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When should traumatic thoracic aortic injury be suspected and how is the diagnosis made?
Traumatic thoracic cardiovascular injury is a potentially lethal sequela of chest trauma carrying an almost 80% mortality in the first hour following the trauma. It should be suspected in every patient with blunt chest trauma. Although the majority of patients sustain the injury from sudden body deceleration after a motor vehicle accident or fall, other mechanisms such as sudden compression of the thoracic vessels between the spine and sternum or ribs can also produce this injury. In almost 90% of instances, the aorta is injured at the isthmus, the junction of its free and fixed portions. Injuries to the ascending portion and the aortic arch are much less frequent than isthmic injuries. A history of violent deceleration, ejection of an unrestrained passenger from the vehicle, death of anyone involved in the accident, a motor vehicle/pedestrian or bicyclist collision, or the pres-ence of high-impact injuries such as diaphragmatic rupture or mesenteric tear should enhance the suspicion for this injury. Additionally, chest trauma patients who develop unexplained hypotension, external signs of direct chest injury, pulse deficits between right and left arms or between upper and lower extremities, requirement for mechanical ventilation, presence of retrosternal or interscapular pain, hoarseness, systolic precordial flow murmur, or lower extremity neurologic deficits may also have an aortic injury. All patients should have a chest radiograph following chest trauma. Only 20–30% of instances of mediastinal widening on chest films are associated with thoracic aortic injury. Other chest radiographic findings suggestive of aortic injury are blurred aortic contours, wide paraspinal interface, opaci-fied pulmonary window, broad paratracheal stripe, displaced left mainstem bronchus, rightward deviation of the esopha-gus and trachea, and left hemothorax.
Aortography is the gold standard for the diagnosis of traumatic aortic injury. However, recent improvements in CT and ultrasound technologies permit reliable noninvasive diagnosis in the majority of patients. Contrast-enhanced spi-ral CT and multiplanar TEE are highly accurate and have substantially decreased the need for aortography. These two techniques are equally capable of diagnosing subadventitial aortic injuries which require surgical intervention. Lesions of the intima and media, which can be treated conservatively but which may later result in a pseudoaneurysm, and concomitant BCI are much more likely to be detected by TEE than by CT. The high diagnostic accuracy of TEE is valuable for both patients and anesthesiologists. Most patients who are admitted do not have major aortic tears, thus their hemodynamic abnormality generally originates from other injuries, such as to the spleen or liver, which require immedi-ate surgery without time for further evaluation of the chest. Intraoperative TEE in these instances eliminates the uncer-tainty about the presence of this injury that was common in the past, and permits appropriate intervention for nonaortic injuries while the diagnosis is made by the anesthesiologist. Aortic branch injuries, however, are difficult to be detected by TEE; angiography provides more accurate diagnosis for these injuries. TEE is also contraindicated in patients with sus-pected esophageal injuries. These patients frequently mani-fest bloody nasogastric tube drainage, severe facial trauma, unstable cervical spine injuries, and pneumoperitoneum. Although TEE is a useful technique in stable patients with mediastinal widening, flail chest, or pulmonary contusion, contrast-enhanced spiral CT appears to be the method of choice for definitive diagnosis.
The TEE findings of traumatic thoracic aortic injury include dilated aortic isthmus with abnormal contour, acute false aneurysm formation or an intraluminal medial flap associated with subadventitial disruption or both, a mobile image appended to the thoracic aortic wall consistent with an intimal tear or a mural thrombus, or a crescentic or circumferential thickening of the aortic wall suggesting the presence of intramural hematoma. In addition, a traumatic hemomediastinum should be considered if the distance between the esophageal probe and the anteromedial wall of the aortic isthmus is >3 mm or there is blood between the posterolateral aortic wall and the left visceral pleura. A left-sided hemothorax can be detected if there is blood between the left lung and the thoracic wall.
The CT findings of traumatic aortic injury include: polypoid or linear intraluminal areas of low attenuation sug-gesting clot or medial flap, false aneurysm, irregular aortic wall or contour, pseudo-coarctation, intramural hematoma, and aortic dissection.
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