Radiography
Findings
The diagnosis of pneumothorax is established by demonstrating the outer margin of the visceral pleura (and lung), known as the pleural line, separated from the parietal pleura (and chest wall) by a lucent gas space devoid of pulmonary vessels (see Image below and Image 2 in Multimedia).
A true pneumothorax line. Note that the visceral pleural line is observed clearly, with the absence of vascular marking beyond the pleural line.
The pleural line may be difficult to detect with a small pneumothorax unless high-quality posteroanterior and lateral chest films are obtained and viewed under a bright light. A skin fold may mimic the pleural line; usually, the patient is asymptomatic (see Image below and Image 3 in Multimedia).
Note that although a skin fold can mimic a subtle pneumothorax, lung markings are visible beyond the skin fold.
In erect patients, pleural gas collects over the apex, and the space between the lung and the chest wall is most notable at that point (see Image below and Image 1 in Multimedia).
A large right-sided pneumothorax has occurred from a rupture of a subpleural bleb.
In the supine position, the juxtacardiac area, the lateral chest wall, and the subpulmonic region are the best areas to search for evidence of pneumothorax (see Image below and Image 4 in Multimedia). The presence of a deep costophrenic angle on a supine film may be the only sign of pneumothorax; this has been termed the deep sulcus sign.
Deep sulcus sign in a supine patient in the ICU. The pneumothorax is subpulmonic.
When a suggested pneumothorax is not definitively observed on an inspiratory film, an expiratory film may be helpful. At end expiration, the constant volume of the pneumothorax gas is accentuated by the reduction of the hemithorax, and the pneumothorax is recognized more easily. Similar accentuation may be obtained with lateral decubitus studies of the appropriate side (for a possible left pneumothorax, a right lateral decubitus film of the chest should be obtained, with the beam centered over the left lung).
The most common radiographic manifestations of tension pneumothorax are mediastinal shift, diaphragmatic depression, and rib cage expansion (see Image below and Image 5 in Multimedia).
An older man admitted to ICU postoperatively. Note the right-sided pneumothorax induced by the incorrectly positioned small-bowel feeding tube in the right-sided bronchial tree. Marked depression of the right hemidiaphragm is noted, and mediastinal shift is to the left side, suggestive of tension pneumothorax. The endotracheal tube is in a good position.
Any significant degree of displacement of the mediastinum from the midline position on maximum inspiration, as well as any depression of the diaphragm, should be taken as evidence of tension (see Image below and Image 6 in Multimedia), although a definite diagnosis of tension pneumothorax is difficult to make on the basis of radiographic findings. The degree of lung collapse is an unreliable sign of tension, since underlying lung disease may prevent collapse even in the presence of tension.
Right main stem intubation resulting in left-sided tension pneumothorax, right mediastinal shift, deep sulcus sign, and subpulmonic pneumothorax
Pleural effusions occur coincident with pneumothorax in 20 – 25% of patients, but they usually are quite small. Hemopneumothorax occurs in 2 – 3% of patients with spontaneous pneumothorax. Bleeding is believed to represent rupture or tearing of vascular adhesions between the visceral and parietal pleura as the lung collapses.
False Positives/Negatives
Differentiating the pleural line of a pneumothorax from that of a skin fold, clothing, tubing, or chest wall artifact is important. Careful inspection of the film may reveal that the artifact extends beyond the thorax or that lung markings are visible beyond the apparent pleural line. In the absence of underlying lung disease, the pleural line of a pneumothorax usually parallels the shape of the chest wall (see Images below and Images 2-3 in Multimedia).
A true pneumothorax line. Note that the visceral pleural line is observed clearly, with the absence of vascular marking beyond the pleural line.
Note that although a skin fold can mimic a subtle pneumothorax, lung markings are visible beyond the skin fold.
Artifactual densities usually do not parallel the course of the chest wall over their entire length. Avascular bullae or thin-walled cysts may be mistaken for a pneumothorax. The pleural line caused by a pneumothorax usually is bowed at the center toward the lateral chest wall. Unlike in pneumothorax, the inner margins of bullae or cysts usually are concave rather than convex and do not conform exactly to the contours of the costophrenic sulcus. A pneumothorax with a pleural adhesion also may simulate bullae or lung cysts.
Computed Tomography
Findings
CT of the chest is being used with increasing frequency in patients with pneumothorax. CT may be necessary to diagnose pneumothorax in critically ill patients in whom upright or decubitus films are not possible. CT may prove helpful in predicting the rate of recurrence in patients with spontaneous pneumothorax.14,15,16,25 One study by Warner et al demonstrated that patients with larger or more numerous blebs, as demonstrated on thoracic CT, are more likely to experience recurrences.21
CT demonstrates focal areas of emphysema in more than 80% of patients with spontaneous pneumothorax, even in lifelong nonsmokers. These areas are situated predominantly in the peripheral regions of the apex of the upper lobes. In patients in whom emphysema is not apparent on CT, it often is evident at surgery or on pathologic examination.
Jordan et al reported on 116 consecutive patients who had undergone thoracotomy for recurrent or persistent PSP or SSP.17 Emphysema with bulla formation was identified histologically in 93 patients (80%); emphysema without bulla formation was seen in 13 patients (11%); isolated bullae were seen in 2 patients (1.7%); blebs were seen in 2 patients (1.7%), and other pulmonary or pleural abnormalities were found in 6 patients (5%).
In another study, by Mitlehner et al, localized emphysema with or without bulla formation was identified on CT in 31 of 35 patients (89%) and on radiographs in 15 of 35 patients (43%).6 Abnormal findings were observed in the lung ipsilateral to the pneumothorax on 28 of 35 CTs (80%) and on 11 of 35 chest radiographs (31%); abnormal findings were observed in the contralateral lung on 23 of 35 CTs (66%) and on 4 of 35 chest radiographs (11%). In most patients, the abnormal findings consisted of a few localized areas of emphysema (n <5) measuring less than 2 cm in diameter.
The mechanism of cyst or bulla rupture in SSP probably also is multifactorial. Local airway obstruction caused by pneumonia, mucous plugs, or bronchoconstriction may be important. In a retrospective study by Wait and Estrera of 120 patients with spontaneous pneumothorax admitted from 1983–1991 to Parkland Memorial Hospital in Dallas, 31 patients (26%) had localized areas of emphysema, bullae, or blebs; 12 patients (10%) had COPD; 32 patients (27%) had AIDS; and 45 patients (37%) had other underlying lung diseases.26 Of those with AIDS, 25 patients (78%) had P jiroveci pneumonia, and the remaining 7 patients (22%) were infected with M tuberculosis or nontuberculous mycobacteria.
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| Overview: Pneumothorax |
 Imaging: Pneumothorax |
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References
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Further Reading
Related eMedicine topics:
Pneumothorax, Iatrogenic, Spontaneous and Pneumomediastinum
Pneumothorax, Tension and Traumatic
Pneumothorax (Thoracic Surgery)
Keywords
pneumothorax, spontaneous pneumothorax, primary spontaneous pneumothorax, secondary spontaneous pneumothorax, traumatic pneumothorax, iatrogenic pneumothorax, pneumomediastinum, catamenial pneumothorax, pneumothorax in AIDS
