Blunt Chest Trauma




Nonmediastinal Injury


Chest trauma is directly responsible for 25% of all trauma deaths and is a major contributor in another 50% of all trauma mortality. Chest trauma may be blunt (90% of cases) or penetrating. Blunt thoracic injuries are the third most common injuries in polytrauma patients, following those of the head and extremity. Although 50% of blunt chest injuries are minor, 33% will require hospital admission. Rib fractures and pulmonary contusions are the most common injuries encountered. A chest radiograph is generally the first modality of radiologic evaluation of the chest trauma patient. It is essentially a screening examination and is used to identify life-threatening conditions such as a large hemothorax, tension pneumothorax, dangerously malpositioned lines and tubes, and mediastinal hematoma. Contrast-enhanced (CE) chest computed tomography (CT) is the gold standard for radiologic evaluation of the chest trauma patient. This chapter will review the spectrum of radiographic and CT imaging findings seen in patients sustaining major thoracic trauma, including the lungs, pleura, bones, and mediastinal structures.




Lung Injury


Pulmonary Contusion


Pulmonary contusions are the most common pulmonary injury and occur in 17% to 70% of blunt chest trauma patients, most commonly from motor vehicle collisions or falls from height. A pulmonary contusion results from injury to the alveolar wall and pulmonary vessels, allowing blood to leak into the alveolar and interstitial spaces of the lung. The causes are thought to include compression of the lung against the chest wall, shearing forces, rib fracture, or previously formed pleural adhesions tearing peripheral tissue as the lung separates from the chest wall at impact. Blast injuries also commonly cause pulmonary contusion.


The appearance of pulmonary contusion on the chest radiograph depends on its severity. Minimal contusion may not be visible or may appear as an ill-defined area of patchy air space opacity ( Fig. 8-1 ). Severe contusion may appear as consolidation of a large area of lung ( Fig. 8-2 ). Air bronchograms may be seen in contused lung if there has not been filling of the airways with blood. Pulmonary contusion is typically nonsegmental and geographic, and it readily crosses pleural fissures, unlike pneumonia or atelectasis.




Figure 8-1


Supine chest radiograph of a patient struck by a motor vehicle.

There is patchy, ill-defined opacity in the peripheral aspect of the right midlung (arrow) . Note adjacent right-sided rib fractures. Although commonly seen in association with pulmonary contusion, fractures need not be present, especially in the more compliant bones of the pediatric population.



Figure 8-2


Supine chest radiograph of a patient involved in motorcycle accident.

There is diffuse air-space opacification throughout the entire right lung, indicating severe, widespread pulmonary contusion. Note is made of right mainstem endotracheal tube intubation.


Compared with radiography, CT is much more sensitive in detection of pulmonary contusion ( Fig. 8-3 ). The appearance of pulmonary contusion may be delayed up to 6 hours on chest radiography but is seen immediately on chest CT. The CT appearance is similar to that of chest radiography. Minimal contusion may manifest as ground-glass density, often with subpleural sparing of 1 to 2 mm (especially in the pediatric population), often in the periphery of the lung or adjacent to bony structures such as the spine (see Fig. 8-3 ). On both radiography and CT, pulmonary contusion often “blossoms” in the first 24 to 48 hours after the injury as blood progressively accumulates in the lung parenchyma ( Figs. 8-4 and 8-5 ).




Figure 8-3


Supine chest radiograph of a trauma patient.

A, Essentially clear lungs. B, Computed tomography (CT) of the same patient demonstrates a small to moderate amount of peripheral contusions in both lungs, right greater than left (arrows) . Note the 1 to 2 mm of subpleural sparing, a common finding in pulmonary contusion but not in other air-space processes such as pneumonia.



Figure 8-4


Chest computed tomography (CT) of a patient involved in motor vehicle collision.

There is extensive pulmonary contusion throughout the entire visualized right lung. The pleural fissures are not respected in pulmonary contusion. Note air bronchograms (arrow) and subpleural sparing (arrowhead) .



Figure 8-5


Chest radiograph of a patient who fell off a roof.

Pulmonary contusion in the mid and lower portions of the right lung. Note a small right pneumothorax and subcutaneous air in the right chest wall.


Contusions are a risk factor for development of pneumonia or acute respiratory distress syndrome. Patients with contusions seen only on the CT image and not on the chest radiograph may have a prognosis similar to those that do not have pulmonary contusions at all on CT (i.e., “CT-only” contusion may have a better outcome than contusions that are visible on both CT and chest x-ray examination). Pulmonary contusion usually resolves in 1 to 14 days ( Fig. 8-6 ). Generally, if the chest radiograph or CT has not cleared by day 14, alternate diagnoses such as development of pneumonia, acute respiratory distress syndrome, or aspiration should be considered.




Figure 8-6


Chest radiograph of a patient involved in a jet-ski accident.

A, Minimal patchy opacity and a large oval lucency (arrows) in the midportion of the left lung. Axial ( B ) and coronal ( C ) computed tomographic (CT) images better show the minimal pulmonary contusion in the left lung, a large pulmonary laceration (arrow) , and at least two smaller pulmonary lacerations (arrowheads) . A left pneumothorax is noted.


Pulmonary Laceration


The mechanism of injury causing a pulmonary laceration is thought to be similar to that of pulmonary contusion: tearing of lung parenchyma due to compression, shearing forces, direct injury from rib fracture(s), or at the site of previously formed pleural adhesions. Pulmonary lacerations are round or oval in shape due to the elastic recoil of the lung ( Fig. 8-7 ). There may be single or innumerable lacerations with size ranging from a few millimeters to several centimeters in diameter ( Fig. 8-8 ). Air, blood, or both may fill in the laceration (see Fig. 8-5 ), and there will often be a thin pseudomembrane due to the compression of surrounding lung tissue. On the chest radiograph, pulmonary lacerations are often obscured for the first 48 to 72 hours because of surrounding pulmonary contusion (see Fig. 8-6 ). Computed tomography is much more sensitive in detection of pulmonary lacerations compared with radiography.




Figure 8-7


Chest computed tomography (CT) of a patient who fell out of a moving vehicle shows multiple pulmonary lacerations of various sizes in the right lower lobe. Note that pulmonary lacerations may be filled with blood (short arrow) , air (arrowhead) , or both (long arrow) , in which case a meniscus sign is seen. Patchy pulmonary contusion surrounds the lacerations.



Figure 8-8


Chest radiograph of a patient who was hit by a train.

A, Extensive pulmonary contusion throughout the right lung and upper medial aspect of the left lung. B, Computed tomography (CT) demonstrates presence of pulmonary lacerations in right lower lobe (arrows) , findings not seen on the chest radiograph.


Active bleeding into a pulmonary laceration may occasionally be seen. On intravenous (IV) CECT active bleeding will appear as linear high density, with Hounsfield units (HU) similar to that of the aorta, within or adjacent to the laceration ( Fig. 8-9 ). A pulmonary laceration will typically take several weeks or months to resolve. During healing the laceration will gradually fill completely with blood and then gradually decrease in size ( Fig. 8-10 ). A blood-filled rounded healing pulmonary laceration could be mistaken for a pulmonary neoplasm if the history of relatively recent chest trauma is not known.




Figure 8-9


Arterial phase chest computed tomography (CT).

A, A large oval pulmonary laceration in the right lower lobe (arrows) that is nearly completely filled with blood. B, There are several small foci of high density along the right lateral margin of the laceration (arrow) that increase in size and remain dense on the portal venous images. These findings indicate active bleeding within the laceration.



Figure 8-10


Admission chest computed tomography (CT) of a patient kicked by a horse.

A, Multiple pulmonary lacerations in left lower lobe (arrows) with surrounding pulmonary contusion. B, Follow-up chest CT obtained 2 months later shows near complete resolution of multiple pulmonary lacerations. A single, blood-filled residual laceration is seen (arrow) . Small left hemothorax and healing left rib fractures are noted.


An uncommon complication of a pulmonary laceration is formation of a bronchopleural fistula. This condition is more likely to occur if the laceration is in the periphery of the lung, with only the thin pseudomembrane between it and the pleural space. Bronchopleural fistula should be suspected if there is a persistent pneumothorax, unrelieved by appropriately positioned single or multiple chest tubes. Rarely, a pulmonary abscess may complicate a pulmonary laceration.




Injuries Involving the Pleural Space


Pneumothorax


A pneumothorax is a collection of air in the pleural space. Air may enter the pleural space during trauma because of penetrating injury from a knife or gunshot, puncture from a fractured rib, rapid deceleration forces causing pulmonary laceration, or alveolar rupture from suddenly increased intrathoracic pressure at the time of impact.


The appearance of a pneumothorax on the chest radiograph will depend greatly on the patient position. The initial chest radiograph of the trauma patient is usually a supine film obtained in the emergency department or trauma bay. When the patient is in the supine position, air will collect in the anterior and medial aspects of the pleural space. On the chest radiograph this may manifest as increased lucency over the lower thorax/upper abdominal quadrant ( Figs. 8-11 and 8-12 ), a deep costophrenic angle sign ( Fig. 8-13 ), or a sharply defined border of the heart or diaphragm. The “double diaphragm” sign, seen when air in the pleural space outlines both the dome and the anterior insertion of the diaphragm, may also be identified. A thin lucency adjacent to the heart border may also be seen and represents air between the medial lung margin and the soft tissues of the mediastinum ( Fig. 8-14 ). In the upright patient a pneumothorax is typically seen as a thin, sharply defined line of the visceral pleura with no lung markings beyond this border ( Fig. 8-15 ).




Figure 8-11


Supine chest radiograph of a patient struck by a moped.

A, There is a thin rim of lucency above the right hemidiaphragm (arrow) , suspicious for inferior pneumothorax. Air in the soft tissues of the right lateral chest wall is another clue that pneumothorax may be present (arrowheads) . B, Coronal reformatted chest computed tomographic (CT) image confirms the presence of a small right inferior pneumothorax (arrow) .



Figure 8-12


Supine chest radiograph of a patient involved in a motor vehicle collision.

There is increased lucency of the left upper quadrant (long arrows) , indicating presence of a left pneumothorax. Also note a small residual right inferior pneumothorax after placement of right-sided chest tube (short arrow) .



Figure 8-13


Supine chest radiograph of a trauma patient demonstrates increased lucency of the right lower hemothorax ( arrows ) producing deep costophrenic sulcus indicating pneumothorax.



Figure 8-14


Supine chest radiograph of a patient involved in four-wheeler accident demonstrates several signs of pneumothorax: lucency between medial lung and heart border (long arrow) , deep costophrenic sulcus sign and hyperlucent right upper quadrant (arrowheads) , and the thin linear density over the right upper lung field with no lung marking distal to this line (short arrow) .



Figure 8-15


Supine chest radiograph of a patient who fell from a balcony demonstrates the typical signs of a pneumothorax: a thin dense line along the periphery of the right hemithorax with no lung markings beyond this line (short arrow). There is also a tiny left apical pneumothorax (long arrow) . Note right rib fractures.


There are numerous mimics of pneumothorax on chest radiography, including bullae, skin folds ( Fig. 8-16 ), bedding or clothing, and overlying tubes or catheters. Computed tomography is much more sensitive for detection of pneumothorax. It is estimated that up to 78% of pneumothoraces are missed by chest radiography.




Figure 8-16


Semiupright chest radiograph of a trauma patient shows a linear density along the periphery of the left hemithorax (arrow) , which upon casual inspection would be suspicious for a pneumothorax. However, there are lung markings distal to this line and two additional linear densities medial to the first (arrowheads) . These findings are due to folds of skin or bedding, and not a pneumothorax.


Generally a chest tube is placed for all pneumothoraces seen on the supine chest radiograph or in any unstable patient with a potential pneumothorax. Occult pneumothorax, defined as a pneumothorax seen only on chest CT and not on the supine chest radiograph, is thought to occur in up to 15% of blunt chest trauma patients ( Fig. 8-17 ). Optimal management of the occult pneumothorax is currently debated. It was previously thought that an occult pneumothorax required a prophylactic chest tube because of risk for enlargement or development of tension pneumothorax, especially in patients on mechanical ventilation. There is growing evidence that a small occult pneumothorax can be safely managed in the majority of patients with close observation, without thoracostomy tube placement. About 10% of patients managed using this guideline will fail conservative management and ultimately require thoracostomy tube placement for symptomatic pneumothorax.




Figure 8-17


Supine chest radiograph of a patient involved in a farming accident.

A, Only a small amount of subcutaneous air in the soft tissues of the left chest wall (arrows) . B, Axial chest computed tomographic (CT) image demonstrates a left pneumothorax (arrow) in addition to the soft tissue air. This would be considered an occult pneumothorax because there were no definite signs of pneumothorax on the supine radiograph.


A tension pneumothorax occurs because of a one-way valve mechanism in which air can enter the pleural space but cannot get out. This results in rapid and progressive accumulation of air in the pleural space with increasing pressure causing contralateral shift of the mediastinum and compression of the vena cavae resulting in decreased cardiac output from impaired venous return ( Fig. 8-18 ). Note that tension pneumothorax is a clinical diagnosis but can be suggested by radiologic signs of increased lucency of the affected hemithorax, contralateral shift of the mediastinum, widened ipsilateral rib interspaces, depression of the ipsilateral hemidiaphragm, and lung collapse toward the hilum. Treatment is immediate decompression with chest tube thoracostomy. Rapid reexpansion of the lung after treatment of tension pneumothorax can lead to pulmonary edema. This occurs immediately after treatment of the pneumothorax and may be unilateral or bilateral. This condition occurs more commonly in patients 20 to 50 years of age. Although tension pneumothorax may be completely asymptomatic, there is a reported mortality rate of up to 20%. If there is persistent pneumothorax or air leak after chest tube placement, incorrect tube placement, bronchopleural fistula, or tracheobronchial injury should be suspected ( Fig. 8-19 ).




Figure 8-18


Chest radiograph shows signs suspicious for the clinical diagnosis of a tension pneumothorax: right lung collapsed toward the hilum with decreased density around the collapsed lung, deep costophrenic angle sign, depressed right hemidiaphragm, and shift of mediastinum to the left. Clinically the patient had severe dyspnea and hypotension that was relieved with chest tube placement.



Figure 8-19


Frontal chest radiograph of a trauma patient.

A, A pneumothorax persists (long arrow) despite the presence of a left chest tube. Note that the distal side hole of the chest tube projects outside of the bony thorax (short arrow) and could be responsible for the residual pneumothorax. B, Chest computed tomography (CT) on soft tissue windows shows the position of the chest tube to be in the subscapular space (arrow) . C, Lung window CT shows the residual left pneumothorax (arrow) .


Hemothorax


Hemothorax is seen in 50% cases of blunt chest trauma. Sources of bleeding can be the intercostal arteries, thoracic spine, lung, great vessels, or heart. Hemothorax can also occur with hemoperitoneum and concurrent ruptured diaphragm.


On chest radiography at least 150 to 200 mL of blood are needed to detect pleural fluid on an upright chest radiograph. A meniscus sign is often seen with pleural fluid of any type and appears as a concave sloping of fluid in the costophrenic angle toward the lateral chest wall. A straight air-fluid level indicates hemopneumothorax. Because most trauma chest radiographs are performed with the patient in the supine position, blood will collect in the dependent portion of the thorax. A hemothorax will be seen on the supine film as a diffuse increase in density over the entire hemithorax. A dense rim of blood may be seen along the lateral lung margin as blood progressively fills the dependent pleural space and compresses the lung medially ( Fig. 8-20 ). A very large hemothorax can cause complete opacification of the affected hemithorax with contralateral shift of the mediastinum ( Fig. 8-21 ).




Figure 8-20


Supine chest radiograph of a patient who fell.

A, Mild increase in density of the entire right hemithorax. B, Axial chest computed tomographic (CT) image shows blood accumulating in the dependent portion of the right pleural space. A meniscus sign is seen as blood slopes up toward the lateral chest wall (arrow) .



Figure 8-21


Tension hemothorax.

Chest computed tomography (CT) of a trauma patient shows a large left hemothorax causing shift of the mediastinum to the right, findings concerning for the clinical diagnosis of tension hemothorax.


On CT, acute hemothorax is seen as hyperdense fluid in the dependent portion of the pleural space. Hounsfield units of acute hemorrhage will be higher than 15, generally in the range of 20 to 45 HU. Slightly higher density in the dependent portion of the hemothorax may be seen because of settling of blood products. As blood clots, the density of the blood increases to 50 to 90 HU. If there is intermittent bleeding in the pleural space, layers of different densities may be seen, constituting the “hematocrit effect.” Active bleeding within the pleural space will appear as a linear tract of high density (within 10 HU of the IV CE aorta) within the pleural space ( Fig. 8-22 ). Angiography with selective embolization may be used for treatment of active bleeding or pseudoaneurysm ( Fig. 8-23 ). The exact site of bleeding needs to be determined whether surgery or catheter embolization is the chosen treatment.




Figure 8-22


Supine chest radiograph of a patient involved in a motor vehicle collision.

A, Opacification of the entire right hemithorax and a thin rim of density along the lateral margin of the right lung (arrow) , indicating right hemothorax. B, Arterial phase chest computed tomography (CT) shows the “hematocrit effect” of layers of slightly different densities in the right pleural space (short arrows) , indicating intermittent bleeding. A hyperdense focus is seen in the periphery of the hemothorax (long arrow) . C, On the portal venous phase CT image this focus remains hyperdense and increases in size, indicating active bleeding (arrow) . D, Selective intercostal angiography image shows active bleeding (arrow) from the right tenth intercostal artery. This was treated with angiographic embolization.



Figure 8-23


Chest radiograph of patient who had undergone median sternotomy one week previously for treatment of traumatic mediastinal injury.

A , Extensive right pleural effusion slightly displacing the heart to the left. B, Axial contrast-enhanced (CE) chest computed tomography (CT) demonstrates fluid of different densities layering in the right thorax (arrowheads) with significant compression of the right lung. A more peripheral rim of lower density indicates more acute hemorrhage (short arrow). There is a lobular appearance of the right internal mammary artery (long arrow). C, Three-dimensional (3-D) reformatted CT image confirms the presence of a traumatic pseudoaneurysm of the right internal mammary artery (arrow).


Simple or serous effusion, bile, chyle, and urine may also accumulate in the pleural space. A sympathetic serous effusion may be seen if there are injuries to the liver, spleen, or pancreas and will have HU density less than 15. Chylous effusion is due to an injury to the thoracic lymphatic duct and may have negative HU density because of the presence of fat. An effusion composed of bile or urine is seen with injury to the biliary or urinary system and a concurrent full-thickness diaphragm tear. Differentiating between bile and urine on CT can be very difficult and may require thoracentesis and analysis of fluid to establish the correct diagnosis ( Fig. 8-24 ). Delayed imaging of the renal collecting system may also be diagnostic if direct contrast leak is identified.




Figure 8-24


A more unusual cause of fluid in the pleural space.

A, Contrast-enhanced (CE) chest computed tomography (CT) shows a malpositioned right central venous catheter ( arrow ). B, CT image of the lower hemithorax shows the very hyperdense tip of the central venous line in the posterior aspect of the hemithorax ( arrow ) surrounded by ill-defined, slightly less dense material. C, Another axial CT image slightly lower in the chest shows active bleeding. D, A coronal reformatted CT image show that the dense material is in the pleural space ( arrow ). These findings represent intravenous (IV) contrast material in the right pleural space secondary to malpositioned right subclavian central venous catheter.


Extrapleural Hematoma


Extrapleural hematoma refers to blood that has collected between the parietal pleural and endothoracic fascia. The cause is usually a rib fracture that has lacerated an intercostal artery. On chest radiograph an extrapleural hematoma typically appears as a focal convex mass along the periphery of the lung. It may also be seen at the lung apex after subclavian vessel trauma or aortic injury ( Fig. 8-25 ). Unlike a pleural effusion or a hemothorax, an extrapleural hematoma will not change shape with a change in patient position. On CT an extrapleural hematoma appears as a fluid collection that causes inward displacement of the extrapleural fat ( Fig. 8-26 ). Active bleeding within the hematoma may be seen and can be treated with angiographic embolization.




Figure 8-25


Chest radiograph of a trauma patient who just had a right subclavian central venous catheter placed.

A rim of increased density along the apex of the right lung (arrows) .



Figure 8-26


Computed tomography (CT) of a multitrauma patient.

A, An oval high-density collection representing extrapleural hematoma adjacent to the posterior right ribs (arrow) . Note the thin rim of fat that separates it from the lung (arrowheads) . B, Sagittal reformatted CT again demonstrates the extrapleural hematoma (long arrow ), thin rim of extrapleural fat anterior to the hematoma and the probable cause of the hematoma: a right posterior rib fracture (short arrow) .




Bony Thorax and Chest Wall


Soft Tissue Contusion


Soft tissue contusion or hematoma may be arterial or venous in origin. A hematoma from a high-pressure arterial injury may enlarge rapidly, whereas a hematoma from a low-pressure venous injury is usually self-limited. The trauma patient who is taking anticoagulants is at higher risk for developing a soft tissue contusion or hematoma from minor trauma.


On the chest radiograph a soft tissue contusion is not usually apparent unless there is a large amount of associated soft tissue hematoma. A large amount of hematoma may appear as increased density of the soft tissues or asymmetry of the soft tissues when compared to the uninjured side. Extensive soft tissue hematoma affecting one side of the chest wall can be hard to distinguish from a layering hemothorax on the supine chest radiograph. Excess soft tissues in an obese patient or a female patient with large breasts may mimic or obscure a chest wall hematoma.


The appearance of chest wall soft tissue trauma on CT will depend on the severity of the injury and can range from minimal fat stranding of the chest wall to a large hematoma with or without active bleeding ( Fig. 8-27 ). A seatbelt mark, identified as soft tissue bruising on the lower neck and center chest, is often seen in patients injured in motor vehicle collisions. The presence of a seat belt bruise or hematoma in the neck may be a marker for underlying cervical vessel injury, and a neck CT angiography may be warranted for further evaluation.




Figure 8-27


Chest radiograph of a female trauma patient.

A, Extensive chest injuries, including scattered left pulmonary contusion, soft tissue air in left chest wall, and left clavicle and bilateral rib fractures. A right mainstem endotracheal tube intubation is also noted. B, Axial chest computed tomographic (CT) image shows a large hematoma in the left breast with central foci of linear high density (arrow) , indicating active bleeding.


Rib Fractures


Rib fractures are the most common thoracic skeletal injury in blunt chest trauma, with an incidence of 50%. Rib fractures are most commonly the result of a motor vehicle collision in the adult patient. Rib fractures in older adults are most commonly due to falls. The lateral aspects of the ribs are the site most commonly fractured because of the chest wall architecture and decreased muscular support in this region. Chest radiography has sensitivity as low as 15% for detection of rib fractures. Computed tomography has a much higher sensitivity, especially when coronal reformatted images are reviewed.


Fractures of the eighth to eleventh ribs are associated with a higher incidence of injury to the spleen (left-sided fractures) or liver (right-sided fractures). When CT is obtained in the trauma patient with lower rib fractures, a routine search for injury involving these organs should be performed. Fractures of the first, second, and third ribs indicate high-velocity trauma and are associated with brachial plexus or subclavian vessel injury in 3% to 15% of blunt chest trauma patients. The rib number and site of each rib fracture should be specified in the radiology report because this provides prognostic information to the trauma surgeon. It has been shown that mortality increases 19% and pneumonia increases 27% in elderly patients with each additional rib fracture.


Flail chest, seen in 6% of blunt trauma patients, indicates the presence of at least two fractures in three or more consecutive ribs ( Fig. 8-28 ). Flail chest is associated with a mortality of 33%. The chest wall instability, paradoxical motion of the fractured segment, and invariable presence of underlying pulmonary contusion cause altered pulmonary mechanics that lead to atelectasis, stasis of secretions, and pneumonia. Recent research shows that open reduction and internal fixation of flail chest may lead to improved outcomes.




Figure 8-28


Admission chest radiograph of a patient involved in a motorcycle collision.

A, Significant chest trauma, including a right pneumothorax, scattered bilateral pulmonary contusions, soft tissue air in the left chest wall, and multiple bilateral rib fractures. B, Three-dimensional (3-D) reformatted computed tomographic (CT) image of the chest better demonstrates the presence of multiple rib fractures. Analysis of the number and site of rib fractures indicates presence of a flail chest.


Sternal Fractures


Sternal fractures are seen in 3% to 8% of blunt chest trauma patients. Fractures of the sternum are high-impact injuries. Motor vehicle collision is the most common cause, and the injury is usually due to the chest striking the steering wheel or the airbag impacting the chest wall. Sternal fractures are associated with rib fractures, cardiac contusion (1.5% to 6%), pericardial effusion, and cervicothoracic spine injuries. Although commonly associated with additional injuries, a nondisplaced sternal fracture can be seen as an isolated injury.


The supine chest radiograph will rarely demonstrate the fractured sternum unless the sternum is significantly displaced laterally. A properly exposed lateral chest radiograph, though rarely obtained in the acute trauma setting, will usually permit identification of at least mildly displaced fractures. Axial CT images will demonstrate most but not all sternal fractures. A clue on the axial CT images that there may be a sternal fracture is the anterior mediastinal or retrosternal hemorrhage that accompanies nearly all of these fractures. There will be a preserved fat plane between the posterior aspect of the retrosternal blood and the aorta ( Fig. 8-29 ). Traumatic aortic injury can also be a source of anterior mediastinal hemorrhage, but there will be no preserved fat plane and hemorrhage will be in direct contact with the aortic wall. Sagittal and coronal reformatted CT images are a significant aid in detection of a sternal fracture ( Figs. 8-30 and 8-31 ). Treatment is conservative in the vast majority of cases. Rarely, nonunion, severe pain, or sternal instability may require open reduction and internal fixation.




Figure 8-29


Axial computed tomographic (CT) image of patient involved in a motor vehicle collision shows a sagittal fracture of the sternum (short arrow) . There is a small amount of anterior mediastinal hemorrhage (MH) in association with the fracture (long arrow) . Note the preserved fat plane between the hemorrhage and the anterior aortic wall.



Figure 8-30


Sagittal reformatted computed tomographic (CT) image shows a severely comminuted but minimally displaced sternal fracture (arrowheads) . A Chance fracture of the lower thoracic spine is noted.



Figure 8-31


Sagittal reformatted computed tomographic (CT) image of a patient involved in a motor vehicle collision.

A, An oblique fracture of the manubrium (arrow) and a small amount of retrosternal blood (arrowheads) . B, Coronal three-dimensional (3-D) reformatted image shows the extent of the fracture across the manubrium (arrow) .




Mediastinal Injury


Tracheobronchial Injury


Tracheal and bronchial injuries from blunt trauma are rare. Actual full-thickness tears are more common in the thoracic than cervical segment and are associated with higher mortality. Most transbronchial tears occur close to the carina and more frequently on the right ( Fig. 8-32 ). Ruptures usually occur in the weaker posterior membranous portion. Mechanisms of the injury involve anterior-posterior compression of the chest forcing the lungs and mainstem bronchi laterally near the carina and exceeding the connective tissue strength of the airway, a sudden rise in intraluminal pressure when the glottis is closed, or by direct trachea crushing between the sternum and spine. The cervical portion can be sheared in rapid deceleration between the relatively immobile carina and cricoid and the more flexible trachea in between, by direct impact, or with sudden hyperextension and longitudinal traction. Tears typically occur across the weaker transverse plane. Injury can also result from a linear force applied across the cervical airway from a “clothesline” horizontal force when the neck impacts fixed linear obstacles like ropes, tree limbs, or wires ( Fig. 8-33 ).




Figure 8-32


Mainstem bronchus injury.

Coronal multidetector computed tomography (MDCT) reformation demonstrates complete cutoff across right mainstem bronchus (arrow) . There is diffuse lung contusion, mainly in the right upper lobe and pneumomediastinum, well seen around the aorta and subcarinal region. The left lower lobe is collapsed.



Figure 8-33


Transverse laceration of the trachea of a young man riding a motorcycle through backyards sustaining an actual “clothesline” laceration.

A, Axial computed tomographic (CT) image across high cervical trachea shows overdistention of endotracheal balloon (red arrows) and extraluminal air anteriorly (white arrow) . B, Sagittal reformatted parasagittal image through the left side of the neck shows extraluminal air in anterior neck (red arrow) , thrombus, and dissection of distal common and left internal carotid artery (white arrow) , and linear soft tissue laceration through posterior cervical muscles (black arrow) . The patient survived the injury with restoration of airway and without cerebral injury. C , Three-dimensional (3-D) image better demonstrates overdistended balloon in ruptured trachea.


The injury may be suggested by clinical signs/symptoms, including hemoptysis, cough, respiratory distress, cyanosis, subcutaneous air, hoarseness, aphonia/dysphonia from recurrent laryngeal nerve injury, and the Hamman “crunch” sign, when cardiac motion impacts adjacent mediastinal air. These findings are neither sensitive nor specific and may not be present with small or incomplete tears. Because of their rarity and other more overt coincident injuries, airway injuries are not suspected based on bedside findings and may be recognized only by imaging or when overt clinical complications arise.


Radiologic findings are more likely when there is positive pressure ventilator support. Air leaks into the mediastinum usually progress rapidly through tissue planes of the chest and beyond along fascial planes throughout the body. Pneumothorax can occur through dissection of air through the lung interstitium and visceral pleura, particularly from peripheral lung tears or through a direct tracheobronchial fistula ( Fig. 8-34 ). A finding suggesting a major airway-pleural communication is failure of a properly placed thoracostomy tube to relieve a simple or tension pneumothorax. When a major airway is breached, air enters the pleural space at the same rate it is evacuated by suction, maintaining the pneumothorax at constant pressure ( Fig. 8-35 ). Rarely an abrupt interruption or irregular tapering of the airway (bayonet sign) can be directly visualized radiographically. If there is a complete mainstem bronchial disconnection, the entire distal lung may collapse and fall into a gravity-dependent position (fallen lung; see Fig. 8-35 ). Airway interruption from blood clot or lacerated tissue occlusion will lead to persistent distal atelectasis.




Figure 8-34


Bronchopleural fistula.

Contrast-enhanced (CE) axial computed tomographic (CT) image in a blunt trauma patient reveals peripheral left upper lobe lung laceration with central hematoma creating trachea-to-pleural space connection (arrow) . There is a large pneumothorax despite a chest tube.



Figure 8-35


Completely torn right mainstem bronchus.

A, Anteroposterior (AP) chest radiograph demonstrates a right tension pneumothorax with depression of right hemidiaphragm, displaced heart and mediastinum to the left, and spread right ribs. A chest tube that was appropriately placed overlies the right hemithorax, and the right lung is partially collapsed. B, Coronal slab three-dimensional (3-D) image highlights complete cutoff of right mainstem bronchus (arrow) .


If the cervical trachea is disrupted, an inflated endotracheal tube cuff may overexpand into the weakened or torn wall, producing an overdistended or caudally displaced balloon ( Fig. 8-36 ; see Fig. 8-32 ). A normally inflated balloon cuff is barely visualized radiographically. The course of the endotracheal tube may rarely deviate from the expected path of the trachea through a wall defect. Small portions of the balloon cuff may protrude/herniate through small tears.




The vast majority of blunt trauma patients with rapid onset and progressive mediastinal air leaks will NOT have injury to a major airway, but positive pressure respiratory support combined with lung laceration. Pneumomediastinum can be absent despite major airway injury when the adventitia remains intact or the tear is occluded by clot or an endotracheal tube balloon.




Figure 8-36


Direct tracheal tear.

A, Axial contrast-enhanced computed tomography (CECT) indicates hyperdistended endotracheal tube balloon cuff (black arrows) and focal linear tear in right lateral wall of thoracic trachea (white arrow) . There is surrounding pneumomediastinum. B, Coronal slab three-dimensional (3-D) image verifies overdistended balloon cuff (arrows) and marked soft tissue air.

(From Mirvis SE, Shanmuganathan K, Miller LA, et al. Case 89. Emergency Radiology . Case Review Series. Philadelphia, PA: Mosby Elsevier; 2009:181.)


Computed tomography will display the same signs as chest radiographs with greater sensitivity and can detect airway tears directly ( Figs. 8-36 to 8-38 ). Major airway injuries can occur in association with clavicular, sternal, upper rib, and vertebral body extension fractures, but these are nonspecific indicators of airway injury and principally indicate a high level of impacting force. Concurrent major vascular injuries should be sought as indicated by mediastinal blood given the same chest compression or a shearing force mechanism of injury responsible for some cases of major airway disruption.




A large amount of mediastinal air around the trachea and mainstem bronchi does not indicate adjacent airway injury, but direct visualization of an airway-mediastinal connection is diagnostic.




Figure 8-37


Direct tracheal tear .

A and B, Axial contrast-enhanced computed tomographic (CECT) images through the carina shows a posterior defect in the membranous trachea (arrows) with adjacent mediastinal air and bilateral posterior mediastinal hematoma.



Figure 8-38


Airway injury at the carina.

A, Axial computed tomographic (CT) image indicates an irregular lumen at level of the carina (arrow) in a blunt trauma patient. B, Coronal volumetric view through the carina verifies a tear and its proximity to the carina. Injury was verified bronchoscopically and successfully managed nonoperatively.


The diagnosis of complete airway disruption can be supported by volumetric rendering, including endoluminal views (virtual bronchoscopy; see Figs. 8-32, 8-34, 8-37 ) or verified with bronchoscopy. Earlier diagnosis of this injury improves the chances for successful surgical airway repair, preserving pulmonary function, and preventing long-term complications of chronic airway narrowing.




Esophageal Injury


Esophageal injury sustained from blunt chest trauma is extremely rare. The injuries occur in the cervical and upper thoracic portions below the cricopharyngeal muscle and at the gastroesophageal junction, where there are transition points between relatively fixed and mobile segments. Not surprisingly, given the central protected location of the esophagus, injury typically requires high-force impacts and thus is likely to be accompanied by other thoracic injuries ( Fig. 8-39 ). Injury mechanisms include crushing between the impacted anterior chest wall and the spine, hyperextension of the spine mainly at the diaphragmatic hiatus, and laceration or entrapment related to fractures or dislocations of the thoracic spine ( Fig. 8-40 ). A sudden increase in intraesophageal pressure by compressive forces may also cause rupture. Injuries are typically in the proximal right posterior and distal left posterior portions. Radiographic signs of full-thickness injury are often absent early but could include pneumomediastinum, left pleural effusion, and abnormal mediastinal contour related to leakage of esophageal content or associated mediastinal hemorrhage. An atypical course of a nasogastric tube traversing a tear is another rare indirect radiologic finding.


Jun 30, 2019 | Posted by in EMERGENCY RADIOLOGY | Comments Off on Blunt Chest Trauma
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