A 22-year-old man complains of shortness of breath and chest pain after a motorcycle crash. He is breathing spontaneously but has decreased breath sounds on the left side. His respiratory rate is 40; his heart rate is 115 beats per minute (bpm); and he has an oxygen saturation of 82% on a non-rebreather mask.

Motor vehicle crash is the most common etiology of thoracic trauma. Rib fractures occur in about 10% of blunt trauma patients and can indicate injuries to the underlying lung parenchyma, pleura, or abdominal viscera. Among patients with rib fractures, flail chest occurs in about 5% of all trauma patients and confers significant morbidity secondary to the underlying pulmonary contusions. Rib fractures can also be seen after episodes of severe coughing, in repetitive sports (most commonly in rowing and golf), and in the setting of metastatic malignancy. Most mortality in rib fracture patients is actually related to extra-thoracic injuries, including head, craniofacial, and intra-abdominal injuries.¹

Pneumothorax is a common problem in acute care surgery, occurring in up to 40% of blunt trauma patients.² In primary pneumothorax, air can gain entry into the pleural space spontaneously from subpleural blebs, or as a result of diffuse pulmonary disease. Secondary causes of pneumothorax are numerous and include penetrating or blunt trauma, barotrauma from mechanical ventilation, thoracic procedures or instrumentation, and central venous catheter placement. Rare causes include esophageal perforation and catamenial pneumothorax secondary to pleural endometriosis.

Hemothorax occurs in up to 50% of blunt trauma cases,² but can also result from malignancy, be iatrogenically induced, or develop spontaneously. A list of causes and examples of hemothorax is given in Table 21–1.

Rib fractures are usually uncomplicated and require no specific treatment, but they can also be associated with significant injuries, including pneumothorax, hemothorax, and pulmonary contusion. Fractures of the lower ribs can signal intra-abdominal injuries, notably of the liver and spleen. Despite traditional teaching, there is no evidence of an association between aortic injuries and first and second rib fractures.³

Flail chest refers to a free-floating segment of the chest wall secondary to consecutive rib fractures. The mobile segment moves paradoxically during respiration (e.g., inward during spontaneous inspiration) and is associated with contusions of the underlying pulmonary parenchyma that confer significant morbidity and mortality. Pulmonary contusions are essentially a bruise of the lung, with alveolar hemorrhage and edema related to capillary leak. Direct disruption of capillary and alveolar walls leads to transudation of fluid and blood into the alveolar space and interstitium, with associated impaired oxygen exchange. In addition, there is a change in vascular resistance, leading to decreased blood flow to healthy lung, decreased surfactant, and resultant atelectasis.

Air that accumulates in the pleural space compresses lung tissue, reduces pulmonary compliance, and compromises ventilation and diffusion of oxygen. If air enters the pleural space without the ability to escape, pressure increases, leading to a tension pneumothorax with compression and shifting of the mediastinum, decreased venous return to the heart, and obstructive shock with cardiorespiratory collapse.

Blunt or penetrating injury can result in bleeding from any structure in the chest, including major and minor vascular structures, the chest wall, the lung, or the heart itself, with resultant hemothorax. Bleeding from tumor is usually related to tumor implants on the pleural surface. Rarely, aneurysmal diseases of the aorta or congenital abnormalities, including sequestrations, can present with hemothorax. Hemothorax can also result from intra-abdominal bleeding via a defect in the diaphragm.

The hemodynamic consequences of hemothorax are related to the severity and speed of blood loss, with hemorrhagic shock possible if the bleeding is brisk, especially if injury to a major cardiovascular structure is the culprit. The respiratory consequences of hemothorax, as with pneumothorax, relate to the space-occupying effect of accumulation of blood in the pleural space, with resultant lung collapse, decrease in ventilation, and decreased compliance. Clotting of blood that enters the pleural space is generally incomplete due to the continuous motion of respiration. Clot lysis begins quickly, which increases oncotic pressure, induces transudation of fluid into the space, and enlarges the effusion within a few days, even without ongoing bleeding. Empyma can result if bacterial contamination of the hemothorax occurs. If a hemothorax is not immediately evacuated, fibrin deposition at the pleural surfaces can prevent a portion of the lung from expanding. This “trapped lung” creates permanent atelectasis and persistent decreased ventilation of a portion of the lung.

Rib fractures often present with pain that worsens with deep breathing. Crepitance and ecchymosis can be seen as well. A click can sometimes be heard. Decreased breath sounds may reflect splinting, pneumothorax, hemothorax, or pulmonary contusion, with crackles sometimes heard with contusion. Flail chest is, by definition, a freely mobile segment of the chest wall, and can be seen as a portion of the chest wall that moves independently and opposite from the uninjured portion of the chest wall.

The presentation of pneumothorax depends on the amount of air in the pleural space as well as the underlying condition of the lung tissue. Patients with secondary spontaneous pneumothorax often have worse symptoms because of decreased lung function. Most patients with small pneumothoraces present with ipsilateral chest pain, usually sharp and pleuritic, as well as labored tachypnea. Patients may complain of dyspnea, a nonproductive cough, or orthopnea. Tension pneumothorax, by contrast, presents with severe symptoms, respiratory embarrassment, and hemodynamic collapse. Physical examination reveals hyperresonance on percussion, decreased chest wall excursion, and diminished breath sounds on auscultation, and occasionally absent fremitus. Accessory muscles are employed to aid breathing. Distended neck veins can be seen. Rarely, subcutaneous emphysema can be palpated or seen, and mediastinal air can be heard on auscultation (Hamman’s sign). Tracheal deviation away from the side of a tension pneumothorax is a rare and late sign. Arterial oxygen tension can be low, and carbon dioxide tension can be elevated.

Patients with hemothorax present in much the same way as patients with pneumothorax. Indeed, most trauma patients with hemothorax will also have associated pneumothorax. Tachypnea, dyspnea, decreased ipsilateral breath sounds, and tachycardia are common, the latter sign often from blood loss. In contrast to pneumothorax, patients with hemothorax demonstrate dullness to percussion on the affected side, and their jugular veins may be flat given hemorrhagic shock.

Rib Fractures

Rib fractures are not often confused with other injuries but can easily be missed on initial imaging. Pulmonary contusion can be confused with intrinsic pulmonary lesions such as pneumonia or aspiration.

Pneumothorax

See Table 21–2.

Hemothorax

See Table 21–3.

Chest x-ray is the most commonly employed test in the diagnosis of chest pathology after trauma and a standard part of the trauma evaluation. In fact, along with the focused assessment with sonography for trauma (FAST) examination, plain film of the chest is an adjunct to the primary survey. Plain films allow visualization of large hemothoraces and pneumothoraces, which are important to exclude early in the trauma evaluation.

The radiologic diagnosis of pneumothorax is usually not difficult. Chest x-ray demonstrates a visceral pleural line without distal lung markings. Lateral and decubitus views can be used in equivocal cases. Many clinicians still use expiratory views to detect small pneumothoraces, though their usefulness is controversial. Two centimeters of visible pneumothorax on plain film is equivalent to about 50% of the hemithorax.⁴ The deep sulcus sign can be seen in cases of tension or in large simple pneumothoraces, especially in supine patients. If the pleura becomes partially adherent or scarred to the chest wall, loculation of the pneumothorax can occur.

Typically, fluid collects in the most dependent portion of the pleural space. Fifty milliliters of blood can be seen on upright chest x-ray in the posterior costophrenic angle, whereas a lateral decubitus film can demonstrate as little as 5 mL.⁵

With regard to rib fractures, these can often be missed on plain films, with a sensitivity in the anterior-posterior view of as low as 15%.⁶ Dedicated rib films with oblique views, while more specific, are often not indicated, as detection of additional fractures rarely alters management. Instead, computed tomography (CT) is more useful to rule out additional injuries, especially pulmonary contusions, which plain film fails to detect in up to one third of cases.^7,8

Chest CT is the most accurate radiographic tool available to diagnose chest pathology in the stable trauma patient. In pneumothorax, chest CT is the gold standard to which other modalities are compared. Very small collections of gas can be detected, and loculated pneumothoraces are easily and safely evacuated by CT guidance. In addition, any underlying disease of the lung can be assessed and described by CT scan.

For possible hemothorax, CT can detect as little as 2 mL of fluid in the pleural space, and the density of pleural fluid on CT can suggest its origin and acuity. CT can characterize rib fractures and can indicate active bleeding and associated injuries that may require additional attention. In addition, CT is the gold standard for describing pulmonary contusion, seen as parenchymal densities in non-lobar distribution that vary from faint, ill-defined areas to extensive opacification, depending on injury severity. These lesions are typically peripherally located and can be contrecoup from the applied force. Contusion often is not seen on initial imaging and is maximal at 48 hours. If patchy consolidations persist beyond 6 to 10 days, consider wrong diagnosis or superimposed pneumonia, atelectasis, aspiration, or adult respiratory distress syndrome.

Ultrasound (US) is being increasingly used to quickly evaluate patients with acute conditions. A high-frequency linear transducer is employed to scan the anterior chest. In one study, US was equally specific and more sensitive than standard chest x-ray (CXR) in the diagnosis of pneumothorax after trauma.⁹ Newer studies confirm the utility of US in the diagnosis of rib fractures¹⁰ and in differentiating between pathologic and traumatic fractures.¹¹ Hemothorax is echoic on ultrasound and can detect as little as 20 mL of fluid. US performed in the emergency department has a sensitivity of 12.5% to 96.2% and specificity of 98.4% to 100% for all but very small hemothoraces compared to CT.^{12, 13, and 14} A scan of the chest can be easily incorporated into the FAST examination as part of the trauma evaluation to evaluate for hemothorax or pneumothorax as a potential cause of shock. However, while US can reliably predict the presence of and even the amount of hemothorax, it is not superior to chest CT and does not provide information about chest wall and mediastinal structures. For these reasons, US should not be considered a definitive test unless CT is unavailable or contraindicated.

Historically, angiography was suggested for first and second rib fractures, out of concern for concurrent aortic injury. Modern evidence suggests, however, that in the absence of a widened mediastinum or other evidence of vascular injury, angiography is not indicated.¹⁵

Other imaging modalities are less helpful for chest trauma in the acute setting. Bone scan can play a role in stress fractures related to sports or repetitive injuries, which are often not visible on plain x-ray imaging; however, such a study in the emergent patient is impractical. Magnetic resonance imaging (MRI) is difficult to interpret and often not a reasonable option in acute trauma but can be useful in stress fractures, though even less so than bone scan.¹⁶

Table 21–4 compares the sensitivity and specificity of various radiological modalities in the diagnosis of pneumothorax.

Plain Film

See Table 21–5.

Normal Chest Film

In a normal chest film, the pleural line is flush with the chest wall, with visible vessels seen extending to the margin of the pleura. As detailed in the following, upright chest films are more helpful than supine films in detailing pathology (Figure 21–1).