Chest radiographs (CXR) are part of the standard initial acute trauma workup, and most commonly these are performed anteroposterior (AP), supine while the patient remains on the backboard. CT angiogram either alone or as part of a trauma pan-scan is the next preferred imaging test if further investigation is necessary and is favoured in blunt and penetrative chest trauma to allow evaluation of vascular injuries and this exhibition will focus on reviewing the CT imaging findings of such injuries.
Pneumothorax
While an initial CXR is the investigation of choice, a common pitfall in the diagnosis of a pneumothorax is mistaking a skin fold as the visceral pleural line. Skin folds occur on supine radiographs when the technologist slides the detector behind the patient who is lying down in bed. The cassette pushes upon the skin and creates a fold such that it may create a superimposing shadow. Misdiagnosed pneumothoraces can result in otherwise normal patients receiving chest tubes. A CT can help distinguish trauma pathology from underlying cystic lung disease or bullous emphysema, which should be considered if the diagnosis of pneumothorax is uncertain prior to chest tube placement.
Haemothorax
A hemothorax is the presence of blood in the pleural space and is commonly seen in the setting of blunt chest trauma. It rarely presents as an isolated finding and concomitant injuries should be suspected, such as rib fractures; pneumothorax; lung contusion or other visceral injuries. Supine and upright CXR may demonstrate fluid within the pleural space. This finding is often mislabeled as a pleural effusion and in the setting of trauma, these are more likely to represent a haemothorax. Hounsfield attenuation units can help differentiate simple fluid from blood and CTA images may be helpful in identifying the source of vascular injury.
Pulmonary contusion
Lung contusion is the most common type of lung injury in blunt chest trauma and is a focal parenchymal injury caused by a disruption of the capillaries in the alveolar walls and septa, which cause a leakage of blood into the alveolar spaces and interstitium. Contusions are not restricted to lobar boundaries and can appear as geographic, non-segmental areas of ground-glass, nodular opacities, or consolidation on CT. Uncomplicated contusions may completely resolve after 3–14 days; a lack of resolution should raise concerns for alternative differential diagnoses.
Pulmonary laceration
Pulmonary laceration results when damage to the lung parenchyma occurs following shearing forces from direct impact, compression, or inertial deceleration. CT findings of pulmonary laceration are a round or oval cavity filled with air, blood, or both. There may be disruption or discontinuity of the lung parenchyma (see Fig. 1). The lung parenchyma and its elastic tensile properties will recoil and the parenchyma surrounding the laceration will retract from the injury itself.
Tracheobronchial Injury
A chest CT is crucial in evaluating great vessel injuries and mediastinal hematomas and may reveal pneumomediastinum, separation in the tracheobronchial air column (see Fig. 2), respiratory tract deviation, or simply an irregular appearance of the bronchus. Other CT findings include disruption of the tracheal and bronchial cartilage rings, thickening of the tracheal or bronchial wall, or laryngeal disruption. Bronchial injuries are more common than tracheal injuries. Bronchial lacerations classically parallel the cartilaginous rings of the bronchi. Pneumomediastinum and pneumothorax are commonly seen, with persistent pneumothorax after chest tube placement. This observation warrants consideration for bronchopleural fistula. Cervical subcutaneous emphysema and pneumomediastinum are common radiologic findings. If chest CT demonstrates injury to the tracheobronchial tree, definitive diagnosis and better evaluation of the extent of disease with bronchoscopy are recommended.
Haemopericardium
The primary mechanism of cardiac injury in blunt chest trauma is the sequelae of compressive forces on the heart from the sternum anteriorly and the thoracic spine posteriorly. This mechanism of injury preferentially affects the right atrium, given its anterior location within the chest. Secondary mechanisms of injury are a result of increased abdominal pressure causing herniation of viscera and rapid changes in atmospheric pressure during blast injury. The gravest myocardial injury in the setting of blunt trauma is a free-wall rupture, which is typically fatal. For patients who survive, pericardial tamponade is present (See Fig. 3). Importantly, myocardial rupture may occur in the weeks following the initial insult. CT findings of myocardial wall rupture include discontinuity of the ventricular wall, communication of the ventricle or atrium with the pericardium, hemopericardium, and/or contrast extravasation into the pericardium[8].
Injury to great vessels
Most aortic injuries from chest trauma are fatal and for those who survive and reach the hospital, a clinical diagnosis can be difficult and ultimately relies on imaging. A degree of suspicion must be maintained in high impact mechanisms of injury such as rapid acceleration-deceleration type forces. CTA is preferred and may demonstrate indirect signs of aortic injury such as mediastinal haematoma and periaortic fat stranding. Periaortic haematoma is more suggestive of an aortic injury than an otherwise isolated mediastinal haematoma. In addition, a CTA demonstrating a vessel transection (see Fig. 4); intraluminal filling defect; intimal flap; abnormal aortic contour; adjacent pseudoaneurysm and extravasation of contrast are all indicative of the diagnosis.
Rib fractures / flail segment
Roughly 10% of patients who experience blunt chest trauma have one or more rib fractures and is the most common mechanism for this injury. A plain CXR is the best initial investigation. Routine use of chest CT is institution and practitioner dependent but may identify subtle fractures. While mild fractures may seem trivial, they can be painful. This is particularly important in the lower ribs, as unexplained pain could herald delayed presentation of abdominal injury. The presence of non-displaced rib fractures may explain the pain and reassure the clinical team that the patient is indeed stable. The presence of rib fractures is more common with advancing age, with a significantly increased mortality associated with 1st and 2nd rib fractures, given the relation to great vessel injury[8]. Flail chest is defined as 3 or more segmental rib fractures (see Fig. 5) or greater than 5 adjacent rib fractures with the flail segment showing paradoxical motion with respiration.
Sternal fractures
Presence of a sternal fracture is highly suggestive of a forceful mechanism such as a direct blow to the anterior chest wall such as in a front-end automobile collision with steering wheel/airbag impact. Sagittal images are very helpful for detecting subtle sternal fractures (see Fig. 6) however the sternum should be inspected in all three planes. A small retrosternal hematoma on CT may be the initial clue to a subtle sternal fracture.