The Radiologic Evaluation of Patients with Chest Trauma: Respiratory System

Symposium on Radiology in Internal Medicine

The Radiologic Evaluation of Patients with Chest Trauma Respiratory System

Santiago Pare des, M.D., * and Florencio A. Hipona, M.D.**

The contribution of radiology to the diagnosis, management and clinical follow-up of patients with chest trauma is considerable. The radiologist's main responsibility is to offer the attending physician an immediate clinico-radiologic diagnosis. The referring clinician may obtain from his radiologist colleague a fast consultation through a direct exchange of information concerning the history, signs and symptoms of each individual patient. The optimal use of diagnostic radiology in chest trauma should be based on an intelligent clinical appraisal of each individual patient, to solve the most urgent problems in a logical order, rather than waste human power, precious time and money by ordering "routine" ("just in case" or "just to be sure") examinations which may not contribute to the patient's benefit. Once the decision has been made concerning the need for pertinent radiologic information, the radiologist should be able to use all the different modalities of examination, from the simplest to the most sophisticated studies, in order to obtain a prompt and accurate diagnosis. In the majority of cases, the diagnosis is based on chest roentgenograms exposed in the supine position and with a poor inspiratory effort by the patient. This change from the normal situation is enough to alter the radiographic configuration of the cardiac outline and the pulmonary vasculature, causing a disadvantage to the diagnostician. In addition, many of these patients are studied with attached endotracheal tubes, respirators, cardiovascular monitors, draining chest tubes and other devices which may interfere with the radiographic image of the thoracic organs. It is good practice to overcome the limitations of radiology by performing examinations optimal in quality, by correlating the radiologic findings with the clinical information, and by following the patient with further studies whenever indicated. "Assistant Professor of Radiology, Boston University School of Medicine, and Associate in Radiology, The Boston City Hospital ':"Professor of Radiology, Harvard Medical School, and Associate Director of Radiology, The Boston City Hospital .

Medical Clinics of North America- Vol. 59, No. 1, January 1975

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The respiratory system may be affected by trauma in four different ways: by direct blunt or penetrating injuries; by inhalation or aspiration of foreign substances; by extension of extrathoracic injuries; and by complication of extrathoracic injuries. Since iatrogenic injuries are not uncommon, some of them are included in the discussion. In this presentation, the radiologic aspects of thoracic trauma are discussed with emphasis on the different types of examinations and maneuvers that a radiologist may use, based on the clinical impression as well as the initial radiologic observations. Many thoracic injuries are of such grave magnitude that more than one system of the body may be compromised. Hence, a separate discussion by systems is intended for practicality.

TRAUMA INVOLVING THE PLEURA Traumatic Pneumothorax Whenever the possibility of air in the pleural space is suspected, some pathophysiologic facts should be kept in mind. (1) In blunt trauma, direct impact can produce pneumothorax with or without rib fracture. Consequently, there is no immediate need to look for small subtle fractures in the presence of pneumothorax on emergency chest roentgenograms. (2) Pneumothorax following closed chest trauma may be due to rib fractures, rupture of the esophagus, or fracture of the tracheobronchial tree. The possibility of the latter serious lesion should be suspected strongly when there are fractures of one or all of the first three ribs, persistent atelectasis and pneumothorax after thoracotomy tube drainage.3 (3) Occasionally, pneumothorax may develop in the opposite side of the injured chest. As with the contrecoup effect in head trauma, transmission of forces may be responsible for this phenomenon. (4) A very common event is pneumothorax induced by thoracocentesis, subclavian intravenous catheters and needle biopsy (Fig. 1). Knowledge of the performance or attempted performance of these procedures is very important for the proper interpretation of post-traumatic roentgenograms. (5) There are cases of penetrating injury through the pleura produced by bullets without the development of pneumothorax. It is possible that the heat of the bullet seals off the pleural tear in these cases. 9 The roentgenographic diagnosis of moderate to severe pneumothorax is usually made without much difficulty. The most important sign is separation of the visceral pleura from the parietal pleura by an abnormal collection of air in the pleural cavity. However, one should be aware of possible pitfalls in this interpretation, mainly in the presence of underlying pleural or pulmonary disease. Skin folds and other extrathoracic artifacts may produce linear densities extending along the thorax which may mimic the signs of pneumothorax. A small pneumothorax is sometimes difficult to recognize. If it is suspected, and if the patient's condition will allow the maneuver, the

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Figure 1. Iatrogenic pneumothorax. A, Right pneumothorax and mediastinal and extensive subcutaneous emphysema of the chest and neck after needle biopsy of the liver. If the needle entry is somewhat high, the needle may traverse the intervening lung tissue at the costophrenic angle before penetrating the liver. B, Note the separation of the visceral pleura or lung border (arrows) from the thoracic cage, after thoracocentesis for diagnostic consideration of pleural effusion.

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Figure 2. Traumatic pneumothorax: the value of upright examination. A, Recumbent view of a 24 year old patient who was in a car accident. There is a fracture of the left second rib in its anterolateral arch (arrow); the sharp jagged edge of the fracture is facing the lung. Pneumothorax is not apparent. The tip of the central venous catheter from the right arm is in the jugular vein instead of the superior vena cava. B, Upright examination in inspiration shows the pneumothorax, not seen in A (arrows).

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c Figure 2 Continued. C, Upright examination in expiration shows a better demonstration of the pneumothorax than the similar study in inspiration.

chest should be examined in the frontal upright position at the end of inspiration and at the end of expiration (Fig. 2). With the reduction of lung volume during expiration, the pneumothorax becomes more obvious. In very ill patients, another way to detect a questionable pneumothorax is to examine the patient in the lateral decubitus position using a horizontal x-ray beam centered on the elevated affected side (Fig. 3). The intrapleural air should collect in the uppermost portion of the affected hemithorax and should outline the visceral pleura. If the pneumothorax is loculated or if there is underlying pulmonary disease such as blebs and localized emphysema, careful examination in different projections will be necessary to establish the diagnosis. Tension pneumothorax can be suggested when the chest roentgenogram shows a moderate to severe pneumothorax causing a contralateral shift of the mediastinum. If the patient's condition will allow fluoroscopy, one may observe persistence of the mediastinal shift during inspiration, as well as limited motion of the ipsilateral hemidiaphragm.lO Traumatic Hydrothorax Penetrating injuries such as stab wounds are the most common cause; however, hydrothorax is also seen after blunt trauma. Hemothorax · is an important complication to look for in cases of ruptured thoracic aorta and cardiac trauma. Chylothorax does not occur as frequently as hemothorax and usually develops several days or weeks after trauma. 25

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Figure 3. Traumatic pneumothorax: the value of decubitus views. A, Supine view of an 18 year old man who was in a car when a cache of firecrackers exploded in the car trunk. There are diffuse, ill-defined densities throughout both lungs, on the right more than the left, indicating severe pulmonary contusion. No pneumothorax is manifest. It is mandatory to be sure that pneumothorax be absent if the patient is to be placed in a respirator. B, Left lateral decubitus view of the chest obtained with a horizontal x-ray beam demonstrates a right pneumothorax (arrows).

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Figure 3 Continued. C, Follow-up examination in one day demonstrates the placement of a right thoracotomy tube and further progression of the massive pulmonary contusion. The differential diagnosis is "shock lung."

With the widespread use of subclavian intravenous catheters (Fig. 4), iatrogenic extrapleural bleeding as well as accumulation of intravenous fluids have been observed by the authors and others.26 This may be mistaken for hemothorax due to trauma. Radiographically, hemothorax and chylothorax appear as fluid densities. It is a well known fact that blood in the pleural space coagulates, but is defibrinized by the constant motion of the heart and lung. Therefore, blood remains as a fluid density which obeys the laws of gravity.25 For this reason, chest roentgenograms taken in the supine position may not be helpful in detecting pleural fluid. It can be suspected if there is a homogeneous, relative opacity of the entire hemithorax compared to the uninvolved side. Pleural fluid is better demonstrated in the erect position. Frontal and lateral projections are usually enough to confirm the diagnosis and to make a rough estimate of the amount of collected fluid. Occasionally, overpenetrated films are necessary to outline the fluid. Identification of a fluid level in the pleural space indicates the additional presence of a pneumothorax (Fig. 5). Another way to demonstrate fluid in the pleural space, including collections in the interlobar fissures, is by positioning the patient in lateral decubitus with the horizontal x-ray beam centered at the dependent side. This also gives information concerning the mobilization or loculation of fluid. Special roentgenographic procedures may be needed in those cases where post-traumatic pleural effusion is due to laceration of certain important organs. Thus, angiography may be used to diagnose hemorrhage

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Figure 4. Iatrogenic injuries in subclavian venous catheter placement. A, Subpleural apical hematoma after unsuccessful catheterization of the subclavian vein (arrows). B, Superior mediastinal infusion of 500 cc of 5 per cent dextrose in water (arrows).

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Figure 4 Continued. C, Left pleural effusion due to slow drip of 2 liters of normal saline. Note that the tip of the catheter is not in the "usual course" of a vein (arrow).

Figure 5. Pneumo-hemothorax. Upright film of a middle-aged man with a stab wound in the left chest. Separation of the lung from the thoracic wall is not manifest, but the superior margin of the pleural effusion exhibits a straight line traversing the entire width of the left hemithorax. This indicates the presence of air in the pleural space (air-fluid interface).

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from a traumatized cardiac chamber, bleeding from ruptured aorta, intercostal arteries or any other thoracic vessels. Lymphangiography may demonstrate the site of tear of the thoracic duct.1s Because of the anatomical position of the duct along the thorax, a rupture in its lower third usually produces a right chylothorax. A left chylothorax is usually due to rupture of the thoracic duct in its upper thoracic position.

INJURIES AFFECTING MAINLY THE LUNG PARENCHYMA Direct Chest Trauma LUNG CONTUSION. Pulmonary contusion is usually the result of lung trauma, with or without rib fractures. The possible mechanism is sudden compression and decompression of the intrathoracic organs, producing severe pressure changes in airways and alveolar spaces. Minor contusions are related to direct impact by mild forces. The end result is edema fluid and a small amount of blood inside the alveolar as well as the interstitial tissue. 28 The diagnosis of these lesions is based on clinical history and roentgenographic findings in standard chest examinations. According to the magnitude of the injury, lung contusion is manifested as air-space consolidation with a patchy or homogeneous pattern, in a nonsegmental distribution. It is usually confined to the traumatized side, but may be bilateral in blast injury (see Figure 3). It has been observed on occasion in the contralateral side. 31 Since the radiographic findings in pulmonary contusion are nonspecific, several features are important. Lung contusion densities usually appear within a few hours following trauma and start to resolve in 24 to 48 hours. If no radiographic improvement is shown after 72 hours, a complication such as infection should be suspected. Finally, in spite of the radiographic appearance, clinical manifestations are usually mild or even nonexistent.28 • 32 LACERATION AND HEMATOMA OF THE LUNG. This type of lesion is more frequently produced by penetrating trauma than by closed chest trauma. Whatever mechanism is involved, the resulting damage is disruption of several alveolar spaces with formation of a cavitary space, usually filled with blood, with the consequent production of a hematoma. On the standard chest roentgenogram, the appearance of a round or oval radiolucency several hours or a few days after trauma represents the area of ruptured alveolar walls forming an empty space surrounded by a very thin walF This lesion is also called traumatic lung cyst. Not infrequently, this lesion may be initially obscured by superimposed contusion, making it an irregularly shaped consolidation (Fig. 6). When this ruptured air space is filled with blood, a round or oval opaque density is seen. Subsequent contraction of the blood clot will produce an appearance simulating a "fungus ball." Air-fluid level densities may be seen in the evolution. The resolution of this "pseudo mass" is usually slow, taking several weeks or more to disappear completely. A small scar tissue density may remain in the lung,27

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Figure 6. Pulmonary hematoma and lacera tion. A, Frontal, and B, lateral upright views of a patient with a gunshot injury in the right anterior chest. There are bullet fragments in the soft tissues of the right chest anteriorly. There is a homogeneous density with ill-defined margins involving mainly the right middle lobe. An "airbronchogram" is seen within the area of consolidation. The patient had a right middle lobectomy for uncontrolled hemoptysis. The right middle lobe was heavily contused, lacerated, and macerated.

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Figure 7. Radiation pneumonitis. A, Frontal film of a middle aged woman who had had a mastectomy and radiation therapy for one month for carcinoma of the left breast. There is a smudgy consolidation involving the medial aspect of the left upper lobe. There is minimal tenting of the left mid heart border (pleuropericarditis) (arrow). B, The lateral chest film shows the lesion to be confined to the anterior aspects of the anterior segment of the left upper lobe and possibly the superior subdivision of the lingula (arrows).

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Figure 7 Continued. C, Follow-up a year later demonstrates clearing of the pneumonitis with some residual fibrotic strands.

In lung laceration produced by a bullet, the shape of the injured tissue is manifested by a radiopaque, linear tract produced by the hematoma. It usually disappears in several weeks without significant residual scarring. 21 POST RADIATION INJURIES. This type of injury is an unavoidable sequel of ionizing radiation directed to the lungs, but there is no direct correlation between a given dose and the clinical manifestations in different patients.3o Some patients may have symptoms and abnormal respiratory function in the absence of radiographic findings.4 Radiographic findings are usually manifest at least one month after cessation of therapy and may persist for three or four months. Standard chest roentgenograms (Fig. 7) are satisfactory for the diagnosis of this complication. Ideally, previous examinations should be available for comparison in order to detect early subtle changes. In the acute stage, bronchiolar and alveolar desquamation as well as reactive exudative changes produce the radiologic features of a consolidation with a patchy or confluent appearance. These areas of consolidation are usually, but not necessarily, distributed in the sites of radiationP Pulmonary fibrosis is observed in the chronic state. The pneumonic lesions resolve slowly in several weeks to months and are replaced by multiple fibrotic strands with significant loss of lung volume. LUNG HERNIATION. A portion of the lung covered by its corresponding portion of parietal and visceral pleura may herniate through a weakened area of the chest wall as a complication of trauma. Characteristically, the patient complains of a bulging mass which appears with in-

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spiration and disappears during expiration. Most post-traumatic herniations of the lung occur near the costochondral junction, and this anatomical feature is important to keep in mind. The most adequate way to demonstrate herniation of the lung radiographically is by exposing the involved region of the chest during expiration-inspiration,29 and at the end of a Valsalva maneuver. With the aid of fluoroscopy, these maneuvers can be performed with ease and the central rays can be directed tangential to the protruding portion of the lungs (Fig. 8).

Accidental Inhalation or Aspiration A large variety of noxious agents are responsible for acute clinical problems which need radiographic confirmation and follow-up. The most usual situations are (1) inhalation of certain noxious gases which produce irritation in the airways as well as the alveoli; (2) ingestion of hydrocarbon products, many of which are used at home; (3) smoke inhalation during fires, in which the damage is believed to be due to the effect of products of incomplete combustion; (4) aspiration of gastric contents, which may consist of food and normal gastric acid secretions, or ingested toxic material; and (5) aspiration of water. Whatever the agents and mechanisms of action are, these injuries probably have a common effect upon the lungs. They produce alterations at the alveolar-capillary level with alveolar and reactive interstitial edemaP' 19 These pathologic changes are manifested on chest roentgenograms as areas of consolidation which are usually diffuse and nonsegmental in distribution (Fig. 9). Aspiration pneumonitis produced by vomiting usually but not always has a characteristic distribution involving the posterior segments of the upper or lower lobes if the patient aspirated the vomitus while in the supine position. Lung Changes Due to Extrathoracic Injuries PosT-TRAUMATIC PULMONARY INSUFFICIENCY. There are no roentgen findings in the first and second clinical stages. The radiographic findings usually appear in the late stages corresponding to the clinical third and fourth phases, when the patient starts failing to respond to 100 per cent oxygen therapy with persistent arterial de saturation and difficulty in maintaining spontaneous ventilation. 5 The radiographic pattern is that of a nonuniform, diffuse, bilateral alveolar consolidation (Fig. 10). Each area tends to increase in extent and become confluent with others. Some of them may represent superimposed infections, especially in the final hours before demise.6 POST-TRAUMA TIC FAT EMBOLISM. This syndrome generally follows trauma involving fractured bones, but it may occur in soft tissue injuries alone, as well as in extensive burns. Respiratory symptoms and radiographic findings usually appear 24 to 48 hours after trauma and disappear in one to four weeks. 1 This time factor, plus the appearance of skin petechiae and mental confusion, are quite diagnostic of systemic fat embolism, which is confirmed by the presence of fat in the urine (lipuria).

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Figure 8. Spontaneous lung hernia. A, Chest roentgenogram of a moderately obese patient who had twisted his body to turn on a television set. He then had severe fits of coughing and a questionable bulging mass in the right chest laterally. This examination as well as others were unremarkable. B, Spot filming under fluoroscopic guidance with minimal rotation of the patient on deep inspiration tangentially demonstrates the herniated lung beyond the confines of the rib cage (arrows).

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Figure 9. Chemical inhalation pneumonia. Chest roentgenogram of a patient who had been spraying insecticide (DDT) for pest control. There is a diffuse, nodular consolidation of ill-defined margins (blotchy in character) involving the medial two thirds of both lungs.

The roentgenographic abnormalities of the chest are reflections of the effects produced by the fat globules and free fatty acids upon the pulmonary capillaries and alveolar membranes. The pattern is that of airspace consolidation due to alveolar edema which is bilateral, almost symmetrical, and peripheral in distribution (Fig. 11). In most instances, the edema is more extensive in the bases than in the apices of the lungs. Characteristically, the heart is not enlarged, and the pulmonary vasculature shows no redistribution as is seen in left-sided heart failure. 24 . Post-traumatic pulmonary insufficiency and post-traumatic pulmonary fat embolism are two conditions which require very careful evaluation and management. Both have some comparable pathophysiologic features responsible for alveolar-capillary alterations, and these produce edema which is detectable on chest roentgenograms. The differentiation may be easier with the knowledge of the difference in the overall pattern, distribution, time of appearance and evolution of the lesions as correlated with the clinical features.

Figure 10. Acute pulmonary insufficiency. A young man had multiple stab wounds of the abdomen, resection of a few feet of small bowel and another exploratory laparotomy for drainage of intraperitoneal abscesses. Chest examinations during his shock state (14 days) were remarkably clear. A, Third stage: At 16 days, he could not be weaned from 100 per cent oxygen, and there was a progressively worsening arterial de saturation. The portable chest film shows prominent vascular markings with ill-defined margins bilaterally. There is a peripheral consolidation of the lateral aspect of the left lower lobe (arrows). B, Final stage: At 21 days, just before demise, there is diffuse, almost homogeneous consolidation of both lungs. (The Swan-Ganz catheter is in place at the left pulmonary artery and the tracheostomy tube is in good position.)

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Figure 11. Pulmonary fat embolism secondary to comminuted fractures of the femur and tibia sustained in a car accident. Chest roentgenograms on admission were normal. The patient started to have chest heaviness and mild tachypnea at 24 hours. Portable chest x-ray at 26 hours shows ill-defined blotchy densities in both upper and right lower lobes. These are mixed with streaky densities particularly in the left upper and right middle lobe and probable air trapping in both lung bases. This is the characteristic appearance of pulmonary fat embolism after 24 to 48 hours. Urinalysis showed lipuria, and follow-up chest examination in 10 days showed almost complete clearing.

INJURIES AFFECTING MAINLY THE AIRWAYS The tracheobronchial tree is well protected anatomically against direct thoracic trauma. For this reason, the most severe forms of damage to the airways are rather uncommon. Obviously, the corresponding lung parenchyma will, sooner or later, be affected by the functional ventilatory deficiency.

Acute Tracheobronchial Obstruction ASPIRATION OF FOREIGN BODIES. This is an accident usually seen in young children and elderly persons. Identification of the foreign body and determination of its location as well as evaluation of the condition of the lungs can ordinarily be achieved with a standard chest roentgenogram exposed on inspiration and expiration. Tomography and fluoroscopy may be necessary in some situations. According to the physical effects of the foreign body's passage along the air passages, two different situations may be observed radiographically: a check valve obstruction, in which the chest appears normal in full inspiration, while at full expiration the affected lung remains unchanged and the normal lung reduces in volume and the mediastinum

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shifts toward the normal side; and complete bronchial obstruction, with the corresponding lung segment or segments showing progressive loss of volume and complete atelectasis developing in a matter of hours. A typical example of this phenomenon is mucus plug obstruction observed in patients following surgery.23 Careful interpretation of repeat roentgenograms after removal of foreign bodies from the airways may reveal recurring obstruction. Nonopaque bodies may be fragmented in the process of being removed and migration of the fragments to other bronchial branches may occur. Two other problems which may be encountered are the release of irritant products from the foreign body (peanuts) and superimposed infection. PERIBRONCHIAL AND BRONCHIAL HEMORRHAGE. These traumatic lesions produce extrinsic or intrinsic bronchial obstruction and are responsible for different degrees of subsegmental, segmental or lobar atelectasis. They are shown as homogeneous opacities with loss of volume. According to their location and extent, associated findings such as elevation of the diaphragm, displacement of the interlobar fissures and shifting of the mediastinum may be observed. IATROGENIC MANIPULATIONS. During bronchoscopy and endotracheal intubation, damage to the airways occurs not infrequently. A common problem is bronchial obstruction produced by advancing the endotracheal tube into the proximal portion of the mainstem bronchus (Fig. 12). Frequently the radiologist is the first person who detects this complication and should immediately communicate with the attending physician in order to avoid acute respiratory problems due to poor aeration of the affected lung. Another complication following prolonged tracheostomy with positive-pressure ventilation is tracheostenosis.2 This can be demonstrated on plain films of the neck or by laminography of the involved area, if necessary. A smooth, symmetrical narrowing of the trachea localized at the surgical site is usually the main finding. Cases of tracheoesophageal and tracheopleural fistula have also been reported following endotracheal intubation. 14 Tracheobronchial Laceration and Fracture These relatively uncommon lesions, resulting mainly from steering wheel injuries, may range from mild lacerations to partial or complete fracture of the trachea or bronchus. Early recognition of the latter is extremely important, since surgical repair is indicated before prolonged damage to the tissues occurs. 3 It is well recognized that the diagnosis of complete bronchial fracture is a challenging one. Intrathoracic injury may be absent in about 10 per cent of cases of bronchial fracture. Clinical and radiologic signs were initially absent in nearly 30 per cent of 90 cases. 3 The injury may be overlooked because of associated injuries, or because the diagnosis was not entertained at the beginning of the patient's evaluation. Fracture of one or all the first three ribs has been found in nearly 90 per cent of cases of bronchial fracture. 3 Pleural fluid is absent from the affected side. Chest roentgenograms often offer the first diagnostic clue. The radiologic pattern depends upon the extent of the injury and its secondary ef-

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Figure 12. Iatrogenic atelectasis. A, Tracheostomy was performed on a teenaged boy with Ludwig's angina. An endotracheal tube was inserted too deeply - note the tip at the right mainstem bronchus (arrow). There was mediastinal shift to the left due to complete atelectasis of the left lung. B, The endotracheal tube was then withdrawn to the trachea, and re-examination in 2 hours showed complete re-expansion of the left lung.

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fects. In the earlier stages, the usual findings are those of pneumothorax associated with pneumomediastinum and subcutaneous emphysema. Due to persistent leakage, the abnormal accumulation of air increases with time, and tension pneumothorax often develops. There is persistent and progressive pneumothorax in spite of thoracotomy tube drainage. In the later stages, separation of the fractured bronchial fragments produces complete lack of communication between the trachea and the affected lung; thus atelectasis results.3 ! Since most bronchial fractures occur near the origin of the mainstem bronchus, massive atelectasis of the affected side is the usual pattern. An interesting radiologic sign that should be looked for in the frontal projection of the chest is the changing position of the collapsed lung as the patient's position changes. With the patient in the supine position, the collapsed lung projects next to its corresponding hilum. In the upright position, the collapsed lung will project near the diaphragm. This "dropping" of the lung is due to the complete separation of the distal fragment of the ruptured bronchus from its proximal attachment. 2o One should remember that fracture of the trachea usually occurs above the carina and bronchial fracture usually at the mainstem bronchus. To properly demonstrate the lesion, the radiologist ought to have Bucky chest films or overpenetrated chest roentgenograms in frontal and lateral views. He may then recommend laminography or bronchography. However, the definitive diagnosis is usually achieved by endoscopy.

INJURIES OF THE THORACIC WALL, DIAPHRAGM AND MEDIASTINUM Clinicians are aware of the serious cardiorespiratory complications that some of these lesions may produce. Initial roentgenographic studies may fail to demonstrate such injuries because of technical limitations, but as soon as they are suspected, thorough radiologic examinations should be done.

Thoracic Wall Injuries For completeness, careful observation of the dorsal spine should be part of the overall evaluation of the chest roentgenograms. Further radiologic studies, such as special views of the spine, laminography and contrast examinations, may be necessary on certain occasions. RIB FRACTURES. Quite often there is a tendency to count the number of fractured ribs in the films without giving proper consideration to their possible clinical implications. The main purpose in ordering a "rib series" for fractures should be to determine their location, the degree of separation of the fragments, how much inward or outward displacement is present, besides determining the number of broken ribs. When the fragments are displaced inward, there is a chance of laceration of the pleura alone or the pleura and lung tissue, with the consequent production of pneumothorax or hemothorax. Damage to the intercostal vessels can also occur by this mechanism, and some cases of intercostal arterial bleeding may be quite severe. When the ruptured fragments are

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displaced outward they may lacerate the soft tissue planes with the production of hematoma. If the injury extends as far as the skin surface, infection may develop as a complication. 13 Subcutaneous emphysema in the presence of rib fractures is almost always due to associated pneumothorax. In rare cases it may happen without the presence of pneumothorax, which could be explained on the basis of preexisting pleural adhesions. When the diagnosis of fractures involving the first ribs is made, one should remember the frequent association with trauma to the tracheobronchial tree, as well as the aorta. Fractures involving the anterior aspects of the ribs should raise the possibility of associated fractures of the costal cartilages, which are very painful and usually difficult to demonstrate radiographic ally. Also, fracture of the sternum should be ruled out in these cases. In cases of severe chest trauma producing multiple fractures of several ribs, the diagnosis of flail chest (Fig. 13) should be entertainedP

Figure 13. Flail chest. Multiple rib fractures (left second to eighth ribs) are seen with a subpleural hematoma in a patient who was in a car accident. On inspiration, the left hemithorax caves in instead of expanding.

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Paradoxical motions of injured parts of the thorax with respiration (inward on inspiration, outward on expiration) are quite characteristic of flail chest. FRACTURES OF THE STERNUM. Most fractures of the sternum do not produce significant functional damage to the thorax. However, where the separation of the fragments is of a certain magnitude, surgical reduction and fixation are necessary for satisfactory healing. Another problem with this type of injury is that the heart and pericardium are usually traumatized due to their proximity to the sternumP Unless there is certain degree of separation or angulation of the fragments, these fractures may not be recognized on standard frontal and lateral chest films (Fig. 14). Special lateral and oblique views with an overpenetration technique, or laminograms of the sternum, are necessary for an adequate radiographic examination. The development of a soft tissue density along the internal surface of the sternum generally corresponds to the formation of hematoma, which should resolve in a few days after trauma. Diaphragmatic Injuries The most common cause of diaphragmatic rupture is steering wheel injuries. The left leaf is the site of rupture in almost 95 per cent of cases, probably because the liver affords protection to the right leaf. Minor diaphragmatic lacerations may result from fractured ribs. 16 A significant number of diaphragmatic injuries are probably overlooked in the initial clinical and radiologic examinations because they are associated with major injuries to other important organs. Recognition of diaphragmatic rupture is very important, since it may produce cardiorespiratory impairment and is a potential source of strangulation of abdominal viscera herniating through. ls Plain roentgenograms may show a lack of definition of the left leaf of the diaphragm and air-containing structures in the corresponding hemithorax (Fig. 15). Usually there is associated displacement of the mediastinum to the right. Less commonly, what may appear to be pneumopericardium is due to rupture of the diaphragm with visceral herniation into the pericardial sac. When rupture of the right leaf occurs with partial herniation of the liver, it might be interpreted as simple diaphragmatic elevation. Other radiologic studies, such as diagnostic pneumoperitoneum, contrast examinations of the gastrointestinal tract and liver scan, may be necessary to support the diagnosis. Mediastinal Injuries Radiologic evidence of mediastinal abnormalities is sometimes subtle and may escape the untrained eye. When they are recognized and the patient's condition allows, other pertinent radiologic studies should be carried out immediately to determine the cause of the mediastinal findings. Traumatic lesions of the respiratory, digestive, cardiovascular and skeletal organs may result in abnormal collections of air, blood or secretions in any of the mediastinal compartments. In general, radiologic

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Figure 14. Depressed fracture of the sternum. A, Anteroposterior roentgenogram of a patient with anterior chest pain following a steering wheel accident. There is minimal cardiomegaly secondary to hypertensive helrrt disease. B, The lateral view demonstrates the transsection fracture of the sternum with depression of the inferior portion of the sternal body. There is soft tissue swelling (hematoma) anteriorly as well as retrosternally. If the sternal fracture is inferiorly located, it may impinge upon and injure the heart.

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Figure 15. Diaphragmatic rupture, multiple rib fractures (left fourth to ninth ribs) and subcutaneous emphysema along the left lateral chest wall suffered in a car accident. Note the gastric fundus (arrow) protruding into the left chest through a tear in the medial aspect of the left hemidiaphragm.

studies should be done with a double purpose: to determine the presence of air, air-fluid densities, or abnormal soft tissue shadows in the mediastinum; and to identify the damaged organ and to determine the type as well as the extent of the lesion. This is accomplished by the use of special procedures. PNEUMOMEDIASTINUM. The diagnosis is based on the demonstration of air collected outside the mediastinal pleura. This usually ap'pears as fine linear lucencies paralleling the cardiac silhouette (Fig. 16). In the lateral chest view, a similar air collection is seen in the retrosternal space. 12 It may be difficult to distinguish between air in the mediastinum and air in the pericardial sac, especially when only a single frontal chest film is available. This problem may be solved by taking roentgenograms with the patient in different positions. Significant changes in the distribution and configuration of the air are consistent with pneumopericardium rather than pneumomediastinum.s MEDIASTINAL HEMORRHAGE. Extravasated blood from injured vessels may accumulate in the mediastinum. The size and configuration of the resulting hematoma will be variable. On plain chest films, mediastinal hematomas are manifested as homogeneous, well delineated and uniform radiodensities. When extensive bleeding occurs near the midline of the chest, a symmetrical widening of the mediastinum appears. When localized and limited, it may appear as a mass density.

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P AREDES

AND FLORENCIO

A.

HIPONA

Figure 16. Pneumomediastinum secondary to a 22 caliber bullet traversing the right chest ending up in the right superior mediastinum. There is a radiolucent stripe parallel to the left heart border which may be mistaken for a pneumopericardium (arrows). On upright examination, air should shift to the superior aspect of the pericardial sac. If the problem still ,exists, a left lateral decubitus examination should be performed which will confirm the pneumomediastinum by failure of the entrapped air to shift. Please note also the subcutaneous emphysema in the right lateral chest wall (site of bullet entry) (arrow).

By analyzing the radiographic configuration of the surrounding organs, one may be able to determine the location of the hematoma. Lack of sharpness of the aortic outline, blurring of the paraspinal lines, displacement of the trachea, bronchial compression, abnormal hilar shadows, and other signs should not be overlooked. Special Radiological Procedures As previously mentioned, in order to identify the source of pneumomediastinum or hemomediastinum, other examinations can be performed according to each individual case. Angiographic procedures are mainly used in cases of possible aortic injury, by the venous or direct arterial puncture approach. Selective venography is indicated in cases of suspected superior cava or other major venous bleeding. Esophagography becomes extremely important when rupture of the esophagus is suspected. A water-soluble iodinated contrast material is generally used to determine the site of perforation. 22 Bronchography is not essential, but may be necessary in cases of suspected tracheal or bronchial fractures.

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REFERENCES 1. Berrigan, T. J., Carsky, E. W., and Heitzman, E. R.: Fat embolism. Roentgenographicpathologic correlation in three cases. Amer. J. Roentgen., 96:967-971,1966. 2. Bogodain, W., Carpathies, J., and Najib, A.: Tracheotomy: Fifty-nine consecutive cases, stressing indications, complications and results. Dis. Chest, 45 :57-62, 1964. 3. B urke, J. F.: Early diagnosis of traumatic rupture ofthe bronchus. J .A.M.A., 181 :682-686, 1962. 4. Cooper, G., Jr., Guerrant, J. L., Harden, A. G., and Teates, D.: Some consequences of pulmonary irradiation. Amer. J. Roentgen., 85:865-874,1961. 5. Dyck, D. R., and Zylak, C. J.: Acute respiratory distress in adults. Radiology, 1 06:497-501, 1973. 6. Eaton, R. J., Senior, R. M., and Pierce, J. A.: Aspects of respiratory care pertinent to the radiologist. RadioL Clin. No. Amer., 11 :93-107, 1973. 7. Fagan, C. J.: Traumatic lung cyst. Amer. J. Roentgen., 97:186-194,1966. 8. Felson, B.: The mediastinum. Seminars in Roentgenology, 4:40-58, 1969. 9. Fraser, R. G., and Pare, J. A. P.: Diagnosis of Diseases of the Chest. Philadelphia, W. B. Saunders Co., 1970, VoL 2, p. 1161. 10. Fraser and Pare, VoL 1, p. 373. 11. Fraser and Pare, VoL 2, p. 1077. 12. Fraser and Pare, VoL 2, p. 1175. 13. Grimes, O. F.: Nonpenetrating injuries to the chest wall and esophagus. Surg. Clin. No. Amer., 52:597-609, 1972. 14. Hardy, J. D., ed.: Critical Surgical Illness. Philadelphia, W. B. Saunders Co. 1971, p. 170. 15. Heilman, R. D., and Collins, V. P.: Identification of laceration of the thoracic duct by lymphangiography: Preoperative radiography of the traumatized thoracic duct. Radiology, 81:470-472,1963. 16. Hill, L. D.: Injuries of the diaphragm following blunt trauma. Surg. Clin. No. Amer., 52:611-624,1972. 17. Jimenez, J. P., and Lester, R. G.: Pulmonary complications following furniture polish ingestion: A report of twenty-one cases. Amer. J. Roentgen., 98:323-333, 1966. 18. Keshishian, J. A., and Cox, P. A.: Diagnosis and management of strangulated diaphragmatic hernias. Surg. Gynec. Obstet., 115 :626-632, 1962. 19. Kleinfield, M.: Acute pulmonary edema of chemical origin. Arch. Environ. Health., 10:942-946,1965. 20. Kumpe, D. A., Oh, K. S., and Wyman, S. M.: A characteristic pulmonary finding in unilateral complete bronchial transection. Amer. J. Roentgen., 110:704-706, 1970. 21. Larose, J. H.: Cavitation of missile tracks in the lung. Radiology., 90:995-998, 1968. 22. Leigh, T. F., and Achord, J. L.: Pharyngeal and esophageal perforations during instrumentation. Amer. J. Roentgen., 91 :757-765,1964. 23. Lubert, M., and Krause, G.: Further observations on lobar collapse. RadioL Clin. No. Amer., 1 :331-346, 1963. 24. Maruyama, Y., and Little, J. B.: Roentgen manifestations of traumatic pulmonary fat embolism. Amer. J. Roentgen., 79:945-952, 1962. 25. Reynolds, J., and Davis, J. T.: Injuries of the chest wall, pleura, pericardium, lungs, bronchi and esophagus. RadioL Clin. No. Amer., 4:383-401, 1966. 26. Rudge, C. J., Bewick, M., and McColl, I.: Hydrothorax after central venous catheterization. Br. Med. J., 3:23-25, 1973. 27. Sorsdahl, O. A., and Powell, J. W.: Cavitary pulmonary lesions following nonpenetrating chest trauma in children. Amer. J. Roentgen., 95:118-124,1965. 28. Stevens, E., and Templeton, A. W.: Traumatic nonpenetrating lung contusion. Radiology, 85:247-252,1965. 29. Taylor, D. A., and Jacobson, H. G.: Post-traumatic herniation of the lun.g. Amer. J. Roentgen., 87:896-899, 1962. 30. Wiernik, G.: Radiation pneumonitis following a low dose of cobalt teletherapy. Brit. J. RadioL, 38:312-314,1965. 31. Williams, J. R., and Stembridge, V. A.: Pulmonary contusion secondary to nonpenetrating chest trauma. Amer. J. Roentgen., 91 :284-290, 1964. 32. Williams, J. R., and Bonte, F. J.: Pulmonary damage in nonpenetrating chest injuries. RadioL Clin. No. Amer., 1 :439-448, 1963. Department of Radiology The Boston City Hospital 818 Harrison Avenue Boston, Massachusetts 02118 (Dr. Hipona)