A pulmonary laceration is a chest injury in which lung tissue is torn or cut. An injury that is potentially more serious than pulmonary contusion, pulmonary laceration involves disruption of the architecture of the lung, while pulmonary contusion does not. Pulmonary laceration is commonly caused by penetrating trauma but may also result from forces involved in blunt trauma such as shear stress. A cavity filled with blood, air, or both can form. The injury is diagnosed when collections of air or fluid are found on a CT scan of the chest. Surgery may be required to stitch the laceration, to drain blood, or even to remove injured parts of the lung. The injury commonly heals quickly with few problems if it is given proper treatment; however it may be associated with scarring of the lung or other complications.
Presentation
Complications Complications are not common but include infection, lung abscess, and bronchopleural fistula (a fistula between the pleural space and the bronchial tree). A bronchopleural fistula results when there is a communication between the laceration, a bronchiole, and the pleura; it can cause air to leak into the pleural space despite the placement of a chest tube. The laceration can also enlarge, as may occur when the injury creates a valve that allows air to enter the laceration, progressively expanding it. One complication, air embolism, in which air enters the bloodstream, is potentially fatal, especially when it occurs on the left side of the heart. Air can enter the circulatory system through a damaged vein in the injured chest and can travel to any organ; it is especially deadly in the heart or brain. Positive pressure ventilation can cause pulmonary embolism by forcing air out of injured lungs and into blood vessels.
Causes Pulmonary laceration is a common result of penetrating trauma but may also be caused by blunt trauma; broken ribs may perforate the lung, or the tissue may be torn due to shearing forces that result from different rates of acceleration or deceleration of different tissues of the lung. Violent compression of the chest can cause lacerations by rupturing or shearing the lung tissue. Pulmonary laceration may result from blunt and penetrating forces that occur in the same injury and may be associated with pulmonary contusion. Lacerations of the lung tissue can also occur by compression of the alveoli against the ribs or spine. As with contusions, pulmonary lacerations usually occur near solid structures in the chest such as ribs. Pulmonary laceration is suspected when rib fractures are present.
Pathophysiology
A pulmonary laceration can cause air to leak out of the lacerated lung and into the pleural space, if the laceration goes through to it. Pulmonary laceration invariably results in pneumothorax (due to torn airways), hemothorax (due to torn blood vessels), or a hemopneumothorax (with both blood and air in the chest cavity). Unlike hemothoraces that occur due to pulmonary contusion, those due to lung laceration may be large and long lasting. However, the lungs do not usually bleed very much because the blood vessels involved are small and the pressure within them is low. Therefore, pneumothorax is usually more of a problem than hemothorax. A pneumothorax may form or be turned into a tension pneumothorax by mechanical ventilation, which may force air out of the tear in the lung. The laceration may also close up by itself, which can cause it to trap blood and potentially form a cyst or hematoma. Because the lung is elastic, the tear forms a round cyst called a traumatic air cyst that may be filled with air, or blood and air, and that usually shrinks over a period of weeks or months. Lacerations that are filled with air are called pneumatoceles, and those that are filled with blood are called pulmonary hematomas. In some cases, both pneumatoceles and hematomas exist in the same injured lung. A pneumatocele can become enlarged, for example when the patient is mechanically ventilated or has acute respiratory distress syndrome, in which case it may not go away for months. Pulmonary hematomas take longer to heal than simple pneumatoceles and commonly leave the lungs scarred. Over time, the walls of lung lacerations tend to grow thicker due to edema and bleeding at the edges.
Diagnosis
Pulmonary laceration may not be visible using chest X-ray because an associated pulmonary contusion or hemorrhage may mask it. As the lung contusion clears (usually within two to four days), lacerations begin to become visible on chest X-ray. CT scanning is more sensitive and better at detecting pulmonary laceration than X-rays are, and often reveals multiple lacerations in cases where chest X-ray showed only a contusion. Before CT scanning was widely available, pulmonary laceration was considered unusual because it was not common to find with X-ray alone. On a CT scan, pulmonary lacerations show up in a contused area of the lung, typically appearing as cavities filled with air or fluid that usually have a round or ovoid shape due to the lung's elasticity. Hematomas appear on chest radiographs as smooth masses that are round or ovoid in shape. Like lacerations, hematomas may initially be hidden on X-ray by lung contusions, but they become more apparent as the contusion begins to heal. Pneumatoceles have a similar shape to that of hematomas but have thin, smooth walls. Lacerations may be filled completely with blood, completely with air, or partially with both. Lacerations filled with both blood and air display a distinctive air-fluid level. A single laceration may occur by itself, or many may be present, creating an appearance like Swiss cheese in the radiography of the lung. Pulmonary laceration is usually accompanied by hemoptysis (coughing up blood or of blood-stained sputum). Thoracoscopy may be used in both diagnosis and treatment of pulmonary laceration. A healing laceration may resemble a lung nodule on radiographs, but unlike pulmonary nodules, lacerations decrease in size over time on radiographs.
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