thoracic trauma imaging

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Thoracic Trauma Imaging

Overview

In many patients with thoracic trauma injury, urgent exploratory thoracotomy or laparotomy may takeprecedence over imaging, whereas in others, diagnosis and treatment are frequently combined withtube thoracostomy or pericardiocentesis. Imaging studies are an essential part of thoracic trauma careonce the patient is stabilized. Imaging has little if any role in the initial treatment of a critically ill andhemodynamically unstable patient.

The first priority in cases of thoracic trauma is the provision of effective therapeutic measures tominimize trauma-related deaths and morbidity. Imaging is not indicated until the airway, breathing,and circulation (ABC) have been secured and stabilized. The initial approach to chest trauma isclinical evaluation, which starts with a thorough examination of the chest after the airway iscontrolled. Severe internal injury may be present without external tenderness.

A chest radiograph is obtained for every patient who has significant trauma. The diagnosis isgenerally obvious with standard chest radiography or CT, but more subtle signs require carefulanalysis of CT images and examination with MRI in some situations. Prolonged observation in amonitored setting is usually not required for patients with suspected myocardial contusion. Patientswith a normal electrocardiogram (ECG) and a normal echocardiogram are usually discharged homeafter 12 hours of monitoring. Cardiac complications are rare in cases of cardiac contusion, particularlyin the young.

Echocardiography is useful for detecting wall-motion abnormalities and pericardial effusions. Incombination with abnormal creatine kinaseMB levels, this may be predictive of complications.Radionuclide angiographic results also may be predictive of complication. Thallium scanning may

depict areas of decreased perfusion but are not useful in differentiating an acute lesion from apreexisting lesion.

Ultrasonography, CT, and magnetic resonance imaging (MRI) may all demonstrate pericardialeffusions and hemopericardium, but they are rarely indicated in a patient with acute traumatictamponade. The roles of CT, MRI, and transesophageal ultrasonography in the evaluation of aorticinjuries have not been clearly defined, although multisection CT scanning is increasingly used for

diagnosis.

Radiography

Chest radiography (see the images below) is indicated in virtually every trauma patient; a series ofradiographs are generally obtained to assess the progress and complications of the trauma. They are

also used to look for malpositioned lines and tubes; in the stress and confusion of an emergencydepartment inadequate and inappropriate placement of lines and tubes is common

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A chest radiograph is usually performed initially in the acute setting. Findings on a chest radiographinclude pneumothorax (which is difficult to see on a supine image), pneumomediastinum, airspaceshadowing (resulting from pulmonary contusion), and pleural hematoma. CT is better for assessing

most of these lesions.


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Repeat chest radiographs are obtained after any invasive intervention, such as intubation or placementof the central venous pressure catheter or chest tube. Iatrogenic lung trauma may occur after lungbiopsy, thoracentesis, cauterization, and other procedures. Mechanical ventilation predisposes thepatient to barotrauma and pneumothorax. Lung injuries may result from the inhalation of toxic andinert substances, as well as in association with blast or radiation.

Portable AP radiographs have several limitations when the images are obtained in an emergencysituation with the patient in a supine position. Expiratory artifacts and the magnification effect of a

short beam distance may make the mediastinum appear widened. Injuries involving the diaphragm areoften missed, and preexisting diaphragmatic eventrations or an elevated hemidiaphragm may mimicdiaphragmatic injuries.

Radiographic findings associated with aortic transection are nonspecific. They may be seen in a

variety of other mediastinal or chest wall injuries, including nonaortic vascular injuries, fractures ofthe sternum, vertebral fractures, and esophageal rupture. Predictions regarding the presence of

mediastinal hemorrhage on supine portable chest radiographs in the setting of trauma are inaccurate.Plain imaging findings of thoracic spinal fractures are often subtle and are difficult to identify because

of the limited quality of many trauma radiographs.

Computed tomography

Advancements in CT imaging have changed the management of blunt lung trauma and permitted thedetection of blood in bronchi and interstitial air or blood with greater accuracy.

[6, 7]Many centers now

screen patients with chest trauma for aortic injuries by using contrast-enhanced CT. CT scans (see theimages below) also demonstrate injuries to the lung, pleura, mediastinum, and chest wall better thanplain radiographs do. Many serious thoracic injuries may be overlooked on initial chest radiographs;

these include tracheobronchial tears, diaphragmatic rupture, esophageal tears, thoracic spine injuries,chest wall and seat-belt injuries, lung contusion, cardiac injuries, pneumothorax, hemothorax, and

chest tube complications.

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CT images demonstrate fractures of the vertebral bodies with great accuracy and readily show therelationship of fractured fragments and displaced disk material to the cord. Sagittal and coronalreconstructions may provide further exquisite detail.

Because of a dramatic reduction in motion and beam-hardening artifacts and significant improvementof spatial resolution, especially along the z-axis, helical and multisection CT scanning allows better

demonstration of the most subtle signs of thoracic trauma, such as a focal indentation of the liver or aright-sided collar sign. In addition, helical and multisection CT is a useful tools in the evaluation of

patients with multiple traumatic injuries.

Patients with severe trauma are often difficult to scan with CT because of resuscitative equipment. CTis an excellent modality, but patients are required to receive contrast agents and be transported fromthe protected resuscitation area to the radiology suite. Therefore, CT scanning is difficult to performin hemodynamically unstable patients.

Magnetic resonance imaging

MRI has many advantages over CT in the evaluation of patients with suspected dorsal spine injuries.It provides excellent detail of intervertebral disks, spinal ligaments, paravertebral soft tissues, and

other spinal contents (eg, cord and nerve roots). MRI is particularly useful in evaluating patients withspinal cord injury without radiographic abnormality (SCIWORA) syndrome. MRIs show cord edema


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or hematoma, which may account for any neurologic deficit the patient may have. MRI is animportant diagnostic and prognostic tool in patients with thoracolumbar compressiontype fractures.

MRI with breath-hold acquisition permits good visualization of diaphragmatic abnormalities, but thistechnique cannot be performed in emergency situations. MRI offers a major advantage in exploring

the cord, disks, and ligaments and in looking for a hematoma. Nevertheless, the indication is carefullyweighed in patients with multiple trauma because of monitoring difficulties during the examination,which may be long.

MRI is expensive and is not universally available in emergency departments. Also, MRI often cannot

be used in patients with ferromagnetic foreign bodies or some types of prosthetic cardiac valves, aswell as in those with claustrophobia. MRI should be performed only in patients when MRI-compatibleresuscitation equipment is readily available.

Echocardiography, ultrasonography, and angiography

Conventional echocardiography has long been used to image the heart, the pericardial space, and the

ascending aorta. Transesophageal ultrasonography is an excellent modality for visualizing the aorticarch and the descending aorta and may be used at the patient's bedside. Because ultrasonography isunique in being portable, rapid, and noninvasive, it is particularly suited to the trauma setting andoffers immediate feedback that may be incorporated into the management plan for the patient.

Ultrasonography is operator dependent and may cause some aortic injuries to be missed.

Conventional or digital subtraction angiography (see the images below) remains the criterion standardfor depicting traumatic aortic rupture and aortic pseudoaneurysm. Angiography is invasive and maycause small aortic tears to be missed. Iodinated contrast media are nephrotoxic and pose a risk ofanaphylaxis

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uclear medicine study

Thallium and multigated acquisition isotope scans are useful for assessing myocardial damage.Similarly, technetium-99m diphosphonate may be used to assess fracture sites when radiographs arenegative and patients are symptomatic.

Injury scoring

The abbreviated injury scale (AIS) and the injury severity score (ISS) are accurate methods for

quantifying trauma severity and have many potential applications. The ability to predict morbidity andmortality from trauma by using injury severity scoring is an obvious application. Such scores may be

used to inform patients and their families if they desire to know the prognosis and apply theknowledge to end-of-life decision making and resource allocations. However, there is alwaysuncertainty in predicting trauma mortality and morbidity in an individual patient. Decisions forindividual patients should never be made solely on the basis of a statistically derived ISS. A variety ofanatomic and physiologic trauma scores are used alone or in combination to score the severity ofinjuries.

[8]

The AIS is an anatomic scoring system first introduced in 1969. Since then, it has been revised severaltimes with regard to survival so that it now provides a reasonably accurate means of ranking the

severity of injury. A scaling committee of the Association for the Advancement of Automotive

Medicine (AAAM) monitors the AIS. The AIS is used to score traumatic injuries in terms of theanatomic location and severity of the injury. Each traumatic injury is assigned a 7-digit number, with


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the last number representing the severity of the injury to be used in tabulating the ISS. AIS numbersmay be found in theAIS Dictionary, distributed by the AAAM.

The ISS is an anatomic scoring system but only recognizes the highest AIS in each of the 6 bodyregions: head, face, chest, abdomen, extremities, and external. The ISS is used to assess survivability;

its results are often compared with various benchmarks (eg, ISS versus length of stay and ISS versusmortality). Only the highest AIS score in each body region is used. The scores for the 3 most severelyinjured body regions are squared and added to produce the ISS.

Injuries are scored on a scale of 1-6, with 1 being minor, 5 being severe, and 6 being lethal. This score

represents the threat to life associated with an injury and is not meant to represent a comprehensivemeasure of severity. The AIS is not an injury scale in that the difference between an AIS score of 1and a score of 2 is not the same as that between 4 and 5. The AIS scale and the organ injury scales of

the American Association for the Surgery of Trauma have many similarities.

AIS scores for injury are as follows:

Minor Moderate Severe Serious Critical Not survivable

thoracic trauma imaging

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