Tracheobronchial Tear Imaging
- Author: Lars J Grimm, MD, MHS; Chief Editor: Eugene C Lin, MD more...
Chest radiography is the standard initial imaging modality for evaluation of most chest conditions, including possible tracheobronchial injury, but computed tomography is preferred if a tracheobronchial tear is suspected.[1, 2] In appropriate circumstances, multiplanar or virtual endoscopic reconstructions from the CT scan data can be performed to clarify questionable findings.[3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
Definitive diagnosis of a tracheobronchial tear is made by bronchoscopy or surgical exploration. If clinical or radiographic findings suggest airway injury, diagnostic bronchoscopy is recommended.
Tracheobronchial tears are rare injuries that are usually related to blunt trauma that involves a partial or complete laceration or puncture of the tracheal or bronchial wall. Most patients have associated rib fractures, which may be the cause of the laceration.
The animation below simulates images from a bronchoscopy.
The radiograph below reveals injury to the right mainstem bronchus.
Other images below display tracheobronchial tears.
Conventional radiography and CT scanning play important roles in the imaging of tracheobronchial tears. Although imaging findings can be highly suggestive in certain instances, radiography and CT scanning are often nonspecific for evaluating tracheobronchial tears.
Radiographic findings of tracheobronchial tears (see the image below) reflect the location and extent of the injury or injuries.
In 10% of affected patients, the tear is incomplete, with preservation of the peritracheal or peribronchial connective tissue sheath or sealing of the tear by fibrin. In these patients, the injury is not apparent on radiographs. In the most severely injured patients, the airway separates completely at the site of the injury with a visibly obvious distortion of the tracheobronchial anatomy. A pneumomediastinum, pneumothorax, or both are usually present in these extensive injuries.
The location of the tear is important in determining whether a pneumomediastinum or pneumothorax develops. The most common site of tear is near the carina, because the airway is fixed and subject to shear injury. Tears within the mediastinal pleura cause a pneumomediastinum; tears beyond the mediastinal pleura cause a pneumothorax. Because the left main bronchus has a longer mediastinal course than the right main bronchus, injury to the left main bronchus is more likely to cause a pneumomediastinum, whereas injury to the right main bronchus is more likely to cause a pneumothorax. Note that in severe injuries, both a pneumomediastinum and a pneumothorax may be present.
A pathognomonic indication of tracheobronchial tears, the fallen-lung sign, is visible in some patients with severe injury. In an uncomplicated pneumothorax, the bronchus remains fixed at the hilum, and the peripheral lung retracts from the parietal pleura toward the hilum. With complete laceration of the main bronchus, the bronchus may become partially or completely detached, allowing the lung to fall into a dependent lateral position and producing the fallen-lung sign.
Other important radiographic findings that are associated with tracheobronchial tears include incorrect location or overdistention of the endotracheal tube (ETT) cuff and a persistent pneumothorax that is unrelieved by appropriate placement of a thoracostomy tube.[16, 17] A bayonet deformity or bronchial discontinuity may be present, and if the tear causes obstruction, peripheral consolidation or atelectasis without air bronchograms may be seen.
In the typical traumatic transection of the cervical trachea, the infrahyoid muscle ruptures and the suprahyoid muscle retracts, raising the hyoid bone. Abnormal hyoid bone elevation suggests a cervical tracheal tear.
Degree of confidence
The most specific signs of tracheobronchial tears are of an appropriately placed ETT that clearly extends beyond the expected tracheal lumen and a classic fallen-lung sign.[16, 17] Other signs are less conclusive and usually require bronchoscopic confirmation. Tracheobronchial tears may not be visible if the tracheal mucosa remains intact or is sealed by fibrin.
CT scanning is the imaging method of choice for evaluating a possible tracheobronchial tear because this modality clarifies and confirms the radiographic signs of tracheobronchial tears and, occasionally, adds unique information (see the images below). Additionally, because tracheobronchial injury occurs in circumstances of severe trauma, CT scanning allows for evaluation of secondary injuries to critical structures such as the aorta or great vessels.
With the patient in the supine position, the affected lung falls posterolaterally away from the hilum in the CT scan variation of the fallen-lung sign. A small pneumothorax or pneumomediastinum is more easily visible on CT scans than on radiographs. These features are seen in the images below.
Subtle airway discontinuity or irregularity and small focal peritracheal or peribronchial gas collections are observed much better on CT scans. Active bleeding from the lacerated airway can occasionally be identified on enhanced CT scan images.
Degree of confidence
In some instances, definitive evidence of a tracheobronchial tear is depicted on CT scans. If the diagnosis remains in doubt, reformatted images along the luminal axis of the airway or virtual endoscopy may be helpful.
The high-quality images that are obtainable with multidetector CT scanners allow excellent virtual endoscopic reconstructions. In other instances, the findings are inconclusive and should be interpreted in the proper clinical context.
CT scanning can be falsely negative, particularly in relatively minor injuries, and bronchoscopy should be performed in patients with a strong clinical suggestion of a tracheobronchial tear.
Magnetic Resonance Imaging
MRI shows findings similar to those seen on CT scanning. The primary strengths of MRI are a multiplanar display and high tissue contrast. However, these strengths are offset by the relative difficulty in preparing the patient for MRI, the fact that monitoring trauma patients is more difficult during the imaging examination, and the lower availability of MRI.
As with CT scanning, the more common findings of tracheobronchial tears in MRI are variable, nonspecific, and only suggestive. MRI occasionally may be useful in depicting the location and extent of injury in this condition.
As with conventional radiography and CT scanning, MRI can be falsely negative, particularly in relatively minor injuries and in patients with a strong clinical suggestion of a tracheobronchial tear.
Patients with tracheobronchial tears have diverse presentations on ventilation-perfusion (V/Q) scans, depending on the severity of the injury. In minor injuries in which there is intact blood flow and no airway obstruction or pneumothorax, a tracheobronchial tear is not detectable. If the tracheobronchial trauma causes partial or complete airway obstruction without an associated vascular injury, normal physiologic response diminishes perfusion to the region of impaired ventilation, yielding a V/Q mismatch. In the most severe injuries, in which there is disruption of airflow and perfusion, a matched defect is visible.
Although these physiologic responses are identifiable on V/Q imaging, CT scanning and bronchoscopy are more specific in the diagnosis of tracheobronchial tears. The degree of confidence is low with nuclear imaging. As with other imaging studies, false-negative examinations can occur in cases in which there are minor injuries.
Angiography is not a primary procedure for evaluating patients who have tracheobronchial trauma; however, angiography is often used to assess any associated thoracic trauma. If active bleeding is present at the tracheobronchial tear, it can be visible on aortography or pulmonary angiography. The degree of confidence is low with angiography. Angiography does not demonstrate a tracheobronchial tear if the tear is not actively bleeding.
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