Imaging Chest Trauma




Diagnostic imaging plays a critical role in the evaluation of many patients with blunt and penetrating chest trauma. In this chapter, we discuss the indications for imaging with chest x-ray, ultrasound, and computed tomography (CT). We review a systematic approach to interpretation of chest x-ray and CT. We also discuss and compare imaging findings of key thoracic injuries using chest x-ray, CT, and ultrasound in those cases where it is commonly applied. Our discussion highlights current controversies in imaging of thoracic trauma.


Thoracic Imaging Modalities


The major diagnostic imaging modalities for blunt and penetrating chest trauma are chest x-ray, ultrasound, and chest CT with intravenous (IV) contrast. Aortography is more rarely used, most often following an abnormal chest x-ray or CT result. We review these modalities here, including a detailed discussion of the indications for and interpretation of each imaging technique.


In this chapter, figures are clustered by patient to illustrate injuries using multiple modalities. As a consequence, the order of reference to figures in the chapter is not always sequential.




Chest X-ray


Chest x-ray is the most commonly used diagnostic modality for all forms of chest trauma. Benefits of chest x-ray include portability (allowing it to be used in the resuscitation bay without moving an unstable patient), speed of acquisition (seconds) and image availability (minutes), low expense (approximately $50 to $100), and low radiation exposure (0.01 mSv, equivalent to 1 day’s background exposure on Earth) ( Table 6-1 ).



TABLE 6-1

Comparison of Portability, Speed, Costs, Radiation Exposure, and Information Provided for Common Chest Imaging Modalities for Trauma


































X-ray Ultrasound CT
Portable Yes Yes No
Speed Seconds to acquire, minutes to view Instantaneous acquisition, simultaneous viewing Seconds to acquire, minutes to view
Expense $50-$100 Depends on local institution; is usually performed by emergency physician; and may be billed separately as a procedure at some institutions Approximately $1000 charge to patient, around $100 institutional cost
Radiation exposure 0.01 mSv, 1 day on Earth None 4-20 mSv, several years on Earth
Information provided


  • Pneumothorax



  • Hemothorax



  • Pericardial effusion



  • Possibly mediastinal injury



  • Pulmonary contusion



  • Fractures



  • Diaphragmatic injury



  • Pneumoperitoneum




  • Pericardial effusion (traditionally performed as part of FAST exam)



  • Pneumothorax



  • Hemothorax

Detailed information about


  • Pneumothorax



  • Hemothorax



  • Pericardial effusion



  • Mediastinal injury, including specific information about aortic injury



  • Pulmonary contusion



  • Fractures



  • Diaphragmatic injury



  • Pneumoperitoneum


From Renton J, Kincaid S, Ehrlich PF: Should helical CT scanning of the thoracic cavity replace the conventional chest x-ray as a primary assessment tool in pediatric trauma? An efficacy and cost analysis. J Pediatr Surg 2003;38(5):793-797, 2003.




Clinical Decision Rules: Which Patients Require Chest X-ray?


Chest x-ray historically has been routinely recommended following blunt or penetrating chest trauma. However, a number of studies have examined the sensitivity of history and physical examination in detection of thoracic injury in children and adults. These studies suggest that in stable and alert blunt trauma patients, injuries are extremely rare with a normal thorax examination and the absence of chest complaints.


Bokhari et al. performed a prospective study of 523 stable patients with blunt trauma and 153 stable patients with penetrating trauma ( Box 6-1 ). Before chest x-ray, patients were interviewed and examined for signs and symptoms of hemo- and/or pneumothorax, including chest pain or tenderness, tachypnea (greater than 20 breaths per minute), and abnormalities of bilateral lung sounds. Distracting injuries such as fractures or peritonitis were also noted. The authors found auscultation to be 100% sensitive for detection of hemo- and/or pneumothorax following blunt trauma. Chest pain and tenderness and tachypnea were insensitive (57% and 43%, respectively) but had negative predictive values of 99%. In the set of patients with penetrating chest trauma, history and examination were insufficient to exclude hemo- and/or pneumothorax. The authors conclude that stable blunt trauma patients with normal lung sounds and no chest pain, tenderness, or dyspnea do not require chest x-ray to evaluate for hemo- and/or pneumothorax. This study suffers from nonconsecutive enrollment with potential selection bias. Moreover, the rate of hemo- and/or pneumothorax in this population of blunt trauma patients was only 1.3% (7 of 523 patients), so negative predictive values provide a distorted view of the clinical value of history and physical exam. In a population with a higher rate of hemopneumothorax, the same sensitivity and specificity values would result in inadequate negative predictive values. Moreover, this study assessed the sensitivity of examination for hemo- and/or pneumothorax but did not assess for other important thoracic injuries such as mediastinal injury. In patients with a high-energy blunt injury mechanism suggesting possible mediastinal injury, the value of physical examination and history in excluding injury is uncertain. Nonetheless, in patients with a low-energy blunt trauma mechanism from which mediastinal injury is unlikely, a normal thoracic physical exam, and no complaints of chest pain, chest x-ray does not appear routinely necessary. FLOAT NOT FOUND


In children with blunt thoracic trauma ( Box 6-2 ), Holmes et al. performed a prospective study of 986 patients below the age of 16 years to derive a clinical decision rule for detection of pulmonary contusion, hemothorax, pneumothorax, pneumomediastinum, tracheal–bronchial disruption, aortic injury, hemopericardium, pneumopericardium, blunt cardiac injury, rib fracture, sternal fracture, or any injury to the diaphragm. Of their population, 8.1% sustained a thoracic injury. The following



Box 6-1


Blunt Trauma


Chest x-ray may not be routinely indicated in stable, alert patients with normal thoracic physical examination and no complaints of chest pain or dyspnea.


Penetrating Trauma


Chest x-ray is routinely required for injuries penetrating the dermis.


Indications for Chest X-ray Following Chest Trauma

Adapted from Bokhari F, Brakenridge S, Nagy K, et al: Prospective evaluation of the sensitivity of physical examination in chest trauma. J Trauma 53(6):1135-1138, 2002.
features identified thoracic injuries: low age-adjusted systolic blood pressure, elevated age-adjusted respiratory rate, abnormal results of thorax exam, abnormal chest auscultation, femur fracture, and Glasgow Coma Scale score less than 15. Sensitivity was 98% with a 95% confidence interval (CI) of 91% to 100%, with a negative predictive value of 99.4% (95% CI = 97.9%-99.9%). FLOAT NOT FOUND


Chest X-ray Technique and Limitations


For acute trauma patients, a portable chest x-ray is often the initial imaging test. The portable chest x-ray is performed as a supine or upright anterior–posterior (AP) examination ( Figure 6-1 ). The supine examination



Box 6-2


Chest x-ray is not required in the absence of these criteria:




  • Low age-adjusted systolic blood pressure



  • Elevated age-adjusted respiratory rate



  • Abnormal results of thorax exam



  • Abnormal chest auscultation



  • Femur fracture



  • Glasgow Coma Scale score <15

Sensitivity 98%, negative predictive value 99.4%


Clinical Decision Rule for Chest X-ray in Pediatric Blunt Trauma Patients

Adapted from Holmes JF, Sokolove PE, Brant WE, et al: A clinical decision rule for identifying children with thoracic injuries after blunt torso trauma. Ann Emerg Med 39(5):492-499, 2002.
is most commonly used in blunt trauma resulting from concern about possible coexisting spine trauma that would contraindicate an upright chest x-ray. On a chest x-ray obtained in the supine position, important diagnostic findings, such as subdiaphragmatic air indicating pneumoperitoneum or the layering fluid level of a hemothorax, may not be appreciated ( Figures 6-2 through 6-10 ). Moreover, a supine portable chest x-ray exaggerates the apparent width of the heart and mediastinum, simulating cardiomegaly and potential mediastinal injury (see Figure 6-1 ). For all of these reasons, when possible, an upright chest x-ray should be performed. Particularly in penetrating chest or abdominal trauma, where spinal injury is less likely, an upright chest x-ray should be obtained to maximize detection of hemothorax (see Figures 6-2 through 6-10 ) and pneumoperitoneum ( Figure 6-11 ). In patients who are completely stable hemodynamically and in whom a low suspicion for mediastinal injury exists based on factors such as low-energy trauma mechanism, a posterior–anterior (PA) and lateral chest x-ray should be obtained if a widened mediastinum on portable chest x-ray raises suspicion of mediastinal injury. In some cases, the mechanism of injury (e.g., a blow with fists to the anterior chest) is not consistent with mediastinal injury, and minor abnormalities on chest x-ray (e.g., a slightly widened mediastinum) may not require further imaging. If a high suspicion exists for mediastinal injury, chest CT with IV contrast should be performed, as the sensitivity of chest x-ray is inadequate to exclude mediastinal injury, as discussed in detail later in this chapter.


Figure 6-1


Differences between anterior–posterior (AP) and posterior–anterior (PA) chest x-rays.

The designation refers to the direction of passage of the x-ray beam through the patient to the receptor. The PA chest x-ray positions the x-ray source farther from the heart, and the x-ray receptor closer to the heart, than does the AP x-ray, resulting in less magnification of the cardiac silhouette relative to the thorax. This is explored in more detail in Chapter 5 .



Figure 6-2


Hemothorax.

Hemothorax and nontraumatic pleural effusions are indistinguishable on chest x-ray, but a key difference in appearance may occur resulting from the use of supine chest x-ray in immobilized trauma patients. In the supine position, pleural fluid (blood or other pleural effusion) layers in the plane of the x-ray, providing a diffuse hazy appearance rather than the fluid level typical on an upright chest x-ray. A small amount of hemothorax may be difficult to appreciate, whereas a large hemothorax makes the affected side appear denser than the unaffected side. A diffuse pulmonary contusion could have a similar appearance. If an upright chest x-ray is obtained, the fluid layers and provides the same diagnostic appearance as a pleural effusion, with blunting of the costophrenic angle, and a meniscus sign at the interface with the chest wall. A, B, Schematic of how the same hemothorax could appear quite different depending on the patient’s position.



Figure 6-3


Hemothorax and pulmonary parenchymal injury.

This gunshot wound victim has a large hemothorax—despite having a thoracostomy tube in place. The patient is supine in this x-ray, so no layering fluid level is seen. Because blood and soft tissues, such as the heart, diaphragm, and spleen, share essentially the same density, none of the margins of these structures can be discerned where they abut one another. The most cephalad portion of the patient’s left thorax appears slightly less dense resulting from the presence of some aerated lung in this region. The two irregular radiopaque structures on the patient’s left are bullet fragments. Compare with the CT scan in Figure 6-4 . Understand that not all hemothoraces require CT for management but we examine corresponding CT images to clarify chest x-ray findings.



Figure 6-4


Hemothorax.

Same patient as Figure 6-3 . This CT with IV contrast clarifies the findings on the chest x-ray. A, Soft tissue window. B, Lung window. The anterior portion of the left lung appears fairly normal (compare with the normal right lung). The posterior left thorax contains two separate denser substances: hemothorax and contused and atelectatic lung. On both the soft-tissue (A) and the lung (B) windows, the hemothorax is visible as a homogeneous collection along the inner aspect of the ribs. The injured lung has been compressed medially by the hemothorax and appears somewhat more heterogeneous resulting from the presence of both air and contrast-filled pulmonary vessels. The hemothorax is causing mass effect upon the heart, deviating it to the patient’s right. The chest tube is visible in cross-section as a bright ring.



Figure 6-5


Hemothorax, CT with IV contrast.

Same patient as Figure 6-4 . These coronal reconstructions were performed for evaluation of the spine, but they provide an interesting perspective on the extent of the hemothorax. Remember that although these images suggest a standing patient, they were acquired with the patient in a supine position. A, A somewhat more anterior plane than B. In both slices, the large hemothorax is seen, and the remaining lung tissue is compressed like an accordion in a medial and cephalad direction. Compare with the patient’s chest x-ray in Figure 6-3 , also taken in a supine position. Now the dense left hemithorax makes sense, including the decreasing density in the upper lung field resulting from partially aerated lung. The left lung tissue is dense from a combination of compressive atelectasis and probable contusion from the patient’s gunshot wound—which are indistinguishable on CT, because both increase the density of lung tissue to a variable extent. Here, we know atelectasis plays a role, because the lung occupies a smaller-than-normal volume.



Figure 6-6


Hemothorax: Upright chest x-ray.

This 21-year-old male was stabbed in the left posterior thorax and had an oxygen saturation of 94%. This upright chest x-ray shows a blunted left costophrenic angle—compare with the normal right side. The diaphragm and heart border cannot be clearly identified, because blood, heart, and diaphragm share the same x-ray density (fluid density). Compare with Figure 6-7 .



Figure 6-7


Hemothorax: Supine vs. upright chest x-ray.

Same patient as Figure 6-6 . A, A supine film just after placement of a left chest tube. The left costophrenic angle appears clearer (and was interpreted by the radiologist as demonstrating decreased pleural fluid), but don’t be fooled. This x-ray was taken in a supine position; thus the fluid moved from its pooled dependent position in the costophrenic angle to a broadly distributed location in the horizontal, supine plane (as discussed in an earlier figure). How can we be sure that the chest tube had not resolved the fluid? B, An upright x-ray a few hours later. Again, the left costophrenic angle is obscured as the hemothorax collects in the dependent costophrenic angle. Incidentally, the thoracostomy tube in both figures takes a suboptimal course toward the diaphragm. Subcutaneous air is visible in the left chest wall from the chest tube placement.



Figure 6-8


Hemothorax: Upright chest x-ray.

Same patient as Figure 6-7 . This chest x-ray was performed 36 hours after the first, after removal of a chest tube that had been placed for both presumed pneumothorax and treatment of the hemothorax. The left costophrenic angle is sharp and distinct resulting from resolution of the hemothorax. This is an upright chest x-ray, so this changed appearance is not simply a result of the patient’s position. Subcutaneous air from the chest tube placement is visible as scattered black densities—compare the right and left chest walls. A few of these patches are labeled—try to identify more collections.



Figure 6-9


Hemothorax: Supine chest x-ray with a subtle density difference.

This supine x-ray shows a subtle increase in density of the right hemithorax compared with the left, indicating a hemothorax. This subtle change is sometimes described as a “veiling opacity.” Because of the supine position of the patient, the hemothorax does not pool in the costophrenic angle but rather distributes broadly across the entire right hemithorax. As a result, the costophrenic angle remains sharp. As you will see in the corresponding CT images in Figure 6-10 , the total amount of fluid is relatively small, so the chest does not appear markedly denser. Can this appearance be distinguished from pulmonary contusion? The two may coexist, but an upright chest x-ray could confirm hemothorax by allowing fluid to become dependent, if the patient’s spine has been cleared. Incidentally, the patient has a right clavicle fracture.



Figure 6-10


Hemothorax, CT with IV contrast.

Same patient as Figure 6-9 . A, Soft-tissue window. B, Lung window of the same slice. C, Close-up from B. Dependent fluid is seen layering in the posterior right thorax—a hemothorax. The immediately adjacent lung appears dense as well; it is impossible on CT to distinguish the increased density of compressive atelectasis resulting from the hemothorax vs. actual pulmonary contusion. Compare with the patient’s normal left chest, where the lung is fully aerated even in the most posterior portion. Can we be sure that the increased density seen on the chest x-ray in the prior figure was a consequence of the hemothorax and not the dense lung? No; both contribute to the increased chest x-ray density.



Figure 6-11


Pneumoperitoneum: Upright chest x-ray.

A, Upright chest x-ray. B, Close-up. An upright chest x-ray is the preferred view for detection of subdiaphragmatic air (pneumoperitoneum). On the supine view commonly obtained in blunt trauma, free air may not be visible, because it may collect in the anterior abdomen, rather than beneath the diaphragm.


Injuries that can be detected or suggested by chest x-ray ( Table 6-2 ) include bony injuries such as rib fractures, clavicle fractures or dislocations, scapular fractures, and thoracic spinal injury; pneumothorax, hemothorax, possible tracheobronchial injury, pulmonary contusion, and subcutaneous emphysema; mediastinal abnormalities, including cardiomegaly suggesting pericardial effusion, pneumopericardium, and a host of findings suggesting aortic injury; diaphragmatic injuries; pneumoperitoneum; and retained foreign bodies, such as bullet fragments.



TABLE 6-2

Injuries Detected or Suggested by Chest X-ray
































Injury Type Specific Injury or Finding Sensitivity
Bony injuries


  • Rib fractures



  • Clavicle fractures or dislocations



  • Scapular fractures



  • Thoracic spinal injury

Varies depending on degree of displacement.
Injuries to the lungs, pleura, or airways


  • Pneumothorax



  • Hemothorax



  • Possible tracheobronchial injury



  • Pulmonary contusion



  • Subcutaneous emphysema

Varies depending on degree of injury. Controversy exists about the necessity for explicit diagnosis and treatment of subtle injuries not evident on chest x-ray. Chest x-ray has been reported to be only 45% sensitive for pneumothorax compared with CT, but the necessity for treatment of CT-only pneumothoraces is unclear.
Mediastinal and cardiac injuries


  • Cardiomegaly, suggesting pericardial effusion



  • Pneumopericardium



  • Findings suggesting aortic injury

Around 86%-93% sensitive for aortic injury.
Diaphragmatic injuries


  • Herniated bowel and solid organs in thorax

Around 60%.
Abdominal injuries


  • Pneumoperitoneum

Varies with degree of pneumoperitoneum. Sensitivity is reportedly around 38% for any pneumoperitoneum but as low as zero in patients with minimal free air (1-mm air pockets) and as high as 100% in patients with ≥13-mm collections.
Foreign bodies


  • Bullets



  • Shrapnel



  • Knives

Varies depending on size and density of object.

From Ball CG, Kirkpatrick AW, Laupland KB, et al. Factors related to the failure of radiographic recognition of occult posttraumatic pneumothoraces. Am J Surg 189(5):541-546, 2005; discussion 546; Smithers BM, O’Loughlin B, Strong RW. Diagnosis of ruptured diaphragm following blunt trauma: Results from 85 cases. Aust N Z J Surg 61(10):737-741, 1991; Stapakis JC, Thickman D. Diagnosis of pneumoperitoneum: Abdominal CT vs. upright chest film. J Comput Assist Tomogr 16(5):713-716, 1992.


Recent studies suggest that chest x-ray is relatively insensitive for a variety of clinical injury patterns. However, detecting radiographically occult injuries with more advanced diagnostic modalities such as CT scan may not always result in clinical benefits to patients. For example, when a hemothorax is visible on chest CT but not on chest x-ray, it is uncertain whether thoracostomy tube drainage is routinely necessary.


Interpretation of Chest X-ray for Trauma


Chest x-ray interpretation in the setting of trauma must be performed rapidly and systematically. Using a checklist of critical pathology can help you avoid the pitfall of stopping interpretation after recognition of a single abnormality. We review a few important points about the AP portable chest x-ray technique relevant to interpretation, and then we proceed with systematic interpretation.


The usual technique for acquisition of chest x-ray in blunt trauma is a supine AP portable chest x-ray. This technique allows maintenance of spinal precautions in patients with possible spine trauma, and it is appropriate for unconscious patients who are unable to sit or stand. The AP supine technique has several consequences:




  • The heart and mediastinum appear enlarged, relative to an erect PA x-ray (see Figure 6-1 ). This results from the shortened distance from x-ray tube to film or digital media (3 feet, compared with 6 feet for a typical PA x-ray), and from the increased distance between the heart (an anterior chest structure) and the detector. The consequence is apparent cardiomegaly and a wide mediastinum in some patients, which may purely be artifacts of the x-ray technique. Unfortunately, these findings can simulate important pathology such as traumatic pericardial effusion or aortic injury. In one study, 38% of blunt trauma patients demonstrated a wide mediastinum on supine x-ray but a normal mediastinum on an upright view. When a high suspicion for mediastinal injury exists, chest x-ray abnormalities should be further evaluated by more definitive imaging, such as ultrasound (for pericardial effusion) or CT (for aortic injury or pericardial fluid). When a low suspicion exists—for example, in the stable, alert, and minimally symptomatic patient—an upright PA x-ray can be performed and is often normal enough to provide reassurance of the absence of injury.



  • Pleural fluid and air tend to layer in the plane of the x-ray (see Figure 6-2 ). This often makes them less apparent. Blunting of the costophrenic angles by pleural fluid is often absent in a supine x-ray, even with large hemothorax. Even a large hemo- or pneumothorax may be invisible. Sometimes a subtle and diffuse density difference between the right and the left chest indicates an abnormality such as a hemothorax layered horizontally in the plane of the x-ray (see Figures 6-2 through 6-10 ). An upright chest x-ray may reveal layering of pleural fluid (hemothorax) with a more familiar meniscus sign (see Figures 6-6 and 6-7 ). Ultrasound or CT may also reveal findings not recognized on chest x-ray.



  • The diaphragms are usually higher than in an upright x-ray. This is caused by the weight of abdominal contents pushing against the diaphragm. It results in a lesser degree of lung inflation, with denser-appearing lung parenchyma.



  • Pneumoperitoneum may not be apparent. Air may not collect in a subdiaphragmatic location in a supine patient; instead, it may collect preferentially at the highest point in the midline abdomen. If free abdominal air is suspected (rare in blunt trauma but common in penetrating trauma), an upright AP or PA x-ray should be obtained whenever possible (see Figure 6-11 ).



In penetrating trauma, an upright chest x-ray is often obtained in stable patients, increasing the sensitivity for pneumoperitoneum and hemothorax. However, the AP portable technique still results in an enlarged cardiac and mediastinal silhouette, as described earlier. With these features in mind, we review a systematic approach to interpretation of the chest radiograph. Many approaches have been described, and any approach that allows rapid but comprehensive assessment is appropriate. Table 6-3 reviews a common mnemonic for interpretation of chest x-ray, which we introduced in Chapter 5 .



TABLE 6-3

Mnemonic for Systematic Interpretation of Chest X-ray in Trauma
























A Airway


  • Review the airway, inspecting the trachea and main-stem bronchi and looking for deviation or evidence of luminal obstruction.




    • Is the trachea deviated, suggesting tension pneumothorax or lobar collapse?


B Bones and Breast Shadows


  • Inspect the bones for radiographic density, fractures, lytic lesions, or bony deformity. Note breast shadows to avoid mistaking these for chest pathology, such as pneumothorax or pulmonary contusion.




    • Are rib fractures present?



    • Is a flail segment present?



    • Is the scapula, clavicle, sternum, or a combination of these fractured?



    • Are spinal fractures present?



    • Is the humerus fractured?



    • Are the acromioclavicular, sternoclavicular, and glenohumeral joints properly located?


C Cardiac Silhouette


  • Assess the cardiac silhouette for general size and contour.




    • Note an enlarged cardiac silhouette, suggesting pericardial effusion.



    • Inspect for pericardial air, air in the soft tissues of the neck, or a continuous diaphragm sign.



    • Note the width of the mediastinum. Other abnormal mediastinal findings are reviewed in more detail in Table 6-4 .


D Diaphragm


  • Assess the diaphragm or diaphragms, with attention to the contour and costophrenic angle, bilaterally.




    • Look for blunted costophrenic angles, suggesting pleural fluid (hemothorax).



    • Note a deep sulcus sign, suggesting tension pneumothorax.



    • Look for an elevated or irregular diaphragm, suggesting diaphragm rupture.



    • Are both diaphragms distinct?



    • Is one diaphragm higher than the other? (Right normally is higher than left.)



    • Are abdominal organs or NG tubes visible in the chest?



    • Is a black line visible beneath the diaphragm, indicating pneumoperitoneum?



    • Is a continuous diaphragm sign visible, indicating pneumopericardium?


E Everything Else


  • Review everything else around the lung fields, including the subcutaneous soft tissues and pleural boundaries.

F Lung Fields


  • Review the lung fields themselves, looking for evidence of pneumothorax, pulmonary contusion, hemothorax, or herniated abdominal contents, suggesting diaphragm rupture.



  • Is a pneumothorax present?




    • Do lung markings extend to the periphery?



    • Is a pleural line visible?



    • Is subcutaneous air visible?




  • Is a hemothorax present?




    • Is the density of one hemithorax different from that of the other?



    • Is a meniscus visible?




  • Is a tension pneumothorax present?




    • Is the mediastinum deviated?



    • Is the diaphragm depressed?



    • Is there a deep sulcus sign?



    • Is the trachea deviated?




  • Is a pulmonary contusion visible?




    • Is the lung denser in some regions than in others?


F Foreign Bodies or Devices


  • Are foreign bodies, such as shrapnel or knives, present? Are two orthogonal views available to confirm the location?



  • Are the following medical devices properly positioned?




    • Endotracheal tube



    • Central venous catheters



    • Thoracostomy tubes



    • NG and OG tubes



From Crausman RS. The ABCs of chest X-ray film interpretation. Chest 113:256-257, 1998.


Pneumothorax and Tension Pneumothorax


A pneumothorax is evident on chest x-ray as an area of increased lucency at the periphery of the lung. The normal lung markings are absent, giving the region of pneumothorax an unusually black appearance compared with the normal appearance ( Figures 6-12 through 6-23 ). Comparison with the contralateral side is useful, although bilateral pneumothoraces may be present. In some cases, the lung edge (visceral pleura) may be visible as a discrete line (see Figures 6-12, 6-13, 6-16, 6-20, and 6-21 ). The average distance from the ipsilateral thoracic cage to the pleural surface (based on three linear measurements) on upright chest x-ray has been described as predicting pneumothorax volume.




Figure 6-12


Pneumothorax.

A, Schematic of normal lung. B, Schematic of pneumothorax. Pneumothoraces can range in size from tiny to massive—we examine some tension pneumothoraces in later figures. Because of the variability in their size and location, pneumothoraces can be difficult to detect on chest x-ray. For example, a pneumothorax that is anterior or posterior rather than lateral may be hidden on frontal chest x-ray, particularly one taken in the supine position. An upright chest x-ray should be obtained if possible. An expiratory film is thought to be more sensitive, because the lung and thorax decrease in size during expiration, but air trapped in the pleural space remains the same size and thus appears relatively larger. Subtle pneumothoraces may not be visible on chest x-ray. In some cases, subcutaneous air may be the only visible clue to underlying lung injury. CT is extremely sensitive for pneumothorax, although controversy remains over the proper management of pneumothoraces seen only on CT (see text). Ultrasound is also thought to be more sensitive than chest x-ray for detection of pneumothorax, although again, the management of pneumothorax seen only on ultrasound is uncertain, because this is a relatively newly described method of detection. The chest x-ray findings of pneumothorax include a lack of the normal lung markings, which should be visible to the periphery of the chest wall. Sometimes a line marking the boundary of the lung and visceral pleura is visible, although this can be confused with ribs and with the medial margin of the scapula. Depending on the degree of pneumothorax and lung collapse, the lung parenchyma may appear denser than the opposite side. In extreme cases of tension pneumothorax, the pressure exerted by the air in the pleural space may begin to displace other structures, including the diaphragm and mediastinum. In tension pneumothorax, the hyperinflated hemithorax may also have abnormally positioned ribs, with a position more horizontal than usual. Review the figures that follow for examples of varying degrees of pneumothorax. Subtle cases can be hard to reproduce in print.



Figure 6-13


Pneumothorax.

A, PA x-ray demonstrating a very large spontaneous pneumothorax. B, Close-up from A. This image demonstrates the classic features described in Figure 6-12 no lung markings to the periphery of the thorax, a visible visceral pleural line, and increased density of the lung parenchyma—resulting from the marked degree of collapse in this case. Is this a tension pneumothorax? Some would argue that the definition of tension pneumothorax is clinical, based on hypotension and exam findings such as jugular venous distension and tracheal deviation. On a radiographic basis, tension pneumothorax is marked by some combination of tracheal deviation, mediastinal deviation to the opposite side, depression of the diaphragm and a deep sulcus (costophrenic angle), and elevation of ribs to a more horizontal position. This patient may have slight tracheal deviation and a degree of mediastinal shift, but the diaphragm appears normal, there is no deep sulcus sign, and the ribs are oriented normally. The white dots seen on each side are nipple markers.



Figure 6-14


Pneumothorax.

Same patient as Figure 6-13 . The lateral chest x-ray is not usually diagnostic, even in dramatic cases such as this one, because the normal thorax is superimposed upon the abnormal. Here, a hint of the complete collapse of the left lung is seen, with increased density near the hilum, but the lateral x-ray is neither necessary nor particularly helpful in this case.



Figure 6-15


Pneumothorax.

The same patient as Figures 6-13 and 6-14 after placement of a thoracostomy tube and reexpansion of the left lung. A, AP chest x-ray. The mediastinum appears wider than in Figure 6-13 because of the AP technique in this x-ray. B, Close-up from A. Although the chest tube placement appears a bit suboptimal, it clearly is functioning, because there is complete resolution of the abnormalities noted on the original x-ray. The thoracostomy tube shows typical features including a radiopaque line, punctuated by breaks marking the location of its fenestrations (B).



Figure 6-16


Pneumothorax.

A, Supine portable chest x-ray. B, Close-up from A. This moderate pneumothorax is much subtler than in Figure 6-13 but demonstrates many of the same findings. A pleural line is faintly visible—beyond this line, no lung markings are visible. Compare this with the opposite side, where the fine markings of pulmonary blood vessels are seen to the periphery of the pleural space. Although the normal result of a pneumothorax is a more lucent hemithorax, the entire right thorax appears somewhat denser in this case; the CT from the same patient in Figure 6-18 illustrates why. It is a good practice to find and follow the scapular border and rib borders to avoid confusion of these lines with the pleural line of a pneumothorax. None of the findings of a tension pneumothorax are present in this chest x-ray. The right costophrenic angle and lateral diaphragm are somewhat indistinct. This, plus the density of the right hemithorax, should make you consider hemothorax or pulmonary contusion, in addition to the pneumothorax.



Figure 6-17


Pneumothorax.

Same patient as Figure 6-16 . A chest tube has been placed, and the previously seen pleural line and absence of lung markings have resolved. The right chest looks somewhat less dense than before.



Figure 6-18


Pneumothorax.

This CT with IV contrast was performed for evaluation of the mediastinum. Chest CT is not routinely needed for evaluation of pneumothorax. Nonetheless, it reveals several interesting findings. First, despite the chest tube, a pneumothorax remains (remember, air is black on all CT windows), and this was not seen on the supine chest x-ray in Figure 6-17 . Why not? The pneumothorax is anterior, so the lung tissue intervening between the x-ray tube and the detector plate prevented recognition of the pneumothorax. The posterior lung tissue is quite dense, and a tiny amount of pleural fluid is present—likely indicating pulmonary contusion and small hemothorax. Alternatively, the posterior lung tissue may be dense resulting from atelectasis. This seems less likely because the left lung does not demonstrate dependent atelectasis. Does the residual pneumothorax require treatment? It will likely resolve with continued use of the existing chest tube, though that chest tube should be examined for kinks and checked for the presence of a continued air leak. When a large pneumothorax persists despite a properly functioning thoracostomy tube, a large airway injury or pulmonary laceration should be suspected.



Figure 6-19


Pneumothorax.

This young male suffered a spontaneous left pneumothorax. The x-ray demonstrates several features typical of pneumothorax and is subtle, though the pneumothorax is relatively large. This pneumothorax appears to be restricted to the left apical region on this upright chest x-ray. There is an absence of lung markings, and the apical thorax appears more lucent than usual resulting from the absence of lung parenchyma. A faint pleural line can be seen. A close-up ( Figure 6-20 ) shows these findings better.



Figure 6-20


Pneumothorax.

Same patient as Figure 6-19 , spontaneous apical pneumothorax. The absence of lung markings is clear, and the pleural boundary can be seen.



Figure 6-21


Pneumothorax.

Same patient as Figures 6-19 and 6-20 . A, Frontal chest x-ray. B, Close-up from A. Needle aspiration of the pneumothorax was performed, and this x-ray was obtained 6 hours later. A small residual pneumothorax is present (B), although lung markings are now visible above the fifth rib, where they were not previously.



Figure 6-22


Pneumothorax with subcutaneous air on chest x-ray but no visible pneumothorax.

This trauma patient has no visible pneumothorax, with lung markings seen to the periphery. However, subcutaneous air (black) in the lateral left chest wall and neck indicate some form of lung or airway injury, as the patient had no external wounds through which air might have been introduced. Subcutaneous air of this degree, while essentially proving the existence of some respiratory (or less likely, aerodigestive tract) injury, would not mandate CT. For example, in a patient with spontaneous chest pain after cough, CT should not be performed to hunt for associated pneumothorax, although a pneumothorax should be suspected. In this case, chest CT was performed to evaluate for possible thoracic spine injury but incidentally provided more information about the source of the subcutaneous air and is reviewed in Figure 6-23 .



Figure 6-23


Small pneumothorax with subcutaneous air on CT with IV contrast.

Same patient as Figure 6-22 . A tiny anterior pneumothorax is visible, as well as some dependent pleural fluid, which is likely hemothorax in the setting of trauma. The subcutaneous air is readily visible on lung windows. How should small pneumothoraces seen only on chest CT be managed? Controversy exists (see text). In general, very small pneumothoraces such as this should not be treated. Some authors advocate prophylactic placement of a thoracostomy tube if the patient will be transported long distances, transported by air, or placed on positive-pressure ventilation, which could result in an enlarging pneumothorax. Small studies show a low risk of increasing pneumothorax with positive-pressure ventilation, though this is an obvious complication that must be anticipated.


A common pitfall is mistaking the medial border of the scapula for such a pleural line or, conversely, mistaking a pneumothorax for a scapular marking. In cases of very large pneumothorax, the lung may be seen as a density contracted medially toward the lung hilum. Although this is a dramatic and overt finding, to the inexperienced viewer, it may not be recognized without forewarning of this possibility (see Figure 6-13 ).


Large pneumothoraces can exert pressure effects, resulting in clinically important hemodynamic compromise. Medical dogma states that a tension pneumothorax should never be recorded on x-ray, as it should be treated empirically as soon as suspected. In reality, some large pneumothoraces are difficult to detect clinically, and some patients remain stable despite radiographic appearances suggesting tension pneumothorax. Classic findings of pressure effects associated with tension pneumothorax include the following ( Figures 6-24 through 6-28 ):




  • A very lucent hemithorax, nearly black compared with the contralateral side, caused by a large pneumothorax.



  • A collapsed lung medially contracted toward the hilum.



  • The “deep sulcus sign,” a particularly deep costophrenic angle, resulting from air under pressure in the pleural space pushing the affected diaphragm inferiorly. In some cases, the sulcus is so deep that the full extent is not visible on the caudad margin of the chest x-ray.



  • A depressed and flattened hemidiaphragm, again resulting from the effect of pressurized air in the pleural space pushing on the diaphragm. In the case of a right-sided tension pneumothorax, the right hemidiaphragm may appear lower than the left, reversing their normal relationship. (Remember that normally the right diaphragm is higher than the left, because the liver is larger than the spleen.)



  • Mediastinal shift, in which the heart and other mediastinal structures are pushed toward the opposite side of the thorax by the effect of pressurized air in the pleural space. In addition to the shift of the heart, the trachea and medical devices such as endotracheal tubes and nasogastric tubes may be shifted to the contralateral side. The superior vena cava may appear kinked on chest x-ray. This can restrict venous return of blood to the heart, which, along with high intrathoracic pressure from the tension pneumothorax, impairs cardiac filling and output, leading to hypotension and the physical examination finding of jugular venous distension.



  • Horizontally oriented ribs on the affected side, caused by hyperinflation of the hemithorax. The normal oblique course of the ribs from posterior to anterior is lost on the frontal chest x-ray projection.




Figure 6-24


Tension pneumothorax on chest x-ray.

A, The normal chest. B, Schematic of tension pneumothorax. In the case of a tension pneumothorax, a large pneumothorax is typically visible, with a dense-appearing, medially displaced, collapsed lung. Increased pressure results in mediastinal shift and tracheal deviation to the opposite side. The affected side has a depressed hemidiaphragm. If tension pneumothorax occurs on the right side, the right hemidiaphragm may be displaced in a caudad direction and may be lower than the left hemidiaphragm—the reverse of their normal positions. In addition, the costophrenic angle may be extremely deep on the abnormal side (the deep sulcus sign).



Figure 6-25


Tracheobronchial injury with tension pneumothorax.

This 46-year-old male presented unresponsive after a motorcycle collision and was noted to have decreased breath sounds with tachycardia and a blood pressure of 120/80. The patient was intubated and chest x-ray was performed, showing findings concerning for tension pneumothorax. Findings included a large pneumothorax, a dense and medially contracted lung, a deep sulcus sign, a flattened diaphragm, and a shift of the mediastinum to the left. Figure 6-26 shows the patient’s chest x-ray after thoracostomy tube placement. His CT ( Figure 6-27 ) suggested a tracheobronchial injury. Bronchoscopy confirmed transection of the bronchus just distal to the takeoff of the right main bronchus. This was repaired operatively.



Figure 6-26


Tracheobronchial injury with tension pneumothorax.

Same patient as in Figure 6-25 . After placement of a right thoracostomy tube, the patient’s findings of tension pneumothorax have resolved.



Figure 6-27


Tracheobronchial injury with tension pneumothorax.

Same patient as in Figures 6-25 and 6-26 . This CT with IV contrast suggests but does not prove a tracheobronchial injury. A moderate-size pneumothorax persists despite the right thoracostomy tube, implying that more air is leaking into the pleural space than can be removed by the chest tube. Explanations for this include a large airway injury, a significant pulmonary parenchymal laceration, or a malfunctioning chest tube that is kinked, is plugged, is not attached to suction, or does not have its fenestrations within the pneumothorax. The pneumothorax is visible on the lung window (A) but not on the soft-tissue window (B) . Other injuries are present but are discussed separately in other figures—return to this figure later and try to identify pleural fluid (hemothorax), pulmonary contusion, rib fractures, and subcutaneous emphysema. This patient was taken to the operating room, where a bronchial injury was confirmed by bronchoscopy.



Figure 6-28


Tracheobronchial injury with tension pneumothorax.

This 19-year-old female struck a telephone pole and was unresponsive at the accident scene. Emergency medical services providers attempted to decompress a suspected left tension pneumothorax. The patient arrested en route to the emergency department, and on arrival a left chest tube was placed, just before this x-ray. The x-ray shows classic findings of tension pneumothorax, with a deep sulcus sign (so deep that the complete sulcus is not visible on the x-ray). The mediastinum is deviated to the left. The right ribs have assumed an abnormally horizontal position resulting from hyperexpansion of the chest. A left chest tube is present, and extensive subcutaneous air is present (compare with the normal right chest wall). Compare these findings to the CT images in Figure 6-29 .


Tracheobronchial Injury


Tracheobronchial injury (see chest x-rays and related CTs, Figures 6-25 through 6-30 ) is a rare but life-threatening injury usually associated with large or tension pneumothorax and requiring surgical intervention. Clues to the presence of this injury include the persistence of a large or even tension pneumothorax despite the apparently appropriate placement of a thoracostomy tube. This finding indicates that the rate of air leaking into the pleural space exceeds the rate at which it is being removed from that space by the thoracostomy tube. Two possibilities explain this scenario:




  • Malfunction of the thoracostomy tube, which may be misplaced (outside of the pleural space), internally clogged with blood or debris, kinked or compressed within the chest cavity or external to the body, not connected to suction or to a pleural vacuum device, or placed so that one or more of its holes are external to the pleural space, allowing air to enter the thoracostomy tube and pleural space. See the later discussion about evaluation of thoracostomy tubes on chest x-ray.



  • A rapid rate of air leak into the chest from a tracheobronchial injury or large pulmonary laceration, exceeding the thoracostomy tube capacity. When a large pneumothorax persists despite a large (e.g., 40-French) and properly functioning thoracostomy tube, a tracheobronchial injury is likely. In some cases this can be temporarily addressed by placement of additional thoracostomy tubes to allow faster egress of pleural air, but definitive surgical management will be necessary. In a stable patient, the injury can be confirmed with CT ( Figures 6-29 and 6-30 ). In an unstable patient, immediate surgical intervention is necessary. Intentional selective intubation of the unaffected main bronchus can prevent delivery of additional air into the affected pleural space.




    Figure 6-29


    Tracheobronchial injury with tension pneumothorax: CT with IV contrast viewed with lung windows.

    A, B, Two sequential axial images. Same patient as in Figures 6-28 and 6-30 . This CT is highly suggestive of tracheobronchial injury. A right chest tube has been placed and is clearly seen entering the right pleural space. Despite this, a large tension pneumothorax is still present. The mediastinum remains deviated to the left. The most likely explanation is a large airway injury, which would allow air to enter the pleural space faster than it can be removed by a large-bore chest tube. An alternative explanation would be complete occlusion of the chest tube by kinking or internal plugging. The patient is intubated and receiving positive pressure ventilation, increasing the risk that a bronchial injury would result in tension pneumothorax. Massive subcutaneous emphysema has accumulated bilaterally.



    Figure 6-30


    Tracheobronchial injury with tension pneumothorax.

    CT with IV contrast, lung windows. A, Axial CT image. B, Close-up from A. Same patient as in Figures 6-28 and 6-29 . The actual tracheobronchial injury is seen. The right main bronchus is seen in direct continuity with the large pneumothorax in right pleural space.



A rarer but more specific sign of tracheobronchial injury is the fallen lung sign, in which the collapsed lung falls away from the mediastinum rather than being retracted medially toward the hilum as a consequence of bronchial transection (see Figure 6-30 ).


Tracheobronchial and esophageal injuries are rare following blunt trauma (occurring in only about 1%) but may be suggested by CT. In cases of tracheobronchial injury, chest x-ray may be nondiagnostic in 30%, whereas CT may show a defect in the wall of major airways. Air in the airway may be contiguous with that in the pleural space or mediastinum when viewed with CT lung windows. In cases of esophageal injury, CT may show pneumomediastinum and esophageal thickening at the level of injury (see Figure 6-36 ). A Gastrografin swallow study followed by barium swallow can be diagnostic. Imaging of the esophagus is discussed in more detail in Chapter 4 . If aerodigestive injuries are suspected but the source of the air leak is unclear from diagnostic imaging, bronchoscopy and esophagoscopy can be used to differentiate the source.




Figure 6-31


Pneumothorax, comparison of chest x-ray and ultrasound findings.

This 19-year-old male had spontaneous right chest pain while playing soccer. This close-up from his chest x-ray shows a moderate apical right pneumothorax. Lung markings are absent at the right apex, and a pleural line is visible.

Ultrasound images from the same patient are shown in Figures 6-32 through 6-34 .



Figure 6-32


B mode ultrasound findings of normal lung and pleura.

The normal left lung from the patient in Figure 6-31 , viewed with B mode ultrasound. The anterior cortices of two adjacent ribs are visible as echogenic, horizontally oriented curves. Deep to these are acoustic shadows cast by the ribs. Between the ribs lies the horizontal pleural line, a bright white reflection at the interface between the parietal and the visceral pleura. Some authors have described the three lines formed by two adjacent ribs and the pleural line as the bat sign resulting from its resemblance to a stylized line drawing of a bat in flight (diagrammed in figure margin; try to identify this for yourself in the ultrasound image). When real-time ultrasound images are viewed, horizontal motion along the pleural line is normally seen—the sliding lung sign. In the presence of pneumothorax, movement along this line is not seen, as the visceral pleura is separated from the parietal pleura by a buffer of air.



Figure 6-33


M mode ultrasound findings of normal lung and pleura—seashore sign.

Figures 6-31 through 6-34 show images from the same case. Most ultrasound machines allow simultaneous acquisition of a B mode image (A) and an M mode image (B) that represents motion through the line in the B mode image. An M mode image of the normal left lung shows the seashore sign. Motionless tissues superficial to the pleural line have the appearance of a laminated series of horizontal lines, like wave fronts approaching a seashore. Deep to the pleural line, respiratory motion of normal lung gives a granular appearance—the “sand” on the sea shore.



Figure 6-34


M mode ultrasound findings of pneumothorax.

Figures 6-31 through 6-34 show images from the same case. Most ultrasound machines allow a split screen mode, showing B mode (typical two-dimensional images, A) and M mode (motion mode, B) on the same screen. In this figure, a B mode image of the chest wall is seen in the upper portion of the screen, A. An acoustic shadow from a rib is visible, just to the right of the vertical white line. This line has been drawn by the emergency ultrasonographer through the pleura between two ribs. Motion along this line is then depicted in the M mode image in B. The M mode image of the abnormal right lung shows the stratosphere sign, consistent with pneumothorax. Most ultrasound machines allow simultaneous acquisition of a B mode image (A) and an M mode image (B), representing motion through the line in the B mode image.



Figure 6-35


Ultrasound findings of normal lung and pneumothorax.

A lung point sign is simulated in this figure. When an M mode image reveals a transition between the abnormal stratosphere sign and the normal seashore sign, this is called the lung point sign. It is an indication of a partial pneumothorax, with the lung surface intermittently contacting the thoracic wall. Compare with Figures 6-33 and 6-34 .



Figure 6-36


Esophageal tear with pneumomediastinum.

CT can demonstrate esophageal injuries following trauma. These are extremely rare following blunt trauma but can occur with penetrating chest trauma. In the case of thoracic gunshot wounds, CT can demonstrate the missile trajectory, indicating its proximity to the esophagus and other mediastinal structures. In addition, focal thickening of the esophagus may be seen at a site of injury. Air leaking from an esophageal injury can create pneumomediastinum visible on CT. In this patient, who has an esophageal injury not from external trauma but from forceful vomiting, the esophagus appears thickened and air is visible surrounding the esophagus (pneumomediastinum). Lung windows reveal air and, in the case of trauma, can reveal a missile trajectory by demonstrating injured lung parenchyma.


Subcutaneous Air


Subcutaneous air, while itself almost never life-threatening, should be carefully sought because it can provide clues to other important injuries including pneumothorax. The appearance is increased lucency (black appearance) in soft tissues resulting from the presence of low-density air. The appearance can be extremely subtle (see Figure 6-22 ) or grossly evident (see Figure 6-28 ), with air outlining muscle fibers and multiple tissue planes. The chest wall, axilla, and neck should be thoroughly inspected. Air within soft tissue can have several sources:




  • An external wound that has introduced air into soft tissues. Common associated findings would be radiodense foreign bodies. The presence of an external wound and foreign bodies do not rule out the concurrent presence of a pneumothorax as the source of subcutaneous air.



  • A pneumothorax with leak of air from the pleural space into adjacent soft tissues (see Figures 6-22 and 6-28 ). Common associated findings are rib fractures in either penetrating or blunt trauma or radiodense foreign bodies in the case of penetrating trauma. The associated pneumothorax may not be visible on chest x-ray in all cases.



  • An esophageal injury with air leak. This is extremely rare in the case of blunt trauma and occurs rarely with penetrating trauma. Radiographic clues to this injury pattern include associated pneumomediastinum.



  • Valsalva maneuver against a closed glottis during blunt trauma. Again, associated pneumothorax is likely but may be small or invisible on chest x-ray.



  • Barotrauma from mechanical ventilation. An associated pneumothorax is not always seen on chest x-ray.



  • Necrotizing infections. These can produce soft-tissue gas but would not be expected in the setting of acute trauma.



Hemothorax


Hemothorax may be subtle (see Figure 6-6 ) or gross (see Figure 6-3 ) on chest x-ray. Technically, chest x-ray reveals the presence of pleural fluid but does not prove it to be blood; a preexisting pleural effusion would have an identical radiographic appearance. The clinical setting is essential to determining the course of action. As described earlier, the commonly used supine portable chest x-ray can compromise detection of hemothorax by causing fluid to layer in the plane of the horizontally positioned x-ray detector. Small amounts of hemothorax may be invisible on supine x-ray; on upright x-ray, these may appear as simple blunting of the costophrenic angles (see Figures 6-2 through 6-10 ). Large hemothoraces may give the entire thorax a denser (whiter) appearance relative to the normal side on supine x-ray, sometimes referred to as a “veiling opacity” (see Figure 6-9 ). On upright AP or PA chest x-ray, these may appear as obvious radiodense layered fluid collections with a curved meniscus where they meet the thoracic wall (see Figure 6-7 ). Other chest x-ray findings commonly associated with hemothorax include pneumothorax, rib fractures, pulmonary contusions, mediastinal injury, and spinal trauma. Large hemothoraces can obscure underlying pulmonary contusions. The diaphragm on the affected side may be obscured, and the possibility of concurrent diaphragmatic injury must be considered. Diaphragm injuries are discussed in more detail later in this chapter and in Chapter 10 . Particularly in the case of penetrating trauma, the subdiaphragmatic area should be assessed for pneumoperitoneum.


Pulmonary Contusion and Laceration


Pulmonary contusion, laceration, and hematoma refer to pulmonary parenchymal injuries that result in hemorrhage into the alveolar space and into interstitial spaces. In blunt trauma, the term contusion is common; in penetrating trauma, the term laceration is more often used, though the chest x-ray appearance is the generally the same. The accumulation of blood, other fluid, and cellular debris increases the density of the normally air-filled alveolar space, making it appear white on chest x-ray (chest x-rays and related CTs, Figures 6-37 through 6-46 ). The interstitial spaces also become more prominent. The affected lung tissue takes on the appearance of a solid organ or fluid. Much confusion exists about the appearance of pulmonary contusion on chest x-ray and the time course over which pulmonary contusion becomes radiographically apparent. Some authors have stated that pulmonary contusion may not be evident for hours, but a more common sense explanation must be understood: If sufficient hemorrhage and injury to lung has occurred to increase the density of the tissue, the injury is immediately apparent on chest x-ray. If a lesser degree of injury is present such that the density of the tissue remains relatively normal, the injury may be invisible initially. If continued hemorrhage or fluid accumulation into the injured tissue occurs, the appearance may become more evident over hours. Pulmonary contusion has no pathognomonic features; the same increased density can occur with pneumonia, aspiration, or pulmonary infarction—all processes that can result in alveolar consolidation. The context of trauma defines the appearance as contusion rather than one of these other processes. It is impossible to distinguish an evolving pulmonary contusion on chest x-ray from a pneumonia developing in the region, because both become visible on chest x-ray by the same process of alveolar and interstitial fluid accumulation. Clinical factors such as the presence of fever are used to make the distinction, which may be impossible even on these grounds. Pulmonary contusion, aspiration, and pneumonia may occur simultaneously. Associated chest x-ray findings can include rib fractures, hemo- or pneumothorax, or radiodense foreign bodies in the setting of penetrating trauma. CT is more sensitive than x-ray and may predict the need for ventilatory support—although it is the clinical state of the patient, not imaging findings, that defines the need for intervention.




Figure 6-37


Pulmonary contusion.

This 77-year-old female was in a car struck by a train. Her chest x-ray shows dense consolidation of the right mid- and lower lung. The costophrenic angle is blunted, and the lateral right diaphragm appears elevated and cannot be distinguished from the consolidation. From Chapter 5 , recall the silhouette sign, the principle that two adjacent tissues of the same density cannot be distinguished on chest x-ray. Because the right lateral and lower lung cannot be distinguished from the diaphragm and liver in this patient, they must share the same soft-tissue (fluid) density. Figure 6-38 demonstrates CT images from this patient. Can pulmonary contusion be distinguished from aspiration or other pneumonia? Not based on the chest x-ray findings. Theoretically, this patient could have aspirated—or could have had pneumonia before her collision with the train.



Figure 6-38


Pulmonary contusion.

This 77-year-old female was in a car struck by a train. Compare these CT with IV contrast images with Figure 6-37 showing her chest x-ray. A, Soft-tissue window settings. B, Lung window settings. These images demonstrate that the injured right lung has taken on the same tissue density as muscle tissue—a remarkable transformation of lung to “solid organ.” On soft-tissue window settings, the lung tissue and pectoral muscle appear nearly the same density. The contused lung parenchyma increased in density resulting from alveolar hemorrhage and fluid leaking from injured lung parenchymal cells. Compare with the fairly normal appearance of the left lung on lung windows. Note the different information provided by the two window settings. The lung window setting demonstrates a pneumothorax that is not visible on the soft-tissue window. Incidentally, the anterior right lung shows extensive bullous changes of emphysema, discussed in more detail in Chapter 5 .



Figure 6-39


Pulmonary laceration or hemorrhage.

Not all pulmonary injuries are contusions from blunt trauma. This 46-year-old male was shot in the right axilla by police. Bullet fragments are visible in the soft tissues of the right axilla, where a large soft-tissue defect is visible. The lung parenchyma is densely consolidated in the trajectory of the bullet—presumably from bleeding into the damaged tissue. The silhouette sign is again seen; the injured lung parenchyma of the right middle lobe is adjacent to the right heart border and shares the same soft-tissue (fluid) density. As a consequence, the right heart margin is obscured. A chest tube has been placed, and no hemopneumothorax is visible, although the supine position of this chest x-ray reduces its sensitivity for these, as described in an earlier figure.



Figure 6-40


Pulmonary contusion.

This 16-year-old male was a restrained passenger in a motor vehicle collision. He self-extricated and ambulated at the scene but complained of chest pain. His chest x-ray shows a subtle consolidation of the right mid lung. The flexible chest wall of pediatric patients may allow lung contusion without rib fracture.



Figure 6-41


Pulmonary contusion.

Same patient as in Figure 6-40 . A, PA chest x-ray. B, Lateral chest x-ray. This chest x-ray was taken 7 hours after the first and shows an evolving pulmonary contusion. Compare with the CT in Figure 6-42 .



Figure 6-42


Pulmonary contusion: CT with IV contrast.

Same patient as Figures 6-40 and 6-41 . This patient has a subtler pulmonary contusion than does the victim of the car–train collision ( Figures 6-37 and 6-38 ). In those figures, the lung tissue was so densely consolidated that it was easily visible on both chest x-ray and CT soft-tissue windows, with the same apparent density as pectoral muscle. The patient in this figure has less severe injury, with less dense lung tissue in the region of injury. Whereas the injured lung is readily visible on lung windows (A), it is invisible on soft-tissue windows (B). Bilateral pulmonary contusions are visible on CT, whereas the initial x-ray demonstrated only the right-sided contusion clearly.



Figure 6-43


Pulmonary contusion with pneumothorax.

A, AP supine chest x-ray. B, Close-up from A. This 34-year-old male was an unrestrained driver who was thrown through his windshield. His chest x-ray shows a pulmonary contusion with density along the superior right heart border. Careful inspection also reveals a lateral right pneumothorax (B) . The width of the upper mediastinum cannot be determined because of the adjacent dense right lung apex. Therefore, CT was performed to evaluate for mediastinal hematoma and aortic injury ( Figure 6-44 ).



Figure 6-44


Pulmonary contusion with pneumothorax.

Same patient as Figure 6-43 . A, CT with IV contrast, axial slice viewed with lung windows. B, Same slice, viewed with soft-tissue windows. Some areas of injured lung are densely consolidated and are visible even on soft-tissue windows. Others are less dense, reflecting less alveolar hemorrhage and parenchymal injury—these are visible only on lung windows (A). A small right anterior pneumothorax persists despite the presence of a chest tube, and a small left pneumothorax is present. The pneumothoraces are not visible on soft-tissue windows (B).



Figure 6-45


Pulmonary contusion with pneumothorax.

This 89-year-old male was in a motor vehicle collision in which his airbags deployed. The patient’s chest x-ray shows extensive subcutaneous emphysema of the left chest wall, extending to the left neck. His left lung appears denser than the right, suggesting pulmonary contusion. A small basilar left pneumothorax is difficult to see on this image but is the likely source of the subcutaneous air.



Figure 6-46


Pulmonary contusion with pneumothorax.

Same patient as Figure 6-45 , 2 days later. Does this x-ray show progression of pulmonary contusion? It is hard to be sure. The patient has a chest tube in place and may have a hemothorax contributing to increased left lung density. He is intubated, and a ventilator-associated pneumonia may be in progress as well. Upright portable chest x-ray cannot differentiate these causes of increased lung density.


Lobar Collapse


Following trauma or as a consequence of endotracheal intubation, lobar collapse with volume loss can occur. Familiarity with the chest x-ray appearance is essential, because this condition can be mistaken for other serious abnormalities, including mediastinal trauma, tension pneumothorax, pulmonary contusion, hemothorax, and diaphragm rupture. Treatment includes maneuvers to reexpand the affected lung segment, sometimes including repositioning of an endotracheal tube or altering ventilator settings. A collapsed lung segment appears dense on chest x-ray ( Figure 6-47 and CT Figure 6-48 ), similar in appearance to other parenchymal abnormalities, such as pulmonary contusion, or to pleural space abnormalities, such as hemothorax. However, because a collapsed lung segment occupies a smaller-than-normal volume, radiographic evidence of volume loss is present. Findings of volume loss include shift of structures toward the area of volume loss. This can include shift of the mediastinum, tracheal deviation, and elevation of the diaphragm on the affected side (see Figure 6-47 ). This is in stark contrast to tension pneumothorax, where structures are shifted away from the affected side. Nevertheless, to an inexperienced observer, the obvious shift of structures may be mistaken for tension pneumothorax. Elevation of the diaphragm can be mistaken for a diaphragmatic injury. If the area of lobar collapse abuts the mediastinum, the mediastinum may appear wide, simulating aortic trauma. In an intubated patient, the position of the endotracheal tube should be noted. Right main bronchus intubation commonly can result in left lung collapse or right upper lobe collapse (because the endotracheal tube may occlude the right upper lobe bronchus). Plugging of bronchi with blood, mucus, or aspirated material can also lead to lobar collapse.




Figure 6-47


Lobar collapse with mediastinal shift resulting from volume loss.

This 38-year-old male was ejected from his vehicle after rolling the car at high speed. (A) His initial chest x-ray shows dramatic mediastinal shift to the right, which in the setting of trauma might first bring to mind left tension pneumothorax. However, mediastinal shift can occur from the “push” of high pressure on the contralateral side (e.g., tension pneumothorax) or from the “pull” of low volume on the ipsilateral side. In this case, the patient has collapse of the right upper lobe, seen as a density in the right lung apex. The minor fissure has tilted diagonally from the accordion-like collapse of the upper lobe, rather than having its normal horizontal configuration. Collapse of the right upper lobe results in volume loss on the right, and the mediastinum shifts right to occupy the resulting space. Was the right upper lobe collapse a traumatic injury? More likely, it represents plugging of the right upper lobe bronchus with mucous or blood. The CT depicting this finding is seen in Figure 6-48 . (B) Same patient 2 hours later. The right upper lobe has reexpanded, although density representing atelectasis or possible pulmonary contusion remains. The mediastinum has shifted back toward its normal position. A left chest tube has been placed, as CT did demonstrate a small left pneumothorax—clearly not the cause of the mediastinal shift.



Figure 6-48


Lobar collapse with mediastinal shift resulting from volume loss.

CT with IV contrast viewed on lung windows to best illustrate lobar collapse. Same patient as Figure 6-47 , in which his initial chest x-ray shows dramatic mediastinal shift to the right. This is due not to left-sided tension pneumothorax but to significant collapse of the right upper lobe. This results in volume loss on the right, and the mediastinum shifts right to occupy the resulting space. A, An axial slice through the upper chest shows a triangular cross section through the collapsed lung segment. The upper mediastinum has shifted right, and the aortic arch has a nearly right–left transverse orientation rather than an anterior–posterior orientation. A small left pneumothorax is visible as air (black) with no lung markings. B, A coronal view, in which the upper lobe collapse is again visible. The heart and trachea appear shifted right. The left lung does not show any evidence of pneumothorax in this view, though other images show a small pneumothorax. Certainly, a tension pneumothorax was not present and was not the cause of the mediastinal shift.


Diaphragm Injury


Injury to the diaphragm is discussed in detail in Chapter 10 . On chest x-ray, the appearance depends on the degree of injury. In cases of overt herniation of intestinal contents into the chest, the appearance can be obvious. In subtle diaphragm tears without herniation of abdominal contents, no radiographic abnormalities may be seen on chest x-ray. Left diaphragmatic injuries are more common than right. In the case of left diaphragm rupture, the stomach (gastric air bubble) and loops of small bowel may be visible within the chest ( Figures 6-49 through 6-55 ). If a nasogastric (NG) or an orogastric (OG) tube is present, it may be visible curled within the thorax (see Figure 6-49 ). Sometimes the appearance suggests only an elevated hemidiaphragm, but diaphragmatic injury must be suspected. When right diaphragm injury is present, the liver may appear to occupy an unusually cephalad position (see Figure 10-33 ). Overall, initial chest x-ray is thought to be only about 17% to 50% sensitive for detection of diaphragm rupture, and positive pressure ventilation is thought to reduce sensitivity, likely resulting from positive pressure pushing the affected diaphragm to a more normal caudad position.




Figure 6-49


Diaphragm injury.

This 68-year-old female was ejected from a vehicle. Her chest x-ray shows several classic features of diaphragmatic rupture. The right diaphragm is normal in appearance, whereas the left diaphragm is not identified. The patient has an orogastric tube in place, which is coiled in the stomach—in the left lower to midthorax. This is consistent with herniation of the stomach through a diaphragmatic injury into the left thorax. Not specific to diaphragm rupture, the patient also has an indistinct aortic arch, concerning for traumatic aortic injury. The left thorax also appears denser than the right, possibly indicating hemothorax or diffuse pulmonary contusion. Compare with the patient’s CT in Figures 6-50 and 6-51 .



Figure 6-50


Diaphragm injury, CT with IV contrast.

CT images from the same patient as Figure 6-49 show the stomach and spleen to be present in the left chest, consistent with a diaphragm rupture. These two images show the same slice, at the level of the left atrium in the chest, on soft-tissue (A) and lung (B) windows. An orogastric tube is seen in the stomach. A portion of the spleen is also seen. On lung windows, no pneumothorax is identified.



Figure 6-51


Diaphragm injury, CT.

CT images from the same patient as Figures 6-49 and 6-50 . These two images show the same slice through the chest, on soft-tissue (A) and lung (B) windows. An orogastric tube is seen in the stomach, with an air–fluid level representing gastric contents. The spleen is also seen herniated into the chest with an area of parenchymal contusion. Perisplenic fluid is also seen. On lung windows, no pneumothorax is identified—the area of air is within the stomach.



Figure 6-52


Diaphragmatic rupture.

This 21-year-old male was a rear-seat passenger in a head-on collision with dump truck. Two other passengers were killed at the scene. The patient was noted to have decreased oxygen saturations and no breath sounds. Needle decompression was performed by emergency medical services. This chest x-ray, taken in the emergency department after placement of a chest tube, shows features of diaphragmatic rupture. The normal curvature of the left diaphragm is not seen. The gastric air bubble is seen in the left chest. Note how closely the chest tube passes to the gastric air bubble, a reminder that care should always be taken to assess for solid organs in the chest when placing a chest tube. Not specific to diaphragm rupture, the patient also has opacification of the left hemithorax, which could represent pulmonary contusion or hemothorax on this supine film. In addition, herniation of abdominal contents into the chest can compress lung tissue, giving it this appearance. Compare this x-ray with the CT findings in Figures 6-53 through 6-55 . Incidentally, the patient has a severe dextroscoliosis that is not a result of trauma.



Figure 6-53


Diaphragmatic rupture, CT with IV contrast.

Figures 6-52 through 6-55 show images from the same case. A, Soft-tissue windows. B, The same slice viewed on lung windows. In these images near the lung apex, the thoracostomy tube is seen passing into consolidated lung parenchyma. From these images, it is not possible to determine whether this increased density of lung tissue represents contused lung from the original blunt injury or compressive atelectasis from the pressure exerted by herniated abdominal contents. A small anterior pneumothorax is seen on lung windows, despite the chest tube. Fluid density is seen surrounding the lung parenchyma on soft-tissue windows, representing hemothorax.



Figure 6-54


Diaphragmatic rupture.

These CT images are from the same patient as Figures 6-52, 6-53, and 6-55 . A, Soft-tissue windows. B, The same slice viewed on lung windows. Here, the stomach is seen in the left chest adjacent to the heart. The air–fluid level represents gastric contents. Note how close to the stomach the thoracostomy tube passes—a reminder to consider diaphragm rupture and to perform a finger sweep when placing a thoracostomy tube for trauma.



Figure 6-55


Diaphragmatic rupture, CT with IV contrast.

Figures 6-52 through 6-55 show images from the same case. A, Soft-tissue windows. B, The same slice viewed on lung windows. Here, the spleen and gastric air bubble are seen adjacent to the heart in the left chest. The right chest appears normal.


Mediastinal and Aortic Injuries


Life-threatening injury to the aorta and other mediastinal structures can occur with blunt or penetrating trauma. A variety of chest x-ray findings can provide clues to these injuries, as we describe later. Of paramount importance is understanding that an aortic injury may be present with a completely normal chest x-ray, albeit rarely. We discuss some controversies surrounding this rare event later in this chapter. Understanding the mechanisms behind aortic injuries can assist both in recognizing the radiographic appearance and in determining when chest x-ray abnormalities require further imaging. Because of the importance of this injury, we have included numerous example figures to illustrate the range of findings ( Figures 6-56 through 6-108 ).




Figure 6-56


Thoracic aortic injury.

This patient has a classically abnormal chest x-ray for aortic injury. The mediastinum is wide, the aortic knob and aortopulmonary window are obscured, the trachea and endotracheal tube are deviated by mediastinal hematoma, and the right paratracheal stripe is extremely wide. The patient’s CT is shown in Figure 6-57 .

Jul 4, 2019 | Posted by in GENERAL RADIOLOGY | Comments Off on Imaging Chest Trauma
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