Imaging of chest trauma: radiological patterns of injury and diagnostic algorithms

European Journal of Radiology 48 (2003) 61
/70 www.elsevier.com/locate/ejrad Imaging of chest trauma: radiological patterns of injury and diagnostic algorithms Fritz M. Lomoschitz *, Edith Eisenhuber, Ken F. Linnau, Philipp Peloschek, Maria Schoder, Alexander A. Bankier Department of Radiology, University of Vienna Medical School, AKH Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria Received 10 June 2003; received in revised form 11 June 2003; accepted 12 June 2003 Abstract In patients after chest trauma, imaging plays a key role for both, the primary diagnostic work-up, and the secondary assessment of potential treatment. Despite its well-known limitations, the anteroposterior chest radiograph remains the starting point of the imaging work-up. Adjunctive imaging with computed tomography, that recently is increasingly often performed on multidetector computed tomography units, adds essential information not readily available on the conventional radiograph. This allows better definition of trauma-associated thoracic injuries not only in acute traumatic aortic injury, but also in pulmonary, tracheobronchial, cardiac, diaphragmal, and thoracic skeletal injuries. This article reviews common radiographic findings in patients after chest trauma, shows typical imaging features resulting from thoracic injury, presents imaging algorithms, and recalls to the reader less common but clinically relevant entities encountered in patients after thoracic trauma. # 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: CT; Thorax; Trauma 1. Introduction Chest trauma is a major cause of hospitalization in Europe and carries a mortality rate ranging from 15 to 77%. Both improved transport and pre-clinical infrastructure now result in rising numbers of chest trauma survivors that reach acute care centers [1,2]. Diagnostic imaging plays a key role in the management of patients after chest trauma and has considerable impact on therapeutic decision making. The information generated by diagnostic imaging procedures not only serves to tailor therapy to the individual needs of patients, but also contributes to determine prognosis and outcome. Given this paramount role of diagnostic imaging in patients after chest trauma, radiologists require familiarity with the radiological features seen in these patients. The aim of this article is to familiarize * Corresponding author. Tel.: /43-1-40400-7620; fax: /43-140400-4898. friedrich.lomoschitz@univie.ac.at (F.M. E-mail address: Lomoschitz). the reader with common and uncommon imaging features of patients after chest trauma and to illustrate diagnostic imaging algorithms applied in the work-up of patients after chest trauma. This article will also present the radiological modalities used in the diagnostic workup of patients with chest trauma, and review the spectrum of traumatic chest injuries, including injuries of the thoracic cage, the pleura, the pulmonary parenchyma, the airways, the esophagus, the heart and aorta, and the diaphragm. 2. Radiological modalities and diagnostic algorithms After clinical stabilization of the patient, the detailed secondary survey comprises imaging of the patient. Initial imaging of the patient, the so-called ‘trauma series’, includes cross-table lateral cervical spine, anteroposterior (ap)-chest and ap-pelvic radiographs. The speed at which a portable chest radiograph can be obtained makes of it a crucial element in the initial evaluation of the traumatized patient, because it pro- 0720-048X/03/$ - see front matter # 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/S0720-048X(03)00202-X 62 F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 vides essential information as to the extent and severity of injuries to the chest. A decision must then be taken as to whether further imaging techniques are to be performed. In general, the decision threshold for computed tomography (CT) imaging is comparably low in traumatized patients [3,4]. Chest CT is highly sensitive for the detection of thoracic injuries and is superior to the conventional chest radiography in the detection of lung contusion, pneumothorax, and hematothorax [3,5]. Moreover, early chest CT has been shown to impact on therapeutic treatment in a significant number of patients [3]. In recent years, multidetector computed tomography (MDCT) has valuably complemented CT technology. MDCT offers better longitudinal and temporal resolution, i.e. factors that are essential in the imaging of severely traumatized patients. A marked increase in scanning speed enables scanning of the same or even a larger volume of interest in substantially less time. Furthermore, the rapid acquisition times improve scan quality by reducing motion artifacts. Thus, MDCT not only improves the quality of axial images, but, due to thinner ‘secondary raw data’ has the capability to create higher quality sagittal and coronal reformatted images. Chest CT scans in the trauma patient should always be viewed in soft-tissue, lung, and bone window settings. Sagittal and coronal reformations should routinely be obtained for improved assessment of the aorta, the tracheobronchial tree, and the thoracic skeleton. 3. Thoracic cage injuries 3.1. Ribs Simple rib fractures are frequently encountered on chest radiographs and rarely require further studies. Rib fractures become radiographically evident as a disruption of the cortex; the degree of fracture dislocation often varies. However, complication of rib fractures such as pneumothorax, hemothorax, lung contusions, and lacerations are of more important clinical impact than the fracture itself (Fig. 1). Injuries associated with rib fractures should therefore also be paid attention to. Fractures of upper ribs may be associated with vascular and brachial plexus injuries, whereas fractures of lower ribs may be associated with concomitant injuries of the liver and spleen. Multiple fractures of the same rib or simple fractures of three or more contiguous ribs comprise a flail segment of the chest wall [6]. This results in paradoxical motion and inhibits normal respiratory motion, leading to impaired ventilation. Impaired ventilation combined with underlying lung parenchyma injury can lead to acute respiratory failure and requires prompt intensive respiratory therapy. Fig. 1. Flail chest due to multiple rib fractures in 43-year-old man after struck by car as pedestrian. (a) Antero-posterior chest radiograph shows asymmetry of left hemithorax due to multiple rib fractures. (b) Enhanced CT scan in lung window shows thoracic asymmetry due to left-sided rib fractures at multiple sites causing flail chest. Consistent pulmonary and soft-tissue hematoma and left-sided soft-tissue emphysema is present. (c) Enhanced CT scan in soft-tissue window shows fracture of scapula with consistent haemorrhage in periscapular muscles. F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 3.2. Scapula Because of the protective effect of the muscles surrounding the scapula, a large force is required to fracture the scapula. Because of these large forces, attention must always be directed to the associated thoracic injuries (Fig. 1). Up to 40% of patients with fractures of the scapula have associated pulmonary contusion, pneumothorax, or hemothorax [7]. In addition, these patients have a high incidence of associated closed head injury and spinal fracture. Scapulothoracic dissociation is a closed forequarter amputation of the upper extremity with varying degrees of neurovascular compromise due to high energy trauma to the shoulder girdle. Injuries commonly associated with scapulothoracic dissociation include sternoclavicular separation, acromioclavicular separation, and distracted clavicle fracture. 63 lumbar spine [9], it is not directly applicable in the thoracic region. Unstable fracture dislocations are relatively common in the thoracic spine. Much of the rigidity of the thoracic spine can be attributed to the presence of the rib cage, and injuries that destabilize this osseous frame work tend to be unstable. Certain features are predictive for a later mechanical instability: these include (1) displacement of a fracture involving the 3.3. Sternum Sternal fractures may be well delineated on a lateral conventional radiograph. However, sagittal and coronal reformation in MDCT imaging offers depiction of both sternal fractures themselves and potentially associated injuries. Most of these fractures are caused by motor vehicle accidents, classically caused by the steering column, and the risk for sternal fractures increases with age. Sternal fractures are often associated with retrosternal hematomas, myocardial contusion, hemopericardium, aortic laceration, trachebronchial tear and thoracic spine injuries. When a retrosternal hematoma is seen on CT, the presence of a fat plane between the hematoma and the aorta implies that the hematoma is not aortic in origin. 3.4. Spine Thoracic spine fractures account for 16
/30% of all spine fractures and often are radiographically occult. About 50% of patients with thoracic spine fractures have associated focal neurologic deficit attributable to the injury. The size of the thoracic cord is quite large in relation to the narrow spinal canal, at least partially explaining the high degree of association. In addition, the thoracic spine is inherently very stable, and injuries that result in fracture are usually caused by high energy. Most thoracic spine injuries occur in flexion and axial loading because rotation in the upper thoracic spine is limited by the rib cage. As a result, fracture dislocations at this anatomical level are more common than compression fractures and burst fractures [8]. Owing to its much higher sensitivity for diagnosing thoracic spine fractures, CT is the imaging modality of choice for evaluation of these injuries (Fig. 2). Although the column concept of spinal stability is very useful in the Fig. 2. Fracture of thoracic spine in 28-year-old man after fall from 5m height. (a) Axial CT scan shows fracture line through body of fifth thoracic vertebra. Note that posterior wall of vertebral body is not fractured although fracture extends into posterior third of vertebral body. (b) Sagittal multiplanar reformation shows fracture-consistent loss of height at the ventral and central portion of fifth thoracic vertebral body and additional fracture of ventral portion of sixth thoracic vertebra. 64 F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 anterior and posterior elements of the spine, i.e. fracture dislocations involving all columns; posttraumatic kyphosis of more than 408 [9]; (2) fractures of the ribs or costovertebral dislocations [9]; (3) sternal fractures; and (4) noncontiguous concomitant spinal fractures, i.e. fractures that occur elsewhere in the spine in a patient with a known injury at a particular level. In the setting of a thoracic spinal fracture, a careful search should therefore be conducted for other accompanying injuries of the thoracic skeleton. 4. Pleural injuries 4.1. Pneumothorax Pneumothorax is frequently seen in both blunt and penetrating trauma. In blunt chest trauma it is the second most common injury after rib fracture, and occurs in 30
/40% of patients [10]. It is also seen as an iatrogenic complication of therapeutic interventions including central line placement and barotrauma from mechanically assisted ventilation. In the supine patient, air in the pleural space accumulates in the anteromedial and subpulmonal recesses and to a lesser extent in the posteromedial recess of the chest. In a polytraumatized patient portable ap-chest radiograph in supine position is usually performed as the initial radiological evaluation of the chest. Signs of a pneumothorax in a supine patient include increased lucency over the lower chest and upper abdomen, a double diaphragm sign, and a deep lateral costophrenic sulcus (Fig. 3) [11]. In severely traumatized patients and critically ill patients, pneumothorax can be missed on the supine ap-chest radiograph in up to 30% of patients [10]. However, the diagnosis of even a small pneumothorax is important, particularly in the positive-pressure ventilated patient, since it may progress to a tension pneumothorax [10]. In general, tension pneumothorax is a clinical diagnosis and should be treated before radiographic evaluation. Radiographic signs of a tension pneumothorax include depression or inversion of the ipsilateral diaphragm, contralateral shift of the mediastinum, and widening of the intercostal space. Because rapid progression to vascular collapse is possible, immediate communication of this finding to the clinician is imperative. Persistent or tension pneumothorax can occur despite the presence of a chest tube on the conventional radiograph. This may be the result of a malfunctioning tube or tube malposition that appears in adequate position on the ap-chest radiograph [12]. CT is more sensitive than radiography for detecting pneumothorax than radiography, and CT is more accurate than radiography in the depiction of incorrect, i.e. extrathoracic or intraparenchymal, position of the thoracostomy tube [3]. Fig. 3. Tension pneuomothorax in 28-year-old woman after motorvehicle accident as unrestrained passenger. (a) Antero-posterior chest radiograph shows left-sided pneumothorax with signs of tension, i.e. contralateral shift of the mediastinum, deep lateral costophrenic sulcus, and increased lucency over left lower chest. Additionally left thoracic wall emphysema is present. (b) Axial CT scan shows small residual anterior pneumothorax after drainage, posterior pulmonary hematoma, soft-tissue emphysema, and fracture of left lateral rib. 4.2. Hemothorax Fluid in the pleural space in a previously healthy acute trauma patient most likely represents blood. Fluid administered from a misplaced central line and chyle from thoracic duct injury are less common causes of fluid in the thoracic cavity. Hemothorax can have multiple causes. Blood arising from injury to the lung is typically low-pressure bleeding and self-limited. Blood originating from an arterial source, such as an intercostal artery, may continue to bleed with rapid accu- F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 65 mulation of blood within the hemithorax. Continued accumulation of blood may require tube thoracostomy or open thoracotomy. On radiography, blood in the pleural space of the supine patient appears as haziness or increased opacity of the hemithorax when compared with the unaffected side. The so-called ‘apical cap’ represents the cephalic extension of the pleural fluid collection in the supine patient. With continued accumulation, blood causes mass effect with compression of the heart and mediastinum to the contralateral side. Bleeding into the pleural space frequently occurs several hours after trauma. Thus, The initial chest radiograph may show no evidence of hemothorax since initially small amounts of fluid, e.g. blood, in the pleural space may be radiographically occult and bleeding into the pleural space frequently occurs for several hours after trauma. Chest CT is superior to chest radiography in identifying a hemothorax (Fig. 4) [3]. Focal areas of high attenuation within a pleural fluid collection usually indicate the presence of blood clots. When this is seen in conjunction with a properly positioned chest tube and unresolving large pleural fluid collection, it usually indicates occlusion of the chest tube by blood clots. 5. Pulmonary parenchymal injuries 5.1. Pulmonary contusions Blunt injury to the chest can cause direct injury to the lung parenchyma resulting in pulmonary contusion. The incidence ranges widely from 17 to 70% [13]. The injury is caused by the energy transmitted from a direct trauma to the chest wall. Extensive pulmonary contusion may be present without external evidence of trauma to the chest. Pulmonary contusion maybe absent on the initial chest radiograph, but radiographic findings of pulmonary contusion will develop over the first 6 h after injury. Pulmonary contusion begins with interstitial hemorrhage followed by edema over the next 1
/2 h. Approximately 24 h post injury, blood and protein have accumulated in the air-space. The contusion reaches its maximum extent at approximately 48 h. Severe pulmonary hemorrhage results in hepatization of the lung. Healing with little residual scarring occurs within 7
/14 days. Physiologic changes accompany these pathologic changes. There is a ventilation-perfusion mismatch, increased lung water, and decreased compliance. Respiratory derangement usually resolves in 3
/5 days. Depending on the stage, the radiographic appearance of pulmonary contusion may comprise a spectrum of abnormalities such as patchy, ill-defined air-space process that ignores segmental anatomic boundaries. Pulmonary contusion may be solitary, multiple, or diffuse and occurs either uni- or bi-laterally (Fig. 5). The process tends to be peripherally located and Fig. 4. Hemothorax in 38-year-old man after motor-bicycle accident. (a) Enhanced axial CT scan in soft-tissue window shows left-sided hemothorax. (b) Bone-window reveals consistent non-dislocated posterio-lateral rib fracture. adjacent to the spine, ribs, or sternum. CT of the chest has been shown to be more sensitive than conventional chest radiography for identifying pulmonary contusion [3]. In 6 h, 21% of contusions observed on CT were not visualized on chest radiography. In addition, the extent of contusion is frequently underestimated on the conventional radiograph [3,5]. Moreover CT has shown prognostic value in evaluating the extent of pulmonary contusion. Patients usually require mechanical ventilation, if areas of contused parenchyma involve about a third of the pulmonary air-space [14]. The differential 66 F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 Fig. 5. Pulmonary contusion in 49-year-old man with blunt injury to the chest. Enhanced axial CT scan in lung window reveals ill-defined air-space consolidations in both lungs representing pulmonary contusions. Fig. 6. Pulmonary laceration in 29-year-old man after stab-wound with knife. Enhanced CT-scan in lung window reveals sharply delineated formation filled with blood at base of left lower lobe representing pulmonary hematoma. Drainage of pneumothorax was already performed and little soft-tissue emphysema is present. diagnosis for pulmonary contusion includes aspiration and atelectasis. Aspiration tends to be located more centrally. Failure of resolution over a period of 7
/14 days may be caused by superimposed infection or the development of respiratory distress syndrome. 6. Airway injuries 5.2. Pulmonary lacerations Laceration of the lung parenchyma may result from a shearing force, rupture of alveoli, or direct injury from adjacent fractured ribs or penetrating injury resulting in a formation of a cavity filled with blood, i.e. hematoma, or air, i.e. pneumatocele (Fig. 6). Concurring findings such as pulmonary contusion or subcutaneous emphysema may prevent identification of a pulmonary laceration on plain chest radiography. CT of the chest better delineates the presence and extent of the pulmonary laceration than a conventional chest radiograph [3]. Because of the elastic recoil of the lung, the laceration will be ovoid with a thin rim of hyperdensity, representing a pseudomembrane [15]. Blood within the laceration may be seen as an air-fluid level. If the blood has clotted, an air meniscus may be identified. Typically, a pulmonary laceration is benign and resolves over a period of weeks. Clot within a laceration may persist for months and slowly resolve as a ‘shrinking’ coin lesion. If the visceral pleura is violated, pulmonary laceration may be complicated by the development of a pneumothorax or a bronchopulmonary fistula. 6.1. Tracheobronchial injury Patients with tracheobronchial injury suffer from a high prehospital mortality rate. A higher survival rate is seen in patients with smaller tears [16]. In addition to tracheobronchial injury from blunt or penetrating trauma, iatrogenic tracheal rupture can occur as a complication of endotracheal intubation. Over 80% of bronchial injuries occur within 2.5 cm of the carina, with the right bronchus more commonly injured than the left. Because of the low frequency of the injury and the nonspecific signs and symptoms, there often is a delay in diagnosis. A persistent large pneumothorax despite a functioning thoracostomy tube, increasing subcutaneous and mediastinal air, and persistent atelectasis should raise suspicion for tracheobronchial injury. Other indirect radiographic signs of tracheal rupture include deviation of the endotracheal tube tip to the right, overdistension of the endotracheal cuff, and migration of the balloon to the endotracheal tube tip [10]. Although uncommon, the ‘fallen lung’-sign, i.e. collapse of the lung toward the lateral chest wall, is pathognomonic for tracheobronchial injury [17,18]. In patients with tracheobronchial tears, disruption of the bronchial wall can sometimes directly be visualized on CT. An acute change in the tracheobronchial caliber or acute angulation can also suggest the injury, which may be best seen on multiplanar reformations. A CT scan F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 67 will reveal smaller amounts of mediastinal air than will a conventional chest radiograph as an indirect sign of tracheobronchial tear. However to date, to confirm the suspicion of radiographically inconclusive tracheobronchial tear, bronchoscopy remains the diagnostic procedure of choice [19]. 6.2. Pneumomediastinum Pneumomediastinum occurs in up to 10% of cases of blunt chest trauma and represents free air collections surrounding mediastinal structures. Air within the mediastinum most commonly results from alveoli rupture caused by sudden increase in intra-alveolar pressure. Simple straining against a closed glottis, such as with the lifting of a heavy object, can increase alveolar pressure enough to cause alveolar rupture. The air tracks centrally through the pulmonary interstitium, along the peribronchovascular sheaths, into the mediastinum (Fig. 7). Other sources of mediastinal air include rupture of the tracheobronchial tree or the esophagus [20]. Radiographically, air can be seen outlining mediastinal structures, such as aorta, large veins, esophagus, trachea, and dissecting along the mediastinal fat. Pneumomediastinum is usually benign. However, air can rupture through the pleura and produce pneumothorax. Air tracking inferiorly into the retroperitoneum can rupture into the peritoneal space and present with an associated pneumoperitoneum. 7. Esopagheal injuries Blunt trauma is a rare cause of injury to the esophagus. Perforation can occur from bone fragments of an adjacent spine farcture or from penetrating trauma, most commonly in the cervical portion of the esophagus. Radiographic findings are nonspecific and include persistent or unexplained pneumomediastinum, left-sided pneumothorax, and left-sided pleural fluid [20]. Evaluation of the injury can be performed with esophagography. First, water-soluble contrast material is used and if the results of the study is negative, this study is followed by a contrast-enhanced examination with barium sulfate. This study may be difficult to perform in the critically injured patient. At CT indirect signs of esophageal injury are thickening of the esophageal wall at the site of perforation, and adjacent mediastinal air collections. The best overall diagnostic accuracy is achieved in combination of esophagography and esophagoscopy [11]. Fig. 7. Pneumomediastinum and pneumopericard in 21-year-old man after motor vehicle accident. (a) Enhanced axial CT scan in lung window reveals air in upper mediastinum around great supra-aortic vessels. Consistent ventral thoracic soft-tissue emphysema is present. (b) Enhanced axial CT scan at cardiac level shows air in the pericardial sac representing pneumopericard. In addition pulmonary contusions and atelectases are present bilaterally. 8. Injuries to the heart and pericardium 8.1. Cardiac trauma Injuries to the heart include cardiac contusion, laceration, and rupture; valve and coronary artery injury; tears of the pericardial sac, hemopericardium, and pneumopericardium [21]. Cardiac contusions occur in up to 76% of blunt chest trauma with the anteriorly 68 F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 located right atrium and ventricle more commonly injured than the left atrium and ventricle. Arrhythmia and conduction disturbances account for most of the clinical manifestations of cardiac injury. Myocardial infarction can occur with coronary dissection, thrombosis, or plaque rupture. Rupture of the heart and pericardium is associated with a high mortality. Findings on CT include hemopericardium, pneumopericardium, and extravasation of contrast material into the pericardial sac from the injured cardiac chamber [11]. consistent with rapid deceleration forces, such as motor vehicle accidents or falls from great heights. It typically occurs at certain sites of predilection due to strain and shearing forces (Fig. 8). The most frequently affected aortic segment for ATAI (90%) is just beyond the isthmus, where the relative mobile thoracic aorta is joined by the arterial ligament, Other less common thoracic locations for ATAI are the ascending aorta immediately superior the aortic valve; the ascending 8.2. Hemopericardium Fluid in the pericardial sac of an acutely injured patient usually represents blood. Unfortunately, the conventional chest radiograph is of limited use in the diagnosis of hemopericardium. Acute cardiac tamponade can cause circulatory collapse before pericardial fluid is suspected on an ap-chest radiograph. Thus, it is crucial to check the pericardium and the motion of the myocardium during abdominal ultrasonography in traumatized patients as indispensable part of ‘focused assessment with sonography for trauma (FAST)’. Pericardial fluid and impaired myocardial contraction can easily be detected by a routine look at the superior left lobe of the liver on a transverse scan at the xiphoid including a four-chamber view of the heart. At CT fluid in the pericardial sac is easily detected [22]. A flattened myocardium in combination with hemopericardium represents the morphologic correlate of cardiac tamponade. 8.3. Pneumopericardium Air within the pericardial sac can occur from penetrating trauma and, occasionally from blunt trauma. Other potential causes to be considered include iatrogenic trauma and infection. Pneumopericardium outlines the heart and is limited superiorly by the pericardial reflection (Fig. 7). Air within the pericardium may be mistaken for or obscured by a pneumomediastinum. A complication of air within the pericardial sac is tension pneumopericardium that can cause cardiac tamponade. Developing tension pneumopericardium has been reported to cause the cardiac silhouette to appear progressively smaller on serial conventional radiographs [23]. A flattened heart seen on chest CT can also indicate tension pneumothorax [24]. 9. Acute traumatic aortic injury Acute traumatic aortic injury (ATAI) is a lesion of the aortic wall extending from the intima to the adventitia. Thoracic ATAI is usually caused by trauma mechanisms Fig. 8. ATAI in 48-year-old man after motor vehicle accident (a) Enhanced axial CT scan in soft-tissue window reveals acute traumatic aneurysm at ventral aspect of distal aortic arch. Small pleural effusions are present bilaterally, but no periaortic mediastinal haemorrhage is depicted. (b) Consistent transarterial aortogram shows acute traumatic aneurysm at typical location at inferior aspect of distal aortic arch. No extravasation as sign of rupture is depicted. F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
/70 aorta in the proximity of the innominate artery; and the descending aorta in the distal segment. Most patients who die after reaching the hospital with ATAI do so within the first 2 h after admission. Typically these patients are admitted with a high injury severity score and hypotension and require emergent thoracotomy without imaging other than chest radiography. After the first two hours the spontaneous rupture and death rate is much lower, which, relatively safely, enables a more sophisticated imaging work up with CT and intraarterial angiography. Thus, portable ap-chest radiograph plays an essential role in raising the suspicion of ATAI. Mediastinal blood is expected in all patients with trauma injury to the thoracic aorta. The assessment of the mediastinum should not depend on any measurement of mediastinal width or mediastinal-to-chest width ratio but rather on the ability to clearly discern the normal outlines of the mediastinum. Radiological markers that serve as accurate markers of mediastinal hemorrhage on a nonrotated ap-chest radiograph include an obscured or abnormal contour of the aortic arch and descending aorta; opacification of the aortopulmonary window; a widened right paratracheal soft-tissue density; a widened left or right paraspinal line, particularly extending along the extrapleural space to the lung apex above the aortic arch, referred to as ‘apical cap’; and displacement of the trachea or esophagus (nasogastric tube) to the right. [25]. The presence of signs of mediastinal hemorrhage has only a 20% predictive value for ATAI. Therefore, in most of the cases of mediastinal hemorrhage, the cause is not major vascular injury. However, the absence of all these signs simultaneously has a nearly 100% negative predictive value for ATAI [25]. CT is more sensitive to confirm or exclude mediastinal hemorrhage than is chest radiography. In addition, IV contrast-enhanced CT provides potential detection of pseudoaneurysm, intimal flaps, aortic or branch vessel abrupt contour abnormalities, pseudocoarctation of the aorta, intraluminal thrombus, and, rarely, contrast extravasation from the aorta [26]. It is anticipated that the abilities of MDCT with greater scanning speed, improved spatial resolution, the possibility of ECG triggering, lesser motion artifacts, and multiplanar reformations based on small isotropic voxels will further improve the diagnostic accuracy of CT for ATAI. Although aortography is considered the standard of reference for assessing ATAI, it suffers from diagnostic difficulties. Interpretive problems arise from the ductus diverticulum, other congenital variants of aortic anatomy, atypical-appearing aortic injuries, and aortic ulceration [27]. The same pitfalls can be potentially confusing factors on CT images. If CT with state-of-the-art equipment is not readily available, the patient should undergo catheter aortography when findings of mediastinal hemorrhage are 69 present on the chest radiograph. If CT is available and shows periaortic blood without direct signs of aortic injury, aortography is recommended [4]. In patients directly showing positive CT findings of aortic injury, the aorta may rupture while awaiting angiographic evaluation before surgery. Thus, some surgeons proceed directly to thoracic surgery without intra-arterial angiography if direct signs of ATAI are present in the typical location. Moreover, the recent development of endovascular techniques provides additional alternatives for the treatment of traumatic aortic injury. 10. Diaphragmatic injury The incidence of traumatic rupture of the diaphragm caused by blunt trauma is 3
/8%. The ratio of left- to right-sided injury in blunt trauma is approximately 3:1, with 4.5% having bilateral rupture [28]. The left-sided predominance is presumed to be a result of the position of the liver, which protects the right hemidiaphragm. The initial evaluation for diaphragmatic injury begins with the conventional chest radiograph. Nonspecific radiographic findings include elevation of the hemidiaphragm, indistinct margins of the diaphragm, pleural fluid, and contralateral shift of the mediastium. Bowel or stomach above the level of the diaphragm with a focal constriction at the site of injury is diagnostic. However, this finding may be obscured on the chest radiograph by pulmonary contusion or aspiration or may be mimicked by a subpulmonic pneumothorax. A nasogastric tube with its tip above the level of the diaphragm can aid in diagnosis. Positive-pressure ventilation can prevent herniation of bowel into the chest, delaying the diagnosis. If the conventional radiograph is inconclusive, oral or rectal contrast material can be used in the diagnostic work-up. Chest CT has limited use in the diagnosis of traumatic rupture of the diaphragm. However, use of sagittal and coronal reformations substantially contributes to the accurate diagnosis of diaphragmatic rupture [29]. On CT the ‘collar sign’, i.e. a focal constriction of the herniated organ at the site of diaphragmatic injury, is highly specific for diaphragmatic injury. 11. Conclusion This article comprises the spectrum of typical imaging features resulting from thoracic injury, including thoracic skeletal, pleural, pulmonary, tracheobronchial, cardiac, aortic, and diaphragmal injuries. Despite its well-known limitations, the ap-chest radiograph remains the obligatory basis of imaging patients with chest trauma. Adjunctive imaging with CT, that recently is increasingly often performed using MDCT, adds essen- 70 F.M. Lomoschitz et al. / European Journal of Radiology 48 (2003) 61
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