AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Background

Lung trauma is an important component of thoracic injuries. Thoracic injuries have immense medical and social impact, contributing to as much as 25% of trauma-related deaths and contributing significantly to another 25% of all deaths.

Thoracic trauma is the leading cause of death, morbidity, hospitalization, and disability in Americans from the age of 1 year until the middle of the fifth decade of life. Trauma is, therefore, a major national health care problem.

Most thoracic injuries are attributable to road traffic accidents. The incidence of thoracic trauma in the United States is 12 per million per day, and 20-25% of deaths resulting from trauma are attributed to thoracic injury. Thoracic trauma is estimated to be responsible for approximately 16,000 deaths per year in the United States.

For excellent patient education resources, visit eMedicine's Lung and Airway Center; Back, Ribs, Neck, and Head Center; and Skin, Hair, and Nails Center. Also, see eMedicine's patient education articles Collapsed Lung, Costochondritis, Chest Pain, Puncture Wound, and Lupus (Systemic Lupus Erythematosus).

Pathophysiology

Blunt versus penetrating trauma

Chest trauma is traditionally described as blunt or penetrating. The trauma is classed as blunt when the chest wall remains intact and as penetrating when the integrity of the chest wall is breached. Traffic accidents (steering-column injuries) are the most common cause of blunt trauma, whereas penetrating trauma may result from stab wounds and bullet and shrapnel injuries. (See also the eMedicine articles Blunt Chest Trauma and Penetrating Chest Trauma, as well as the article Injuries to the Chest, on Medscape.)

Blunt trauma

Blunt trauma is more common than penetrating chest injury, accounting for more than 90% of thoracic injuries. Two mechanisms occur in blunt trauma: (1) the direct transfer of energy to the chest wall and thoracic organs and (2) differential deceleration, experienced by the thoracic organs at the time of the impact. A direct blow to the thoracic wall produces crush and shear injury associated with fractures of soft tissues and bones, such as the ribs. Injury to the thorax with substantial pressure may sufficiently increase the intrathoracic pressure to cause rupture of gas- or fluid-filled organs.

Injury from deceleration occurs when forward motion of the thorax is abruptly stopped while the intrathoracic viscera continue to move forward, as in a steering-column injury. In deceleration injury, the visceral structures not bound to the chest wall move forward until they are halted by the inner surface of the thoracic wall in a second internal collision or until the stresses created by the motion exceed tolerance of the tissue, causing injury.

Ribs may be fractured at the point of impact, and damage to the underlying lung may produce lung bruising or puncture. The ribs usually become fairly stable within 10 days to 2 weeks. Firm healing with callus formation is seen after about 6 weeks.

Penetrating trauma

Penetrating injury is usually the result of the abrupt, direct application of a mechanical force to a focal area. A knife or projectile, for example, produces tissue damage by stretching and crushing, and injury is usually confined to tissues in the path of penetration. The severity of the internal injury depends on the organ penetrated and on how vital the organ is.

The degree of injury also depends on the biomechanics of the penetrating projectile and includes, among other factors, the efficiency with which energy is transferred from the object to the body tissues. Other factors that dictate the severity of injury include the physical characteristics of the weapon, such as its velocity, size of impact face, and deformability, and the density of the body tissues penetrated. The velocity of the penetrating projectile is the single most important factor that determines the severity of the wound.

Knives usually produce limited injury because they are classified as low-velocity projectiles. Knife wounds are confined to the areas that have been penetrated. Knife wounds are usually well tolerated, and even stabbing of the heart can often be survived with prompt medical attention.

Bullets are classified as high-velocity projectiles, particularly bullets that can achieve velocities faster than 1800-2000 ft/s. High-velocity projectiles cause injuries of similar severity to knife wounds and tissue damage in the path of the penetrating bullet. However, unlike knives, bullets also produce injury in structures adjacent to the bullet path. They produce tissue cavitation and, by producing shock waves, extend the area of tissue damage. Thus, a bullet passing through body tissues not only damages tissues directly in its path but also causes adjacent tissues to extend outward; in doing so, the bullet expands the sphere of injury.

The outward displacement of tissues produces a temporary cavity, the diameter of which may be 20-30 times the diameter of the bullet. Thus, unlike a knife wound, high-velocity bullet wounds produce injury far beyond the flight path of the bullet. Furthermore, the subatmospheric pressure generated within the cavities produced by bullets may suck dirt and debris into the wound, which compromises the injury and adds to its severity.

Impalement injuries, in which a large foreign body traverses a body cavity or extremity, produce a life-threatening situation. Impalement is uncommon, with only occasional reports in the literature. Reports of impalement injuries limited to the thorax are even less common. The heart, great vessels, lungs, and thoracic cage may be impaled. Major impalement injury can involve any part of the body, with each appearing as an anatomically distinct injury. Because the impaling object may penetrate several organs in its path, a complete assessment for life-threatening injuries is important. The cardinal rule of management is to leave the impaling object in situ while the patient is rapidly transported to an operating theater, because it can have a tamponadelike effect on damaged vascular structures. The object should be removed only in a controlled surgical environment.

Complications of lung trauma

Chest-wall injuries, such as rib fractures, can impair breathing because of associated pain. Ventilation and gas exchange can be compromised in this fashion. Direct lung injuries, such as pulmonary contusions, interfere with gas exchange because of the shunting and dead-space ventilation resulting from the presence of blood or fluid-filled alveoli and injured pulmonary microvasculature. Pneumothoraces and hemothoraces are space-occupying lesions that interfere with gas exchange primarily by compressing otherwise healthy lung parenchyma. A component of direct pulmonary parenchymal injury is frequently found with these etiologies.

Pneumothorax

A frequent complication of chest trauma is a pneumothorax, or the collection of air within the pleural cavity. The lungs are elastic organs with an inherent tendency to collapse. The pleural space has a negative pressure compared with atmospheric pressure, and because the alveolar pressure is always greater than the pleural pressure, a communication between an alveolus and the pleural space results in airflow down the pressure gradient until equilibrium occurs or until the communication is sealed. (See also the eMedicine articles Pneumothorax and Pneumothorax, Iatrogenic, Spontaneous and Pneumomediastinum.)

As the pneumothorax enlarges, the lung becomes smaller. The main complication of this process is a decrease in the vital capacity and in the partial pressure of oxygen. Healthy and young individuals can tolerate these changes fairly well, with minimal changes in vital signs and symptoms. However, persons with underlying lung disease may have respiratory distress.

Pneumomediastinum

Excessive intra-alveolar pressures may lead to rupture of perivascular alveoli. Air escapes into the perivascular connective tissue, with subsequent dissection into the mediastinum, causing a pneumomediastinum. Air from a pneumomediastinum may then dissect into the visceral, retropharyngeal, and subcutaneous spaces of the neck. From the neck, the subcutaneous compartment is continuous throughout the body; thus, air can distribute widely. (See also the eMedicine article Pneumomediastinum.)

Mediastinal air can also track down into the retroperitoneum and other extraperitoneal compartments. If the mediastinal pressure rises abruptly or if decompression in not sufficient, the mediastinal parietal pleura may rupture and cause a pneumothorax (in 10-18% of patients).

Hemothorax

A hemithorax can accommodate approximately 40% of the total blood volume. Aspiration of large amounts of blood (>1500 mL) in the initial drainage from the chest tube suggests injury to a major vessel or cardiac rupture. This finding is an indication for thoracotomy. (See also the eMedicine articles Hemothorax [in the Thoracic Surgery section] and Hemothorax [in the Pediatrics section].)

Bronchial injury

Bronchial or tracheal ruptures are rare consequences of blunt injury (0.4%) and are usually caused by deceleration or compression injury. A bronchial or tracheal rupture may appear as either a pneumothorax that fails to resolve or a persistent air leak through the thoracostomy tube.

Fallen lung

A partial tear or complete transection of the major airways as a result of penetrating or blunt trauma may result in fallen lung. Most of these injuries are related to high-speed road accidents. More than 80% of tracheobronchial ruptures occur within 2.5 cm of the carina.

Two basic mechanisms producing major airway disruption in blunt trauma have been implicated: The first is reflex closure of the glottis and compression of the tracheobronchial tree, causing intraluminal pressure to quickly reach a level too high for the airway to sustain. The second is deceleration injury produced by shearing forces, the result of sudden deceleration and rotation of the lung on the relatively fixed carina.

Lung contusion

A lung contusion represents a bruise of the lung and is usually caused by blunt trauma. Following blunt trauma, such as that produced by a deceleration or blast injury, a pressure wave compresses the thoracic cavity, injuring the underlying lung. In the young, the pliable thoracic wall usually returns to its initial state, and no rib fracture may occur despite underlying lung injury. In older individuals, rib fractures with underlying lung contusion are common.

A lung contusion is usually a combination of alveolar hemorrhage with interstitial hemorrhage and edema. Most patients have minimal respiratory deficit due to the injury. Extensive contusions may result in respiratory difficulty or progress to adult respiratory distress syndrome.

Lung laceration

Pulmonary lacerations are tears in the lung parenchyma. If the laceration fills with blood, a spherical hematoma forms. If it fills with air, a traumatic pneumatocele or air cyst forms. If blood and air are present, an air-fluid level also may be seen.

Aortic injury

An aortic rupture is usually placed at the isthmus just distal to the left subclavian artery. Approximately 80-90% of patients with rupture of the thoracic aorta die before reaching the hospital. Surviving patients who reach the hospital may have minimal if any symptoms. After cardiovascular stabilization, emergency surgery is necessary. (See also the eMedicine article Aorta, Trauma.)

Blunt cardiac injury

A variety of injuries may follow blunt trauma to the heart. These include myocardial concussion, contusion, and myocardial rupture. The right atrium and ventricle are the chambers most frequently injured by virtue of their anterior position in the thorax, followed by the left atrium and left ventricle. The survival rate with a 1-chamber rupture is about 40%. A 2-chamber rupture has uniform mortality.

Pericardial tamponade

Cardiac rupture, aortic disruption, or myocardial contusion without rupture may cause pericardial tamponade. The diagnosis of pericardial tamponade is usually suspected clinically when persistent hypotension cannot be explained on the basis of hemorrhage, tension pneumothorax, or hemothorax. Neck vein distention is an important physical sign, but it may be masked by the cervical collar. Urgent pericardial drainage with the patient under local anesthesia should be considered and may be curative.

Diaphragmatic rupture

Symptoms similar to a pneumothorax may develop from a diaphragmatic rupture, as lung compression may cause hypoxemia. Intubation and mechanical ventilation may be needed for adequate oxygenation. Hemothorax may be from a ruptured spleen.

Esophageal tears

Esophageal tears are estimated to occur in 1% of patients with blunt trauma, but they are far more common with penetrating or iatrogenic trauma. Esophageal rupture carries a high mortality rate secondary to rapidly developing mediastinitis. Survival improves dramatically if the esophageal injury is recognized and treated within 24 hours of its occurrence.

About 82% of esophageal tears caused by blunt trauma occur in the cervical and upper thoracic esophagus. It is postulated that compression of the esophagus between the sternum and vertebral column is the mechanism of injury. Tears may also occur in the distal esophagus just above the gastroesophageal junction along the left posterolateral wall. The mechanism of injury in this setting is probably similar to spontaneous rupture in Boerhaave syndrome when esophageal pressures rise against a closed glottis.

Iatrogenic lung complications

Iatrogenic tracheal rupture is a serious complication with potentially high postoperative mortality (which is mostly influenced by the underlying disease). Early surgical repair is a preferred treatment. The incidence of tracheobronchial rupture is lower in children than in adults, with a ratio of 1:10.

Blunt trauma is the most common cause, although tracheobronchial rupture may occur as a complication of tracheotomy or bronchoscopy. Because most patients with severe blunt or penetrating trauma are treated in an emergency setting before imaging is performed, iatrogenic injury from placement of catheters, chest tubes, endotracheal tubes, feeding tubes, pacemaker electrodes, and counter pulsation balloons is common. Simple radiologic procedures, such as chest radiography and fluoroscopy, permit diagnosis of unsuspected and clinically silent complications.

Clinically important iatrogenic trauma to the lung depends on the increasing use of overpressure ventilation. Experimental evidence shows that the lung can be damaged with interstitial emphysema at peak pressures as low as 40 cm water. The chest radiograph may show an early pathognomonic finding of perivascular air collections. The respirator treatment should then be adjusted to avoid pneumomediastinum and pneumothorax. Follow-up chest radiography after these procedures is therefore important.

Other lung injuries or illnesses

Iatrogenic intrathoracic trauma can occur after procedures such as lung biopsy and thoracentesis, among others. Mechanical ventilation with positive end-expiratory pressure predisposes the patient to the development of barotrauma and pneumothorax. Thoracic injuries can also be produced by inhalation of toxic and inert substances, blast-related injuries, and radiation.

Iatrogenic trauma

Thoracostomy tubes in a traumatized patient are often placed in an emergency setting. Malpositioned placement of chest tubes commonly occurs. The tubes may be malpositioned in extrathoracic, intraparenchymal, mediastinal, or intrafissural locations (26-58%). Misplaced chest tubes may cause intercostal artery lacerations, liver lacerations, splenic injuries, and diaphragmatic tears. Extrathoracic, mediastinal, and intraparenchymal chest tubes require immediate repositioning or replacement.

The significance of chest tubes within the fissure is controversial, although development of empyema with intrafissural chest tubes has been reported. Computed tomography (CT) scanning is more accurate than portable anteroposterior (AP) chest radiography in identifying malpositioned chest tubes in the patient with trauma.

Drug-induced lung disease

Drug-induced lung disease is a relatively common condition. Many mechanisms are involved; some are dose related, whereas others result from a hypersensitivity reaction that requires prior sensitization. It is often impossible to predict who will develop drug-treatment–associated lung disease.

The clinical and radiographic changes in drug-induced disease are nonspecific. Many drugs may produce a similar clinical picture, and individual drugs may cause different types of reactions. Chest radiographs and CT scans must be correlated with the patient's clinical and drug history, response to alterations in therapy, and laboratory data.

Drug-induced lung disease may manifest in a variety of forms:

• Allergic-type reactions: asthma, hypersensitivity pneumonitis, or eosinophilic pneumonia
• Cough or bronchitis caused by inflammation of the air sacs, pneumonitis, or pulmonary infiltrate
• Interstitial fibrosis
• Noncardiogenic pulmonary edema
• Alveolar hemorrhage
• Pleural effusion
• Lung vasculitis
• Mediastinal inflammation
• Hilar/mediastinal lymphadenopathy
• Respiratory failure
• Granulomatous lung disease
• Drug-induced systemic lupus erythematosus

Direct toxicity

Lung toxicity has been described with many drugs, such as amiodarone, angiotensin-converting enzyme (ACE) inhibitors, and retinoid acid. However, lung toxicity is particularly common with cytotoxic agents, such as bleomycin, busulfan, and carmustine. In many cases, the toxicity is dose related. The toxicity may be accentuated by other factors, such as increasing patient age, decreased renal function, radiation therapy, oxygen therapy, and other associated cytotoxic drug therapy.

The pathologic changes are those of increased permeability of the alveolar sacs, which causes pulmonary edema and leads to diffuse alveolar damage. This is followed by interstitial pulmonary fibrosis. The pulmonary fibrosis develops as a chronic, insidious disease.

The radiologic features are those of diffuse lung opacities, reticular or reticulonodular pattern, or airspace consolidation, mainly seen at the lung bases. High-resolution CT scanning more effectively shows the reticular or reticulonodular pattern and airspace consolidation. High-resolution CT scanning also depicts ground-glass attenuation, which is often associated with intralobular lines, traction bronchiectasis, traction bronchiolectasis, and honeycombing.

Hypersensitivity reaction

A hypersensitivity reaction affecting the lungs may occur after exposure to a variety of drugs and extrinsic agents. Sulfasalazine is the drug most frequently associated with hypersensitivity reactions. Drug-related hypersensitivity is not dose related and requires prior sensitization to the drug. The reaction is a result of interactions between the drug and humeral antibodies or sensitized lymphocytes.

Fever, peripheral eosinophilia, and asthmatic dyspnea are the usual clinical features. The radiographic findings are those of bilateral peripheral areas of fleeting airspace consolidation. Lung parenchymal changes are similar to those of acute or chronic eosinophilic pneumonia. Most patients generally respond to withdrawal of the drug, although some patients may need steroid therapy.

Pulmonary edema

Noncardiogenic pulmonary edema may occur as a complication of the use of a variety of drugs, especially when cytotoxic agents, such as interleukin, methotrexate, cytosine, and arabinosine, are used. Pulmonary edema characteristically occurs within hours of the drug use. The radiologic and clinical features may be indistinguishable from those of cardiogenic edema.

Pulmonary hemorrhage

Pulmonary hemorrhage is most commonly associated with anticoagulant therapy or drug-induced thrombocythemia, but it has also been reported with nitrofurantoin, quinidine, oxyphenbutazone, and penicillamine. In rare cases, pulmonary hemorrhage is associated with pulmonary renal syndrome similar to Goodpasture syndrome. Hemoptysis is a common manifestation. The radiologic appearance consists of diffuse patchy areas of airspace consolidation, which can be extensive and severe.

Lupus erythematosus syndrome

Drug-induced systemic lupus erythematosus may be associated with procainamides, hydralazine, isoniazid, or phenytoin. Most patients have positive antinuclear antibodies. The clinical and radiologic manifestations of drug-induced systemic lupus erythematosus do not differ from those of the idiopathic form of systemic lupus erythematosus. Pleural effusion, often with concomitant pericardial effusion, is a common manifestation. Subsegmental atelectasis and basilar consolidation are typical radiographic findings.

Pulmonary granulomas

Pulmonary granulomas can develop as a result of complications from a variety of drugs, such as methotrexate and nitrofurantoin. Histologically, the granulomas are composed of macrophages. Granulomatous reaction may also occur as a complication of chronic aspiration of mineral oils, which form chronic conglomerate masses in the basilar aspects of the lungs. Pulmonary granulomas are a known complication when a particulate suspending agent for oral use (eg, talc) is deliberately or accidentally injected intravenously.

Bronchiolitis obliterans

Bronchiolitis obliterans is a frequent complication of penicillamine therapy prescribed for rheumatoid arthritis.

Lipoid pneumonia

Lipoid pneumonia may occur as a complication of accidental aspiration of mineral or vegetable oil. Mineral or vegetable oils are often used as laxatives or lubricants, which may be chronically aspirated. The risk is especially great in elderly patients with swallowing difficulties or hiatal hernia, in which night reflux may be aspirated.

Radiation pneumonitis and fibrosis

When the normal lung is exposed to irradiation, 2 well-recognized adverse effects may follow: pneumonitis and fibrosis. Radiation pneumonitis occurs during the acute injury phase, typically within the first 6 months after treatment. Lung injury is initiated within the irradiation field, resulting in damage at the capillary-alveolar level, with collagen deposition occurring in the alveolar wall and alveolar spaces. The characteristic histologic finding in patients with radiation pneumonitis is a prominent inflammatory cell infiltrate in the alveoli and in the pulmonary interstitium.

Radiation-induced lung fibrosis occurs months to years after irradiation. Its pathogenesis is less well defined than that of radiation pneumonitis, although some evidence suggests that cytokines and growth factors play a role. The target cells of radiation injury in the lung are thought to be the type II pneumocytes, which are found in the alveoli, and the vascular endothelial cells, but inflammatory cell infiltrates play an accessory role. Once the target cells sustain injury, the recruitment of inflammatory cells in the alveolar interstitium contributes to the acute inflammatory response, the subsequent deposition of collagen in the lung, and the development of noncompliant lungs.

Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a term used for severe acute respiratory failure of diverse etiology. The associated morbidity and mortality rates are high (50-70%). Regardless of etiology, the basic pathogenesis of ARDS is a systemic inflammatory response leading to a diffuse inflammatory process that involves both lungs. The result is diffuse alveolar and endothelial damage with increased pulmonary capillary permeability and excessive extravascular water accumulation in the lung.

ARDS is associated with a variety of serious illnesses and is most commonly associated with sepsis and multiple organ failure. The clinical presentation is that of progressive hypoxemia, radiographic evidence of pulmonary edema, decreased lung compliance, and pulmonary hypertension. There is no specific treatment of ARDS, and its management remains supportive. Therapeutic goals include resolution of underlying conditions, the maintenance of acceptable gas exchange and tissue oxygenation, and the prevention of iatrogenic lung injury.

Gas embolism

Gas embolism is an uncommon complication of lung injury, decompression sickness, surgery, or the accidental infusion of gas during various diagnostic procedures. Iatrogenic gas embolism is often not considered or recognized. As a result, mortality and morbidity rates can be high. Gas embolism must always be considered as a differential diagnosis when a patient presents with unexplained neurologic symptoms in the appropriate clinical setting. Hyperbaric oxygen treatment may be lifesaving.

Fat-embolism syndrome

The clinical fat-embolism syndrome, a rare condition that is characterized by progressive pulmonary insufficiency, cerebral dysfunction, and petechiae, is typically associated with severe skeletal injuries. Fat droplets appear in the circulating blood and embolize to the capillaries of the lungs and other organs. Whether fat droplets are of mechanical or chemical origin remains controversial. These fat droplets cause mechanical occlusion of lung capillaries followed by chemical changes associated with hydrolysis of the neutral fat to free fatty acids. The free fatty acids produce a toxic and inflammatory reaction resulting in pulmonary edema, hemorrhage, and microatelectasis.¹

The clinical and radiographic abnormalities appear after an initial 12- to 72-hour latent period. The chest radiographic findings, which are nonspecific, comprise bilateral patchy or diffuse alveolar and interstitial lung densities. Aggressive management has markedly improved the survival rate, and mortality is now rare.

Curtis and associates reviewed the clinical course and radiographs of 30 patients with fat-embolism syndrome.² All 30 displayed the syndrome's classic triad of neurologic dysfunction, respiratory insufficiency, and petechiae. Responses to embolized fat were noted in 3 patients. The hyperacute response was demonstrated by 2 patients with paradoxical embolization of fat to the systemic circulation. A classic response, with transient respiratory compromise and variable radiographic findings, was found in 18 patients. Two deaths in the classical response group were considered to be the result of massive pulmonary emboli. The last 10 patients displayed a chest radiograph compatible with pulmonary edema in the clinical setting of ARDS. The degree of respiratory dysfunction and pulmonary damage in members of this third group correlated with the development of disseminated intravascular coagulation.

Traumatic asphyxia

Traumatic asphyxia is unique to the pediatric population; it commonly results from blunt compressing thoracic trauma, with sudden airway obstruction and abrupt retrograde high pressure in the superior vena cava. Children with traumatic asphyxia have a dramatic physical presentation characterized by cervical and facial petechial hemorrhages or cyanosis associated with vascular engorgement and subconjunctival hemorrhage. Despite the alarming presentation, the prognosis is good. Central nervous system injuries, pulmonary contusions, and intra-abdominal injuries are common associated injuries.

Lung hernia

Lung hernia is a rare complication of lung trauma or inadequate healing from recent or remote thoracic surgery, although a congenital variety has been reported. Most patients with a lung hernia present with acute respiratory symptoms. Awareness of the clinical and radiologic appearance of lung hernia helps prevent its confusion with other conditions, such as subcutaneous emphysema, chest tumor, pneumothorax, or a focus of infection.

Frequency

United States

Blunt chest trauma accounts for 100,000 hospital admissions per year in the United States, and chest injuries are the third most frequent type of injury following high-speed motor vehicle accidents.

The age-adjusted incidence of primary spontaneous pneumothorax is 7.4 cases per 100,000 men and 1.2 cases per 100,000 women. The age-adjusted incidence of secondary spontaneous pneumothorax is 6.3 cases per 100,000 men and 2 cases per 100,000 women. The incidence of iatrogenic pneumothorax is not known, but it is probably higher than those of the primary and secondary spontaneous pneumothoraces combined. Pneumomediastinum occurs in approximately 1 per 10,000 hospital admissions.

International

No accurate data are available on the incidence of lung trauma.

Mortality/Morbidity

In the United States, thoracic trauma accounts for about 25% of all trauma deaths.³ Overall, thoracic trauma has an approximate 10% mortality rate, with chest injuries causing 25% of trauma deaths in the United States. Many of these deaths could be prevented with prompt diagnosis and treatment. Among patients who are transferred to the operating room within 24 hours of admission, the incidence of blunt thoracic trauma has been reported to be as high as 62.5%.⁴

In a 5-year Canadian study of patients admitted to an urban trauma unit, 96.3% had sustained blunt trauma; the remaining 3.7% were injured with a penetrating mechanism. The causes of blunt injuries were attributed to motor vehicle accidents (70%), suicides (10%), falls (8%), homicides (7%), and others (5%). The incidence of thoracic trauma was 46%. Patients with thoracic injuries had a mortality rate of 15.7%, and those without thoracic injuries, 12.8%.⁵

A spontaneous pneumothorax is a benign condition, but rare deaths have been reported. Secondary spontaneous pneumothoraces can be life threatening, depending on the severity of the underlying disease and the size of the pneumothorax. Compared with similar patients without pneumothorax, age-matched patients with chronic obstructive pulmonary disease have a 3.5-fold increase in relative mortality when a spontaneous pneumothorax occurs.

Mortality rates in patients with chronic obstructive pulmonary disease and spontaneous pneumothorax vary in the range of 1-17%. Iatrogenic pneumothorax may cause substantial morbidity and, rarely, death.

A number of long-term sequelae may follow unrecognized bronchial tears, such as bronchial stenosis, bronchomalacia, and recurrent atelectasis or pneumonia of the affected lobe. Strictures also may follow repairs of bronchial tears.

Thoracic aorta rupture occurs in patients experiencing severe decelerating forces, such as those from high-speed car accidents or a fall from a great height. They have a high mortality rate. Aortic transection causes 16% of all deaths from automobile accidents. Of patients sustaining an aortic transection, 85% die before reaching the hospital. Of the remaining short-term survivors, 50% die within 24 hours.

Race

There is no racial predilection for lung trauma.

Sex

Although exact figures are not available, lung trauma is more common in men than in women.

Age

Any age can be involved, although thoracic trauma typically affects the young and is the leading cause of death in the first 3 decades of life. Injury accounts for more than 50% of deaths in children and is the third leading cause of death, after cancer and arteriosclerosis, in all age groups.

Anatomy

Anatomy and physiology of the lung

The lung is a complex organ composed primarily of air sacs, or alveoli, enmeshed within a rich blood supply. The lungs receive the entire output of the right ventricle. Lung trauma has the potential to cause significant systemic pathophysiologic conditions as a result of interference with gas exchange or significant blood loss if major pulmonary vessels are injured. Injury to surrounding or supporting structures in the chest can compromise lung function as well.

The major physiologic functions of the lung include uptake and diffusion of oxygen to restore acceptable oxygen tension of blood returning to the systemic circulation, and offloading and elimination of carbon dioxide and other gaseous by-products of metabolism that arrive via the pulmonary arteries.

Host-tissue characteristics and lung trauma

Host-tissue characteristics, especially the prestress state, are important in determining the type and extent of injury. In experimental settings, myocardial damage is more likely to occur when the impact occurs during systole rather than diastole. Rib fractures are more common in the elderly, who have inelastic bones, than in children, who have more elastic ribs. Therefore, the young can have a substantial intrathoracic injury without rib fractures, whereas in the elderly, simple trauma can cause rib fractures.

Tissue characteristics are an important determinant of the susceptibility of tissue to injury. The most important determinant is tissue density. Bones and muscles tend to absorb a large amount of kinetic energy from projectiles passing through them. This process decreases the likelihood of deeper-organ damage, but the absorbed energy produces significant muscle and skeletal damage. Because the lungs are porous, elastic projectiles pass through the lungs unimpaired, so that injury to the lungs with high-velocity projectiles is limited to the projectile path.

The major threat from high-velocity projectiles is to other intrathoracic vital organs, such as major vessels, myocardium, the esophagus, and organs that do not tolerate penetrating trauma, as well as to the lungs.

Fractures of the upper 3 ribs may be associated with injury to the major vessels. Fractures of the lower ribs should raise suspicion of injury to the liver, spleen, or diaphragm. Because of the compliance of the chest wall in the young, severe intrathoracic injury may occur without associated rib fractures.

Clinical Details

Physical examination

Symptoms of chest trauma are variable and primarily depend on the thoracic organ that has been traumatized or has taken the brunt of traumatic impact. Most patients with significant trauma present with shock. Trauma to the chest, as from a motor vehicle accident or other injury, can cause hemoptysis immediately following the incident or later.

Rib fractures should be taken in context. Fractures of the upper 3 ribs are highly suggestive of injury to the major vessels. Fractures of the lower ribs should raise suspicion of injury to the liver, spleen, or diaphragm. Because of the compliance of the chest wall in the young, severe intrathoracic injury may occur without associated rib fractures. Their presence indicates a need for examining the underlying lung for contusion, laceration, hemothorax, or pneumothorax. Multiple rib fractures may cause a flail segment.

Patients with multiple rib fractures may harbor a subclinical pneumothorax and may require prophylactic thoracostomy. A persistent pneumothorax despite adequate placement of chest tubes, increasing subcutaneous emphysema, pneumomediastinum, and/or pneumothorax may indicate a bronchial or tracheal rupture.

Patients present with sudden onset of dyspnea, chest pain, and cough. Cyanosis, mediastinal shift, an enlarged ipsilateral hemithorax, decreased chest expansion, hyperresonance, and decreased breath sounds are characteristic physical findings.

Tension pneumothorax is present when the air leak is progressive. Venous return decreases, resulting in decreasing blood pressure, tachycardia, worsening shortness of breath, and hypoxemia.

Rupture of the trachea or major bronchi is a serious injury with an overall estimated mortality rate of at least 50%. About 80% of the ruptures of bronchi are within 2.5 cm of the carina. The usual signs of tracheobronchial disruption are hemoptysis, dyspnea, subcutaneous and mediastinal emphysema, and, occasionally, cyanosis.

Esophageal injuries with blunt trauma are rare; penetrating trauma more often causes esophageal perforating injury. Esophageal perforation is lethal if unrecognized because it is often associated with mediastinitis. Patients often complain of sudden, sharp epigastric pain radiating to the interscapular area. Dyspnea, cyanosis, and shock are late symptoms.

Monitoring and testing

No prolonged observation in a monitored setting is usually required for patients with suspected myocardial contusion. Patients with a normal electrocardiogram (ECG) and echocardiogram are usually discharged home after 12 hours of monitoring. Cardiac complications are rare in a cardiac contusion setting, particularly in the young.

Biochemical tests, such as determinations of creatine kinase–MB isoenzyme levels, may be nondiagnostic. Cardiac troponin I, a more specific agent for myocardial damage, has not been evaluated. Echocardiography is useful for detecting wall-motion abnormalities and pericardial effusions. In combination with abnormal creatine kinase–MB levels, this may be predictive of complications. Radionuclide angiographic results also may be predictive of complication. Thallium scanning can depict areas of decreased perfusion but cannot differentiate an acute lesion from a preexisting lesion.

Injury scoring

Use of the Abbreviated Injury Scale (AIS) and the Injury Severity Score (ISS) is an accurate method for quantifying trauma severity and has many potential applications. The ability to predict morbidity and mortality from trauma by using injury severity scoring is an obvious application. Such scores can be used to inform patients and their families if they desire to know the prognosis and apply the knowledge to end-of-life decision making and resource allocations. However, there is always uncertainty in predicting trauma mortality and morbidity in an individual patient. Decisions for individual patients should never be based solely on a statistically derived ISS. A variety of anatomic and physiologic trauma scores are used alone or in combination to score the severity of injuries.⁶

The AIS is an anatomic scoring system first introduced in 1969. Since then, it has been revised several times against survival so that it now provides a reasonably accurate means of ranking the severity of injury. A scaling committee of the Association for the Advancement of Automotive Medicine (AAAM) monitors the AIS. The AIS is used to score traumatic injuries in terms of the anatomic location and severity of the injury. Each traumatic injury is assigned a 7-digit number, with the last number representing the severity of the injury to be used in tabulating the ISS. AIS numbers can be found in the AIS Dictionary, distributed by the AAAM.

The ISS also is an anatomic scoring system but only recognizes the highest AIS in each of the 6 body regions: head, face, chest, abdomen, extremities, and external. The ISS is used to assess survivability and is often compared with various benchmarks (eg, ISS versus length of stay and ISS versus mortality). Only the highest AIS score in each body region is used. The scores for the 3 most severely injured body regions are squared and added to produce the ISS.

Injuries are scored on a scale of 1-6, with 1 being minor, 5 being severe, and 6 being lethal. This score represents the threat to life associated with an injury and is not meant to represent a comprehensive measure of severity. The AIS is not an injury scale in that the difference between an AIS score of 1 and a score of 2 is not the same as that between 4 and 5. The AIS scale and the Organ Injury Scales of the American Association for the Surgery of Trauma have many similarities.

AIS scores for injury are as follows:

• Minor
• Moderate
• Severe
• Serious
• Critical
• Not survivable

Prognosis

The presence of respiratory distress is ominous. About 50% of trauma patients presenting to the emergency department in respiratory distress die. Mortality for those with both respiratory distress and shock is 75%.

Preferred Examination

Clinical examination

The first priority in thoracic trauma is the provision of effective therapeutic measures to minimize trauma-related deaths and morbidity. Imaging is not indicated until the airway, breathing, and circulation (ABCs) have been secured and stabilized.

The initial approach to chest trauma is clinical evaluation, which starts with a thorough examination of the chest after the airway is controlled. Severe internal injury may be present without external tenderness. A chest radiograph is obtained for every patient who has significant trauma.

Imaging examination

Imaging has little if any role in the initial treatment of a critically ill and hemodynamically unstable patient. In many patients, urgent exploratory thoracotomy or laparotomy may take precedence over imaging, whereas in others, diagnosis and treatment are frequently combined with tube thoracostomy or pericardiocentesis. Imaging studies are an essential part of thoracic trauma care once the patient is stabilized.

Ultrasonography, CT scanning, and magnetic resonance imaging (MRI) can all demonstrate pericardial effusions and hemopericardium, but they are rarely indicated in a patient with acute traumatic tamponade. The roles of CT scanning, MRI, and transesophageal sonography in the evaluation of aortic injuries have not been clearly defined, although multisection CT scanning is increasingly used for diagnosis.

The diagnosis is generally obvious with standard chest radiography or CT scanning, but more subtle signs require careful analysis of CT images and examination with MRI in some situations.

Radiography

Chest radiography is indicated in virtually every trauma patient, and a series of radiographs are generally obtained to assess the progress and complications of the trauma. They are also used to look for malpositioned lines and tubes, which are often placed in the stress and confusion of an emergency department (and so have high rates of inadequate and inappropriate placement).

A chest radiograph is usually an initial image performed in the acute setting. Findings on a chest radiograph include pneumothorax (which is difficult to see on a supine image), pneumomediastinum, airspace shadowing resulting from pulmonary contusion, and pleural hematoma. CT scanning is better for assessing most of these lesions.

Repeat chest radiographs are obtained after any invasive intervention, such as intubation or placement of the central venous pressure catheter or chest tube. Iatrogenic lung trauma can occur after lung biopsy, thoracentesis, cauterization, and other procedures. Mechanical ventilation predisposes the patient to barotrauma and pneumothorax. Lung injuries can also be produced by the inhalation of toxic and inert substances, by blast-related injuries, and by radiation.

Computed tomography scanning

Advancements in CT imaging have changed the management of blunt lung trauma and permitted the detection of blood in bronchi and interstitial air or blood with greater accuracy. Many centers now screen patients with chest trauma for aortic injuries by using contrast-enhanced CT scanning. CT scanning also demonstrates injuries to the lung, pleura, mediastinum, and chest wall better than plain radiographs. Many serious thoracic injuries may be overlooked on initial chest radiographs; these include tracheobronchial tears, diaphragmatic rupture, esophageal tears, thoracic spine injuries, chest wall and seat-belt injuries, lung contusion, cardiac injuries, pneumothorax, hemothorax, and chest tube complications.

CT images demonstrate fractures of the vertebral bodies with great accuracy and can readily show the relationship of fractured fragments and displaced disk material to the cord. Sagittal and coronal reconstructions can provide further exquisite detail.

Echocardiography and ultrasonography

Conventional echocardiography has long been used to image the heart, the pericardial space, and the ascending aorta. Transesophageal ultrasonography is an excellent modality for visualizing the aortic arch and the descending aorta and can be used at the patient's bedside.

Angiography

Conventional or digital subtraction angiography remains the criterion standard for depicting traumatic aortic rupture and aortic pseudoaneurysm.

Magnetic resonance imaging

MRI has many advantages over CT scanning in the evaluation of patients with suspected dorsal spine injuries. It provides excellent detail of intervertebral disks, spinal ligaments, paravertebral soft tissues, and other spinal contents (eg, cord and nerve roots). MRI is particularly useful in evaluating patients with spinal cord injury without radiographic abnormality (SCIWORA) syndrome. MRIs show cord edema or hematoma, which may account for any neurologic deficit the patient may have.

Nuclear medicine study

Thallium and multigated acquisition isotope scans are useful for assessing myocardial damage. Similarly, technetium-99m diphosphonate can be used to assess fracture sites when radiographs are negative and patients are symptomatic.

Limitations of Techniques

Each method of imaging evaluation has advantages and pitfalls according to the type of injury.

Radiography

Portable AP radiographs have several limitations when the images are obtained in an emergency situation with the patient in a supine position. Expiratory artifacts and the magnification effect of a short beam distance may make the mediastinum appear widened. Injuries involving the diaphragm are often missed, and preexisting diaphragmatic eventrations or an elevated hemidiaphragm may mimic diaphragmatic injuries.

Radiographic findings associated with aortic transection are nonspecific. They may be seen in a variety of other mediastinal or chest wall injuries, including nonaortic vascular injuries, fractures of the sternum, vertebral fractures, and esophageal rupture. Predicting the presence of mediastinal hemorrhage on supine portable chest radiographs in the setting of trauma is inaccurate. Plain imaging findings of thoracic spinal fractures are often subtle and difficult to identify because of the limited quality of many trauma radiographs.

Computed tomography

Because of a dramatic reduction in motion and beam-hardening artifacts and significant improvement of spatial resolution, especially along the z-axis, helical and multisection CT scanning allow better demonstration of the most subtle signs of thoracic trauma, such as a focal indentation of the liver or a right-sided collar sign. In addition, helical and multisection CT scanning are useful tools in the evaluation of patients with multiple traumatic injuries.

Patients with severe trauma are often difficult to scan with CT because of resuscitative equipment.

CT scanning is an excellent modality but requires the patient to receive contrast agents and be transported from the protected resuscitation area to the radiology suite. Therefore, CT scanning is difficult to perform in hemodynamically unstable patients.

Magnetic resonance imaging

MRI is expensive and not universally available in emergency departments. Also, MRI often cannot be used in patients with ferromagnetic foreign bodies, some types of prosthetic cardiac valve, or claustrophobia. MRI should be performed only in patients when MRI-compatible resuscitation equipment is readily available. Ultrasonography is operator dependent and may cause some aortic injuries to be missed.

MRI with breath-hold acquisition permits good visualization of diaphragmatic abnormalities, but this technique cannot be performed in emergency situations. MRI offers a major advantage in exploring the cord, disks, and ligaments and in looking for a hematoma. Nevertheless, the indication is carefully weighed in patients with multiple trauma because of monitoring difficulties during the examination, which may be long. MRI is an important diagnostic and prognostic tool in patients with thoracolumbar compression–type fractures.

Ultrasonography

Because sonography is unique in being portable, rapid, and noninvasive, ultrasonography is particularly suited to the trauma setting and offers immediate feedback that can be incorporated into the management plan for the patient.

Nuclear medicine study

Findings on radionuclide scans are nonspecific.

Angiography

Angiography is invasive and may cause small aortic tears to be missed. Iodinated contrast media are nephrotoxic and pose a risk of anaphylaxis.

RADIOGRAPH

Section 3 of 11  

• Authors and Editors
• Introduction
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Chest radiography is of paramount importance in thoracic trauma, and only attention to life-threatening problems should delay obtaining radiographs. Systematic review of the radiograph may reveal suspected and unsuspected pathology. The bony thorax, including ribs, clavicles, scapulae, and vertebrae, should be examined for fractures. Rib fractures should be taken in context.

Flail chest

Flail chest is present when there are 5 or more rib fractures in a row or when 3 or more segmental fractures (2 fractures in 1 rib) are present. The significance of recognizing a flail chest is that respiratory failure may develop from paradoxical movement of the flail segment. (See also the eMedicine article Flail Chest.)

The soft tissues should be evaluated for surgical emphysema or opacification. The lung fields may likewise demonstrate pneumothorax, hemothorax, and consolidation suggestive of lung contusion. Radiographic abnormalities of the mediastinum, particularly pneumomediastinum, widening of the mediastinum, or shift of the mediastinum, suggest airway rupture, aortic disruption, and tension pneumothorax. Finally, assessment of the cardiac silhouette may aid in the diagnosis of blunt myocardial injury, including tamponade.

Chest wall injuries

These injuries may give clues to associated injuries. Fractures of the first 3 ribs, in particular, indicate significant trauma. Subclavian vascular injury should be suspected in patients with fractures of the first 3 ribs, clavicle, and scapula, particularly when they are associated with significant fracture displacement, extrapleural hematoma, brachial plexus neuropathy, or radiologic evidence of mediastinal hemorrhage. Thoracic outlet fractures may be associated with brachial plexus or vascular injuries.

Fractures of the sternum are rare and require lateral and oblique thoracic views for diagnosis. The presence of a fractured sternum and an abnormal mediastinal contour should prompt a search for injury to the great vessels.

Pneumomediastinum

A pneumomediastinum is usually the result of a disruption of the parenchyma, with interstitial tracking of air secondary to momentary marked chest compression and reexpansion. On a chest radiograph, it is most obvious along the left heart border, outlining the parietal pleura, but the presence of visible air under the cardiac shadow, the so-called continuous diaphragm, also is a useful sign. Subcutaneous emphysema, extending into the soft tissues of the neck, often accompanies a pneumomediastinum.

The parietal pleura may be visible along the left mediastinal border. A sharply defined edge may be observed to the descending aorta. This can often be followed into the upper abdomen. Subcutaneous, retroperitoneal, or intraperitoneal emphysema may be present.

Pneumopericardium

Findings may include air lucency around the heart that does not rise above the level of pericardial reflection at the root of the great vessels.

Hemopericardium

Rapid accumulation of blood in the pericardial space often causes cardiac tamponade without altering the appearance of the cardiac silhouette.

Pulmonary contusion

Pulmonary contusion has a variable radiographic picture. Airspace opacification is present without any evidence of an air bronchogram, as the small airways are filled with blood. The shadowing may be patchy or extensive and confluent, solitary, multifocal or diffuse, and unilateral or bilateral, depending on the extent and force of the trauma. Focal hematomas may become cavitated as they begin to organize. An air bronchogram is rare because of blood in the small airways. The distribution of the consolidation is nonsegmental and often progresses rapidly over the first 1-2 days.

Pulmonary contusion may also be associated with adjacent rib fractures and homogeneous infiltrates, which tend to be peripheral and nonsegmental.

Resolution is usually rapid, and the lung often returns to normal within a week. Failure of resolution usually suggests superimposed infection, atelectasis, aspiration, or a blood clot in a laceration. Contusions are generally associated with the area of maximal impact, but countercoup injuries may occur. Fractures in the overlying area of impact may be seen.

Pulmonary laceration or traumatic pneumatocele is often present in association with contusion but not identified on the radiograph. CT scanning is more sensitive than radiography. Lacerations usually appear as oval cavities. They have a pseudomembrane a few millimeters thick. An air-fluid level may be present because of hemorrhage into the cavity, or a crescent sign may be present as a result of air outlining a hematoma. These are slowly resolving lesions and may leave residual opacities for several months.

Hemorrhage into the alveolar or bronchiolar cavities spreads and fills other normal alveoli; because these alveoli can clear themselves, the radiograph of pulmonary contusion frequently shows impressive resolution within 6 days. Contusion can be complicated by venous thrombosis spreading from the site of injury in the first few days after trauma.

Pleural effusion

Pleural effusion may be associated with uniformly increased opacity over the hemithorax and a pleural cap.

Diaphragmatic rupture

Diaphragmatic rupture is diagnosed with chest radiographs. Loss of the diaphragmatic contour, an elevated asymmetric or irregular diaphragm, the presence of bowel or a nasogastric tube within the chest (U-shaped course of the nasogastric tube), and a shift of the mediastinum to the opposite side or elevation of the hemidiaphragm are findings suggestive of a diaphragmatic rupture.

Diaphragmatic injuries should be suspected in any penetrating, left-sided thoracic wound below the fourth intercostal space anteriorly, the sixth intercostal space laterally, or the eighth intercostal space posteriorly. Serial chest images may show progressive changes diagnostic of diaphragmatic rupture. Associated atelectasis, pleural effusions, lung contusions, or phrenic nerve paralysis may mask or mimic traumatic diaphragmatic tears.

Ruptured hemidiaphragm is more common on the left side than on the right. Nonspecific signs include apparent elevation of the hemidiaphragm, obliteration or distortion of the contour of the hemidiaphragm, contralateral displacement of mediastinum, and pleural effusion. The presence of gas-containing viscera in the thorax, particularly with a focal constriction across gas-containing bowel, is pathognomonic.

Hemopneumothorax may be misdiagnosed when a dilated stomach gives a horizontal air-fluid interface on erect chest radiographs. In the absence of a right rib, a small right hemothorax with a high right diaphragm is suggestive of a ruptured diaphragm. Findings may initially be absent in 25-50% of patients.

Pneumothorax

A high index of suspicion for the presence of a pneumothorax must be maintained in all patients with blunt trauma. Auscultation may be difficult in the emergency department. Other signs of tension pneumothorax, tracheal deviation, hypotension, or hypoxemia should trigger chest decompression prior to chest radiography.

If the patient is stable, radiography may precede the thoracostomy. Patients with multiple rib fractures may have a subclinical pneumothorax and may require prophylactic thoracostomy.

In summary, findings in pneumothorax include the following:

• Deep costophrenic sulcus
• Double-diaphragm contour with or without depression of the hemidiaphragm
• Hyperlucency in the lower thorax and upper abdomen
• Sharp demarcation of the cardiac apex
• Possible outlining of the visceral pleura at the base of the lung

Bronchial tear

A bronchial tear should be suspected on a plain radiograph when a pneumothorax persists despite adequate placement of chest drains, increasing subcutaneous emphysema, pneumomediastinum, and/or pneumothorax. Tracheal transection may occur in the setting of neck trauma.

Radiographic findings include elevation of the hyoid bone on lateral cervical spine radiographs. The hyoid bone may lie above the level of the C3 vertebral body or greater cornu, less than 2 cm from the angle of the mandible. The elevation of the hyoid bone is said to be related to rupture of the infrahyoid muscles with unopposed action of the suprahyoid muscles.

Aortic injury

Aortic injury should be suspected on chest radiographs showing mediastinal widening of more than 8 cm, loss of definition of the aortic knuckle, displacement of the nasogastric tube to the right of the T4 spinous process, and a left apical pleural cap. Further evidence is gained from widened paraspinal lines, a right paratracheal stripe widened by more than 5 mm, and loss of the descending aorta line. The negative predictive value of a normal chest radiograph is high at 98%.

Esophageal rupture

A large left pneumothorax, extensive pneumomediastinum, subcutaneous emphysema, left pleural effusion, left lower-lobe atelectasis, and the V sign of Naclerio on a plain radiograph suggests an esophageal rupture.

Thoracic spinal fracture

Radiographic findings of thoracic spinal fractures include widening of the paraspinal lines, mediastinal widening, loss of height of the vertebral body or obscuration of a pedicle or pedicles, left apical cap, and deviation of the nasogastric tube.

Despite the serious clinical implications of thoracic spine fractures, they often go undetected during the initial critical hours of patient evaluation and treatment. This is often related to the fact that the thoracic spine is infrequently examined radiologically in the acute setting. A deliberate and meticulous search should be made on the initial supine chest radiograph for spinal fractures.

Thoracic spinal fractures include a cortical breach, abnormality of shape, and paraspinal soft-tissue swelling appearing as widening of the right or left paravertebral stripe (produced by an associated paravertebral hematoma).

The rules of 2s provide further evidence of vertebral fractures. The rules state the following:

• The distance between the spinous processes of adjacent vertebral bodies should not vary by more than 2 mm from the interspinous distance measured below and above.
• The interpedicular distance of contiguous vertebral bodies should not vary by more than 2 mm.
• The vertical distance between the pedicles of contiguous vertebral bodies should not vary by more than 2 mm from the interpedicular distance between adjacent pairs of vertebral bodies immediately above and below the level of concern.
• The width of facet joints should be less than 2 mm at all levels.
• The posterior height of a thoracic vertebral body should not be over 2 mm greater than the anterior height except at D11 and D12, where the vertebral bodies are inherently wedged anteriorly.

Discovery of a fracture of the spine should prompt a search for others, as 10% of spinal fractures are multiple. Examination of the whole of the spine is necessary because 80% of spinal fractures are not contiguous.

Impalement injuries

With impalement injuries, a chest radiograph may show the intrathoracic foreign body—particularly if the foreign body is metallic and there are associated pneumothorax/pleural effusions and lung lacerations—and also show the proximity of the foreign body to vital intrathoracic structures. If time allows, CT scanning may depict vascular injuries more clearly. Aortography also may be useful when hematomas lie close to the aorta or when an aortic or major arterial leak is suspected.

Injuries associated with thoracic trauma

Radiographs of other parts of the body are often required in the setting of thoracic trauma. Images may include those of the lateral cervical spine and pelvis, which are generally obtained for every patient with blunt trauma.

Degree of Confidence

Hehir and colleagues assessed the accuracy of the first chest radiograph in diagnosing moderate-to-severe chest injuries.⁷ In 1985, the prospective Westmead Trauma Registry identified 100 patients as having a chest injury with an AIS score of 3 or greater. The male-to-female ratio was 4.9:1, and the age range was 5-74 years. Interpretations of the first chest radiograph were compared with the chest injuries finally diagnosed. In 19 of 77 survivors and in 8 of 17 patients who underwent radiography prior to death, significant abnormalities (primarily pneumothorax, hemothorax, and spinal and sternal injuries) went undiagnosed on the first chest radiograph.

A standard posteroanterior chest radiograph and lateral projections are said to accurately show most major intrathoracic pathology. However, first chest radiographs of trauma patients are often obtained with the patient supine, suboptimally, and soon after his or her arrival, even though a chest injury may not be immediately apparent. The limitations of a mobile chest radiograph must be appreciated, and more formal chest radiography, with posteroanterior and lateral imaging, is advised at a later stage if the clinical situation permits.

False Positives/Negatives

There are several technical factors regarding the AP portable radiograph obtained in the emergency setting. These include the supine position, the expiratory image, and the magnification effect of a short beam distance. All of these factors may make the mediastinum appear widened.

Diaphragmatic injuries are often missed on plain radiographs. Preexisting conditions, such as diaphragmatic eventrations or an elevated hemidiaphragm, may mimic diaphragmatic injuries. Most plain imaging findings associated with aortic transection are nonspecific. They may be seen in a variety of mediastinal or chest wall injuries, including nonaortic vascular injuries, fractures of the sternum, vertebral fractures, and esophageal ruptures.

Radiographic findings of thoracic spinal fractures are often subtle and difficult to identify because of the limited quality of many trauma radiographs. Only 51% of spinal fractures were identified on the initial chest radiography in one series. Many plain radiographic findings are not specific for vertebral body injury and can be seen with other mediastinal injuries, including traumatic aortic rupture. In fact, 69% of patients with thoracic spine fractures have chest imaging findings suggestive of aortic transection.

About 78% of patients with an abnormal chest radiograph showing mediastinal widening have normal CT scans, and 80% do not have aortic injury on angiograms. Predicting the presence of mediastinal hemorrhage on supine portable chest images in the setting of trauma is inaccurate.

CT SCAN

Section 4 of 11  

• Authors and Editors
• Introduction
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

The advent of fast scanning helical and multisection CT scanning has changed the management of blunt lung trauma and permitted the detection of blood in the bronchi, as well as interstitial air or blood, with greater accuracy. Many centers now screen patients with chest trauma for aortic injuries by using chest CT scanning.

CT scans demonstrate other lung, pleural, mediastinal, and chest wall injuries better than radiographs. About 90% of patients do not have aortic injuries, but many other serious, unsuspected injuries can be identified on chest CT scans and with greater frequency. Many serious thoracic injuries may be overlooked on initial chest radiographs; these include tracheobronchial tears, diaphragmatic rupture, esophageal tears, thoracic spine injuries, chest wall and seat-belt injuries, lung contusion, cardiac injuries, pneumothorax, hemothorax, and complications related to chest tubes.^{8, 9}

Chest wall trauma

Rib fractures are common in blunt chest trauma (60%). Portable supine chest images are insensitive and depict only about 20% of all rib fractures. Fractures of the first rib are an indication of severe blunt chest trauma and may be associated with aortic tears, bronchial tears, and injuries to the subclavian vessels.

Other chest wall trauma includes soft-tissue hematomas and contusions. These are often evident on CT scans of the chest and often indicate the region of primary impact. Overlying soft-tissue edema or hematoma on CT scans often indicates an underlying rib or other bony injury; these should be sought by reviewing the images using bone window settings that have been reformatted using an edge-enhancing algorithm. Using the cine or paging mode facilitates bone-image review. Lacerations of chest-wall arterial vessels can result in massive chest-wall hematomas.

Seat-belt injuries related to a 3-point restraint may cause bruises in the subcutaneous tissues and fat of the anterior chest wall. These may be identified on CT scans. Seat-belt injuries severe enough to cause skin abrasions are associated with significant internal injuries in 30% of patients. Thus, the identification of seat-belt bruises on CT scans should prompt a careful search for the following:

• Fractures of the sternum, ribs, clavicles, and transverse processes of C7 or T1
• Aortic transection
• Cardiac contusions or ventricular rupture
• Vascular injuries to the subclavian artery or superior vena cava
• Tracheal or laryngeal tears
• Diaphragmatic rupture

The incidence of sternal fractures is actually higher in seat-belt users than in nonusers, and most fractures occur within 2 cm of the manubrial-sternal junction.

CT scanning often reveals unsuspected sternal fractures in blunt thoracic trauma, sternoclavicular dislocations, unsuspected rib and vertebral body fractures, and unrecognized scapular and shoulder injuries. These injuries are usually difficult to identify on hard-copy images and are more easily seen on a monitor in cine or paging mode. Two-dimensional coronal and sagittal reconstructed images often demonstrate sternal fractures and sternoclavicular dislocations better than transaxial images.

Fractures of the thoracic spine occur in 3% of patients with blunt thoracic trauma and are associated with spinal cord injury in a high percentage. The site most vulnerable to fractures is the thoracoabdominal junction involving the T9-T11 vertebral bodies. Sternal fractures are often associated with thoracic spinal fractures.

Signs of vertebral body fractures on CT scans include the following:

• Paraspinal hematoma
• Disruption or fracture of the vertebral body, pedicle, and/or spinous processes
• Mediastinal hematoma confined to the posterior mediastinum, which often suggests a vertebral body fracture
• Compression fractures, which may be easily overlooked on axial CT scans of the chest unless bone windows are used

Reconstructed sagittal and coronal multiplanar images are often useful to confirm a simple compression fracture. One may also verify compression fractures by reviewing the lateral CT scanogram.

Pneumothorax and hemothorax

Small-to-moderate pneumothoraces may not be appreciated on plain chest radiographs but are readily identified on CT scans. CT scanning is also more specific than plain radiography in characterizing pleural effusions. Hemothoraces often show areas of high CT attenuation as a result of blood. A rapidly accumulating pleural effusion in the setting of trauma may be caused by a hemothorax or a chylothorax resulting from a ruptured thoracic duct.

A persistent or increasing pneumothorax or hemothorax may have a variety of causes, including bronchial tears, vascular injuries, and malfunctioning or malpositioned chest tubes. Hemothorax is more common in penetrating injuries than in nonpenetrating injuries to the chest. If the hemorrhage is severe, hypovolemic shock and respiratory distress can result from compression of the lung on the involved side.

A tension pneumothorax develops when air enters the pleural space but cannot leave. The consequence is progressively increasing intrathoracic pressure in the affected side, resulting in mediastinal shift. The patient will become short of breath and hypoxic. Urgent needle decompression is required prior to the insertion of an intercostal drain. The trachea may be displaced (late sign) and is pushed away from the midline by the air under tension.

Lung contusion and laceration

CT scanning often shows more extensive edema and hemorrhage than are seen on the chest radiograph. A plain chest radiograph also causes gross underestimation of the frequency of lung laceration in the lung contusion.

A common finding on CT scans is an irregular lucency within the contusion, which is often adjacent to the area of rib injury. A lung laceration often becomes visible on a chest radiograph when the contusion regresses. The appearance of a laceration is variable and depends on the substance filling the laceration. When full of blood, the laceration may appear as an oval opacity, but it may appear as a lucency when full of air, as an air-fluid level when both air and fluid are present, and as a mass within a lucency when air and a blood clot are present.

Lacerations may have a more complex appearance, and many lacerations show several appearances during the course of their resolution. Regression often takes weeks, and residual nodules or scars may persist for weeks or months. In severe blunt chest trauma, one may see pulverized lung on CT scans or an area of airspace opacification with multiple, small (5 mm to 1 cm) air cysts disrupting the lung parenchyma. CT scanning is more sensitive than plain radiography for detection of contusions and lacerations, by a factor of 3 to 1.

Pulmonary contusion is a potentially life-threatening condition. The onset of symptoms may be slow and progress for 24 hours after the injury. Pulmonary contusion is likely to occur in cases of high-speed accidents, falls from great heights, and injuries by high-velocity bullets. Symptoms and signs include dyspnea, hypoxemia, tachycardia, rare or absent breath sounds, rib fractures, and cyanosis.

Several other causes of airspace opacification may be seen on plain radiographs and on CT scans, in the setting of thoracic trauma. These include aspiration pneumonia, atelectasis caused by splinting or mucous plugs, and cardiogenic and noncardiogenic pulmonary edema. After 24 hours, one must also consider fat embolism and ARDS, particularly in cases of severe trauma with long bone fractures.

Tracheobronchial tears

Tears or fractures of the airways occur in approximately 1.5% of cases of blunt chest trauma. They frequently go unrecognized on initial examination, and delayed diagnosis is common. Bronchial fractures occur within 2.5 cm of the carina in 80% of patients.

CT scan findings of bronchial fractures include the following:

• A large pneumothorax despite adequate placement of 1 or more chest tubes
• Massive pneumomediastinum and subcutaneous emphysema
• Focal peribronchial collections of air
• Discontinuity or irregularity of the bronchial wall
• Drooping, or collapsed lung or lobe of the lung

The fallen-lung sign refers to the unusual appearance of a collapsed lung or lobe in the setting of bronchial injury. A fallen-lung sign is thought to result from disruption of the normal hilar attachments of the lung, causing the collapsed lung to droop peripherally rather than centrally.

Another clue to tracheal tears, on plain radiographs and CT scans, is abnormality in the appearance or position of the endotracheal tube (ET). Abnormalities include overdistention of the ET cuff, protrusion of the ET tube wall beyond the expected margins of the tracheal lumen, and an extraluminal position at the tip of the tube. Associated fractures of the upper thorax—including fractures of the first 3 ribs, the clavicle, the sternum, and the scapula—occur in 40% of patients with tracheobronchial injuries. Suspected tracheobronchial tears are confirmed with bronchoscopy.

Esophageal rupture

CT scan findings of esophageal rupture include focal extraluminal air collections at the site of tear and a hematoma of the mediastinal or esophageal wall. Occasionally, a tract at the site of the tear can be identified on CT scans. In the setting of severe blunt chest trauma, the esophagus can also be obstructed and entrapped by fracture-dislocations of the thoracic spine, as demonstrated on chest or thoracic spinal CT scans. The diagnosis of esophageal rupture is usually confirmed with a swallow study involving nonionic oral contrast material.

Cardiac injury

Based on autopsy data, the frequency of cardiac injury from blunt trauma is estimated to be 10%. In patients with blunt chest trauma, myocardial contusion is associated with fractures of the sternum or ribs. Cardiac contusion can simulate a myocardial infarction. This type of injury is more common than realized and may cause sudden death well after the accident. Cardiac injuries resulting from blunt chest trauma include cardiac contusions, cardiac rupture, pneumopericardium and hemopericardium, cardiac tamponade, and cardiac valve dysfunction.

The diagnosis of cardiac contusion is supported by abnormalities on ECG and elevation of serial cardiac enzyme levels if these are available. Cardiac injury is suspected when abnormal ECG tracings are recorded and when hemopericardium are recognized on CT scans as the presence of air or high attenuation blood in the pericardial sac. Both may cause cardiac tamponade and may require emergent pericardial drainage. Constrictive pericarditis may develop as a long-term complication of hemopericardium.

Echocardiography is often used at the bedside to evaluate the patient for cardiac injuries, but hemopericardium, in particular, can be missed on echocardiograms because of the change in the echo properties of hemorrhagic fluid.

Pericardial tamponade

Penetrating cardiac injuries are a leading cause of death in urban areas. It is rare to have pericardial tamponade with blunt trauma.

Pericardiocentesis must be undertaken early if this injury is considered likely. Pericardial tamponade should be suspected in patients presenting with shock, distended neck veins, cool extremities and no pneumothorax, or muffled heart sounds.

Injury to the pulmonary veins and arteries is often fatal and is 1 of the major causes of on-site death.

Aortic injury

One of the major advantages of employing CT scanning in the setting of possible aortic injury may be that it can also be used to identify other, unsuspected thoracic injuries. In thoracic trauma patients with a negative chest radiograph, only 3% have occult mediastinal hemorrhage, as discovered at CT scan, and only 0.4% have an aortic injury. Unfortunately, the reverse is not true. About 78% of patients with an abnormal chest radiograph that shows mediastinal widening have normal CT scans.

The use of CT scanning to screen for aortic injury is controversial. Nevertheless, a negative CT scan prevents unneeded invasive angiography in a significant number of patients. The disadvantages of using CT scanning to screen patients for aortic injury include a delay in obtaining the definitive aortogram and in taking the patient to surgery while the scan is being performed; these delays may adversely affect prognosis in patients with aortic tears. Mediastinal hemorrhage is fairly common after blunt chest trauma and does not necessarily indicate aortic injury.

Another major disadvantage is that few if any surgeons perform surgery for a diagnosis based on CT scan findings without angiographic confirmation of aortic injury. The patients therefore eventually undergo 2 contrast-enhanced studies in quick succession. The effectiveness of CT scanning in detecting injury to the branch vessels is not known. Injuries to the great vessels occur in 1-2% of patients.

Mirvis and colleagues retrospectively reviewed 677 patients who underwent conventional CT scanning for evaluation of aortic injury; 84% had a negative CT scan. In 79 patients (12%), CT scans showed mediastinal hemorrhage as the only abnormality; angiography was negative in 77 of the 79 (97%). Twenty-one of the 77 patients (3%) had an aortic-contour deformity, pseudoaneurysm, intimal flap, or pseudocoarctation; angiography was positive in 19 of the 21 (90%). The specificity of mediastinal hemorrhage alone for aortic injury was only 87%, compared with a specificity of 99% for the other direct CT scan findings of aortic injury. However, the sensitivity for aortic injury on the basis of mediastinal hemorrhage as the criteria was high (100%). With the other direct signs of aortic injury, the sensitivity decreased to 90%.

Gavant and colleagues used helical CT scanning to examine 1518 patients with blunt chest trauma.¹⁰ Among them, 127 patients (8.3%) had abnormal chest CT scans with mediastinal hematoma and/or aortic injury; in 89 of the 127 patients (70.1%), images showed only a mediastinal hematoma with a normal aorta. None had a positive aortogram. Had direct CT scan evidence of aortic injury been used to diagnose aortic injury instead of mediastinal hemorrhage, helical CT scanning would have been 100% sensitive and 81.7% specific. The authors stated that 67% of the aortographic studies could have been avoided if patients with CT scans showing only mediastinal hematoma but normal aortas did not undergo aortography.

The critical area to evaluate on CT scans is the aorta at the level of the left main pulmonary artery (region of the ligamentum arteriosus). Gavant reported that 90% of all CT-detected aortic injuries begin at or just above this level and that 85% of aortic injuries end at or just below it.

In Mirvis's series, all patients with aortic injury had mediastinal hemorrhage in the periaortic and/or superior and middle mediastinum.

Other features to investigate include an aortic-contour deformity, an intimal flap, a thrombus protruding into the aortic lumen, a pseudoaneurysm, an abrupt change in caliber of the descending aorta compared with the ascending aorta (pseudocoarctation), and extravasation of contrast material (rare).

Seventeen percent of aortic injuries have only aortic-contour or luminal abnormalities without significant para-aortic or mediastinal hematoma.

Diaphragmatic rupture

Diaphragm rupture occurs in 0.8-8% of cases of blunt thoracic trauma. The plain chest radiograph is abnormal in 77% of patients, but the findings are nonspecific and the diagnosis is initially missed in most cases. The mortality rate in unrecognized cases is 30% as a result of delayed herniation of abdominal viscera and bowel strangulation. Early recognition and repair of diaphragmatic tears improves the prognosis.

In recognized cases, diaphragmatic rupture is more common on the left side (77-90%) than on the right. Most tears are large (>10 cm) and occur in a radial orientation in the posterolateral location. The diaphragm is the weakest at this location because this is where the pleuroperitoneal membrane finally closes during embryogenesis. Visceral herniation occurs in 32-58% of patients with diaphragmatic tears, and the stomach is the most common abdominal viscus to become herniated. About 72% of patients with diaphragmatic rupture have other intra-abdominal injuries, and 42% have pelvic fractures, which are indicative of the severity of trauma in these cases.

The helical scanning technique should include thin, overlapping sections acquired during a single breath-hold so that multiplanar reconstructions in the sagittal and coronal plane can be generated to detect discontinuities of the diaphragm. The reported sensitivity and specificity of CT scanning for the detection of diaphragmatic rupture are 61% and 87%, respectively. Sagittal and coronal reformations are superior to axial images in detecting tears and the herniation of abdominal contents into the thorax.

Normal discontinuities in the posterior aspects of the diaphragm are identified in approximately 6-11% of patients with no prior history of trauma and may be related to congenital Bochdalek hernias. Moreover, with aging, acquired diaphragmatic humps and bumps become more prevalent and have been reported in 35% of patients in the 70-year-old age group.

CT findings of diaphragmatic rupture include the following:

• Discontinuity of the diaphragm (73-82%)
• Herniation of peritoneal fat, bowel, or abdominal organs into the chest (55%)
• Collar sign or a waistlike constriction of bowel (27%)
• Peritoneal fat, bowel, or viscera lateral to the lung or diaphragm or posterior to the crus of the diaphragm
• Absent diaphragm sign
• Concurrent pneumothorax and pneumoperitoneum
• Concurrent hemothorax and hemoperitoneum

Dependent viscera sign

Bergin and colleagues coined the phrase "dependent viscera sign" to describe CT scan findings associated with a ruptured diaphragm.¹¹ Besides noting discontinuity of the diaphragm, intrathoracic herniation of abdominal contents, and waistlike constriction of bowel (the collar sign), they also assessed whether the upper one third of the liver abutted the posterior right ribs or whether the bowel or stomach was in contact with the posterior left ribs. Either of the last 2 findings was referred to as the dependent viscera sign.

Using CT scanning, the authors observed the dependent viscera sign in 100% of patients with a left-sided diaphragmatic rupture and in 83% of patients with a right-sided diaphragmatic rupture. Using the dependent viscera sign, the radiologists' overall detection rate for diaphragmatic rupture was 90%.

False Positives/Negatives

When data from multiple studies are combined, the false-positive rate for CT scanning with a variety of techniques is estimated to be 0-39%, and the false-negative rate is 0.7%.

False-positive results arise from mimics of mediastinal hemorrhage, which include residual thymic tissue, periaortic atelectasis, volume averaging of the pulmonary artery, and pleural effusions adjacent to the descending aorta. False-positive findings may also result from image degrading caused by patient motion, streak artifacts from ECG leads and other monitoring devices, and streak artifacts from opaque intravenous contrast material.

Atherosclerotic plaques can cause interpretation difficulties, and a prominent ductus arteriosus remnant can mimic a traumatic pseudoaneurysm. False-positive diagnoses of intimal flaps have been caused by crossing vessels and volume averaging of the left brachiocephalic vein as it crosses in front of the aortic arch, the left superior intercostal vein, and right bronchial arteries coming off the descending aorta.

Aortic injuries may be missed in certain anatomic locations, such as near the root of the aorta (as a result of cardiac pulsation). Because of the obliquity of the scanning plane, small tears confined to the distal aortic arch at the transition point between the distal arch and the proximal descending aorta also have the potential for a false-negative examination.

MRI

Section 5 of 11  

• Authors and Editors
• Introduction
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

MRI also may be valuable in documenting disruption of the diaphragm. With MRI, one can directly acquire coronal and sagittal T1-weighted images to trace the course of the diaphragm from its insertion sites to the dome of the hemidiaphragm on the suspected side.

MRI can be particularly helpful in difficult cases in which the differential diagnosis is between diaphragmatic injury and eventration or preexisting elevation of the hemidiaphragm. The hemidiaphragm can be visualized with MRI as a hypointense band throughout its course, outlined by hyperintense abdominal and mediastinal fat on the left and by the liver on the right. Also, low tears involving the crus of the diaphragm are more convincingly displayed with coronal T1-weighted images than with axial CT scans.

MRI is usually reserved for the evaluation of stable patients in whom CT scanning results are equivocal or nondiagnostic. MRI is also an excellent tool in the diagnosis of vascular injuries in stable patients. MRI is a sensitive technique in the diagnosis of vertebral, sternal, and scapular fractures.

Degree of Confidence

MRI has many advantages over CT scanning in the evaluation of patients with suspected dorsal spine injuries. MRI provides excellent detail of intervertebral discs, spinal ligaments, paravertebral soft tissues, and other spinal contents (eg, cord and nerve roots). This study is particularly useful in evaluating patients with spinal cord injury without radiographic abnormality (SCIWORA) syndrome. The images show cord edema or hematoma to account for any neurologic deficit the patient may have. Diaphragmatic injuries occur in 0.8-8% of patients after blunt trauma.

The ability to directly acquire coronal, axial, and sagittal images is a major advantage of MRI in evaluating diaphragmatic injuries. MRI accurately depicts the anatomy of the diaphragm. This modality may be used for late diagnosis or for the evaluation of a patient in stable condition who has an equivocal diagnosis and no need for laparotomy (some penetrating injuries).

False Positives/Negatives

MRI appears to be useful, although a normal MRI does not rule out SCIWORA syndrome.

ULTRASOUND

Section 6 of 11  

• Authors and Editors
• Introduction
• Radiograph
• CT Scan
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Ultrasonography

A targeted ultrasonographic examination is a quick and noninvasive procedure that can be performed at the patient's bedside. This study may also be used as a part of a clinical examination in a patient with severe trauma.

Focused assessment for the sonographic examination of the trauma patient (FAST) can be completed in about 2.5 minutes by using a 3.5-MHz transducer. A sequential examination is performed beginning with the pericardial area, right and left upper quadrants, and pelvis. The pericardial area is scrutinized for the presence of blood for the detection hemopericardium. A prompt evacuation of pericardial blood through a pericardiocentesis, under ultrasonographic guidance, is mandatory for cardiac tamponade. Thoracic sonograms are obtained by moving the transducer slightly cephalad when the right and left upper quadrants of the abdomen are evaluated during FAST, with scanning performed through the intercostal spaces along the anterolateral thoracic wall.

Sisley and colleagues compared the speed and accuracy of sonography