Blunt Chest Trauma - Clinical Tree

Nonmediastinal Injury

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

Lung Injury

Pulmonary Contusion

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

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

Figure 8-1, Supine chest radiograph of a patient struck by a motor vehicle.

Figure 8-2, Supine chest radiograph of a patient involved in motorcycle accident.

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

Figure 8-3, Supine chest radiograph of a trauma patient.

Figure 8-4, Chest computed tomography (CT) of a patient involved in motor vehicle collision.

Figure 8-5, Chest radiograph of a patient who fell off a roof.

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

Figure 8-6, Chest radiograph of a patient involved in a jet-ski accident.

Pulmonary Laceration

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

Figure 8-8, Chest radiograph of a patient who was hit by a train.

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

Figure 8-9, Arterial phase chest computed tomography (CT).

Figure 8-10, Admission chest computed tomography (CT) of a patient kicked by a horse.

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

Injuries Involving the Pleural Space

Pneumothorax

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

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

Figure 8-11, Supine chest radiograph of a patient struck by a moped.

Figure 8-12, Supine chest radiograph of a patient involved in a motor vehicle collision.

Figure 8-13, Supine chest radiograph of a trauma patient demonstrates increased lucency of the right lower hemothorax ( arrows ) producing deep costophrenic sulcus indicating pneumothorax.

Figure 8-14, Supine chest radiograph of a patient involved in four-wheeler accident demonstrates several signs of pneumothorax: lucency between medial lung and heart border (long arrow) , deep costophrenic sulcus sign and hyperlucent right upper quadrant (arrowheads) , and the thin linear density over the right upper lung field with no lung marking distal to this line (short arrow) .

$Figure 8-15, Supine chest radiograph of a patient who fell from a balcony demonstrates the typical signs of a pneumothorax: a thin dense line along the periphery of the right hemithorax with no lung markings beyond this line (short arrow). There is also a tiny left apical pneumothorax (long arrow) . Note right rib fractures.$

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

Figure 8-16, Semiupright chest radiograph of a trauma patient shows a linear density along the periphery of the left hemithorax (arrow) , which upon casual inspection would be suspicious for a pneumothorax. However, there are lung markings distal to this line and two additional linear densities medial to the first (arrowheads) . These findings are due to folds of skin or bedding, and not a pneumothorax.

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

Figure 8-17, Supine chest radiograph of a patient involved in a farming accident.

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

Figure 8-18, Chest radiograph shows signs suspicious for the clinical diagnosis of a tension pneumothorax: right lung collapsed toward the hilum with decreased density around the collapsed lung, deep costophrenic angle sign, depressed right hemidiaphragm, and shift of mediastinum to the left. Clinically the patient had severe dyspnea and hypotension that was relieved with chest tube placement.

Figure 8-19, Frontal chest radiograph of a trauma patient.

Hemothorax

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

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

Figure 8-20, Supine chest radiograph of a patient who fell.

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

Figure 8-22, Supine chest radiograph of a patient involved in a motor vehicle collision.

Figure 8-23, Chest radiograph of patient who had undergone median sternotomy one week previously for treatment of traumatic mediastinal injury.

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

Figure 8-24, A more unusual cause of fluid in the pleural space.

Extrapleural Hematoma

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

Figure 8-25, Chest radiograph of a trauma patient who just had a right subclavian central venous catheter placed.

Figure 8-26, Computed tomography (CT) of a multitrauma patient.

Bony Thorax and Chest Wall

Soft Tissue Contusion

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

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

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

Figure 8-27, Chest radiograph of a female trauma patient.

Rib Fractures

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

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

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

Figure 8-28, Admission chest radiograph of a patient involved in a motorcycle collision.

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