Contusion of the lung parenchyma is quite common in patients with major blunt thoracic trauma and can occur at the site of injury (coup) or in other parts of the lung (contrecoup injury).120. ^{and 121.} Contusion results from laceration of the pulmonary parenchyma by sudden compression and shear forces. ¹²² Lung injury may be further compounded by fractured ribs or tearing of pleural adhesions. Alveolar hemorrhage and parenchymal destruction are usually greatest during the first 24 hours after injury.^{6.120. and 121.} Nevertheless, radiographs obtained within the first few hours of injury may not show findings of contusion. Radiographs obtained shortly thereafter, however, will show either focal or diffuse homogeneous opacities (Figs 17.19 and 17.20). Because the interlobar fissures do not impede the shock wave, lung contusion does not usually localize in a lobar (or segmental) pattern. Although the opacities may appear to progress on chest radiographs for a day or 2, they tend to stabilize and then clear fairly rapidly, usually within 7 days (Fig. 17.19).^{120. and 121.} Lung contusion can result in considerable respiratory distress leading to mechanical ventilation, acute respiratory distress syndrome (ARDS), and, in some cases, long-term respiratory disability.^{120. and 121.}

CT is clearly more sensitive for lung contusion than chest radiography (Fig. 17.21).^{120.123.124.125. and 126.} Schild et al. ¹²⁷ imaged experimentally induced pulmonary contusions in an animal model with CT and chest radiographs. CT detected 100% of contusions immediately after the trauma, whereas radiographs failed to detect 20% of contusions even on sequential examinations. Miller et al. ¹²⁶ used CT to quantify the volume of contusion and found a correlation between contusion volume and risk for ARDS. Donnelly et al. ¹²⁴ reported that lung contusion in children very frequently (95% of cases) showed subpleural sparing on CT, a finding of potential utility for differentiating contusion from infection and aspiration.

Pulmonary laceration can also result in formation of posttraumatic lung cysts (pneumatoceles, Figs 17.21 and 17.22) or focal hematomas (Figs 17.23 and 17.24). ¹²⁸ Such lesions may be solitary or multiple. Most range from 2 cm to 5 cm in diameter, but extremely large hematomas, up to 14 cm in diameter, are reported. Pneumatoceles or hematomas may be radiographically apparent within a few hours of injury. However, the lesions may not be apparent on initial chest radiographs because of associated parenchymal contusion. In such instances, the lesions will become more visible as the surrounding pulmonary parenchymal contusion clears. As is the case with lung contusion, CT is more sensitive than chest radiography for detection of posttraumatic lung cysts and parenchymal hematomas. Both lesions tend to resolve with time; pneumatoceles tend to resolve faster than hematomas. Hematomas may take many months to resolve completely and for a considerable period of time may be the only visible sequela of previous injury. Since by this stage a hematoma is a circumscribed lung mass, the lesion may be mistaken for a neoplasm (Fig. 17.23). In such a case, Takahashi et al. ¹²⁹ were able to identify the lesion as a hematoma by its signal characteristics on MRI. During resolution, a hematoma may communicate with the airway and manifest as a cavitary mass (Fig. 17.24). Awareness of these features is important to avoid confusion with more serious pulmonary processes such as lung cancer. Cavitating hematomas resolve without treatment.

Pneumothoraces (Fig. 17.25) and pleural effusions (Fig. 17.19) commonly accompany lung parenchymal injury and may require prompt chest tube drainage. Severely injured patients are usually radiographed in the supine position, which can make detecting air and fluid in the pleural space difficult, unless the fluid or air is localized to the minor fissure, the subpulmonic spaces, or the mediastinal pleural space. In the supine position air tends to collect anteriorly and fluid tends to layer posteriorly. Anterior pneumothoraces can be detected on frontal projections taken with the patient supine, but the findings are subtle and easily overlooked.^{130. and 131.} The mediastinal contours on the affected side may be seen with unusual clarity, and the anterior portion of the diaphragm may be depressed, revealing more of the base of the heart on that side.^{130. and 132.} The lateral costophrenic sulcus may also be seen with unusual clarity and appear asymmetrically deep – the so-called ‘deep sulcus sign’. ¹³² Pleural effusions may cause a diffuse haze over the lungs resulting from the filtering effect of the posteriorly positioned fluid layer (Fig. 17.19B). If the effusion is large enough, it may extend around the lung and produce a band of density along the lateral chest wall and over the apex. Cross-table lateral views can be helpful for detecting both pneumothoraces and pleural effusions. CT is highly accurate for both, and the lung bases should always be covered during the abdominal CT examination for visceral injury. ¹³³ One study showed that CT detected 100% of pneumothoraces, whereas supine frontal chest radiographs detected only 40%. ¹³⁴ Two other studies found that supine chest radiographs detected only about 50% of pneumothoraces in trauma patients.^{135. and 136.} However, Holmes et al. ¹³⁶ also found that many of the pneumothoraces detected only by abdominal CT did not require tube thoracostomy. Wolfman et al. ¹³⁷ used CT to grade the size of such incidental pneumothoraces and found that very small ones did not require tube thoracostomy.

Tracheal or bronchial rupture most frequently results from penetrating thoracic injuries or instrumentation. ¹³⁸ Injury due to blunt trauma is rare and, because of the significant force required, is frequently associated with injuries to other structures such as the aorta and great vessels, thoracic cage, and lungs.^{139.140.141. and 142.} The imaging findings of airway rupture are often subtle and may be overshadowed by other injuries. A considerable proportion of cases may go undetected until complications develop either at the site of rupture, such as bronchial stenosis, or in the lung distal to the rupture, such as septic complications or persistent atelectasis.143.^{144.145. and 146.} Definitive diagnosis frequently requires fiberoptic bronchoscopy. ¹⁴⁰

There are two major indirect manifestations of tracheal or bronchial rupture – evidence of air leak and abnormal lung ventilation distal to the injury. Evidence of air leak is the more crucial finding and is seen in up to 90% of cases of tracheobronchial injury. ¹⁴⁷ However, in up to 10% of cases, the adventitial sleeve remains intact and air leak may not occur, making the diagnosis of airway injury more difficult. The most common imaging finding of air leak is pneumothorax, seen in 60–100% of cases.^{148. and 149.} Pneumothoraces due to major airway injury are frequently large and persistent despite insertion of multiple pleural tubes (Figs 17.26 and 17.27); they may also be under tension. Pneumomediastinum is another important indicator of airway injury (Figs 17.27 and 17.28)^{149. and 150.} and is a more specific sign than pneumothorax. Pneumomediastinum may be the only sign of air leak in patients with tracheal or intramediastinal bronchial rupture (particularly the left main bronchus). ¹⁵¹ Pneumomediastinum due to airway injury typically manifests on chest radiographs with streaky lucencies around the carina and these extend superiorly as the air dissects in the tissue planes around the trachea, aorta, and great vessels. At the margins of the mediastinum, air dissects and elevates the mediastinal parietal pleura from the aorta and heart. On lateral radiographs, pneumomediastinum is best appreciated in the retrosternal space. Pneumothorax and pneumomediastinum seen on chest radiographs obtained after severe blunt thoracic trauma are highly suggestive of airway injury.

The second major indirect manifestation of major airway injury is abnormal ventilation of the affected lung. ¹⁵² This can result in ventilation–perfusion mismatch with hypoxia and cyanosis. Loss of bronchial continuity combined with intraairway hemorrhage and edema can also result in significant atelectasis. The diagnostic problems in these cases are numerous. In severely traumatized patients, atelectasis may develop for reasons other than bronchial rupture. Furthermore, significant associated pulmonary abnormalities such as lung contusion or aspiration may also be present. Collapse of a lung is expected in the presence of a pneumothorax, particularly if the pneumothorax is large and under tension. Atelectasis in patients with bronchial rupture is usually persistent and unresponsive to normal therapeutic maneuvers. Bronchial stenosis or occlusion at the site of rupture can occur if the injury is not promptly diagnosed and repaired. Septic complications including pneumonia and abscess can also be encountered in the affected lung.

Further important, but infrequently observed, indirect findings of major airway injury include abnormally positioned endotracheal tubes or overdistended endotracheal tube balloons.^{153. and 154.} Chen et al. ¹⁵⁵ reported that balloon overinflation occurred in 71% and balloon herniation through the defect in 29% of cases of tracheal rupture. The overinflated balloon may also assume a more rounded configuration than is normally seen. Tracheal perforation due to traumatic intubation can result in the tip of the endotracheal tube projecting too far to the right of the tracheal air column on supine chest radiographs. ¹³⁸

A rare but characteristic feature of bronchial rupture is the so-called ‘fallen lung’ sign, which can be seen on chest radiographs or CT^{139. and 156.} (Fig. 17.26). This finding occurs in the setting of a complete bronchial transection and a large pneumothorax that allows the lung to sag away from the hilum inferiorly and laterally and, on supine CT, posteriorly. The vascular pedicle remains intact and the lung remains perfused but underventilated. ¹⁵⁷ The consequent ventilation–perfusion mismatch can result in hypoxia and cyanosis.

CT has been used with success to diagnose airway injuries (Figs 17.27 and 17.28).^{139.155.156.158.159.160.161.162. and 163.} CT is clearly more sensitive than chest radiography for detecting small air-leaks in the mediastinum that suggest the presence of airway injury. However, the sensitivity of CT for direct visualization of the site of injury is not 100%. Chen et al. ¹⁵⁵ studied a group of patients with tracheal rupture and reported that CT identified the direct site of injury in 71%, whereas, in another study, direct CT evidence of tracheal rupture was seen in only 10% of patients. ¹⁶⁰ Thus, the primary role of CT in diagnosis of airway injuries is probably to suggest the possibility of injury when extraluminal air is identified adjacent to major airways. Ultimately, the diagnosis depends on awareness of the possibility of airway injury in cases of severe thoracic trauma. In a considerable number of instances the diagnosis is missed in the acute phase and is detected only because of persistent lung or lobar atelectasis. Bronchoscopy should be performed in any case in which the radiographic or CT findings suggest airway rupture.

Instrumentation is the most common cause of traumatic esophageal rupture.^{164. and 165.} Most noniatrogenic traumatic esophageal injuries are due to gunshot wounds. ¹⁶⁶ Esophageal rupture due to blunt thoracic trauma is quite rare, accounting for only 10% of all noniatrogenic cases.^{167. and 168.} The radiographic features of esophageal rupture are more fully discussed elsewhere (see p. 921) and include pneumomediastinum, pneumothorax, or pleural effusion, most commonly on the left side, and evidence of mediastinitis, including abscess formation. Diagnosis of esophageal rupture in the trauma patient can be quite difficult because these findings may be attributed to other injuries and considerable delay in diagnosis is common.^{165. and 167.} Unfortunately, this delay in diagnosis results in a higher incidence of infectious complications. The majority of esophageal ruptures due to blunt trauma occur in the cervical and upper thoracic region (Fig. 17.29) but distal esophageal rupture following blunt external trauma has been described.^{169. and 170.} In many cases, particularly with gunshot wounds, the diagnosis is made by surgical exploration. Otherwise, an esophagram using water-soluble contrast will readily confirm the injury.

Injuries to the thoracic duct are usually due either to penetrating trauma or to surgical injury during thoracic exploration (Figs 17.30 and 17.31).^{171. and 172.} Thoracic duct injury from blunt external trauma is exceedingly rare. ¹⁷³ Rupture of the thoracic duct can result in chylothorax (Fig. 17.30) or, occasionally, a localized lymphocele (Fig. 17.31). ¹⁷⁴ Fluid accumulation is characteristically slow and many days may pass before considerable quantities of fluid accumulate. Definitive diagnosis rests on determining that the fluid collection is chylous or that it communicates with the thoracic duct.^{174.175. and 176.} The site of injury to the thoracic duct determines the side on which the fluid accumulates. The duct enters the thorax through the aortic hiatus in the diaphragm and ascends along the right anterolateral aspect of the spine. In the midthoracic region (about the level of the sixth thoracic vertebral body), the duct crosses the midline and ascends along the left anterolateral aspect of the spine. Finally, it arches forward to enter the venous system in the region of the left jugular and subclavian vein junction. As the duct arches into the left cervical region, it is particularly vulnerable to penetrating injury. Worthington et al. ¹⁷⁷ described eight cases of rupture involving the upper portion of the thoracic duct above the level of the aortic arch, seven of which were caused by knife wounds. All seven were associated with left chylothorax. On the other hand, injuries to the duct below the level of the sixth thoracic vertebral body usually result in right-sided chylothorax or lymphocele formation. Because the duct lies in close proximity to the spine, there is a significant association between thoracic duct injury and fracture-dislocation injuries of the thoracic spine. ¹⁷⁸ Large persistent pleural effusions in patients with such fractures suggest the possibility of thoracic duct injury.

Lymphangiography has been used successfully to determine the site of leakage prior to surgical intervention. Sachs et al. ¹⁷⁹ studied 12 patients with chylous ascites or chylothorax following surgery and found abnormal lymphangiograms in seven. Lymphoscintigraphy (Fig. 17.31), ¹⁷⁴ CT-guided needle aspiration, ¹⁷⁶ and magnetic resonance (MR) Lymphangiography have also been used to successfully diagnose chylothoraces and lymphoceles^{180. and 181.} due to thoracic duct trauma.

Acute diaphragm rupture can result from either penetrating injury or blunt thoracoabdominal trauma¹⁸² (see Box 17.9). Rupture can result in herniation of abdominal contents into the chest, either acutely or in a delayed fashion. Herniated viscera can cause respiratory distress because of heart or lung compression. Herniated bowel can also strangulate, sometimes years after the initial injury. ¹⁸³

Penetrating injuries to the diaphragm are usually caused by knife or bullet wounds (Fig. 17.32). These injuries usually cause shorter diaphragmatic tears than those seen after blunt trauma. ¹⁸⁴ Because the tear is usually so small, herniation of abdominal contents is uncommon. Furthermore, because adjacent lung is frequently injured, the contours of the diaphragm may be obscured on the frontal chest radiograph, making detection of small hernias (if present) difficult. Thus, definitive diagnosis may be delayed. For example, Demetriades et al. ¹⁸⁵ found herniation of abdominal contents in only 15% of 150 patients with penetrating injuries of the diaphragm. Diagnosis was delayed in almost half of the affected patients. Because associated abdominal injuries that require exploratory laparotomy (e.g. liver, spleen, or bowel laceration) occur in at least 75% of affected patients, diaphragmatic injuries due to penetrating trauma are usually detected by direct inspection. Diaphragm rupture due to blunt thoracoabdominal trauma is usually the result of a high-speed motor vehicle accident or a fall from a considerable height. The high incidence of associated injury is reflected in reported mortality rates of up to 25%.186.^{187. and 188.} Over 80% of patients with traumatic rupture of the diaphragm have concomitant intraabdominal injuries, typically liver and spleen lacerations. ¹⁸⁹ Pelvic and spinal fractures are frequent, as is closed head injury. Further, up to 10% of patients with diaphragm rupture due to blunt trauma also have aortic injury¹⁹⁰ (Fig. 17.33). Diaphragm rupture due to blunt trauma is more commonly seen on the left, possibly because the liver acts as a buffer on the right. In several large series, 67–88% of ruptures were left sided (Fig. 17.33), 12–28% were right sided (Fig. 17.34) and 5% were either bilateral or central in location.^{184.187. and 191.} While this left-sided predominance may be due to the protective effect of the liver, it may also reflect difficulties in diagnosis of right-sided injuries and that patients with right-sided injuries may have more associated and severe injuries. Autopsy studies of trauma victims who died at the accident site or before hospitalization report an equal frequency of right and left-sided ruptures, ¹⁸⁹ in marked contrast to the left-sided predominance noted in surgical series.^{184.187. and 191.} This finding suggests that patients with right-sided ruptures are more likely to die acutely, due to other severe injuries. For example, Boulanger et al. ¹⁸⁹ found that 100% of patients with right-sided ruptures had associated intraabdominal injuries whereas only 77% of patients with left-sided rupture had such injuries.

Preoperative diagnosis of diaphragmatic rupture after blunt trauma can be difficult. Diagnosis by chest radiography depends on demonstration of herniated abdominal contents within the thorax (see below). However, herniation of abdominal contents does not always occur in cases of traumatic rupture, particularly if positive-pressure ventilation is used (Fig. 17.34).^{192. and 193.} Prior to widespread use of CT in the setting of trauma, a significant number of diaphragmatic injuries were discovered at exploratory laparotomy.^{186.187. and 192.} Shah et al. ¹⁹⁴ reviewed 980 reported cases of traumatic rupture and found that only 44% were diagnosed prior to exploratory surgery. Over 40% of the ruptures were diagnosed during surgery or at autopsy and, in 15% of cases, the injury was not diagnosed during the initial hospitalization. Beal and McKennan, ¹⁹⁵

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