INTRODUCTION:

The chest radiography serves as the primary initial screening examination in thoracic trauma due to its cost-effectiveness and noninvasiveness. Particularly, portable chest X-rays are commonly employed in major trauma cases as they can be easily obtained at the bedside and are crucial for detecting life-threatening injuries. 

For high-energy trauma, CT scans become mandatory, offering a comprehensive evaluation of traumatic lesions and concurrent abdominal and skeletal injuries. Contrast-enhanced CT with multiplanar reformations is the standard imaging tool, providing superior sensitivity and specificity compared to chest radiography. Single-phase imaging acquisition may be performed front the thoracic inlet through the pelvis, with an approximately 70-second delay. In some cases, specially when active bleeding is suspected, a multiphasic protocol is useful, wherein images are obtained from the thoracic inlet through the abdomen in systemic arterial phase followed by a portal venous phase through the abdomen and pelvis.

INJURIES OF THE CHEST WALL

Rib fractures:

Most common thoracic injury in blunt chest trauma. 

Fractures are usually multiple and 4th to 9th ribs are the most commonly fractured.

Radiographs are specific but not sensitive; the main role of chest radiograph is to identify complications (pneumothorax, pleural effusion). 

CT is more sensitive and helps in the assessment of underlying visceral injuries.

Flail chest: Segmental fractures of ≥ 3 adjacent ribs or fractures or > 5 adjacent ribs.

Fig 1: Rib fractures.

Sternal fractures:

They indicate high-energy trauma. 

The most common location is approximately 2 cm below the sternal manubrium. They are usually transverse and non-displaced.

They are usually not seen on anteroposterior chest radiographs and may be difficult to see on lateral chest radiographs. However, nearly all sternal fractures are visible on CT, specially with sagittal reformations.

CT also helps identify associated injuries: retrosternal hematoma, mediastinal hematoma, aortic injury, myocardial contusion…

Fig 2: Sternal fractures.

Scapular fractures:

They indicate high-energy trauma.

92% of them are associated with other injuries (pneumothorax, axillary nerve and axillary or subclavian artery injuries).

They are difficult to diagnose on chest radiographs. CT allows assessing the fracture line and its displacement, the possible associated injuries, and the joint involvement.

Fig 3: Scapular fractures.

Fractures of the thoracic spine:

More common  from T9 to T11. 10% are multiple, which makes it necessary to study the entire spine (in 80% of cases, they are not contiguous vertebrae).

The spinal cord is injured more frequently than in cases of cervical or lumbar fractures.

Radiographs demonstrate only 10-30% of vertebral fractures, so CT scan with sagittal and coronal reformations is essential.

INJURIES OF THE PLEURAL SPACE:

Pneumothorax:

It refers to air in pleural space following blunt trauma.

The diagnosis is usually made at chest radiography. However, 10%–50% of pneumothorax  from blunt trauma are not visualized at chest radiography performed in supine patients but can be seen at CT.

The most common direct sign is the visualization of the visceral pleura displaced from the parietal pleura by the gas collection.

Fig 4: Pneumothorax: visceral pleura displaced from the parietal pleura by the gas collection.

Other signs in chest radiographs are: increased lucency at the affected lung base,  the “deep sulcus” sign,  the “double diaphragm” sign or a  better definition of mediastinal contour.

When air collects in the pleural space to the point where the intrapleural pressure exceeds that of the atmosphere, a tension pneumothorax occurs. It is a clinical diagnosis, however it may be suggested at imaging when the following signs are present in addition to the pneumothorax: mediastinal shift to the contralateral side, flattening or inversion of the ipsilateral hemidiaphragm and hyperexpanded ipsilateral chest.

Fig 5: Three dimensional CT image shows multiple rib fractures and a comminuted scapula fracture. CT scan shows a tension pneumothorax (red arrow) with contralateral shift of the mediastinum, hemothorax (green arrow) and subcutaneous emphysema (yellow arrow). As an unexpected finding, (*) represents a rock on the back of the patient, as one of the mechanisms of injury.

Hemothorax:

It refers to blood in the pleural space following blunt trauma. Its causes include: intercostal vessel injury, pulmonary laceration, diaphragmatic or mediastinal rupture, and injury to a larger vessel in the mediastinum or paravertebral region.

The appearance of hemothorax on chest radiographs depends on the blood volume: with 200-300 ml, it may go unnoticed; with more than 200 ml, there is increased density in one or both hemithoraces with the "meniscus sign". 

CT allows differentiation between pleural effusion (low density) and blood-containing effusion (densities of 35-70 HU). In cases of intermittent bleeding, accumulation of blood with heterogeneous attenuation can be observed (acute bleeding appears hyperdense and chronic bleeding hypodense). 

Active contrast extravasation foci may also be found (useful when angiographic embolization may be needed).

Fig 6: Left hemothorax on chest radiograph and coronal reformatted CT scan.

INJURIES OF THE LUNGS:

Pulmonary contusion:

It is the most common lung injury from blunt chest trauma, as well as one of the main morbidity factors.

It represents traumatic injury to the alveoli with alveolar hemorrage, but without significant alveolar disruption.

They occur at the time of the injury and at site of impact, usually in lung regions adjacent to solid structures such as vertebrae, ribs, liver, and heart.

The typical imaging appearance consists of patchy opacities or consolidations with ill defined borders and with non-segmental distribution.

CT can often detect pulmonary contusions immediately after injury, whereas visualization in chest radiographs may not be possible up to 6 hours later. They usually increase in size in the first 48 hours and begin to resolve at 72 hours, with complete clearing in 1-2 weeks.

Fig 7: Time lapse that shows the evolution of pulmonary contusions. Immediately after the injury, there are no pathologic findings. After 24h, the red circle shows a consolidation on the left lung base representing an area of pulmonary contusion. After one week the contusion resolves and the chest radiograph shows smaller ovoid areas (red arrows) that represent pulmonary lacerations.

Pulmonary laceration:

Focal disruption of the lung parenchyma caused by compression of the parenchyma or direct damage by a fragment of rib fracture, resulting in a cavity in the lung. They have a spherical or ovoid morphology due to the elastic capacity of the lung.

Fig 8: Types of pulmonary lacerations.

In chest radiographs, they may not be clearly identified in the first 48 hours as they may be surrounded by areas of contusion. Resolution of lung lacerations can take up to 3-5 weeks.

CT is more sensitive and shows rounded or oval air-filled cavities (pneumatoceles), blood-filled cavities (hematoceles), or both with air-fluid levels (pneumohematoceles).

Fig 9: CT scan shows rounded cavities with air-fluid levels (pulmonary lacerations), surrounded by areas of pulmonary contusion.

INJURIES OF THE AIRWAYS:

Tracheobronchial laceration:

They are caused by a sudden increase in intrathoracic pressure with the glottis closed at the moment of impact or by compression between the spine and the sternum.

Tracheal laceration occurs most frequently in the thoracic segment. They have a vertical trajectory and are located at the junction of the cartilaginous and membranous portion of the trachea.

Injuries to the main bronchi are more common, especially those of the proximal segment of the right bronchus, within a distance of less than 2.5 cm from the carina. They run parallel to the cartilaginous rings and occur more frequently in the posterior wall of the bronchi.

The best diagnostic clue is the presence of pneumothorax and/or pneumomediastinum that persists or progresses after chest tube placement.

Fig 10: The atelectatic lung does not re-expand despite the correct chest tube placement. Fibrobronchoscopy confirmed the presence of tracheal laceration.

INJURIES OF THE AORTA:

They occur due to deceleration. 

The most common location is the aortic isthmus (>90%), distal to the origin of the left subclavian artery.

On chest radiographs, detection of an aortic injury depends on the presence of a mediastinal hematoma (mediastinal widening of more than 8 cm).

The sensitivity and specificity of CT with multiplanar reconstructions is close to 100%. The most common sign on CT is the presence of a mediastinal hematoma. The most frequent direct confirmatory sign of aortic trauma is the presence of a pseudoaneurysm, which appears as a contained extravascular protrusion of contrast.

There are four grades of traumatic aortic injury: 1. intimal tear, 2. intramural hematoma, 3. pseudoaneurysm, 4. free rupture.

Fig 11: Traumatic aortic pseudoaneurysm. CT images show an aortic pseudoaneurysm of the aortic arch (red arrows) and a large middle mediastinal hematoma (green arrows) with tracheal and esophageal deviation. Chest radiograph shows an enlarged mediastinum (green arrows) due to the large volume mediastinal hematoma. An endovascular aortic repair was performed (yellow arrows) with no complications during the procedure or in the following CT scan.

INJURIES OF THE DIAPHRAGM:

Consequence of a sudden increase in intraabdominal or intrathoracic pressure or by fragments of rib fractures.

The left diaphragm is more frequently injured than the right diaphragm.

The most common site of rupture is the musculoskeletal junction.

Radiography has low sensitivity (50% for left-sided and 20% for right-sided tears). It may show abnormal diaphragmatic contour or intrathoracic air-filled bowel or enteric tube.

Signs suggesting diaphragmatic rupture on CT scan include: discontinuity of the diaphragm, intrathoracic herniation of abdominal organs, "collar sign" (focal constriction of the herniated organ by the rupture hole), "dependent viscera sign" (towards the posterior costal arches of the herniated viscera).

Fig 12: Diaphragmatic rupture. Chest radiograph shows elevation of the left hemidiaphragm and intrathoracic herniation of the stomach. CT scan shows discontinuity of the left hemidiaphragm (green arrow) with herniation of the stomach, splenic angle of the colon, spleen and pancreatic tail. Red arrows represent the “dependent viscera” sign, which occurs when a patient with a ruptured diaphragm lies supine and the herniated viscera (since they are no longer supported by the diaphragm), falls to a dependent position against the posterior chest wall. Yellow arrows represent the “collar sign”, which is seen in coronal and sagittal reformatted CT images, and refers to a waist-like constriction of the herniated viscera (in this case, the stomach) from the abdomen to the chest in the site of herniation.