Pneumothorax

Spontaneous pneumothorax most often occurs in otherwise healthy, slender young men, most commonly as a result of rupture of apical bullae or blebs. One third to one half of people who experience spontaneous pneumothorax have a recurrence.

Pneumothorax may also occur as a complication of many acute or chronic pulmonary diseases, including: interstitial diseases, such as Langerhans cell histiocytosis, sarcoidosis, pulmonary fibrosis with honeycombing and lymphangiomyomatosis; infections, including cavitary tuberculosis, pulmonary fungal infections, septic emboli or pneumocystis carinii pneumonia with cyst formation, and airway disorders such as cystic fibrosis, asthma and bullous emphysema. Pneumothorax may be the presenting feature in many of these diseases, and careful inspection of chest radiographs for signs of underlying pulmonary disease is essential following the re-expansion of lung.

Iatrogenic pneumothorax, the result of puncture of the visceral pleura, may occur as a complication of many diagnostic and therapeutic procedures, including thoracentesis, thoracoscopy, thoracotomy, transthoracic lung biopsy or placement of central venous catheteters (see postbiopsy pneumothorax). Barotrauma from mechanical ventilation is a frequent cause of pneumothorax in the intensive care unit population.

Catamenial pneumothorax is classically seen in young women during the menstruation and is more common on the right side. Pulmonary metastasis, especially from osteosarcoma, and inhalation of crack cocaine may also cause pneumothorax.

The presence of air within the pleural space uncouples the visceral and parietal pleura, and disrupts their suspensory forces on the lung. Consequently, the elastic recoil of the lung retracts it toward the hilum, and the lung collapses.

The diagnosis of pneumothorax requires visualization of the visceral pleural line, which is seen as a thin curvilinear opacity on an upright chest radiograph (Fig.1). Confusion can be caused by skin folds, adhesive tapes, dressings, rib margins or bullae. However, the absence of lung markings beyond the visceral pleural line permits the correct diagnosis. Various maneouvres may be performed to enhance visualization of pneumothorax in equivocal cases. Expiratory chest radiographs are occasionally helpful because the pleural line is further displaced from the chest wall, facilitating its detection. Lateral decubitus views with the suspect side up, are helpful in critically ill patients who cannot sit upright. For pneumothorax in the supine patient, see below. CT is not only very sensitive in the detection of pneumothorax, but is also invaluable in determining the underlying cause of a pneumothorax and any associated abnormalities.

A small pneumothorax in a patient with healthy lungs causes little physiological deficit. However, it is im pneumothorax increases.

The anteromedial recess is located in front of the heart and surrounded by the anterior mediastinal structures. Air in this space accounts for the sharp delineation of mediastinal contours on chest radiographs. Sharply outlined superior vena cava, azygos vein, left subclavian vein, superior pulmonary vein, anterior junctional line, heart border, inferior vena cava, pericardial fat pad, medial diaphragm under the heart and deep anterior cardiophrenic sulcus are the earliest signs of pneumothorax in the supine patient. Additionally, absence of silhouette sign in the presence of extensive parenchymal disease should raise the suspicion of pneumomediastinum or pneumothorax. Unless sufficient air is present to separate the lateral visceral and parietal pleura, the pleural line may not be evident radiographically. The subpulmonary recess is another less dependent space between the lung base and the diaphragm. Pneumothorax in this space accounts for a hyperlucent upper quadrant of abdomen, an unusually sharply outlined diaphragm, a deep lateral sulcus and visualization of the anterior costophrenic sulcus and the inferior surface of the consolidated lung (Fig.2). The anterior and posterior subpulmonary pneumothoraces need to be differentiated for the placement of chest tube. The anterior subpulmonary space is shallow and runs an oblique course from the lateral costophrenic angle to the 7th costochondral junction, and air in this space outlines the anterior structures such as the heart or the anterior junctional line. The posterior subpulmonary space is much deeper with an almost horizontal course from the posterior costophrenic angle to the costovertabral sulcus, and air in this space merges with posterior structures such as the paraspinal line and azygoesophageal recess.

An apicolateral pneumothorax may also be seen in the supine patient as the volume of pneumothorax increases. Visualization of a thin, white visceral pleural line with no margins beyond it, and a radiolucent space close to the chest wall are the main signs of apicolateral pneumothorax but extensive parenchymal disease and/or pleural effusion may obliterate the visceral pleural line.

Despite thorough knowledge of the radiographic signs of pneumothorax, many pneumothoraces may escape detection in a supine patient. If an erect radiograph cannot be performed, it is often feasible to obtain a lateral decubitus view with the side in question uppermost to demonstrate a subtle pneumothorax. This radiograph may also be used to differentiate subpulmonary pneumothorax from subdiaphragmatic air. Chest CT is an invaluable tool in the diagnosis and treatment planning of pneumothorax.

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