Pneumothorax Workup

History and physical examination remain the keys to making the diagnosis. When pneumothorax is suspected, confirmation by chest radiography affords additional information beyond confirmation, such as the extent of pneumothorax, potential causes, a baseline study from which to go forward, and assistance with the therapeutic plan.

In the evaluation of trauma patients, airway and breathing collectively are the primary concern. Portable chest radiography is veritably always included in the initial radiographic evaluation of a major trauma victim, as significant chest injuries may be masked by lack of physical findings or associated injuries. Chest trauma carries an estimated 10-50% risk of associated pneumothorax. Chest computed tomography (CT) scanning likewise should always be performed for significant chest injuries, because plain radiographs may miss associated thoracic trauma. Specifically for pneumothorax, the presence of a pneumothorax seen only on CT scans defines it as occult. In stable patients, however, chest radiography is often unnecessary.^{[34, 35]}

Tension pneumothorax is a clinical diagnosis that now is more readily recognized because of improvements in emergency medical services (EMS) and the widespread application of educational programs such as Advanced Trauma Life Support (ATLS) and Fundamental Critical Care Support (FCCS).

Although laboratory and imaging studies help determine a diagnosis, as discussed earlier, tension pneumothorax primarily is a clinical diagnosis based on patient presentation. Suspicion of tension pneumothorax, especially in late stages, mandates immediate treatment and does not require potentially prolonged diagnostic studies (see the image below).

Go to Radiologic Diagnosis of Pneumothorax for complete information on this topic.

Arterial blood gas (ABG) studies measure the degrees of acidemia, hypercarbia, and hypoxemia, the occurrence of which depends on the extent of cardiopulmonary compromise at the time of collection.

In patients with severe underlying lung disease and in those with persistent respiratory distress despite treatment, hypoxemia not only occurs with increased alveolar-arterial oxygen tension gradient, but it also tends to be more severe in patients with secondary spontaneous pneumothoraces.

ABG analysis does not replace physical diagnosis nor should treatment be delayed while awaiting results if symptomatic pneumothorax is suspected. However, ABG analysis may be useful in evaluating hypoxia and hypercarbia and respiratory acidosis.

When evaluating the chest radiograph for pneumothorax, one should use a systematic approach. Always assess rotation, which can obscure a pneumothorax and mimic a mediastinal shift. Compare the symmetry and shape of the clavicles, and look at the relative lengths of the ribs in the middle lung fields on each side on the anteroposterior (AP) or posteroanterior (PA) views. On an image with rotation, the ribs on each side often have unequal lengths.

In a nonloculated pneumothorax, air generally rises to the nondependent portion of the pleural cavity. Therefore, carefully examine the apices of an upright chest radiograph, and scrutinize the costophrenic and cardiophrenic angles on a supine chest radiograph.

Finding of pneumothorax on chest radiographs may include the following:

• A linear shadow of visceral pleura with lack of lung markings peripheral to the shadow may be observed, indicating collapsed lung.
• An ipsilateral lung edge may be seen parallel to the chest wall.
• In supine patients, deep sulcus sign (very dark and deep costophrenic angle) with radiolucency along costophrenic sulcus may help to identify occult pneumothorax. The anterior costophrenic recess becomes the highest point in the hemithorax, resulting in an unusually sharp definition of the anterior diaphragmatic surface due to gas collection and a depressed costophrenic angle
• Small pleural effusions commonly are present and increase in size if the pneumothorax does not reexpand.
• Mediastinal shift toward the contralateral lung may also be apparent.
• Airway or parenchymal abnormalities in the contralateral lung suggest causes of secondary pneumothorax. Evaluation of the parenchyma in the collapsed lung is less reliable.

Although expiratory images are thought to better depict subtle pneumothoraces (the volume of the pneumothorax is constant and hence proportionally higher on expiratory images), a randomized controlled trial revealed no difference in the ability of radiologists to detect pneumothoraces on inspiratory and expiratory images after procedures with the potential to cause pneumothoraces.

The following images depict chest radiographs of pneumothoraces.

Tension pneumothorax

Imaging studies should not delay the diagnosis and treatment of tension pneumothorax, as this condition is a medical emergency. When considering radiography, utilizing a risk-benefit analysis has been suggested, in which the time taken to obtain the radiograph is balanced against the expected clinical course, with decompression preceding chest radiography in ventilated patients who are prone to rapid decompensation.

In a very select subset of patients, it may be preferable to radiologically confirm and localize tension pneumothorax before subjecting the patient to potential morbidities arising from decompression. The subset of patients are those who are awake, stable, and not in any distress in whom an immediate chest film can be obtained, with a continuously accompanying clinician ready to perform urgent decompression should the need arise.

In the rare case that a chest radiograph is obtained safely, findings can include ipsilateral lung collapse at the hilum, increased thoracic volume, trachea and mediastinum deviation to the contralateral side, widened intercostal spaces on the affected side, heart border ipsilateral flattening. With a left hemithorax, the left hemidiaphragm may be depressed, but the liver prevents this occurrence on the right side. See some examples of tension pneumothorax below.

Although the initial chest radiograph may show no evidence of pneumothorax, one must consider the possibility of delayed traumatic pneumothorax developing in any penetrating chest wound. Stable patients without pneumothorax on initial films can be observed with serial chest radiographs at 3 hours after injury to rule this out.^[36]

Pneumomediastinum

Mediastinal emphysema appears as a thin line of radiolucency that outlines the cardiac silhouette, as well as thin, lucent, vertically oriented streaks of air within the mediastinum (see the image below). The aorta and other posterior mediastinal structures are highlighted, and a well-defined lucency around the right pulmonary artery (“ring around the artery” sign) may be seen.

Air most easily is detected retrosternally on the lateral chest radiograph. An AP chest radiograph may not depict the finding in 50% of cases. An expiratory radiograph may help detect small apical pneumothoraces. Unlike air in a pneumothorax or pneumopericardium, the air remains fixed in pneumomediastinum and does not rise to the highest point.

Estimating the size of the pneumothorax

In evaluating the chest radiograph, first impressions of pneumothorax size can be misleading. The following methods may be used to estimate the size of the pneumothorax:

• Calculate the ratio of the transverse radius of the pneumothorax (cubed) to the transverse radius of the hemithorax (cubed). To express the pneumothorax size as a percentage, multiply the fractional size by 100. This formula assumes a constant shape of the lung when it collapses and is invalid if pleural adhesions are present. The ratio of lung size to hemithorax size to estimate pneumothorax size avoids the subjective underestimation of pneumothorax expressed as a percentage of previous lung volume.
• A 2.5-cm margin of gas peripheral to the collapsing lung corresponds to a pneumothorax of about 30%. Complete collapse of the lung is a 100% pneumothorax.
• A simple approach involves measuring the distance from the apex of the lung to the top margin of the visceral pleura (thoracic cupola) on the upright chest radiograph, such that a small pneumothorax is a distance to the apex that measures less than 3 cm and large pneumothorax has greater than 3 cm distance to the apex.

The cut-point distinguishing small and large pneumothoraces varies somewhat among professional societies and experts. The British Thoracic Society uses 2 cm as the cut-off,^[37] the American College of Chest Physicians uses 3 cm as the cut-point,^[38] and the Light Index uses 15% of the thoracic volume on the posterior-anterior film as the cut point.^[39]

Disadvantages of chest radiographs

Chest radiographs may fail to reveal pneumothorax or radiologists or interpreting physicians may fail to recognize the presence of the pneumothorax. Other disadvantages are as follows:

• In patients with underlying pulmonary disease, the classic visceral pleural line may be harder to detect, because the lung is hyperlucent, and little difference exists in the radiographic density between the pneumothorax and the emphysematous lung.
• A vertical skin line can be mistaken for a pneumothorax, leading to unnecessary and possibly harmful therapy.
• Large bulla can simulate pneumothorax on chest radiographs, such that computed tomography (CT) scanning may be required to clarify the diagnosis.
• Occasionally, skin folds, the scapula, and bed sheets can mimic the pleural line, falsely suggesting pneumothorax on the chest radiograph. Unlike pneumothoraces, skin folds usually continue beyond the chest wall, and lung markings can be seen peripheral to the skin fold line. Viewing the film under the hot lamp may be necessary to discern obscure peripheral lung markings.
• As ultrasonography becomes increasingly available in emergency situations, the already limited role of radiography in tension pneumothorax will be further minimized. Multiple recent studies have shown bedside ultrasonography to be more accurate than supine chest radiography in detecting and quantifying the presence of pneumothorax, including traumatic pneumothorax.

Go to Radiologic Diagnosis of Pneumothorax for complete information on this topic.

Confirmation of a suspected pneumothorax that is not readily observed on standard supine anteroposterior (AP) radiograph can be demonstrated by obtaining a lateral decubitus film with the involved hemithorax positioned uppermost (see the following images).

In neonatal patients, translumination may reveal an increased transmission of light through the chest on the affected side.

If emesis or retching is the precipitating event for a pneumothorax, an esophagogram should be obtained to evaluate for Boerhaave syndrome (an esophageal tear), which has a high mortality rate. This is the study of choice in all cases of suspected esophageal perforation (ie, postendoscopy patients). Esophagoscopy could further be performed for esophageal perforations.

Computed tomography (CT) scanning is the most reliable imaging study for the diagnosis of pneumothorax, but it is not recommended for routine use in pneumothorax. This imaging modality can help to accomplish the following:

• Distinguish between a large bulla and a pneumothorax
• Indicate underlying emphysema or emphysemalike changes (ELCs)
• Determine the exact size of the pneumothorax, especially if it is small
• Confirm the diagnosis of pneumothorax in patients with head trauma who are mechanically ventilated
• Detect occult/small pneumothoraces and pneumomediastinum (although the clinical significance of these occult pneumothoraces is unclear, particularly in the stable nonintubated patient)

CT scanning is widely used in actual clinical practice to assess the possibility of associated concurrent pulmonary disease because of the inherent superiority of CT scans to visualize the details of lung parenchyma and pleura, as can be seen in the images below.

Spontaneous pneumothorax

When performed on primary spontaneous pneumothorax patients, CT detects multiple blebs and bullae in the setting of negative chest radiographic findings. This may not impact management, as there has been no correlation between number of blebs and recurrence. However, CT scanning may have a role in secondary spontaneous pneumothorax, especially to differentiate from giant bullous emphysema.

Traumatic and tension pneumothorax

CT scanning can detect occult pneumothorax in patients in trauma and emergency surgery settings. If the patient requires mechanical ventilation and/or anesthesia, all participants should be made aware of the findings; sometimes, prophylactic tube thoracostomy may be performed.^{[40, 41]} This modality has also been shown to be more sensitive than radiography for hemothorax and pulmonary contusion.

Collapse of the lung, air in the pleural cavity, and deviation of mediastinal structures are present in tension pneumothorax.

Pneumomediastinum

CT scanning may improve diagnostic sensitivity in pneumomediastinum, and if clinical suspicion is present for this condition, should be obtained. One small study suggested that mild pneumomediastinum was underdiagnosed based on chest radiographic findings, and CT scanning was needed to make the diagnosis.

Go to Radiologic Diagnosis of Pneumothorax for complete information on this topic.

Prehospital, portable ultrasonography may provide diagnostic and therapeutic benefit when conducted by a proficient examiner who used goal-directed and time-sensitive protocols, as determined in an air rescue setting.^[42] Further study in this area may help to determine the indications and role of prehospital ultrasonography. A recent study reports that in experienced hands, ultrasonography can be quicker and more accurate than radiography for distinguishing free pleural effusion (a finding in pneumothorax) in time-sensitive evaluations.^[43]

Ultrasonography is increasingly used in the acute care setting as a readily available bedside tool, especially in the intensive care unit (ICU) and emergency department (ED) settings. This modality provides a rapid imaging option for diagnosis of pneumothorax, but this evaluation should not delay treatment of a clinically apparent tension pneumothorax.^{[44, 45, 46]}

Many trauma centers are incorporating chest ultrasonography as an adjunct to the Focused Assessment with Sonography in Trauma (FAST) examination. Knudtson et al, in a prospective analysis of 328 consecutive trauma patients at a level 1 trauma center, obtained a specificity of 99.7% and an accuracy of 99.4%, and concluded that ultrasonography was a reliable modality for the diagnosis of pneumothorax in the injured patient.^[45]

A prospective study by Brook et al designed to assess the accuracy of radiology residents in detecting pneumothoraces as part of the extended focused assessment with sonography for trauma (eFAST) concluded that ultrasonographic pneumothorax detection by these radiology residents was both accurate and efficient in the early detection of clinically important pneumothoraces.^[47] The investigators compared ultrasonographic pneumothorax detection (by the absence of parietal-over-visceral lung sliding with "comet tail" artifacts behind it) with the reference standard of chest CT scans in 169 consecutive trauma patients (ie, 338 lung fields). A sensitivity of 47%, specificity of 99%, positive predictive value of 87%, and negative predictive value of 93% was found; none of the small pneumothoraces missed by ultrasonography required drainage during the hospitalization period.^[47]

In addition, Hernandez et al noted that ultrasonography is the only radiographic modality allowing patients with nonarrhythmogenic cardiac arrest to continue undergoing resuscitation while clinicians searching for easily reversible causes of asystole or pulseless electrical activity (PEA).^[48] Their proposal is for further investigation into a protocol (using the acronym CAUSE for cardiac arrest ultrasound exam) in which cardiac arrest patients, concurrent with resuscitation, receive bedside ultrasonography to look for cardiac tamponade, massive pulmonary embolus, severe hypovolemia, and tension pneumothorax.^[48] Their hope is that the eventual adoption of ultrasonography in this setting may allow increased "real-time" diagnostic acumen, decreasing the time required to receive appropriate condition-related therapy.

Ultrasonographic findings

Features of the ultrasonographic examination for the diagnosis of pneumothorax include absence of lung sliding (high sensitivity and specificity), absence of comet-tail artifact (high sensitivity, lower specificity), and presence of lung point (high specificity, lower sensitivity).

In the absence of pleural disease, visceral pleura move against parietal pleura while breathing. This movement of the 2 pleura is detected by the ultrasound as lung sliding, which is a "kind of twinkling synchronized with respiration" seen in real-time and time-motion modes. That is, lung sliding refers to normal pleural movement in patients without pneumothorax.^[49] One study showed absent lung sliding from an anterior approach indicated pneumothorax with 81% sensitivity and 100% specificity.

Comet-tail artifacts are vertical air artifacts that arise from the visceral pleural line (or in the case of parietal emphysema or shotgun pellets may arise above the pleural line). Lung point is the location that lung-sliding and absent lung-sliding alternately appear; it has been shown in multiple studies to allow determination of the size of a pneumothorax. Zhang et al obtained a 79% sensitivity in lung point's ability to determine pneumothorax size.^[50]

Advantages of ultrasonography

Ultrasonography has high sensitivity (95.65%), specificity (100%), and diagnostic effectiveness (98.91%) for pneumothorax when using computed tomography (CT) scanning as the criterion standard. In another study, ultrasonography performed on patients with blunt thoracic trauma had 94% sensitivity and 100% specificity for pneumothorax detection compared with spiral CT scanning.

This imaging modality can be used as a possible bedside technique to detect pneumothorax, which may be useful in unstable patients. A prospective study involving 135 patients with multiple trauma using bedside ultrasonography performed by ED clinicians obtained 86% sensitivity and 97% specificity for the detection of pneumothorax. Traumatic pneumothorax in the ICU setting can also be followed accurately and early (initial 24 hours) with ultrasonography alone for resolution of the lesion. Ultrasonography does not use ionizing radiation and is repeatable.

Disadvantages of ultrasonography

Ultrasonography is heavily operator dependent. In addition, this modality cannot be used to discriminate between a chronic obstructive pulmonary disease (COPD)–associated bleb and pneumothorax.^[51]

The sensitivity ultrasonography drops in the ICU, especially in patients with acute respiratory distress syndrome (ARDS),^[52] Moreover, in a preliminary study by Dente et al, although ultrasonographic evaluation for pneumothorax was found to be very accurate for the first 24 hours after insertion of a thoracostomy tube, its accuracy was not sustained over time.^[44] Twenty-four hours after thoracostomy, diagnostic sensitivity of ultrasonography for pneumothorax fell to 55%, and its positive predictive value to 43%. This may be related to intrapleural adhesion formation.^[44]

Go to Radiologic Diagnosis of Pneumothorax for complete information on this topic.