MDCT PROTOCOL FOR SUSPECTED THORACIC INJURY

Chest CT scans for suspected thoracic trauma should be performed with intravenous contrast material in order to demonstrate any sites of active bleeding and to opacify the heart, aorta, and thoracic blood vessels. CT scanning of the chest following trauma is best performed in the arterial phase after a 25- to 30-second delay. Scans should be acquired at thin detector configurations so that high-quality multiplanar volumetric reformations and a CT arteriogram can be produced from the thin axial images. Routine coronal and sagittal reformations of the chest are recommended on all chest trauma patients in order to better demonstrate injuries, particularly injuries to the major vessels, diaphragm, or spine, which are best shown on these planes. A detector configuration of 16 • 1.25 mm is preferable for 16-slice scanners, while 64-slice scanners would utilize axial slices having less than 1-mm thickness. The thin slices may be reformatted to 2.5 mm for viewing axial slices and transmitted to the Picture Archival Computer System (PACS) along with the coronal and sagittal reformations for formal examination interpretation. All axial and multiplanar images should be reviewed on soft tissue, lung, and bone windows.

INJURIES OF THE PLEURAL SPACE

A hemothorax, blood in the pleural space, may result from injury to the chest wall, diaphragm, lung, or mediastinal structures. CT may confirm a hemothorax when a pleural fluid collection in a trauma patient seen on CT measures blood density over 35 to 40 Hounsfield units (HU) (Fig. 2-1). A pneumothorax, air in the pleural space, may result from a lung injury, tracheobronchial injury, or esophageal rupture. The most common cause is lung injury associated with a rib fracture. A pneumothorax occurs in about 15% to 40% of patients with acute chest trauma. Many small and even moderate-sized pneumothoraces that are not visible on the supine chest film may be identified on CT. A pneumothorax seen on CT that cannot be identified on a supine chest film is referred to as an “occult” pneumothorax. Studies estimate that 10% to 50% of pneumothoraces seen on CT are not evident on the supine anteroposterior film. Radiographic signs of pneumothorax may be subtle. In the supine patient air collects in nondependent locations such as the anterior costophrenic sulcus. This region extends from the seventh costal cartilage to the eleventh rib in the midaxillary line. The air collection appears as an abnormal lucency in the lower chest or upper abdomen, frequently referred to as the “deep sulcus” sign. Additional signs of pneumothorax in a supine patient include a sharply outlined cardiac or diaphragmatic border and depression of the hemidiaphragm (Fig. 2-2). Detection of even a small pneumothorax is important as it may enlarge during positive-pressure ventilation or general anesthesia. A tension pneumothorax is an emergency condition resulting from a lung or airway injury associated with a one-way accumulation of air within the pleural space. As intrapleural pressure rises the mediastinal structures are compressed, decreasing venous return to the heart, leading to hemodynamic instability. Radiography and CT will show mediastinal shift to the contralateral hemithorax, hyperexpansion of the ipsilateral thorax, and depression of the ipsilateral hemidiaphragm.

Figure 2-1 A, Axial CT shows high-density blood layering within the pleural space consistent with a hemothorax (black arrow). Red arrow indicates adjacent opacified lung. B, Sagittal image shows both hemothorax (black arrow) and opacified lung (white arrow).

Figure 2-2 A, Anteroposterior chest radiograph findings of tension pneumothorax including the “deep sulcus” sign (black arrow), sharply outlined cardiac and diaphragmatic border (arrowhead), and depression of the hemidiaphragm (white arrow). Note rightward deviation of the mediastinum consistent with tension. B, Axial image from MDCT demonstrates air collecting nondependently in the anterior costophrenic sulcus. Note rightward deviation of the heart indicating developing tension. C, Coronal image demonstrates depression of the hemidiaphragm and rightward deviation of the mediastinum. D, Chest tube placement results in normal positioning of the hemidiaphragm and mediastinum.

ESOPHAGEAL INJURIES

Blunt trauma to the esophagus is extremely rare since this structure is well protected in the posterior mediastinum. Most esophageal injuries occur from penetrating or iatrogenic trauma. Blunt trauma may result in rupture or intramural hematoma. These injuries normally involve the upper thoracic esophagus or the lower esophagus just above the gastroesophageal junction. The most commonly accepted theory regarding the pathophysiology of rupture is similar to the mechanism in Boerhaave syndrome in that an increase in intraluminal pressure against a closed glottis results in a tear at the weakest point of the esophageal wall, usually the distal third of the esophagus on the left where there is less protection from the pleural lining and the heart. Other etiologies for injury include disruption of the esophageal blood supply, resulting in ischemia and late perforation, and a blast effect caused by a concomitant tracheal injury. Direct injury may also result from adjacent thoracic spine fractures or compression between the sternum and thoracic spine, as observed in high-speed road traffic accidents. Esophageal injuries are often associated with clinical symptoms, including blood in the esophagus or pain on swallowing. CT may suggest the diagnosis of traumatic esophageal perforation with the presence of pneumomediastinum, mediastinitis, hydropneumothorax, or leakage of oral contrast medium into the mediastinum or the pleural space. Water-soluble contrast esophagography, followed by flexible esophagoscopy, may be required to fully evaluate the site of injury.

CARDIAC INJURIES

Cardiac and pericardial injuries are uncommon with blunt thoracic trauma but do occur with severe blows to the anterior chest. The diagnosis of blunt cardiac injury relies on a high clinical suspicion. Cardiac injuries often occur in conjunction with sternal fractures. The anterior aspect of the heart that abuts the sternum is most vulnerable to injury. Patients with cardiac injuries may have an abnormal electrocardiogram and elevated cardiac enzymes. Cardiac injuries include cardiac contusion, cardiac rupture, pneumopericardium, hemopericardium, cardiac tamponade, and cardiac valve injury. Hemopericardium from a cardiac injury or cardiac rupture may quickly produce cardiac tamponade with hemodynamic compromise (Fig. 2-3). Cardiomegaly may be seen on the plain chest radiograph, while CT or cardiac sonography may confirm hemopericardium.

Figure 2-3 A 28-year-old male with a gunshot injury. A, Anteriorposterior view of the chest demonstrates bullet fragments projecting over the cardiac silhouette. B, Axial CT demonstrates a bullet fragment in the myocardium of the left ventricle (black arrow). Note hemopericardium (black arrowhead) and adjacent lung contusion (white arrow). C, Axial CT in lung windows better demonstrates adjacent lung contusion. D, Coronal CT demonstrates multiple rib fractures resulting from penetrating injury.

AORTIC AND GREAT VESSEL INJURIES

Injuries of the aorta account for a significant number of fatalities following blunt trauma. Seventy percent of all thoracic aortic injuries are fatal at the scene of trauma. Of patients who are transported to the hospital, 90% of aortic rupture occurs at the aortic isthmus, located at the junction of the posterior aortic arch and descending aorta, just distal to the origin of the left subclavian artery. The proposed mechanism of injury is rapid deceleration producing shear injury at the site where the rate of deceleration of the mobile aortic arch differs from that of the relatively fixed descending aorta. In addition, bending stress occurs because the aorta is flexed over the left pulmonary artery and left mainstem bronchus. Only 5% of aortic injuries in clinical series involve the ascending aorta, and these injuries may be associated with life-threatening cardiac and pericardial injuries. Rarely, aortic injuries may involve the descending aorta at the level of the diaphragmatic hiatus.

A normal chest radiograph has a high negative predictive value (98%) but a low positive predictive value for aortic injury. The chest film findings suggestive of aortic injury include mediastinal widening greater than 8 cm, loss of the normal aortic arch contour, a left apical pleural cap, displacement of the nasogastric tube to the right, widened paraspinal lines, and loss of the descending aortic line. Most of the plain film findings of aortic injury are nonspecific. The gold standard for the diagnosis of aortic injury has traditionally been aortography; however, at most trauma centers today, aortography has been replaced with MDCT.

The sensitivity of CT has been reported to be 92% to 100% and specificity 62% to 100% for the detection of aortic injury. The accuracy of aortic trauma detection with CT has been improving in parallel with technological improvements in CT scanning. Current fast MDCT scanners decrease motion artifact and provide higher-quality two- and three-dimensional reformations for diagnosis and treatment planning.

The CT findings of aortic trauma include indirect signs, such as mediastinal hematoma surrounding the posterior aortic arch and proximal descending aorta, as well as the direct signs of intimal tear/flap, aortic contour abnormality, thrombus protruding into the aortic lumen, false aneurysm formation, pseudocoarctation, and extravasation of intravenous contrast material. If only direct signs are utilized, the sensitive and negative predictive value remains at 100% but the specificity increases to 96% (Fig. 2-4).

Figure 2-4 A, Portable chest radiograph shows an enlarged indistinct aortic arch (black arrow), a left apical pleural cap, and upper rib fractures (white arrows). B, Axial CT demonstrates mediastinal hematoma, intimal flap, and pseudoaneurysm (arrow). C, Oblique coronal reformation shows the extent of pseudoaneurysm (arrow). D and E, Thoracic aortography before and after treatment with an aortic stent.

A common aortic injury is a traumatic false aneurysm resulting from disruption of the vessel intima and media while the adventitia remains intact. The intravascular blood confined by only the adventitia bulges outward forming a pseudoaneurysm. In many cases, the aortic injury may be limited to a partial circumferential tear. CT findings typically consist of a saccular out-pouching demarcated from the aortic lumen by torn intima. It frequently results in hemomediastinum. Treatment of a pseudoaneurysm may today be performed with intravascular stent grafting. False positive examinations may be related to a prominent ductus diverticulum or an ulcerated atheromatous plaque. A traumatic pseudoaneurysm is usually surrounded by mediastinal blood whereas a ductus diverticulum and an ulcerated atheromatous plaque are not (Figs. 2-5 to 2-7).

Figure 2-5 A 39-year-old female involved in a rollover motor vehicle accident. A, Portable chest radiograph demonstrates widened superior mediastinum (arrow). B, Axial CT section shows intimal flap and pseudoaneurysm formation with extraluminal extension of contrast (arrow). C, Lower axial section shows hemopericardium; the patient had cardiac enzyme elevation consistent with cardiac contusion (arrow). D, Sagittal volume-rendered image shows pseudoaneurysm more clearly (arrow). E, Three-dimensional images demonstrate pseudoaneurysm formation.

Figure 2-6 A 53-year-old female following a motor vehicle accident. A and B, Axial and coronal sections at the level of the diaphragm demonstrate intimal flap formation (arrow) within the aortic lumen in conjunction with periaortic hematoma. C, Patient after stent graft repair of the aorta.

Figure 2-7 A 21-year-old patient after a high-speed motor vehicle accident. The patient was an unrestrained driver. A, Portable anteroposterior chest radiograph showing patchy opacity in the right lung representing pulmonary contusion. B, Axial CT section demonstrates mediastinal hematoma with intimal flap formation (arrow) and contour irregularity of the aortic lumen. C, Three-dimensional reformation demonstrates a small pseudoaneurysm. D, Note stent graft placement for treatment of pseudoaneurysm.

LUNG INJURIES AND LUNG CONTUSION

Lung contusion results from traumatic extravasation of blood and edema fluid into the pulmonary interstitium and air spaces of the lung as a result of disruption of alveolar-capillary integrity without significant disruption of the pulmonary parenchyma. The injury is caused by energy transmitted directly to the lung from an impact to the overlying chest wall. On radiographs, contusion appears as patchy areas of consolidation (Fig. 2-8). When extensive, radiographs may show diffuse dense homogeneous lung consolidation. These opacities resulting from lung contusion are said to differ from those of bronchopneumonia and aspiration in that they are not confined to the anatomic limits of various segments or lobes. This may be difficult to definitively ascertain on an initial anteroposterior chest radiograph. Contusion may be absent on the initial chest film but usually becomes evident within 6 hours of injury. CT can usually detect pulmonary contusion immediately after injury. Contusions usually resolve rapidly and disappear in a few days.

Figure 2-8 A 19-year-old male patient following a motor vehicle accident. A, Initial chest radiograph demonstrates left upper lung patchy consolidation consistent with contusion. B, Chest radiograph 3 days later demonstrates rapid resolution of pulmonary contusion. C, Axial section through a CT scan demonstrates left-sided contusion affecting both the upper and lower lobes, not confined to a single lobe. D, There is sparing of 1 to 2 mm of subpleural space (arrow). E, Coronal image demonstrates extent of lung contusion.

CT may show areas of consolidation often directly beneath the site of injury in a nonsegmental distribution and often sparing 1 to 2 mm of the subpleural lung parenchyma. The opacities may be single or multiple and both coup and contracoup contusions may be identified. Contusion is often seen surrounding pulmonary lacerations.

LUNG LACERATION

Pulmonary lacerations are tears of the lung parenchyma that fill with air, blood, or both. If the laceration fills with air the injury is termed a traumatic pneumatocele. If it fills with blood a spherical hematoma or hematocele forms. If both air and fluid are present, an air–fluid level may be identified. The spherical shape of intraparenchymal lacerations has been attributed to normal elastic recoil of the lung parenchyma pulling centrifugally in all directions on the disrupted region (Fig. 2-9).

Figure 2-9 A 55-year-old patient stabbed in the chest. A, Anteroposterior chest radiograph demonstrates patchy opacities surrounding a lucent cavity lesion consistent with pulmonary pneumatocele with surrounding contusion resulting from penetrating stab injury. B, Axial CT image demonstrates lung laceration with track to the skin surface. C, Follow-up chest CT 6 days after injury demonstrates resolution of contusion with involution of hematocele. D, Remote follow-up chest radiograph demonstrates scarring related to laceration.

On chest radiograph, lacerations may initially be obscured by surrounding lung contusion; however, they become visible once the contusion clears. In contrast, acute lung lacerations are nearly always detected on CT imaging. Four types have been described with blunt trauma (Fig. 2-10): type 1, compression rupture laceration, resulting from sudden compression of a pliable chest wall wherein the air-containing lung is ruptured; type 2, compression shear laceration, which occurs in a para-vertebral lower lobe of the lung (the mechanism occurs when the more pliable lower chest wall is acutely compressed causing the lower lobe to shift suddenly across the vertebral body in a shearing-type injury, Fig. 2-11); type 3, rib penetration tear, causing a peripheral injury adjacent to a rib fracture (a pneumothorax is generally associated with this type of injury as it represents a penetrating injury); type 4, adhesion tear, which results from tear of prior pleural-pulmonary adhesions causing the lung to tear when the overlying chest wall is violently moved inward or fractured. Lung lacerations may also result from penetrating trauma, most frequently from stab wounds and gunshot wounds. Pulmonary lacerations are better shown and more extensively evaluated with CT than with plain films. Unlike pulmonary contusion, lung lacerations may take weeks or months to heal and may result in residual lung scarring. Frequently, as lacerations resolve they appear as lung nodules (Fig. 2-12).

Figure 2-10 Four types of pulmonary lacerations. (1) Compression rupture injury, (2) compression shear injury, (3) rib penetration injury, and (4) adhesion tear injury.

Figure 2-11 A 41-year-old male with a history of multiple suicide attempts and poly-substance abuse who fell from the second story of a burning building. A, Chest film demonstrates patchy opacification of the right hemithorax consistent with contusion. B, Axial image demonstrates both compression rupture (black arrow) and compression shear type lacerations (white arrow).

Figure 2-12 A 40-year-old male after a fall from a third floor window. A, Initial axial CT image demonstrates multiple lung lacerations (arrows) with surrounding contusion. B, Follow-up CT 3 weeks after initial event demonstrates involution of hematoceles, which now have the appearance of pulmonary nodules.

TRACHEOBRONCHiAL INJURIES

Injuries to the airways are uncommon, occurring in approximately 1.5% of blunt trauma cases. Tears and fractures of the tracheobronchial tree are frequently not recognized on initial imaging, and delayed diagnosis is common. Eighty percent of tracheobroncheal injuries occur within 2 cm of the carina. Rupture of the left and right mainstem bronchi occur with equal frequency. Chest radiograph findings most commonly include pneumomediastinum and subcutaneous emphysema (Fig. 2-13). Air continuously leaks through the rupture and flows into the surrounding mediastinal soft tissues with dissection up into the neck. Pneumomediastinum is an anticipated accompaniment of tracheobronchial injury. Large volumes of pneumomediastinum are easy to identify on plain radiographs, but volumes may not be visible on the initial portable chest radiograph. Pneumomediastinal air should initiate a search for possible tracheobronchial injury; however, there are other causes of pneumomediastinum, including complications of dyspnea, aggressive mechanical ventilation, and esophageal rupture. In the presence of a tracheobronchial laceration, air dissects into fascial planes as a consequence of the continuous air leak. Hence, on sequential radiographs, the subcutaneous emphysema is expected to persist or increase (Fig. 2-14).

Figure 2-13 A 22-year-old male after a motor vehicle accident. A and B, Posteroanterior and lateral view of the chest demonstrate both pneumomediastinum (arrow) and subcutaneous emphysema. C and D, Axial and coronal CT images demonstrating extensive pneumomediastinum.

Figure 2-14 An 18-year-old patient after a motor vehicle crash involving a manhole cover, which blew from the street and acted as a projectile into a front window of a moving truck. The patient was an unrestrained passenger and was struck by the manhole cover, sustaining maxillofacial, right humerus, right clavicle, and upper thoracic injuries, among others. A, Portable anteroposterior image of the chest demonstrates extensive subcutaneous emphysema and patchy opacification of the lungs consistent with contusion. B, Axial image demonstrates lung contusion and lacerations. There is extensive subcutaneous emphysema (arrowhead) and pneumomediastinum. C, Axial image demonstrates a laceration in the posterior aspect of the right bronchus intermedius (arrow). D, Coronal image demonstrates bronchial laceration in the bronchus intermedius. E, Thick-section maximal intensity projection improves visualization of the laceration.

Tracheal lacerations are usually longitudinal and located at the junction of the cartilaginous and membranous parts of the trachea. Tears of the trachea or proximal left main bronchus normally cause central dissection of air with mediastinal and cervical emphysema without pneumothorax. In bronchial injuries the majority of cases also have an associated pneumothorax. Pneumothorax in patients with tracheobronchial transection is the result of rupture of the mediastinal pleura, or injury to the right mainstem bronchus or distal left bronchus. Air is allowed to enter the pleural space on the ipsilateral side. The classic clinical feature of this condition is a pneumothorax that does not resolve despite chest tube suction secondary to a continuous leakage of air through the airway rupture. However, resolution of a pneumothorax after chest tube placement does not exclude the diagnosis. Another pathognomonic finding is that of a “fallen lung,” which is a sign of complete bronchial transection. This occurs when the lung collapses toward the lateral chest wall or diaphragm, rather than toward the pulmonary hilum, which is the usual situation.

Other signs of tracheobronchial injury include a sharply angulated bronchus, bronchial discontinuity, and bronchial “cut-off.” Abnormalities of an endotracheal tube balloon may also be noted with tracheal laceration. The balloon may appear overinflated or more spherical as it actually herniates through a vertical laceration of the trachea. An extratracheal location of the endotracheal tube might be seen, but it is rare. All of these findings are better depicted on CT than on plain radiography. CT can reveal the exact site of tracheal injury by directly showing focal defects or the circumferential absence of the tracheal wall, a contour deformity, or abnormal communication with other mediastinal structures. CT can show more subtle secondary signs, such as smaller volumes of pneumomediastinum, than can the chest radiograph.

The diagnosis of tracheobronchial injury should be confirmed by flexible bronchoscopy. Late complications of untreated tracheobronchial injury include bronchial stenosis, recurrent pneumonia, and bronchiectasis. Prompt diagnosis and treatment generally lead to good functional recovery.

DIAPHRAGMATIC INJURIES

Diaphragmatic rupture is an uncommon injury seen in about 5% of patients undergoing laparotomy or thoracotomy for trauma. The postulated mechanism for blunt diaphragmatic injuries is a lateral blow causing shearing of the diaphragm and disruption of the attachments to the chest wall with concomitant increase in intra-abdominal pressure resulting from a frontal impact. Hence, diaphragm rupture is more common with lateral impact motor vehicle collisions. Early diagnosis of diaphragmatic rupture is clinically important, as complications related to visceral herniation through the lacerated diaphragm may result in respiratory compromise due to impairment of lung inflation. As well, visceral incarceration may lead to strangulation and possible perforation.

Left-sided injuries are more common, having a reported left-to-right ratio of 3:1. Bilateral and central tendon ruptures are uncommon. The increased frequency of left-sided injury has been attributed to an area of congenital weakness in the posterolateral diaphragm with central radiation of the tear. Right-sided injuries are thought to be less frequent because of the inherent increased strength of the right hemidiaphragm and the protective effect of the liver (Fig. 2-15).

Figure 2-15 A 19-year-old male after a fall. A, Anteroposterior view of the chest demonstrates elevation of the right hemidiaphragm. B, Sagittal CT image demonstrates that a portion of the upper third of the liver abuts the posterior chest wall, consistent with the “dependent viscera” sign. C, Coronal CT image shows elevation of the liver through a diaphragmatic defect.

Imaging of diaphragmatic rupture may be difficult owing to the great variation in the normal diaphragm. These normal variants include incidental posterolateral diaphragmatic defects (Bochdalek hernia), localized diaphragmatic thinning (i.e., eventration), and areas of diaphragmatic discontinuity. These defects of the diaphragm advance with age and are uncommon in younger age groups.

The chest radiograph is usually the initial imaging examination of trauma patients. The supine positioning and portable technique may limit the ability to evaluate for diaphragmatic integrity. The chest radiograph may show an intrathoracic location of abdominal viscera with possible focal constriction known as the “collar” sign (Fig. 2-16). A nasogastric tube tip may be visible above the left hemidiaphragm. Significant elevation of the hemidiaphragm without associated atelectasis may be a sign of diaphragm rupture (Fig. 2-17).

Figure 2-16 A 52-year-old male after a motor vehicle accident. A, Anteroposterior view of the chest demonstrates elevation of the right hemidiaphragm. B, Axial CT image shows the liver in contact with the posterior chest wall. Note impression on the liver from the diaphragm (arrow). C and D, Sagittal and coronal images demonstrate the “dependent viscera” sign with a portion of the upper third of the liver in contact with the posterior chest wall (black arrow). The “collar” sign can also be appreciated with the ruptured diaphragm, causing constriction of the liver (white arrows).

Figure 2-17 A 25-year-old male patient ejected from a motor vehicle following a crash. A, Anteroposterior view of the chest demonstrates a nasogastric tube within the lumen of the stomach, which is located in the left chest (arrow). B, Axial CT image shows the stomach abutting the posterior chest wall. Note the shift of the mediastinum to the right.

Today, MDCT axial scans combined with high-quality coronal and sagittal reformations may show both large and small ruptures of the diaphragm, in addition to showing any abdominal organs herniated across the rupture. CT signs of diaphragm injury include the direct visualization of injury, intrathoracic herniation of viscera with a “collar” sign, the “dependent viscera” sign, and peridiaphragmatic active contrast extravasation. Additional findings of hemothorax, hemoperitoneum, and adjacent visceral injury may increase the suspicion of diaphragm injury. Of particular note, intrathoracic herniation of viscera is highly sensitive (up to 90.9%) when limited to left-sided injury. When abdominal viscera herniate through a diaphragm tear, the edges of the diaphragm may constrict the herniated organ, resulting in the “collar.” The “dependent viscera” sign is diagnostic of diaphragm rupture (Fig. 2-18). An intact diaphragm prevents the upper abdominal viscera from directly contacting the posterior chest wall in the supine patient. Conversely, when the diaphragm is torn, the viscera may lie dependently against the posterior chest wall.

Figure 2-18 A 42-year-old male after a motor vehicle collision. A, Anteroposterior view of the chest demonstrates elevation of the left hemidiaphragm. B and C, Coronal and sagittal CT images demonstrate herniation of the stomach through a defect in the diaphragm. Again, note that the “dependent viscera” and “collar” signs are present.

INJURIES OF THE THORACIC SKELETON

Skeletal injuries of the thorax may be apparent on initial portable chest radiograph imaging. Therefore, a careful evaluation for rib fractures should be performed. Knowledge of the presence of rib fractures may result in a CT scan for further evaluation given that the fractures may be a harbinger of more extensive underlying injury. Fractured ribs may lacerate the pleura or lung. Upper rib fractures indicate “high-energy” trauma, as these ribs are relatively well protected by the shoulder girdle and adjacent musculature. Upper rib fractures may be associated with injuries of the aorta, great vessels, or brachial plexus. Lower rib fractures may be associated with injuries to the liver, spleen, or kidneys. Flail chest occurs when five contiguous simple or three contiguous segmental rib fractures occur and result in paradoxical movement of the chest wall (Fig. 2-19). Flail chest may lead to altered chest wall mechanics and interfere with ventilation, and may lead to respiratory failure. There is a much greater incidence of rib fractures in older patients, whose ribs are fairly inelastic, as compared with children where the incidence of fracture is low secondary to more pliable and resilient ribs. Chest radiographs are limited, as they may show only 40% to 50% of rib fractures. Nearly all skeletal injuries are better shown with CT.

Figure 2-19 Three-dimensional reformation from a chest CT demonstrates segmental fractures of three posterior ribs (arrows). This results in a flail chest.

Rarely, a segment of lung may herniate through a defect in the chest wall created by rib or costochondral fracture (Figs. 2-20 and 2-21). The incidence of transthoracic lung herniation increases with the use of positive-pressure ventilation. Lung herniation may occur as a result of blunt chest trauma or iatrogenic surgical trauma. The herniated lung may become entrapped or strangulated. Since lung herniation may increase with positive-pressure ventilation, it may require treatment before mechanical ventilation and general anesthesia.

Figure 2-20 Axial CT image demonstrates herniation of lung parenchyma through the chest wall following ejection from a motor vehicle.

Figure 2-21 A, Axial CT image demonstrates herniation of the lung through a fracture at the costochondral junction. B, Three-dimensional reformation shows the herniated portion of the lung (arrow).

Other common injuries of the thoracic skeleton include scapular fractures, sternal fractures, sternoclavicular dislocation, and thoracic spine injuries. Posterior sternoclavicular dislocation typically results from a posterior blow to the shoulder or a blow to the medial clavicle; the latter results in a posteriorly displaced clavicular head relative to the manubrium (Fig. 2-22). Serious morbidity and even death have been associated with posterior dislocation of the clavicle at the sternoclavicular joint, as the displaced clavicle head may impinge on or injure the trachea, esophagus, great vessels, or major nerves in the superior mediastinum. Anterior sternoclavicular dislocations usually result from an anterior blow to the shoulder. Anterior dislocations are more common than posterior dislocations, and typically are less dangerous as there is no significant risk of great vessel injury. Sternoclavicular dislocation is generally well shown by CT.

Figure 2-22 A and B, Axial CT images demonstrate posterior displacement of the clavicular head with impingement on the underlying aorta. C, Sagittal CT image with posterior dislocation of the sternoclavicular joint. There is adjacent hematoma. D and E, Three-dimensional images beautifully demonstrate the relationship of the sternoclavicular joints.

Sternal fractures are usually not seen on the anteroposterior portable chest radiograph and may be difficult to see on the lateral chest radiograph. However, nearly all sternal fractures are visible on CT, especially on sagittal reformations (Fig. 2-23). As well, CT frequently shows any associated retrosternal hematoma. Sternal fractures have a high association with both aortic and cardiac injuries. Most patients with sternal fractures are monitored for myocardial contusion with serial enzyme analysis and telemetry monitoring (Fig. 2-24).

Figure 2-23 Sagittal CT image demonstrates fracture of the sternum (arrow).

Figure 2-24 Anteroposterior (A) and lateral (B) radiographs of a 32-year-old male patient after a motor vehicle collision. No sternal injury can be appreciated on these images. C, Sagittal reconstructed images through the sternum clearly show the minimally displaced sternal fracture that was not seen on plain radiographs.

Fractures of the thoracic spine account for 15% to 30% of all spine fractures. These fractures often result from hyperflexion or axial loading forces. The most vulnerable segment of the thoracic spine is at the thoracoabdominal junction from T9 to T12. The most common fractures are anterior wedge compression and burst fractures. Multiple fractures, often present, are frequently at noncontiguous levels, which highlights the need to evaluate the entire spine. The thoracic spinal cord is very susceptible to injury because the thoracic cord is tightly packed into the central canal and is easily injured by displaced bone fragments or disc material. Moreover, the blood supply of the mid-thoracic spinal cord is tenuous. Only 12% of patients with fracture-dislocation of the thoracic spine are neurologically intact; 62% of patients with thoracic spine fracture-dislocation have complete neurologic deficits.

Thoracic spine fractures are occasionally detected on a portable chest radiograph. The radiographic signs might include flattened vertebral body, increased intrapedicular distance, and loss of vertebral body height. A possible sign on plain radiograph of thoracic spine fracture is widening of the right or left paravertebral stripe, which results from a paraspinal hematoma. Between 10% and 30% of thoracic spine fractures are not visible on portable radiograph. CT scan with coronal and sagittal reformations can both diagnose fractures with greater accuracy and better define the relationship of osseous fragments to the spinal cord. Magnetic resonance imaging is better for defining spinal cord or nerve root injury.