoxical motion of the fractured ribs with respect to the remaining chest wall during inspiration. (Figure 1) Identification of these injuries is important as a severe flail chest injury may be an indication for epidural catheter placement to administer anesthesia.7 Chest radiography Posterior rib fractures are usually readily detected on chest radiography, as are displaced fractures. However, the sensitivity of chest radiography for non-displaced fractures is limited. Focused radiography of the ribs is often more effective at identifying rib fractures but is still somewhat limited.3
Computed tomography CT is the preferred imaging modality for diagnosis of rib fractures.8 Careful examination of each rib along its course is necessary and documentation of multiple fractures should be performed to allow prompt clinical evaluation for flail chest. In additional to standard axial evaluation, coronal reformatted images are helpful to clarify equivocal findings. Two different typical morphologies have been described for rib fractures – buckling of the cortex and an actual fracture gap. Special attention should be given to buckle fractures, which are frequently missed.8 Additionally, CT allows for evaluation of the costal cartilage, where fractures are commonly missed radiographically.9 (Figure 2) Three dimensional reconstructions using surface rendering may be helpful to evaluate the cartilage. Sonography and bone scintigraphy can be useful adjuncts to further evaluate the costal cartilage.
Sternum Fractures of the sternum are often secondary to direct trauma or deceleration injuries.3,10 These are an indication of high-energy trauma and often associated with other soft tissue injuries. Cardiac injuries in particular are a major concern, as the right ventricular free wall typically lies immediately posterior to the sternum. Mediastinal hematoma is almost always seen with sternal fractures. Sternal fractures are rarely apparent on frontal chest radiography. Lateral radiographs improve the ability to detect sternal fractures, but still provide limited sensitivity.3 Axial CT offers another pitfall in identifying sternal fractures, as the orientation of the injury is typically transverse to the long axis of the sternum. Multiplanar reconstructions are essential to fully evaluate the sternum.10 (Figure 10 c and d)
Sternoclavicular Joint and Clavicle Although a rare occurrence in blunt thoracic trauma, the sternoclavicular joint may dislocate anteriorly or posteriorly, with different implications on morbidity and management. Anterior dislocations are typically managed conservatively with closed reduction (of varying success), and less likely to cause any secondary injuries.11 Posterior dislocations, however, carry a greater risk of injury to adjacent organs such as the lung, esophagus, or neurovascular structures.12 While closed reduction may be attempted, the risk of associated complications may necessitate surgical intervention. Clavicle fractures on the other hand are very common in blunt thoracic trauma, and often of little clinical significance.3 Non-operative management is preferred, but open reduction and internal fixation may be indicated depending on the location and degree of angulation of the fragments.13
Chest Radiography The sternoclavicular joint is very poorly evaluated on traditional chest radiography, but clavicle fractures are readily identified. One exception to this is a distal clavicle fracture that may be excluded in an overly collimated image. Angled radiography may allow identification of sternoclavicular joint dislocations3 but is rarely performed. Computed tomography The use of axial CT with multiplanar reformations allows for distinguishing between anterior and posterior dislocations of the sternoclavicular joint. Of greater importance, however, is the ability to recognize associated soft tissue injuries from posterior dislocation.10,14 With left sided dislocations, the left brachiocephalic vein is particularly at risk of injury due to its course immediately behind the clavicular head. On the right, the innominate artery is at risk because of its course.
Scapula Scapula fractures are an uncommon injury seen in very high energy trauma. The direction of force is often from lateral to medial and downward into the shoulder and these are almost always associated with additional thoracic or upper extremity injuries.15 Chest radiography can identify the presence of a scapular fracture as well as associated injuries to the thorax or arm, but has limited utility in precise characterization of the extent of the fracture and specific involvement of the different parts of the scapula. CT with three dimensional reconstructions is often performed to delineate fracture orientation and articular involvement for treatment planning. The majority of fractures extend inferior to the glenoid with a lateral to medial orientation, while a minority of scapular fractures will involve the glenoid.15 (Figure 3)
Diaphragm Although more common in penetrating trauma, traumatic diaphragmatic injury is an important entity in blunt thoracic trauma. If missed, a diaphragmatic defect may enlarge and allow progressive herniation of abdominal contents through the defect with potential strangulation or obstruction.16,17 Blunt diaphragmatic injury is almost always associated with other injuries.16 (Figure 4) Chest Radiography Radiographic signs of blunt diaphragmatic injury are nonspecific and must be correlated to CT findings. Potential radiographic signs include elevation of the hemidiaphragm in question, the “cottage bread” sign of herniation of abdominal organs through the diaphragmatic defect3, or frank extension of abdominal viscera into the ipsilateral hemithorax. In the “cottage bread” sign, the abdominal contents
take on the appearance of a brioche as they herniate through the diaphragmatic defect. Abnormal course of a nasogastric tube above the hemidiaphragm is also a finding suggestive of diaphragmatic injury.18 Computed tomography Many CT signs of diaphragmatic rupture have been described and these have been classified into direct (i.e. defect in diaphragm is visualized) and indirect signs (i.e. sequela of diaphragmatic injury are seen).16 These provide varying degrees of confidence in the presence of diaphragmatic injury. The most convincing are the direct signs, where either a partial or complete defect in the diaphragm is visualized. Indirect signs of diaphragmatic injury which indicate high likelihood of diaphragmatic injury include visceral herniation (through a defect), the dependent viscera sign (where the viscera directly abut the ribs in the thorax), and elevation of abdominal organs above the contralateral hemidiaphragm.17 The band and collar signs, both created by constriction of an organ herniated through a diaphragmatic defect, are less common and less reliable signs of diaphragmatic injury. Common pitfalls of CT in diaphragmatic injury include distinguishing true diaphragmatic injuries from common congenital hernias (i.e. Bochdalek and Morgagni), diaphragmatic eventration, and acquired defects such as a very large hiatal hernia.16 Right sided diaphragmatic injuries are harder to see and are more commonly missed than those on the left.17 We have found the collar sign to be useful in making the diagnosis of a right-sided defect. In this sign a constricting band (corresponding to the diaphragm) can be seen at the level of the defect. Less commonly, the band sign can be seen where the herniated liver is edematous from venous congestion and lower in attenuation.
Pleura Pneumothorax A collection of air in the pleural space, pneumothorax, is common in blunt thoracic trauma. Early recognition is critical due to the risk of progression to tension pneumothorax, which can be exacerbated by positive pressure ventilation.
Chest Radiography: Most commonly, the “visceral pleural line sign” indicating separation of the visceral and parietal pleura is used to identify a pneumothorax radiographically.3 (Figure 5) More subtle findings of pneumothorax on supine radiography include the “deep sulcus sign” of a hyperlucent and deepened costophrenic sulcus, hyperlucency in the lung bases, and the “double diaphragm sign” where the anterior and posterior hemidiaphragm are outlined by gas in the pleural space.3,10,19 An additional uncommon finding of pneumothorax is unilateral hyperlucent lung where the air collects anteriorly and there is no identifiable pleural separation in the supine position.
Radiographic findings of tension pneumothorax include mediastinal shift, which may be most evident by the tracheal position, widened intercostal spaces, and depression of the diaphragm.3 Depression of the diaphragm may be seen before mediastinal shift in the setting of positive end expiratory pressure ventilation (PEEP).
Computed tomography: In the supine position, pleural gas often moves anteromedially10, limiting the sensitivity of radiography. Up to 55% of pneumothoraces identified on CT may be radiographically occult.20 (Figure 6) The use of lung parenchymal windows readily allows the differentiation of lung from pneumothorax on CT, including allowing the identification of those pneumothoraces which are either too small or in a position where they cannot be identified by radiography. The additional advantage of CT in evaluation of pneumothorax is to help identify the cause. In blunt trauma, a pneumothorax may be cause by an “outside-in” mechanism whereby the parietal pleural is lacerated by fragments from an adjacent rib fracture. Alternatively, an “inside-out” mechanism may be responsible where compression of the chest causes increase in intrathoracic pressure which results in alveolar rupture.21 The “inside-out” mechanism may cause either pneumomediastinum or pneumothorax, depending on the direction in which air dissects through the interstitium. Uncommonly, congenital or developmental defects in the diaphragm may allow air to dissect into the peritoneal cavity and cause pneumoperitoneum in the absence of abdominal hollow viscus injury. Subcutaneous dissection into the abdominal wall or retroperitoneal space can also present a potential mimic of true pneumoperitoneum.22
Hemothorax Similar to a pneumothorax, the accumulation of blood in the pleural space, i.e. hemothorax, is a common occurrence in the setting of blunt thoracic trauma, and can be associated with early and late morbidity. Drainage with a thoracostomy tube is considered for all hemothoraces, although smaller collections often resolve spontaneously.3 In the case of massive hemothorax with greater than 1500 ml output and clinical signs of hemodynamic compromise, surgical management may be required.23 Early recognition and management are important to prevent clotting, which increases the difficulty of drainage and resultant fibrothorax.
Chest radiography The identification of pleural effusion on chest radiography in the setting of blunt trauma should raise concern for hemothorax. The common findings include blunting of the costophrenic angles and opacification of the lower hemithorax from posteriorly layering fluid. Uncommonly, a massive
hemothorax may result in complete opacification of the hemithorax.3 Inversion of the ipsilateral hemidiaphragm and mediastinal shift3,24 can be suggestive of tension with a pleural effusion as well as hemothorax. Often, a hemothorax will present with a concomitant pneumothorax. The radiographic finding will often consist of a pleural effusion that is more lucent than usual.
Computed tomography In addition to identifying the presence of fluid in the pleural space, CT allows further characterization by measuring the Hounsfield units. While simple fluid in the pleural space typically has attenuation less than 15 HU, blood in the acute setting will measure 30-45 HU.19 (Figure 8c) As time progresses, evolution of blood products including clotting will further increase the attenuation to up to 90 HU.25 CT also allows the added advantage of identifying any contrast blush. This blush may be indicative of active extravasation or pseudoaneurysm formation. The presence of a blush will often prompt either surgical or interventional radiology management and can direct the intervention to the site of active bleeding.
Lung Injuries There are two types of parenchymal injury to the lungs seen in blunt thoracic trauma – pulmonary contusion and pulmonary laceration. Pathologically, the distinguishing feature of these entities is the absence (contusion) or presence (laceration) of alveolar disruption.
Pulmonary contusion Pulmonary contusions are more common than pulmonary lacerations. They are frequently seen on imaging in blunt thoracic trauma patients with multiple injuries, where they have been reported to occur in 17-70% of patients.26,27 (Figure 7) Chest Radiography Contusions can be seen as geographic areas of airspace opacification versus a ground-glass appearance. They typically are evident at 6 hours after injury and resolve in 5-7 days.3 The time course of findings may help distinguish contusion from non-traumatic pulmonary diseases such as aspiration or pneumonia10, and chest radiography is particularly useful in establishing a time course as it is routinely performed at regular intervals. Computed Tomography CT may be able to identify contusions at an earlier stage. Findings include patchy airspace consolidation which is not limited by segmental anatomy, as well as possible subpleural sparing.10 Minor contusions may simply present with geographic areas of ground glass. The extent can be quite variable – contusions
may be uni- or bilateral, focal or multifocal, or diffuse.28 They may be adjacent to the site of injury (coup) or opposite (contre coup).
Pulmonary Laceration The mechanical disruption of alveoli from blunt trauma, as seen in pulmonary laceration, is an indication of a more severe injury.3 These frequently coexist with pulmonary contusions.27 Typically, the elastic recoil of lung tissue after alveolar disruption causes the lacerated lung to retract and create a cavity.10 The resulting cavity may be seen as an air (traumatic pneumatocele) or blood (traumatic hematocele) filled structure. More frequently, a combination of the two entities is formed (traumatic hemopneumatocele). Pulmonary lacerations can take weeks to months to resolve.3 When the laceration extends through the visceral pleura (including the fissures), a pneumothorax may be formed.27 (Figure 8) Chest radiography Lacerations most commonly present radiographically as airspace opacification when the cavity fills with blood. When a traumatic pneumatocele is formed, the loculated air collection may be identified on chest radiography.3 Rarely, the laceration will simulate a pulmonary nodule. Computed tomography Identification of the cavity as either an air-filled, blood-filled, or a combination of the two is typically seen on CT. The presence of an air fluid level within the cavity of a traumatic hemopneumatocele is the most common identifying feature of a pulmonary laceration. Pulmonary lacerations have been classified into 4 types27, which help correlate the mechanism of injury and location of the laceration, as follow: Type 1: Sudden compression to the chest wall causes rupture of air containing lung. This is the most common type and typically occurs in the deep/central lung. These occur more commonly in younger people, especially children, who have a more flexible chest wall. Type 2: Compression of the lower lobes results in a shearing injury across the spine. This injury occurs in the lower lobes and is seen in the paravertebral lung. The compressive force is directed side-to-side. Type 3: A fractured rib causes a direct laceration of the adjacent lung. This type of laceration is seen in the peripheral lung and is generally also associated with pneumothorax. Type 4: Tearing of the lung due to altered biomechanics in the setting of previously formed pleuropulmonary adhesions. CT may not be able to distinguish this type of mechanism but prior examinations or prior surgical history may help clarify this injury. CT with contrast will also allow for identification of any contrast blush within the parenchyma. As with the hemothorax, these may be indicative of a pseudoaneurysm or active extravasation. Their presence often prompts further treatment (either percutaneous embolization or surgery).
Airways Injuries to the airways are uncommonly seen on imaging in blunt thoracic trauma as the majority of these are fatal prior to arrival in the hospital.10,19,29 The typical setting of injury to the airways is a motor vehicle collision with high-speed deceleration; crush injuries represent an additional possible mechanism. When they occur, lacerations to the trachea or bronchi may be caused by compression against osseous structures, shearing at fixation points, or elevation in intrathoracic pressure against a closed glottis.10 Transverse tears can occur in the trachea and bronchi between cartilaginous rings, while longitudinal tears can occur in the trachea along the posterior membrane at its junction with the cartilaginous rings.3,10 Bronchial injuries occur more commonly than tracheal injuries and are more common on the right than on the left.29 Almost all tracheobronchial injuries occur within 2 cm of the carina. (Figure 9) Chest Radiography The identification of airway injuries on chest radiography is limited to recognizing sequela of the injury. Typical manifestations of tracheal injury which can be identified radiographically are extensive pneumomediastinum leading to subcutaneous emphysema, and pneumothorax which does not resolve despite thoracostomy tube placement.25 Hemorrhage into the airways may lead to postobstructive pneumonia or atelectasis. Computed tomography In a majority of cases, CT is able to identify the site of tracheal or bronchial injury10 as a defect in the wall, oriented either transverse to the cartilage rings or in the trachea along the posterior membrane. This may represent the site of the greatest amount of extraluminal air. An indirect sign which may be seen in a complete bronchial laceration is the “fallen lung” sign, where the now unattached and collapsed lung is able to fall to the dependent aspect of the ipsilateral hemithorax.3,19
Esophagus Blunt traumatic injury to the esophagus is a rare occurrence. When it does occur, the injury is more likely to occur in the cervical esophagus from trauma to the neck. Thoracic esophageal injuries are less common due to the central location and protection by adjacent tissues.10,30 However, traumatic injury to the esophagus has been reported from a high-level fall.30 Chest radiography and CT may be able to identify the sequela of esophageal perforation, i.e. pneumomediastinum and hydropneumothorax, but even CT is usually unable to identify a specific site of injury. Thus, the diagnosis is difficult to make on conventional imaging, and a water-soluble contrast swallow study is the preferred method of imaging. Early diagnosis can help avoid the major complication of missed esophageal injury, which is mediastinitis.3,10,30 Almost all esophageal injuries will have some concomitant aspiration pneumonia.
Heart When they occur, myocardial injuries may be among the most fatal traumatic injuries in the chest.10,19,31 In blunt trauma, myocardial injury may occur from direct impact, rapid deceleration, or the most common method which is compression of the heart between the sternum and the spine.31,32 The right ventricular free wall, based on its location immediately subjacent to the sternum, is the most susceptible cardiac chamber to blunt trauma. (Figure 10) However among valves, the aortic valve, followed by the mitral valve, is the most susceptible to traumatic injury due to increased left heart pressures. 31 Less commonly, the interventricular septum or papillary muscles may be injured.3 Cardiac dysfunction can occur as a result of blunt trauma with no identifiable injury. The term “myocardial concussion” is used to describe cardiac injury with no proven anatomic or histologic disruption, while “myocardial contusion” indicates anatomic injury or cellular disruption identified by elevated cardiac enzymes.33,34 Increasingly, the term “blunt cardiac injury” is being used to describe both entities. Although chest pain is the most common manifestation of cardiac injury, it is ubiquitous to all forms of thoracic trauma and thus nonspecific. Less common clinical findings such as pulmonary edema, cardiogenic shock, or a new murmur should lead to careful examination for cardiac injury.34 Chest Radiography Although it is usually normal, acute enlargement of the cardiac silhouette may be the only finding of cardiac injury on radiography. Most cardiac injuries are associated with hemopericardium10, although myocardial injury may cause myocardial dysfunction and subsequent cardiomegaly.31 Additionally, the presence of myocardial dysfunction can lead to acute congestive heart failure, and thus pulmonary edema is an additional manifestation of cardiac injury.3 Computed tomography The same findings identified on chest radiography can be seen on CT to a greater degree of sensitivity – identification of hemopericardium and pulmonary edema. Additional injuries in the trajectory between the sternum and spine, which is the most common mechanism of cardiac injury, may also be identified on CT. Extravasation of intravenous contrast into the pericardial space or mediastinum may also be seen in the setting of cardiac injury with chamber perforation.10 Decreased attenuation of the injured myocardium after contrast administration is another infrequently seen finding. Magnetic Resonance Imaging Although not useful in the emergent setting, magnetic resonance imaging may be helpful to assess the extent of myocardial injury as focal wall motion abnormalities or abnormally enhancing myocardium.35
Pericardium Traumatic pericardial laceration is often associated with other injuries (particularly cardiac), although it has been reported as an isolated finding.36 The majority of these occur on the left at the junction between the pleura and pericardium37, but injuries can also occur at the pericardial-diaphragmatic interface with associated diaphragmatic injury.38 Injuries to the pericardium may result in pericardial effusion, which can be hemopericardium, transudative fluid, or pneumopericardium.3 (Figure 11) Emergent pericardiocentesis is indicated if there is physiologic evidence of cardiac tamponade. Another potential consequence of pericardial laceration is herniation of portions of the heart through the acquired defect.36,37 Chest Radiograph Although nonspecific, the presence of pericardial effusion or pneumopericardium is the most likely radiographic manifestation. Radiographic signs of pericardial effusion include global enlargement of the cardiac silhouette, or the “water bottle” sign, and separation of pericardial and epicardial fat pads, or the “Oreo cookie” sign.3 Pneumopericardium is often more readily identifiable radiographically, as increased lucency outlining the heart. Air may also be seen in the transverse pericardial sinus on erect radiographs or in the retrosternal space on lateral radiographs. Rarely, an abnormal contour of the heart may be seen, indicating herniation through a pericardial defect.3 Computed tomography As with radiography, the most likely evidence of pericardial injury on CT is the presence of hemopericardium or pneumopericardium. However, CT may allow better detection of the rare cardiac herniation through a pericardial defect. When the heart herniates through a left sided pericardial defect, it often attains a more transverse orientation secondary to clockwise rotation. (Figure 12)
Conclusions Thoracic injury is a common occurrence in patients arriving to the hospital with blunt trauma, and both chest radiography and CT provide valuable information to direct clinical management. Recognition of the common and uncommon manifestations of injury to superficial and visceral structures is of critical importance in initial evaluation. Using a systematic approach, such as the “outside-in” sequence presented here, helps facilitate comprehensive evaluation of all potential injuries.
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Figures: Imaging of Blunt Thoracic Trauma. To The Journal Editors: Please use the separately provided image files, and not the images included in this file to aid in editing.
Figure 1. Flail Chest. Volumetric reconstruction demonstrates segmental fractures of the right fourth through eighth ribs in a patient with flail chest after crush injury. Post-processing techniques such as volumetric reconstructions can elucidate osseous injuries.
Figure 2. Costal Cartilage Fractures. Oblique axial CT image (A) shows a displaced fracture of the cartilaginous right seventh rib with surrounding gas and hemorrhage. Volume-rendered image (B) from
the same examination depicts cartilage fractures of the right sixth and seventh ribs (white arrows) as well as osseous right fifth and sixth rib fractures.
Figure 3. Scapula Fracture. Chest radiograph (A) shows a fracture of the left scapula (white arrow) which appears to enter the glenoid, although it is difficult to follow the full extent. Also note presence of left clavicle fracture. Volumetric reconstruction (B) performed from subsequent CT examination more clearly defines the fracture orientation through the scapular body with involvement of the glenoid fossa.
Figure 4. Diaphragmatic Injury. Chest radiograph (A) shows elevation of the left hemidiaphragm with gas-filled viscus (stomach) in the left hemithorax. Multiplanar CT images (B, C, D) confirm rupture of the left hemidiaphragm. Black arrow (B) indicates the “dependent viscera” sign and white arrows (C and D) delineate the site of left hemidiaphragm defect.
Figure 5. Pneumothorax. Chest radiograph (A) depicts a right pneumothorax indicated by the “visceral pleural line sign”. The pneumothorax is more evident on subsequent right shoulder radiograph (B) where it is indicated by white arrows. Black arrows show right second and third rib fractures and right acromioclavicular joint dislocation, which were more difficult to identify on the chest radiograph.
Figure 6. Pneumothorax. Chest radiograph (A) shows no definite pneumothorax, although in retrospect the black arrow likely represents basilar lucency from pneumothorax. Axial CT image (B) shows a moderate-sized left pneumothorax with associated left third rib fracture (black arrow). An apparent pneumatocele (white arrow) actually represents pneumothorax extending into the major fissure.
Figure 7. Pulmonary Contusions. Chest radiograph (A) shows non-specific upper lobe airspace consolidation. Axial CT image (B) shows bilateral lower lobe and right upper lobe pulmonary contusion. Consolidation crossing the right major fissure (black arrows) distinguishes contusion from aspiration.
Figure 8. Pulmonary Lacerations and Hemothorax. Chest radiograph (A) shows increased attenuation of the left hemithorax and bilateral rib fractures. Oblique axial CT image at lung window (B) shows a type 3 pulmonary laceration in the left lower lobe adjacent to a left eighth rib fracture (black arrows) and a type 2 laceration in the medial right lower lobe adjacent to the T7 vertebral body (white arrow). CT image at soft tissue window (C) demonstrates the left pleural fluid to be greater attenuation than simple fluid (in this case approximately 50 HU), consistent with hemothorax.
Figure 9. Bronchial Avulsion. Chest radiograph (A) shows a collapsed right lung with large pneumothorax despite thoracostomy tube placement, along with subcutaneous emphysema, pneumomediastinum, and mediastinal shift to the left. Axial CT image (B) shows the “fallen lung” sign where collapsed lung falls into the medial and dependent ipsilateral hemithorax, in this case rotated counterclockwise. The site of bronchial injury was not seen on CT due to motion artifact but confirmed intraoperatively.
Figure 10. Myocardial Injury. Chest radiograph (A) shows enlargement of the cardiac silhouette, corresponding to hemopericardium. Reformatted CT image along the long axis of the heart (B) shows contrast extravasation through a defect in the right ventricular free wall, as well as hemopneumopericardium corresponding to radiographic findings. Axial and sagittal CT images at bone window (C and D) show a transversely-oriented fracture of the sternum, a finding which can be seen in association with cardiac injury.
Figure 11. Pericardial injury. Chest radiograph (A) shows lucency along the right heart border, indicating pneumopericardium. Axial CT image (B) confirms the presence of pneumopericardium with a defect in the pericardium indicated by the black arrow. Bilateral pulmonary contusions and right pneumothorax are also noted.
Figure 12. Pericardial Injury. Chest radiographs obtained immediately after (A) a motor vehicle collision and 6 hours later (B) show interval displacement of the heart into the left hemithorax. Left basilar pneumothorax is also seen on the delayed examination after thoracostomy tube placement. CT images obtained at soft tissue (C) and lung (D) window show clockwise rotation of the heart, indicating herniation through an acquired defect in the left pericardium, along with bilateral pneumothoraces and pneumopericardium.