Pneumomediastinum is uncommon and occurs when air leaks into the mediastinum. The diagnosis can be confirmed via chest X-ray showing a radiolucent outline around the heart and mediastinum or via CT scanning of the thorax.

Ultrasound is commonly used in the evaluation of people who have sustained physical trauma, for example with the FAST protocol. Ultrasound may be more sensitive than chest X-rays in the identification of pneumothorax after blunt trauma to the chest. Ultrasound may also provide a rapid diagnosis in other emergency situations, and allow the quantification of the size of the pneumothorax. Several particular features on ultrasonography of the chest can be used to confirm or exclude the diagnosis.

Computed tomography (CT, or "CAT scan") is not necessary for the diagnosis of pneumothorax, but it can be useful in particular situations. In some lung diseases, especially emphysema, it is possible for abnormal lung areas such as bullae (large air-filled sacs) to have the same appearance as a pneumothorax on chest X-ray, and it may not be safe to apply any treatment before the distinction is made and before the exact location and size of the pneumothorax is determined. In trauma, where it may not be possible to perform an upright film, chest radiography may miss up to a third of pneumothoraces, while CT remains very sensitive.

A further use of CT is in the identification of underlying lung lesions. In presumed primary pneumothorax, it may help to identify blebs or cystic lesions (in anticipation of treatment, see below), and in secondary pneumothorax it can help to identify most of the causes listed above.

A chest x-ray is useful to confirm or rule out a pneumothorax, pulmonary edema, or pneumonia. Spiral computed tomography with intravenous radiocontrast is the imaging study of choice to evaluate for pulmonary embolism.

Significant cases of subcutaneous emphysema are easy to diagnose because of the characteristic signs of the condition. In some cases, the signs are subtle, making diagnosis more difficult. Medical imaging is used to diagnose the condition or confirm a diagnosis made using clinical signs. On a chest radiograph, subcutaneous emphysema may be seen as radiolucent striations in the pattern expected from the pectoralis major muscle group. Air in the subcutaneous tissues may interfere with radiography of the chest, potentially obscuring serious conditions such as pneumothorax. It can also reduce the effectiveness of chest ultrasound. On the other hand, since subcutaneous emphysema may become apparent in chest X-rays before a pneumothorax does, its presence may be used to infer that of the latter injury. Subcutaneous emphysema can also be seen in CT scans, with the air pockets appearing as dark areas. CT scanning is so sensitive that it commonly makes it possible to find the exact spot from which air is entering the soft tissues. In 1994, M.T. Macklin and C.C. Macklin published further insights into the pathophysiology of spontaneous Macklin's Syndrome occurring from a severe asthmatic attack.

The presence of subcutaneous emphysema in a person who appears quite ill and febrile after bout of vomiting followed by left chest pain is very suggestive of the diagnosis of Boerhaave's syndrome, which is a life-threatening emergency caused by rupture of the distal esophagus.

A number of labs may be helpful in determining the cause of shortness of breath. D-dimer while useful to rule out a pulmonary embolism in those who are at low risk is not of much value if it is positive as it may be positive in a number of conditions that lead to shortness of breath. A low level of brain natriuretic peptide is useful in ruling out congestive heart failure; however, a high level while supportive of the diagnosis could also be due to advanced age, renal failure, acute coronary syndrome, or a large pulmonary embolism.

Pulmonary ultrasound, performed at the bedside or on the accident scene, is being explored as a diagnosis for pulmonary contusion. Its use is still not widespread, being limited to facilities which are comfortable with its use for other applications, like pneumothorax, airway management, and hemothorax. Accuracy has been found to be comparable to CT scanning.

Chest radiography is the preferred means of initial diagnosis for hemothorax. Upright radiography is preferred but supine films may be taken when upright radiography is not feasible due to the clinical situation. Tube thoracostomy may be done prior to imaging when patients have sustained blunt or penetrating thoracic trauma and display unstable hemodynamics, have respiratory failure with absent or decreased breath sounds, show tracheal deviation, or have serious penetrating injuries. In upright radiography, hemothorax is suggested by blunting of the costophrenic angle or partial or complete opacification of the hemithorax, in which the lateral side of the chest appears bright and the lung appears pushed away toward the center; the air-filled lung normally appears as a dark space on radiographic film. In the case of a small hemothorax, several hundred milliliters of blood can be hidden by the diaphragm and abdominal viscera. In supine patients, signs of hemothorax may also be subtle on radiographic film, because the blood will layer in the pleural space, and can be seen as a haziness in one half of the thorax relative to the other side.

Ultrasonography is also used for detection of hemothorax and other pleural effusions, particularly in the critical care and trauma settings, because it provides rapid, reliable results in order to make a diagnosis in an emergency situation. Computed tomography (CT or CAT) scans can detect much smaller amounts of fluid than chest radiography, but computed tomography is not a primary method of diagnosis within the trauma setting, due to the time required for imaging, the requirement that a patient remain supine, and the need to transport a critically ill patient to the scanner.

Diagnosis is by medical imaging with either plain X ray or CT scan.

Once a pleural effusion is diagnosed, its cause must be determined. Pleural fluid is drawn out of the pleural space in a process called thoracentesis, and it should be done in almost all patients who have pleural fluid that is at least 10 mm in thickness on CT, ultrasonography, or lateral decubitus X-ray and that is new or of uncertain etiology. In general, the only patients who do not require thoracentesis are those who have heart failure with symmetric pleural effusions and no chest pain or fever; in these patients, diuresis can be tried, and thoracentesis is avoided unless effusions persist for more than 3 days. In a thoracentesis, a needle is inserted through the back of the chest wall in the sixth, seventh, or eighth intercostal space on the midaxillary line, into the pleural space. The use of ultrasound to guide the procedure is now standard of care as it increases accuracy and decreases complications. After removal, the fluid may then be evaluated for:

1. Chemical composition including protein, lactate dehydrogenase (LDH), albumin, amylase, pH, and glucose

2. Gram stain and culture to identify possible bacterial infections

3. White and red blood cell counts and differential white blood cell counts

4. Cytopathology to identify cancer cells, but may also identify some infective organisms

5. Other tests as suggested by the clinical situation – lipids, fungal culture, viral culture, tuberculosis cultures, lupus cell prep, specific immunoglobulins

Computed tomography (CT scanning) is a more sensitive test for pulmonary contusion, and it can identify abdominal, chest, or other injuries that accompany the contusion. In one study, chest X-ray detected pulmonary contusions in 16.3% of people with serious blunt trauma, while CT detected them in 31.2% of the same people. Unlike X-ray, CT scanning can detect the contusion almost immediately after the injury. However, in both X-ray and CT a contusion may become more visible over the first 24–48 hours after trauma as bleeding and edema into lung tissues progress. CT scanning also helps determine the size of a contusion, which is useful in determining whether a patient needs mechanical ventilation; a larger volume of contused lung on CT scan is associated with an increased likelihood that ventilation will be needed. CT scans also help differentiate between contusion and pulmonary hematoma, which may be difficult to tell apart otherwise. However, pulmonary contusions that are visible on CT but not chest X-ray are usually not severe enough to affect outcome or treatment.

A pleural effusion appears as an area of whiteness on a standard posteroanterior chest X-ray. Normally, the space between the visceral pleura and the parietal pleura cannot be seen. A pleural effusion infiltrates the space between these layers. Because the pleural effusion has a density similar to water, it can be seen on radiographs. Since the effusion has greater density than the rest of the lung, it gravitates towards the lower portions of the pleural cavity. The pleural effusion behaves according to basic fluid dynamics, conforming to the shape of pleural space, which is determined by the lung and chest wall. If the pleural space contains both air and fluid, then an air-fluid level that is horizontal will be present, instead of conforming to the lung space. Chest radiographs in the lateral decubitus position (with the patient lying on the side of the pleural effusion) are more sensitive and can detect as little as 50 mL of fluid. At least 300 mL of fluid must be present before upright chest X-rays can detect a pleural effusion (e.g., blunted costophrenic angles).

Chest computed tomography is more accurate for diagnosis and may be obtained to better characterize the presence, size, and characteristics of a pleural effusion. Lung ultrasound, nearly as accurate as CT and more accurate than chest X-ray, is increasingly being used at the point of care to diagnose pleural effusions, with the advantage that it is a safe, dynamic, and repeatable imaging modality. To increase diagnostic accuracy of detection of pleural effusion sonographically, markers such as boomerang and VIP signs can be utilized.

The tissues in the mediastinum will slowly resorb the air in the cavity so most pneumomediastinums are treated conservatively. Breathing high flow oxygen will increase the absorption of the air.

If the air is under pressure and compressing the heart, a needle may be inserted into the cavity, releasing the air.

Surgery may be needed to repair the hole in the trachea, esophagus or bowel.

If there is lung collapse, it is imperative the affected individual lies on the side of the collapse, although painful, this allows full inflation of the unaffected lung.

The death rate of people with flail chest depends on the severity of their condition, ranging from 10 to 25%.

Rapid diagnosis and treatment are important in the care of TBI; if the injury is not diagnosed shortly after the injury, the risk of complications is higher. Bronchoscopy is the most effective method to diagnose, locate, and determine the severity of TBI, and it is usually the only method that allows a definitive diagnosis. Diagnosis with a flexible bronchoscope, which allows the injury to be visualized directly, is the fastest and most reliable technique. In people with TBI, bronchoscopy may reveal that the airway is torn, or that the airways are blocked by blood, or that a bronchus has collapsed, obscuring more distal (lower) bronchi from view.

Chest x-ray is the initial imaging technique used to diagnose TBI. The film may not have any signs in an otherwise asymptomatic patient. Indications of TBI seen on radiographs include deformity in the trachea or a defect in the tracheal wall. Radiography may also show cervical emphysema, air in the tissues of the neck. X-rays may also show accompanying injuries and signs such as fractures and subcutaneous emphysema. If subcutaneous emphysema occurs and the hyoid bone appears in an X-ray to be sitting unusually high in the throat, it may be an indication that the trachea has been severed. TBI is also suspected if an endotracheal tube appears in an X-ray to be out of place, or if its cuff appears to be more full than normal or to protrude through a tear in the airway. If a bronchus is torn all the way around, the lung may collapse outward toward the chest wall (rather than inward, as it usually does in pneumothorax) because it loses the attachment to the bronchus which normally holds it toward the center. In a person lying face-up, the lung collapses toward the diaphragm and the back. This sign, described in 1969, is called fallen lung sign and is pathognomonic of TBI (that is, it is diagnostic for TBI because it does not occur in other conditions); however it occurs only rarely. In as many as one in five cases, people with blunt trauma and TBI have no signs of the injury on chest X-ray. CT scanning detects over 90% of TBI resulting from blunt trauma, but neither X-ray nor CT are a replacement for bronchoscopy.

At least 30% of TBI are not discovered at first; this number may be as high as 50%. In about 10% of cases, TBI has no specific signs either clinically or on chest radiography, and its detection may be further complicated by concurrent injuries, since TBI tends to occur after high-energy accidents. Weeks or months may go by before the injury is diagnosed, even though the injury is better known than it was in the past.

As with other chest injuries such as pulmonary contusion, hemothorax, and pneumothorax, pulmonary laceration can often be treated with just supplemental oxygen, ventilation, and drainage of fluids from the chest cavity. A thoracostomy tube can be used to remove blood and air from the chest cavity. About 5% of cases require surgery, called thoracotomy. Thoracotomy is especially likely to be needed if a lung fails to re-expand; if pneumothorax, bleeding, or coughing up blood persist; or in order to remove clotted blood from a hemothorax. Surgical treatment includes suturing, stapling, oversewing, and wedging out of the laceration. Occasionally, surgeons must perform a lobectomy, in which a lobe of the lung is removed, or a pneumonectomy, in which an entire lung is removed.

Ectopic endometrial tissue reaches the pleural space of the lung or the right hemi-diaphragmatic region and erodes the visceral pleura, causing the formation of a spontaneous pneumothorax. The condition is often cyclical, due to its associations with the beginning of the menstrual cycle.

Affected persons usually present with recurrent spontaneous pneumothorax associated with the onset of the menstrual cycle. Additionally, chest/scapular pain and/or evidence of endometriosis in the abdominopelvic cavity are other manifestations.

On radiological studies, pneumothorax is visualized using conventional chest x-rays and CT scans. In 90% of the cases, the pneumothorax is located on the right side. In some cases, small nodules can be seen in the pleura using CT scans. Confirmation can be done using video assisted thoracoscopic surgery (VATS).

Treatment for the pneumothorax is with chest tube placement. As for the ectopic endometrial tissue, therapy with gonadotropin-releasing–hormone or resection of the lesions can improve symptoms.

Subcutaneous emphysema is usually benign. Most of the time, SCE itself does not need treatment (though the conditions from which it results may); however, if the amount of air is large, it can interfere with breathing and be uncomfortable. It occasionally progresses to a state "Massive Subcutaneous Emphysema" which is quite uncomfortable and requires surgical drainage. When the amount of air pushed out of the airways or lung becomes massive, usually due to positive pressure ventilation, the eyelids swell so much that the patient cannot see. Also the pressure of the air may impede the blood flow to the areolae of the breast and skin of the scrotum or labia. This can lead to necrosis of the skin in these areas. The latter are urgent situations requiring rapid, adequate decompression. Severe cases can compress the trachea and do require treatment.

In severe cases of subcutaneous emphysema, catheters can be placed in the subcutaneous tissue to release the air. Small cuts, or "blow holes", may be made in the skin to release the gas. When subcutaneous emphysema occurs due to pneumothorax, a chest tube is frequently used to control the latter; this eliminates the source of the air entering the subcutaneous space. If the volume of subcutaneous air is increasing, it may be that the chest tube is not removing air rapidly enough, so it may be replaced with a larger one. Suction may also be applied to the tube to remove air faster. The progression of the condition can be monitored by marking the boundaries with a special pencil for marking on skin.

Since treatment usually involves dealing with the underlying condition, cases of spontaneous subcutaneous emphysema may require nothing more than bed rest, medication to control pain, and perhaps supplemental oxygen. Breathing oxygen may help the body to absorb the subcutaneous air more quickly.

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 pulmonary nodule on radiographs, but unlike pulmonary nodules, lacerations decrease in size over time on radiographs.

Following thoracoabdominal trauma, most commonly a penetrating injury, laceration of the diaphragm, and spleen allows ectopic splenic tissue to reach the pleural space of the lung.

Affected persons are usually asymptomatic. However, on rare occasions, thoracic splenosis can present with chest pain and/or hemoptysis.

On radiological studies, thoracic splenic lesions are visualized using CT scans. Visualized lesions can be described as solitary or multiple nodules. The locations of the lesions are mostly in the lower left pleural space and/or splenic bed. Confirmation can be done using scintigraphy with 99mTc tagged heat-damaged red blood cells.

No treatment is required since thoracic splenosis is a benign condition.

Magnetic resonance imaging (MRI), also called nuclear magnetic resonance (NMR) scanning, uses powerful magnets to show pleural effusions and tumors.

A CT scan provides a computer-generated picture of the lungs that can show pockets of fluid. It also may show signs of pneumonia, a lung abscess, or a tumor.

In rounded atelectasis (Folded lung or Blesovsky syndrome), an outer portion of the lung slowly collapses as a result of scarring and shrinkage of the membrane layers covering the lungs (pleura), which would show as visceral pleural thickening and entrapment of lung tissue. This produces a rounded appearance on x-ray that doctors may mistake for a tumor. Rounded atelectasis is usually a complication of asbestos-induced disease of the pleura, but it may also result from other types of chronic scarring and thickening of the pleura.

On magnetic resonance imaging (MRI), the calcific lesions usually show hypointensity or a signal void on T1- and T2-weighted images.

A hemothorax is managed by removing the source of bleeding and by draining the blood already in the thoracic cavity. Blood in the cavity can be removed by inserting a drain (chest tube) in a procedure called a tube thoracostomy. Generally, the thoracostomy tube is placed between the ribs in the sixth or seventh intercostal space at the mid-axillary line. Usually the lung will expand and the bleeding will stop after a chest tube is inserted.

The blood in the chest can thicken as the clotting cascade is activated when the blood leaves the blood vessels and comes into contact with the pleural surface, injured lung or chest wall, or with the chest tube. As the blood thickens, it can clot in the pleural space (leading to a retained hemothorax) or within the chest tube, leading to chest tube clogging or occlusion. Chest tube clogging or occlusion can lead to worse outcomes as it prevents adequate drainage of the pleural space, contributing to the problem of retained hemothorax. In this case, patients can be hypoxic, short of breath, or in some cases, the retained hemothorax can become infected (empyema).

Retained hemothorax occurs when blood remains in the pleural space, and is a risk factor for the development of complications, including the accumulation of pus in the pleural space and fibrothorax. It is treated by inserting a second chest tube or by drainage by video-assisted thoracoscopy. Fibrolytic therapy has also been studied as a treatment.

When hemothorax is treated with a chest tube, it is important that it maintain its function so that the blood cannot clot in the chest or the tube. If clogging occurs, internal chest tube clearing can be performed using an open or closed technique. Manual manipulation, which may also be called milking, stripping, or tapping, of chest tubes is commonly performed to maintain an open tube, but no conclusive evidence has demonstrated that any of these techniques are more effective than the others, or that they improve chest tube drainage.

In some cases bleeding continues and surgery is necessary to stop the source of bleeding. For example, if the hemothorax was caused by aortic rupture in high energy trauma, surgical intervention is mandatory.