contractility of the elastic lungs and compression of the laceration by the expanding hemothorax. Massive intrapleural bleeding occurs, however, if the laceration is large and involves large blood vessels. Hemothorax might be augmented by bleeding from lacerations of the mediastinal tissues, diaphragm, and internal mammary or intercostal arteries following fractures of the sternum and/or ribs. Blunt chest trauma can overstretch and lacerate old pleural adhesions, producing intrapleural bleeding. The amount of bleeding is dependent on the degree of vascularization of the pleural adhesions. During therapeutic or diagnostic thoracentesis, the needle may puncture and lacerate the intercostal artery, causing bleeding into the pleural cavity. Perforation of a pulmonary artery by a Swan-Ganz catheter may occur with a resultant hemothorax (Figure 5.5).
Lacerated wounds of the lung can also result in leakage of air into the pleural cavity, producing a pneumothorax. When the pneumothorax is associated with intrapleural bleeding, it is called a pneumohemothorax. A tension pneumothorax can develop when the laceration penetrates deep into the lung and severs a large bronchus. With each inspiration, air entering the bronchus escapes into the pleural cavity. On expiration, the lacerated edges of the bronchus act as a valve to prevent the air from passing out of the pleural cavity through the bronchus. With each inspiration, the volume and pressure of the trapped air increases until the air pressure is high enough to collapse the lung and displace the mediastinum and heart to the opposite side. At autopsy, the pleural cavity contains a collapsed lung with air under pressure, a concave depressed diaphragm, and displacement of the heart and mediastinum to the opposite side. When a lacerated wound of the lung involves a pulmonary vein and adjacent bronchus, air exiting the bronchus may enter the pulmonary vein and be conveyed to the left atrium and ventricle, with resultant cardiac and cerebral air embolus.
If the blood in a pleural cavity is not removed, it will gradually break down, undergoing a series of color changes, red to brown, with the ultimate formation of a chocolate brown pigment deposit and turbid brown fluid. Intrapleural blood may be diluted by serous effusion. The lacerated lung, hemothorax, and diluting serous fluid are vulnerable to bacterial injection with production of pneumonia, lung abscesses, pleurisy, and empyema.
A diagnostic needle biopsy of the pleura or lung or a diagnostic or therapeutic thoracentesis may terminate in sudden death during insertion of the needle into the pleural cavity with no anatomical cause of death at autopsy. The exact mechanism of death is unknown.
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