Differential Diagnosis
None
Discussion
Background
Pneumothorax is a frequent complication after blunt or penetrating chest trauma. In blunt trauma, it is the second most common injury after rib fractures, occurring in 30-40% of patients. Although often small in volume, the diagnosis is important as an unsuspected pneumothorax may rapidly enlarge and become symptomatic in patients receiving mechanical ventilation or undergoing general anesthesia (Fig. 2A; 2B). The anatomic localization of pleural air depends on the position of the patient, the volume of intrapleural air, the presence or absence of pleural adhesions, and atelectasis.
In the erect or semi-erect patient, pleural air rises to the most non-dependent region of the hemithorax (i.e., the apex or the lateral hemithorax). The diagnosis of pneumothorax is made by identifying a thin curvilinear white visceral line and the absence of vascular markings extending beyond its lateral border (Fig. 3). In the supine patient, the most non-dependent region of the thorax changes and pleural air may accumulate in several recesses, which may not be delineated by a perceptible visceral reflection. When supine, the anteromedial recess becomes the most non-dependent region, accumulates air earliest, and accounts for up to 30% of pneumothoraces, but may not be recognized on frontal supine chest radiographs in as many as 30-50% of trauma patients. Left unrecognized and untreated, such pneumothoraces can progress to tension in one-third of affected patients. Radiographic features of an anterior medial pneumothorax include the “deep sulcus” sign manifest by a deep radiolucent costophrenic sulcus (Fig. 1), a relative increase in lucency over the affected lung base (Fig. 4A) and a “double diaphragm” sign in which air outlines the central dome and anterior insertion of the diaphragm. The subpulmonic recess is the second most common region to accumulate pleural air and represents an extension of the anteromedial recess (Fig. 4B). Both recesses may accumulate air simultaneously. The apicolateral recess fills with pleural air in 22% of supine patients. Air within the posteromedial recess may manifest radiographically as a lucent line sharply delineating the ipsilateral paraspinal line, descending thoracic aorta and or the posterior costophrenic sulcus.
Caveats
The visceral pleural line visible as a thin curvilinear opacity along the lung and separated by the chest wall by intrapleural air on upright chest radiographs is commonly NOT identified on supine chest radiographs even in the setting of very large pneumothoraces.
It is important that both lateral sulci are included on each and every critical care and trauma bay chest radiograph, otherwise a potential “deep sulcus” may go unrecognized and left untreated can progress to a life-threatening tension pneumothorax.
A lateral decubitus or cross-table lateral chest radiograph can confirm the presence of a pneumothorax in unclear or questionable cases of a true “deep sulcus”.
Selected Readings
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Primack SL, Collins J. Blunt nonaortic chest trauma: radiographic and CT findings. Emerg Radiol 2002; 9: 5-12.
Lomoschitz FM, Eisenhuber E, Linnau KF, Peloschek P, Schoder M, Bankier AA. Imaging of chest trauma: radiological patterns of injury and diagnostic algorithms. Eur J Radiol 2003; 48: 61-70.
Tocino IM, Miller MH, Fairfax WR. Distribution of pneumothorax in the supine and semi recumbent critically ill adult. AJR Am J Roentgenol 1985; 144: 901-905.