The Core Curriculum: Cardiopulmonary Imaging, 1st Edition (2004)

Chapter 12. Thoracic Trauma

Trauma is one of the leading causes of death and disability, often affecting young otherwise healthy individuals (1,2). Chest injuries are a significant contributor to trauma-related deaths and disability. After head and neck injuries, which affect the brain and cervical spinal cord, thoracic injuries affect the next most vital structures, including the heart, aorta, lungs, and thoracic spinal cord. This chapter reviews some of the mechanisms of injury to the various organs and structures within the thorax, along with their imaging features and evaluation.

Biomechanics

Thoracic trauma is the result of either penetrating or blunt injuries or a combination of the two. Knife and gunshot wounds are typical examples of penetrating injuries. Motor vehicle accidents, falls from a great height, and direct blows to the chest are common examples of blunt injuries. Explosions can cause combined injuries, with flying debris causing penetrating injuries and the shock wave of the blast causing blunt injuries. Velocity is an important factor contributing to both penetrating and blunt injuries. Relatively slow moving objects, such as knives and clubs, cause limited local injuries along the path of the blade or at the site of impact. Faster moving objects, such as bullets, not only cause damage along their flight paths but can also create compression shock waves, which travel through adjacent tissues and cause additional injuries. High-speed blunt impacts, such as those resulting from motor vehicle accidents or falls, not only cause direct blow injuries, but also result in the variable deceleration of internal structures, leading to shearing stresses and torsional forces at sites of fixation that can lacerate tissues and tear vessels. In addition, sudden or rapid compression of the chest or abdomen can cause an abrupt pressure increase, resulting in rupture of viscera (1,2).

Aortic Injuries

Acute traumatic aortic injury (ATAI) is a devastating and often lethal consequence of thoracic trauma. Proposed mechanisms of injury include the following:

1. Variable deceleration of the thoracic aorta producing shearing stresses, particularly at points of fixation such as the aortic root, the aortic isthmus (just distal to the left subclavian artery origin near the attachment of the ligamentum arteriosus), and the diaphragmatic hiatus;

2. Chest or abdominal wall compression, resulting in a sudden increase in the intraaortic pressure;

3. Chest compression, crushing the aorta between the sternum and spine.

Eighty-five percent of patients with an ATAI will suffer a complete full-thickness tear or rupture of the aortic wall, exsanguinate, and die before reaching the hospital. The remaining 15% of patients with an ATAI will have incomplete partial tears of the aortic wall, forming a pseudoaneurysm. Approximately 50% of these survivors will develop pseudoaneurysm rupture within the first 24 hours after the traumatic event if untreated.

Less than 5% of patients will survive long term with a pseudoaneurysm (3). The chest radiograph and computed tomography (CT) of one such patient with a chronic pseudoaneurysm are shown in Fig. 12.1.

The most common location of traumatic aortic rupture is the aortic root; however, these patients usually do not survive to reach the hospital.

Figure 12.1 Chronic aortic pseudoaneurysm. A and B. Frontal and lateral chest radiographs of a patient with a remote history of motor vehicle accident. Note the lobulated contour in the region of the aortic isthmus with mural calcification and a double density in the region of the aortic knob on the frontal view (arrows). C and D. Contrast enhanced computed tomography demonstrates a chronic pseudoaneurysm in the region of the aortic isthmus with mural calcification (arrows). Note the location of the pseudoaneurysm (arrow) adjacent to the pulmonary artery (PA) near the attachment of the ligamentum arteriosus in D.

Table 12.1: Chest Radiograph Signs of Mediastinal Hematoma

Widening of the superior mediastinum
Obscuration of the aortic arch
Abnormal aortic contour
Fullness, opacification, or loss of definition of the aorticopulmonary window
Caudal displacement of the left main bronchus
Rightward deviation of the trachea
Rightward deviation of a nasogastric tube in the esophagus
Widening of the paraspinal stripe in the absence of a vertebral fracture
Widening of the right paratracheal stripe
Left apical cap and left pleural fluid

ATAI is strongly associated with mediastinal hemorrhage; however, this blood does not arise from the aortic tear itself because the intact adventitia of the pseudoaneurysm maintains aortic integrity and blood flow. The mediastinal hematoma results from concomitant injury to other mediastinal, paraspinal, and intercostal vessels, usually veins and small arteries. Plain chest radiographs do not directly image an aortic tear; only CT and aortography can do this. However, plain films can detect mediastinal hematoma, an indirect sign of ATAI. Therefore, plain films are a useful screening tool and may help guide further imaging evaluation. Although no single plain film finding is totally sensitive or specific for a mediastinal hematoma, the following abnormalities have the greatest diagnostic value: (a) widening of the superior mediastinum; (b) obscuration of the aortic arch; (c) abnormal aortic contour; (d) fullness, opacification, or loss of definition of the aorticopulmonary window; (e) caudal displacement of the left main bronchus; (f) rightward deviation of the trachea; (g) rightward deviation of a nasogastric tube in the esophagus; (h) widening of the paraspinal stripe in the absence of a vertebral fracture; (i) widening of the right paratracheal stripe; and (j) left apical cap and left pleural fluid (Table 12.1) (4). Detection of one or more of these findings should prompt further evaluation with CT aortography. This requires helical CT at a collimation no greater than 3 mm with overlapping reconstructions, coupled with rapid intravenous contrast administration at 4 mL/s.

Direct CT signs of ATAI should be specifically sought and include (a) intraluminal irregularities or areas of low attenuation (polypoid clot, linear-intimal flap), (b) change in caliber of the aorta (pseudoaneurysm, pseudocoarctation), (c) abnormal or irregular aortic wall or contour, (d) abnormal contour of great vessels, and (e) intramural hematoma or dissection (Table 12.2) (5,6). Approximately 90% of these ATAIs should be in the region of the aortic isthmus (3). CT findings of mediastinal fat stranding, mediastinal hemorrhage, perivascular hematoma, and periaortic hematoma are indirect signs of ATAI and are also seen with nonaortic mediastinal injuries. Nonetheless, these findings require clinical follow-up or, in the case of periaortic hematoma, further evaluation with catheter aortography (5). Figures 12.212.312.4 and 12.5 are the chest radiographs and accompanying CTs and/or aortograms from four cases of ATAI. The cases in Figs. 12.212.3 and 12.4 demonstrate the typical location of ATAI at the aortic isthmus, whereas the case in Fig. 12.5 is from the 10% of ATAIs that occur in other locations.

Table 12.2: CT Signs of Acute Traumatic Aortic Injury

Direct Signs

Indirect Signs

Intraluminal irregularities or areas of low attenuation (polypoid clot, linear-intimal flap)
Change in caliber of the aorta (pseudoaneurysm, pseudocoarctation)
Abnormal or irregular aortic wall or contour
Abnormal contour of great vessels
Intramural hematoma or dissection

Mediastinal fat stranding
Mediastinal hemorrhage
Perivascular hematoma
Periaortic hematoma

CT, Computed tomography.

Figure 12.2 Acute traumatic aortic injury with large mediastinal hematoma. A. Portable chest radiograph with extensive subcutaneous emphysema, multiple lines and tubes, and a pulmonary contusion (C). The initial “busy” appearance of this study must not distract from the more salient findings of mediastinal hematoma. These findings include widening of the mediastinum, obscuration of the aortic arch (A), fullness of the aortopulmonary window (W), caudal displacement of the left main bronchus (B), rightward deviation of the trachea (T), and rightward deviation of the nasogastric tube (arrows)B. Aortogram demonstrates partial tear (arrows) of the aortic wall, forming a pseudoaneurysm at the aortic isthmus.

Figure 12.3 Acute traumatic aortic injury with a mediastinal hematoma. A. Portable chest radiograph with findings of mediastinal hematoma including obscuration of the aortic arch (A), rightward deviation of the nasogastric tube (arrow), and widening of the paraspinal stripe (S, arrows). B. Aortogram demonstrates pseudoaneurysm (P) at the aortic isthmus.

Figure 12.4 Acute traumatic aortic injury. A. Portable chest radiograph with finding of mediastinal hematoma including widening of the mediastinum, obscuration of the aortic arch (A), and apical cap (C). B. Contrast enhanced computed tomography demonstrates direct signs of aortic injury including abnormal aortic wall contour (arrows) and small pseudoaneurysm adjacent to the pulmonary artery (PA) near the attachment of the ligamentum arteriosus. Also, note a left pleural effusion (E).

The most common location of aortic rupture seen clinically is the proximal descending thoracic aorta at the ligamentum arteriosum.

Figure 12.5 Acute traumatic aortic injury. After this young man’s motor vehicle accident, he walked to a nearby house to phone for help and then rode in the tow truck to the garage with his car before presenting to the hospital complaining of back pain. A. Chest radiograph demonstrates widening of the mediastinum, obscuration of the aortic arch (A), caudal displacement of the left main bronchus (B), and widening of the paraspinal stripe (S, arrows). B and C. Contrast enhanced computed tomography demonstrates both direct and indirect signs of aortic injury. The direct signs are best seen in C and include intraluminal curvilinear low attenuation (arrows), abnormal aortic wall contour, and caliber change when comparing the dilated descending aorta in C with the normal size descending aorta in B. Both B and C demonstrate the indirect sign of periaortic hematoma (H). D. Aortogram demonstrates partial tear (arrows) of the aortic wall, forming a pseudoaneurysm involving the descending thoracic aorta.

Osseous Injuries

Rib fractures are the most common sequela of chest trauma, occurring in over half of blunt trauma cases (7,8,9). However, many of these injuries are not initially detected because they are uncomplicated nondisplaced fractures or involve radiographically undetectable costochondral separation (2,7,8,10). This is acceptable because the goal of imaging is not so much to detect the rib fracture itself, but rather the potential associated complications of rib fractures (10). These complications include injury to the intercostal vessels, which can lead to hemothorax or an extrapleural hematoma; lung contusion or laceration; pneumothorax; and subcutaneous emphysema (Figs. 12.6and 12.7) (2,9,10). The most serious consequence of rib fractures is flail chest (2,7). Flail chest is the result of five or more adjacent rib fractures or more than three segmental rib fractures (a single rib fractured in two or more locations) (Figs. 12.8 and 12.9) (2,7,8).

This creates an abnormally mobile segment of the chest wall that will move paradoxically with respiration (2,7,8). Flail chest can lead to respiratory failure in part secondary to associated lung and pleural injuries and in part secondary to pendelluft (2). Pendelluft is the pendulum-like movement of gas from the normal hemithorax to the flail hemithorax during expiration and then back again during inspiration due to the paradoxical motion of the flail segment. In other words, when the normal hemithorax exhales, the flail hemithorax will paradoxically inhale and vice versa. This results in impaired ventilation due to rebreathing of the same air back and forth between the hemithoraces. This can be treated with mechanical ventilation (2,7,8).

Fractures of thoracic bones are an indication of the force of trauma and are commonly associated with organ injury.

Figure 12.6 Rib fractures with associated hemothorax. Chest radiograph demonstrates minimally displaced fractures (arrows) of the right sixth and seventh ribs. There is a also hazy opacity obscuring the right costophrenic angle with blunting consistent with a small associated hemothorax.

A fail chest is the fracture of three or more ribs in two or more locations each, or the fracture of five or more adjacent ribs.

Figure 12.7 Rib fractures with associated pneumothorax and hemothorax. Chest radiograph demonstrates displaced fractures (arrows) of the left third through the seventh ribs. There is a large associated left pneumothorax (P) with significant collapse of the left lung (L). There is also blunting of the left costophrenic angle consistent with a small associated hemothorax.

Fractures of the first three ribs, particularly the first rib (Fig. 12.10), are a marker of severe trauma (2,7,10). Considerable force is required to break these ribs because they are protected by the clavicle, shoulder, scapula, and heavy surrounding musculature (2,7). These fractures are often associated with airway, spinal, vascular, and brachial plexus injuries. Fractures of the lower three ribs are associated with injuries to the spleen, liver, or kidneys (2,10).

Lower rib fractures are associated with injury to the liver, spleen, and kidneys.

Figure 12.8 Flail chest. Chest radiograph demonstrates displaced fractures (arrows) of five consecutive left ribs (fifth through ninth), with three of the ribs (57, and 8) exhibiting segmental fractures. Blunting of the left costophrenic angle indicates a small associated hemothorax.

Sternal fractures can result from steering wheel injuries, seat-belt injuries, crush injuries, and aggressive resuscitation (2,8). Sternal fractures can be important because they are associated with other mediastinal injuries; however, they are virtually impossible to detect on frontal radiographs (10). Lateral views or CT are required to detect sternal fractures, which are usually transverse and near the manubrium (2,8,10). Sagittal and/or coronal reconstructions can be useful (8). An associated retrosternal hematoma is often noted, which if separated from the aorta by a fat plane suggests that the hematoma is not aortic in origin (2,11). Sternoclavicular dislocations can also be detected with CT (8,9).

Sternal fractures are associated with mediastinal vascular injury.

Figure 12.9 Bilateral flail chest. This patient sustained a severe crush injury. Chest radiograph demonstrates displaced fractures(arrows) of six consecutive right ribs (third through eighth), all of which are segmental fractures. In fact, the right sixth rib is actually fractured in three locations. There are also displaced fractures (arrows) of five consecutive left ribs (third to seventh). Blunting of both costophrenic angles, pleural thickening, and diffuse hazy increased opacity of both hemithoraces (left greater than right) indicate bilateral associated hemothoraces.

Figure 12.10 First rib fracture. Coned down view of the left apex demonstrates a left first rib fracture (arrows). Also, note the adjacent left apical pleural thickening (arrowhead) indicating an associated extrapleural hematoma.

Thoracic vertebral fractures can result from motor vehicle accidents or falls from a great height. They are produced by hyperflexion and/or axial loading and account for 25% to 30% of all spine fractures (1). Most injuries occur at the functional thoracolumbar junction, which extends from T-9 to T-11 (1,7,8,12). The thoracic spinal cord is unusually susceptible to injury. This vulnerability is the result of two main factors. First, the thoracic spinal cord is tightly packed in the spinal canal, predisposing it to injury by displaced fragments of bone or disc material and compression by hematoma and cord edema. Second, the vascular supply to the mid-thoracic cord is quite tenuous and can be disrupted easily, resulting in cord ischemia or infarction with associated neurologic impairment (1). The radiographic findings of thoracic spine fractures can be subtle and difficult to identify (8). Initial evaluation should include the frontal chest radiograph and a cross-table lateral view of the spine. There are both direct and indirect plain film signs of thoracic fractures (Table 12.3). Direct signs include cortical disruption and abnormal vertebral body size, shape, opacity, and location (Fig. 12.11) (1). Indirect signs are secondary to paravertebral hematoma (Fig. 12.5) and can overlap with signs of aortic injury. Indirect signs include widening of the paraspinal stripe, mediastinal widening, left apical cap, and deviation of a nasogastric tube (1,7,8,13). If a thoracic spine fracture is suspected, then further evaluation with CT and/or magnetic resonance imaging (MRI) is indicated. Reformatted sagittal and coronal CT images are helpful (1,8). A mediastinal hematoma that is confined to the posterior compartment suggests a vertebral fracture (8).

A portable chest trauma radiograph may suggest thoracic spine fracture but is insufficient to exclude it.

Table 12.3: Radiographic Findings of Thoracic Spine Fractures

Direct

Indirect

Cortical disruption

Widening of the paraspinal stripe

Abnormal vertebral body size

Mediastinal widening

Abnormal vertebral body shape

Apical cap

Abnormal vertebral body opacity

Deviation of a nasogastric tube

Abnormal vertebral body location

Figure 12.11 Vertebral fracture. Coned down view of the lower thoracic spine demonstrates direct signs of a T-9 compression fracture dislocation, including markedly decreased height of T-9 and malalignment of T-8 with respect to T-10. Paraspinal stripe widening(arrows), an indirect sign of spinal injury, is also present.

Lung and Pleural Injuries

Contusion in the most common pulmonary parenchymal injury, occurring in approximately half of patients after blunt trauma (2,8,11). The mechanism of injury is local comprehensive and recoil forces within the lung that disrupt small vessels, leading to intraalveolar hemorrhage or a parenchymal bruise (2,9,10,11,14). Interstitial injury with associated capillary leak and edema can also occur but is usually seen with more severe trauma accompanied by blast or shock wave injuries (Fig. 12.12) (14). Contusion appears rapidly and usually reaches its full extent within the first day after trauma (Fig. 12.13). Contusion tends to occur adjacent to solid structure such as the ribs, spine, and solid organs like the heart and liver (2). Contusions may have a varied radiographic appearance, ranging from coarse irregular nodular opacities that may be confluent or discrete to homogenous consolidation with diffuse hazy or focal, poorly defined, fluffy lung opacities, or a combination of these findings (Figs. 12.14 and 12.15) (9,11,14). The presence and extent of contusion are much better defined with CT than chest radiographs (Figs. 12.14 and 12.15) (2,8,11,14). Contusion may be difficult to distinguish from or may be obscured by other forms of posttraumatic consolidation, including aspiration, edema, and atelectasis (2). Contusion usually begins to resolve within a few days, completely resolving within 1 to 2 weeks (2,8).

Lung contusions usually develop and reach maximum size with 24 hours of trauma.

Figure 12.12 Pulmonary contusion. Chest radiograph demonstrates findings of a self-inflicted gunshot wound to the left axilla, including multiple metallic bullet fragments. A large area of focal increased opacity is seen occupying the left upper lung representing alveolar hemorrhage and edema secondary to pulmonary contusion and interstitial injury caused by the shock wave associated with the adjacent gunshot blast. Also note the left apical pleural thickening (arrows) secondary to an associated hemothorax.

Figure 12.13 Progression of pulmonary contusion. A. Chest radiograph demonstrates increased opacity in the left mid and upper lung secondary to pulmonary contusion. There is also hyperlucency on the right secondary to a pneumothorax, subcutaneous emphysema in the supraclavicular regions, and apparent elevation of the left hemidiaphragm secondary to a diaphragmatic rupture. B. Chest radiograph 1 day later demonstrates further opacification of the left lung and new opacity in the right medial lung secondary to progression of the contusion. Also, note the up-turned nasogastric tube (arrows) in the herniated stomach and resolution of the right pneumothorax after chest tube insertion.

Figure 12.14 Pulmonary contusion and pneumothoraces. A. Chest radiograph demonstrates coarse irregular nodular opacities predominantly in the right lung and more diffuse, hazy to focal, poorly defined, fluffy lung opacities predominantly in the left lung consistent with the varied radiographic appearance of contusion. Also, there is a right pneumothorax (arrows), but much less apparent is a small left pneumothorax (single arrow on right). B and C. Computed tomography images more clearly demonstrate similar findings of irregular nodular opacities, areas of homogenous consolidation, and areas of fluffy focal opacity. Notice the distribution of some of these opacities adjacent to solid structures, such as the ribs peripherally and the spine medially, in B. The right pneumothorax is readily apparent in both B and C; in addition, notice the ease of detection of the small left pneumothorax (arrow) in C.

Figure 12.15 Pulmonary contusion. A. Chest radiograph demonstrates areas of focal hazy opacity in the left mid lung and right mid-upper lung medially. Also, note the metallic bullet fragment in the right axillary region (arrow) and subcutaneous emphysema. B and C.Computed tomography images demonstrate focal opacities with bubbly lucency’s anteriorly on the right in B and on the left in C. These contusions/lacerations relate to the flight paths of the patient’s gunshot wounds. Areas of confluent homogenous consolidation are seen posteriorly in C adjacent to solid structures (i.e., the ribs and spine). These contusions relate to the shock wave injuries secondary to the gunshot wounds. Also, notice the subcutaneous emphysema, which is readily apparent in both B and C.

 

Pulmonary laceration results from shearing forces caused by blunt trauma or direct puncture secondary to penetrating trauma (Fig. 12.15) (2,9,10,14). The initial linear tear of the laceration rapidly becomes an ovoid space secondary to the elastic recoil properties of the adjacent normal lung (2,14). Lacerations can be obscured by surrounding contusion and may not become apparent until the contusion begins to resolve (2). The postlaceration space can fill with blood, becoming a pulmonary hematoma or air resulting in a pneumatocele (8,10,11,14). A pneumatocele can also form as the hemorrhage in a pulmonary hematoma begins to resolve and is replaced by air (Fig. 12.16) (11,15). Radiographically, hematomas and pneumatoceles will appear as well-circumscribed round areas of focal opacity or lucency (11). Again, CT is much more sensitive for detecting lacerations than plain films (2,8,14).

Figure 12.16 Pulmonary laceration/hematoma and contusion evolving into a pneumatocele. A. Computed tomography image demonstrates areas of focal and band-like opacities predominantly in the right lung. These represent a combination of pulmonary laceration/hematoma and contusion. B. Computed tomography image of the same patient 3 weeks later demonstrates a predominantly air-filled space in the same location. Over time, as the contusion and hemorrhage in the hematoma resolved, they were replaced with air, forming a pneumatocele.

A pulmonary laceration can extend through the visceral pleura and with associated air leak result in a pneumothorax (14). Compression injuries can cause alveolar rupture and air leak, which can also lead to pneumothorax (2). Figure 12.17 demonstrates a large left pneumothorax that could have resulted from either of these mechanisms. If the air leak from alveolar rupture tracts along the bronchovascular bundles, pneumomediastinum can result (Fig. 12.18) (9,16,17). Similarly, if the air leak tracts along the adventitia of the pulmonary veins, pneumopericardium can occur (16). Obviously, penetrating injuries can violate the pleura and cause pneumothorax. Pneumothorax can be difficult to detect in the posttrauma patient because they are often radiographed in the supine position with the intrapleural air collecting nondependently along the anterior chest wall (1,10). Signs of a pneumothorax on a supine chest radiograph include a deep costophrenic sulcus (the so-called deep sulcus sign; Fig. 17.13), basilar hyperlucency, and unusually sharp delineation of the mediastinal contour (Figs. 12.13A and 12.19) (1,10). Occasionally, decubitus or cross-table lateral views can be helpful to detect pneumothorax (1,10). CT is the most accurate method for detecting a pneumothorax (Fig. 12.14) and should be considered if the patient is to be placed on positive pressure mechanical ventilation, because this can cause even the tiniest pneumothorax to rapidly increase in size and possibly become a tension pneumothorax (1,2,10). Tension pneumothorax can be a life-threatening situation. Radiographic signs of tension pneumothorax include contralateral displacement of mediastinal structures, inferior displacement of the diaphragm, hyperlucent hemithorax, and ipsilateral collapse of the lung (Figs. 12.19 and 12.20).

Figure 12.17 Large left pneumothorax. Chest radiograph demonstrates a large left pneumothorax (P) with significant collapse of the left lung (L). There were no rib fractures or history of penetrating trauma; therefore, this pneumothorax must be the result of a parenchymal or airway injury.

Figure 12.18 Pneumomediastinum. Coned down view of the mediastinum demonstrates streaky linear lucency’s throughout the mediastinum and lucencies surrounding the aortic knob (A, arrows), the so-called ring around the artery sign. These findings indicate a pneumomediastinum.

On portable supine trauma chest radiographs, pneumothorax collects at the lung bases and is often occult radiographically.

Figure 12.19 “Deep sulcus” sign. Supine chest radiograph demonstrates a deep lucent costophrenic sulcus on the right (arrow), the so-called deep sulcus sign. This indicates a right pneumothorax. Also, note contralateral shift of the heart and mediastinum to the left and inferior displacement of the right hemidiaphragm. These findings indicate that this pneumothorax is under tension. The generalized hazy opacity in the right hemithorax is secondary to a dependently layering right hemothorax.

Figure 12.20 Tension pneumothorax. Chest radiograph demonstrates a hyperlucent right hemithorax with significant collapse of the right lung, inferior displacement of the right hemidiaphragm, and contralateral displacement of the mediastinal structures to the left. These findings indicate a right tension pneumothorax, despite the presence of a small bore right chest tube.

Just as air can accumulate in the pleural space after parenchymal injuries, so can blood secondary to hemorrhage at the site of injury, resulting in a hemothorax (1,2,10). Bleeding from low pressure pulmonary vessels is usually self-limited; however, injury to large central pulmonary vessels, systemic thoracic veins or arteries, or lacerated viscera can lead to a large potentially life-threatening hemothorax requiring surgical intervention (1). Again, similar to pneumothorax, hemothorax can be difficult to detect on supine radiographs, in this case due to dependent posterior layering. Signs of hemothorax on a supine chest radiograph include apical cap, hazy increased opacity projected over the hemithorax, and confluent lateral pleural thickening (Figs. 12.412.912.12, and 12.19) (1,10). Again, CT is the most accurate way to detect even small amounts of pleural fluid (Fig. 12.4) (10). Fibrothorax can be the late result of an untreated undrained hemothorax (2). The delayed or late appearance of pleural fluid that continues to slowly accumulate over several days, particularly after a penetrating injury or recent thoracic surgery, raises the possibility of a chylous effusion secondary to thoracic duct disruption (2,10).

Rare complications of thoracic trauma include lung herniation through a defect in the chest wall and torsion of the lung about the hilar structures secondary to disruption of the inferior pulmonary ligament, which normally anchors the lung (2,10).

Tracheobronchial Injuries

Tracheobronchial injuries (TBIs) occur in about 1% of major chest traumas and have a high mortality, about 30% (2,7,8). Intrathoracic TBIs can occur as a result of compression of the trachea against the spine, shearing forces, or by sudden increased intraluminal pressure. Most injuries (80%) occur within 2.5 cm of the carina and favor the right main bronchus (7). TBIs are often associated with fractures involving one or more of the first three ribs (Fig. 12.10), clavicle, sternum, or scapula (8,18). The clinical and radiographic manifestations of TBIs depend on the location and extent of the airway tear. Airway tears can be partial or incomplete and may remain occult. Diagnosis may be delayed until high-pressure mechanical ventilation is instituted, leading to pneumomediastinum and/or pneumothorax (2). Delayed diagnosis of an airway injury can result in airway stenosis secondary to partial healing. This can lead to air trapping, recurrent atelectasis, or postobstructive pneumonia (2,8). It is unusual to directly visualize the site of airway injury, even with CT. If an airway injury is suspected, then bronchoscopy is indicated.

Most tracheobronchial injuries occur within 2.5 cm of the carina.

Figure 12.21 Pneumomediastinum and subcutaneous emphysema. A. Chest radiograph demonstrates streaky linear lucencies throughout the mediastinum and subcutaneous tissues in the supraclavicular and axillary regions. These gas collections are the result of an air leak secondary to a tracheal injury. B. Computed tomography image of the same patient demonstrates extensive pneumomediastinum.

Figure 12.22 “P” and “fallen lung” signs. Chest radiograph demonstrates a right tension pneumothorax despite the presence of a right chest tube. The right lung exhibits significant collapse and has “fallen” inferiorly secondary to complete disruption of the right main bronchus.

Air leaks associated with tears of the trachea and proximal (extrapleural) left main bronchus tend to be confined to the mediastinum and interstitial planes of the neck and subcutaneous tissues (Fig. 12.21) (2,18). Tears of the right main and distal left main bronchi manifest as pneumothorax (Fig. 12.17). TBIs can cause the so-called P sign (persistent progressive pneumothorax), especially if the pneumothorax persists after chest tube insertion (Figs. 12.20 and 12.22) (7,10). The “fallen lung” sign occurs with complete disruption of a main bronchus. The lung falls inferiorly and laterally to the base of the hemithorax (Fig. 12.22), in contrast to a simple pneumothorax or a pneumothorax from a partial bronchial tear in which the lung collapses medially and centrally (2,8,18). Although the fallen lung sign is specific, it is rare (7). Other signs of airway disruption include interstitial air within the wall of the airway, ectopic location of an endotracheal tube, and overdistention of the endotracheal tube cuff balloon (18) (Table 12.4).

Table 12.4: Chest Radiograph Findings of Airway Injury

Pneumomediastinum
Pneumothorax
“P” sign (persistent, progessive, pneumothorax)
“Fallen lung” sign
Interstitial air within the airway wall
Ectopic location of an endotracheal tube
Overdistention of the endotracheal tube cuff balloon

Persistent or unexplained pneumomediastinum in a trauma patient should raise suspicion of airway rupture or esophageal rupture.

Esophageal Injuries

Esophageal tear after trauma is relatively rare, occurring in less than 1% of patients; however, prompt detection and diagnosis are imperative to avoid the possibility of an ensuing mediastinitis, which carries a high morbidity and mortality (7,8,10). This injury can result from a sudden increase in intraesophageal pressure that may in part be due to the violent ejection of stomach contents into the esophagus, with a pathophysiology similar to Boerhaave syndrome (7,8,10). The resulting tear usually occurs in the left posterolateral wall of the distal esophagus; this is a location where the esophagus is devoid of striated muscle and deficient in extramural support. Other mechanisms of injury can include compression of the esophagus between the sternum and spine, traction from cervical hyperextension, and penetrating injuries, including bone fragments from spinal fractures (8). Chest radiographs cannot directly identify an esophageal tear; therefore, indirect signs must be used. These indirect signs include pneumomediastinum (Figs. 12.18 and 12.21), left pneumothorax, left pleural effusion, and left lower lobe atelectasis (Table 12.5Fig. 12.23) (8). If an esophageal injury is suspected, an esophagram or endoscopy should be considered. If an esophagram is performed, water-soluble non-ionic contrast should be used initially and, if negative, can be followed by a barium study.

An esophagram is the test of choice for diagnosing esophageal rupture.

Table 12.5: Chest Radiograph Findings of Esophageal Injury

Pneumomediastinum
Left pneumothorax
Left pleural effusion
Left lower lobe atelectasis

Figure 12.23 Esophageal tear. Chest radiograph demonstrates an air-fluid level (arrows) at the left base consistent with a hydropneumothorax. There is also increased opacity at the left base with mild elevation of the left hemidiaphragm compatible with basilar atelectasis. These findings are secondary to an esophageal tear.

Cardiac Injuries

The heart and pericardium are subject to both penetrating and blunt injuries. Thoracic trauma can induce a variety of cardiac injuries, including myocardial contusion, coronary artery occlusion, myocardial infarction, myocardial rupture or laceration, pericardial tamponade, damage to the valve apparatus, and pericardial rupture or tear, which can lead to cardiac herniation or dislocation (10). Myocardial contusion is common but frequently asymptomatic. Myocardial contusion is difficult to image but is usually evident secondary to elevated creatine phosphokinase enzymes and/or an abnormal electrocardiogram. The right ventricle is most commonly affected because of its immediate retrosternal location. Pericardial tamponade may be secondary to blood or air accumulating in the pericardial sac (8). Pneumopericardium can result from air tracking along the adventitia of pulmonary veins into the pericardial space. Detection of pericardial tamponade secondary to hemopericardium can be challenging radiographically because only a small amount of blood can tamponade cardiac motion acutely without changing the cardiac silhouette size significantly. However, diagnosis can be made if the cardiac size is noted to be increasing on serial radiographs. Cardiac tamponade can also be secondary to anterior mediastinal hematomas, often resulting from arterial sources, which can compress the myocardium. CT can easily detect both mediastinal hematomas and hemopericardium (Fig. 12.24). Bedside echocardiography can also readily detect the presence of pericardial fluid.

Myocardial contusion is the most common cardiac injury in blunt trauma and is occult radiographically.

Figure 12.24 Hemopericardium. Computed tomography image demonstrates high attenuation fluid in the pericardial space consistent with a hemopericardium (H).

Diaphragm Injuries

Diaphragmatic rupture occurs in about 5% of patients with blunt trauma (1,19,20,21,22,23,23). Mechanisms of injury in these cases include lateral impact, which distorts the chest wall and creates shearing forces along the diaphragm, and direct frontal impact, which causes increased intraabdominal pressure that “blows out” the diaphragm (19,22). Most diaphragmatic ruptures are associated with significant intraabdominal injuries (22). Although left- and right-sided ruptures likely occur with equal frequency, right-sided ruptures are more often clinically occult, probably because of some protective effect of the liver, and more difficult to diagnose, leading to underreporting of right-sided ruptures (1,20). Therefore, left-sided ruptures are reported in 75% to 90% of cases (8,19). Most of these left-sided tears occur in the posterolateral portion of the diaphragm at the musculotendinous junction, which is the weakest portion of the diaphragm because it is where the pleuroperitoneal membrane finally closes during fetal development (8,19,20,22,23). Most diaphragmatic tears resulting from blunt trauma are greater than 2 cm in length, with many left-sided tears being 10 cm or more in length (8,19,20,22,23,24).

An elevated hemidiaphragm in the setting of trauma should raise suspicion for diaphragmatic rupture.

Left-sided diaphragmatic ruptures are much more common clinically than right-sided ones.

Visceral herniation occurs in approximately half of the cases of diaphragmatic ruptures (8). On the right side the organs most commonly herniated are the liver and occasionally the colon. On the left side the stomach and colon are the most common, but the small bowel, spleen, and kidney can also herniate (23). Herniation is an important complication that can lead to strangulation with associated ischemia, infarction, and/or obstruction (1,19,22,23). Herniation can be delayed after a diaphragmatic injury, but over time negative intrathoracic pressure and positive intraperitoneal pressure lead to progressive enlargement of the diaphragmatic defect, increasing the likelihood of herniation of intraabdominal contents into the thorax (1,19,21,22,23). This process can be inhibited if the patient requires positive pressure assisted ventilation after the traumatic event, because this will eliminate and actually reverse the pressure gradient between the thorax and abdomen (19,22,24). The period of delay between the diaphragmatic injury and the presentation of herniation is known as the latent phase and can last from months to years. Most cases that result in strangulation occur within 3 years of the traumatic event (1,23).

Plain chest radiography cannot directly image a diaphragmatic tear; therefore, plain film diagnosis of a diaphragmatic rupture depends on secondary signs of herniation of intraabdominal contents into the thorax (10). Chest radiograph findings of diaphragmatic herniation include (a) apparent diaphragmatic elevation; (b) irregular, obscured, or discontinuous diaphragmatic contour; (c) contralateral mediastinal shift; (d) air containing viscera above the hemidiaphragm; (e) basilar opacification; and (f) abnormal U-shaped course of a nasogastric tube with an elevated tip (Table 12.6Figs. 12.1312.25, and 12.26) (1,2,8,10,23,24). However, these findings are nonspecific and can be attributed to or obscured by other abnormalities, such as atelectasis, pulmonary contusion, pleural effusion, posttraumatic lung cysts, pneumothorax, hiatal hernia, and phrenic nerve paralysis (1,8,10). Preexisting diaphragmatic eventration or elevation can also mimic a diaphragmatic injury (8). Thus, the plain film diagnosis of diaphragmatic rupture is difficult. Serial radiographs can be helpful and in particular should be performed after a trauma patient is removed from positive pressure mechanical ventilation (19,22,24).

Table 12.6: Chest Radiograph Findings of Diaphragmatic Herniation

Apparent diaphragmatic elevation
Irregular, obscured, or discontinuous diaphragmatic contour
Contralateral mediastinal shift
Air containing viscera above the hemidiaphragm
Basilar opacification
Abnormal U-shaped course of a nasogastric tube with an elevated tip

Figure 12.25 Diaphragmatic hernia. Chest radiograph demonstrates apparent elevation and obscuration of the left hemidiaphragm, herniated bowel (B, arrows) above the diaphragm, and left basilar opacification. These findings are consistent with a diaphragmatic tear with associated bowels herniation.

Delayed diaphragmatic rupture may present years after trauma, either through radiographic detection or symptoms of bowel strangulation.

CT is superior to plain films for the detection and diagnosis of diaphragmatic rupture, and helical CT with multiplanar reformatted images is of further benefit (11,19,21,22). The CT findings of diaphragmatic injury include (a) sharp focal discontinuity of the diaphragm; (b) the “absent diaphragm” sign (nonvisualization of the diaphragm or a large gap between the torn ends of the diaphragm); (c) herniation of peritoneal fat, omentum, bowel, or an organ; (d) the “collar” sign (focal constriction of the bowel or an organ at the site of herniation); (e) the “dependent viscera” sign (herniated organs or bowel no longer supported posteriorly by the ruptured diaphragm fall dependently abutting the posterior ribs); and (f) concomitant pneumothorax and pneumoperitoneum and/or concomitant hemothorax and hemoperitoneum (Table 12.7Figs. 12.27 and 12.28) (8,11,19,20,21,22).

Figure 12.26 Diaphragmatic hernia. Chest radiograph demonstrates apparent elevation of the left hemidiaphragm, herniated gas filled stomach (S) above the diaphragm, and U-shaped course of the nasogastric tube (arrows). These findings are consistent with a diaphragmatic tear and gastric herniation.

 

MRI is also helpful for diagnosing diaphragm injuries but is generally not used in the acute trauma setting. MRI is generally used in stable patients with a delayed presentation in whom the CT findings are nondiagnostic or equivocal. (8,19) The MRI findings of diaphragmatic rupture are similar to the CT findings (Fig. 12.29). However, MRI has the advantage of direct coronal and sagittal imaging, allowing evaluation of diaphragm integrity from its insertion site to the dome. Optimal visualization is achieved with T1-weighted images, with the diaphragm appearing as a hypointense band outlined by hyperintense mediastinal and abdominal fat or the liver (8,19,25). Other studies, such as contrast studies of the intestine and radionuclide liver/spleen scans, can occasionally be useful.

Table 12.7: CT Findings of Diaphragmatic Injury

Sharp focal discontinuity of the diaphragm
“Absent diaphragm” sign
Herniation of peritoneal fat, omentum, bowel, or an organ
“Collar” sign
“Dependent viscera” sign
Concomitant pneumothorax and pneumoperitoneum
Concomitant hemothorax and hemoperitoneum

CT, computed tomography.

Figure 12.27 Diaphragmatic hernia. A. Computed tomography image demonstrates nonvisualization of the diaphragm (“absent diaphragm” sign), herniation of peritoneal fat and bowel, and bowel abutting the posterior ribs (“dependent viscera” sign). B. Computed tomography image demonstrates sharp focal discontinuity of the diaphragm (arrow) and “dependent viscera” sign. C. Computed tomography image demonstrates retraction and bunching of the torn diaphragm at the left crus (arrow).

Figure 12.28 Diaphragmatic hernia. A and B. Computed tomography images demonstrate the stomach and spleen abutting the posterior ribs consistent with the “dependent viscera” sign secondary to diaphragmatic rupture with associated herniation.

Figure 12.29 Diaphragmatic hernia. A. coronal and (B) sagittal magnetic resonance images demonstrate focal constriction of the liver as it herniates through a tear in the right hemidiaphragm (“collar” sign).

A rare but interesting complication of diaphragmatic rupture is intrathoracic splenosis. This can occur when diaphragmatic rupture is associated with splenic rupture, allowing pieces of spleen to cross the diaphragmatic defect into the thorax and implant on the pleura. This leads to the appearance of pleural-based masses that can be mistaken for a neoplasm (Fig. 12.30). Liver–spleen scans are diagnostic, demonstrating radiocolloid uptake in the masses and confirming splenic tissue (10).

Figure 12.30 Intrathoracic splenosis. This patient was involved in a motor vehicle accident several years before and suffered splenic rupture along with a left diaphragmatic tear. Subsequently, a splenectomy and diaphragmatic repair were performed. A and B.Computed tomography images demonstrate an absent spleen consistent with the history of splenectomy and multiple enhancing pleural based nodules (arrows). A follow-up radiocolloid liver–spleen scan demonstrated uptake within these pleural based nodules, confirming splenic tissue.

Penetrating injuries of the diaphragm are more common than blunt injuries. The site of injury is more random, depending on the tTLVectory of the penetrating object. These injuries also tend to be smaller; most are less than 2 cm and many are less than 1 cm, related to the size of the penetrating object. Visceral herniation is uncommon with these smaller injuries. These injuries are usually diagnosed clinically by relying on the entry site and direction of the wound. Patients with penetrating injuries commonly undergo exploratory surgery, at which time the diaphragmatic injury is diagnosed and repaired. Imaging findings include pneumothorax, hemothorax, or radiopaque material associated with the projectile near the diaphragm or indicating a path through the diaphragm (23,24).

Upper Abdominal Injuries

It is important to scrutinize the portions of the upper abdomen that are visible at the inferior aspect of the chest radiograph. This is particularly true if fractures of the lower three ribs or signs of diaphragmatic injury are detected, because these findings are associated with significant intraabdominal injuries.

Prominent soft tissue opacity in the left upper quadrant along with medial deviation of the gastric air bubble, medial deviation of a nasogastric tube within the stomach, or inferior displacement of the splenic flexure suggests splenic injury with an associated perisplenic hematoma (26). Rigler sign (visualization of the bowel wall outlined by intraluminal air on the inside and free intraperitoneal air on the outside of a bowel loop) is evidence of pneumoperitoneum on a supine study (Fig. 12.31). Bowel wall thickening can be a sign of intramural hematoma or ischemia, which in turn can be secondary to hypotension and shock or vascular injury and compromise. Gastric distension can predispose to vomiting and aspiration and can be seen with improper ventilation (Fig. 12.32) or gastric outlet problems related to duodenal injury (26).

An upright chest radiograph is the screening test of choice for detecting free intraperitoneal air.

Figure 12.31 Pneumoperitoneum. Supine chest radiograph demonstrates Rigler sign (arrows) in the left upper quadrant.

Figure 12.32 Esophageal intubation. Chest radiograph demonstrates significant gaseous distension of the stomach (S). The radiopaque stripe of an endotracheal tube (arrow) can be seen projecting outside of the tracheal (T) air column. Also, note the hypoventilatory changes in the lungs.

Figure 12.33 Traumatically inserted and malpositioned pulmonary artery catheter. Chest radiograph demonstrates the tip of a pulmonary artery catheter (arrow) located peripherally within the right lung. Adjacent parenchymal opacity represents a hematoma (H) caused by rupture of a small pulmonary artery branch secondary to peripheral inflation of the catheter tip balloon. There is also a left apical pneumothorax (arrowheads) secondary to previous unsuccessful attempts at placing the catheter into the left subclavian vein. The patient died the next day due to complications of these iatrogenic injuries.

Iatrogenic Injuries

Iatrogenic injuries are those resulting from or occurring during the course of treatment by a health care professional. Vigorous cardiopulmonary resuscitation can cause sternal and rib fractures (2). Misplaced, malpositioned, or traumatically inserted lines and tubes can cause vascular, airway, esophageal, and lung injuries, resulting in hematomas, hemothorax, pneumothorax, pneumomediastinum, and atelectasis (Figs. 12.3212.3312.34, and 12.35) (1,7,8).

All lines, tubes, and devices should be checked for correct or incorrect position and complications.

Figure 12.34 Malpositioned endotracheal tube. Chest radiograph demonstrates the endotracheal tube tip (arrow) in the right main bronchus. Notice the underinflation of the left lung and the overinflation of the right lung.

Figure 12.35 Misplaced feeding tube. Chest radiograph demonstrates tip of a feeding tube (arrow) in the region of the right costophrenic angle. Fortunately, this was detected before the initiation of tube feeds. However, the patient developed a pneumothorax that required insertion of a chest tube after removal of the feeding tube.

Summary

Many important concepts and radiographic findings of thoracic trauma have been presented and reviewed in this chapter. The challenge is to recall and apply this knowledge quickly and efficiently when interpreting trauma studies in the hectic setting of the emergency room. A simple mnemonic based on the ABCs has been proposed to achieve this goal (7): A, aortic injuries; B, bronchial and tracheal injuries; C, cord and spine injuries; C, contusions and lacerations; D, diaphragm injuries; E, esophageal injuries; F, fractures (ribs, sternum, vertebra, clavicle, scapula); F, flail chest; G, gas (pneumothorax, pneumomediastinum, subcutaneous emphysema, pneumopericardium, pneumoperitoneum); H, heart and pericardial abnormalities (contusion, hemopericardium); H, hemothorax, hematoma, and hemorrhage; I, iatrogenic injuries (Table 12.8). (A multimedia presentation of the “ABCs of Blunt Chest Trauma” can be viewed at Jud Gurney’s website, http://www.chestx-ray.com.)

Table 12.8: The ABCs of Thoracic Trauma

A

Aortic injuries

B

Bronchial and tracheal injuries

C

Cord and spinal injuries

C

Contusions and lacerations

D

Diaphragm injuries

E

Esophageal injuries

F

Fractures (ribs, sternum, vertebra, clavicle, scapula)

F

Flail chest

G

Gas (pneumothorax, pneumomediastinum, subcutaneous emphysema, pneumopericardium, pneumoperitoneum)

H

Heart and pericardial abnormalities (contusion, hemopericardium)

H

Hemothorax, hematoma, and hemorrhage

I

Iatrogenic injuries

From Gurney JW. ABCs of blunt chest trauma. In: Thoracic imaging, 1996. Reston, VA: Society of Thoracic Radiology, 1996:349–352, with permission.

Remember the portable trauma chest radiograph is a screening tool used to guide and determine the need for additional imaging studies, usually CT. Aortic injuries, cardiac tamponade, and tension pneumothorax are the most immediate life-threatening conditions—followed closely by TBIs, esophageal injuries, hemothorax or hematoma caused by systemic arterial injuries, and flail chest. The diagnoses of diaphragmatic injuries, pericardial effusions, and thoracic duct injuries are often initially missed or delayed and may require serial studies. Positive pressure ventilation exacerbates TBIs and pneumothoraces and can also delay the appearance of a diaphragmatic hernia.

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