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THORACIC TRAUMA
VASCULAR TRAUMA

 

 

Chest Trauma
Traumatic Aortic Injury

Blunt aortic injury

Up to 15% of all deaths following motor vehicle collisions are due to injury to the thoracic aorta. Many of these patients are dead at scene from complete aortic transection. Patients who survive to the emergency department usually have small tears or partial-thickness tears of the aortic wall with pseudoaneurysm formation.

Most blunt aortic injuries occur in the proximal thoracic aorta, although any portion of the aorta is at risk. The proximal descending aorta, where the relatively mobile aortic arch can move against the fixed descending aorta (ligamentum arteriousm), is at greatest risk from the shearing forces of sudden deceleration. Thus the aorta is a greatest risk in frontal or side impacts, and falls from heights. Other postulated mechanisms for aortic injury are compression between the sternum and the spine, and sudden increases in intra-luminal aortic pressure at the moment of impact.

Patients with blunt aortic injury tend to fall into 3 major categories:

Presentation
Injury Type
Management priority
Dead Aortic transection / rupture  
Haemodynamically unstable

Haemorrhage from other sites/organs

OR

Aortic haemorrhage

Control haemorrhage
Haemodynamically stable Contained aortic injury Blood pressure control

Most blunt aortic injuries surviving to hospital are partial-transections, and should be managed with blood pressure control until the defintivie repair. Thus the priority in the management of haemodynamically unstable patients with potential aortic injury is to rapidly identify and control on-going haemorrhage from other sites, and to avoid over-resuscitation. Sites of concealed haemorrhage are identified with Chest and Pelvis radiographs and FAST ultrasound or Diagnostic Peritoneal Lavage.

The caveat to these cases is the patient with and aortic tear and impending rupture. These patients classically present as 'meta-stable' - ie they respond to fluid resuscitation and then drop their blood pressure in a cyclical manner. It is important to recognise this futile cycle early and avoid aggressive cyclical resuscitation, as this will ultimately lead to free fupture of the aorta and an iatrogenic hypothermia & coagulopathy. Beware the 'meta-stable' patient with a widened mediastinum and a left-sided haemothorax!
 

CHEST TRAUMA

INITIAL EVALUATION
PNEUMOTHORAX
TENSION PNEUMO
OPEN PNEUMO
HAEMOTHORAX
CONTUSION
RIB FRACTURE / FLAIL
AORTIC INJURY
CHEST DRAINS

Blunt aortic injury from lateral & frontal collisions

AORTIC INJURY

PRIMARY SURVEY
AIRWAY
BREATHING
CIRCULATION
DISABILITY
EXPOSURE

ADJUNCTS
CXR

SECONDARY

 

 

Diagnosis

Clinical signs of traumatic aortic injury are rarely present, and diagnosis is based on a high index of suspicion based on mechanism of injury, and the results of imaging studies. However, a chest tube placed for haemothorax that drains a large initial rush of bright red arterial blood, or has significant on-going losses (>200mls) has a major intra-thoracic injury and should be transferred to the operating room for thoracotomy.

L Haemothorax +
Lots of bright red blood

 
 

Chest X-ray
The Chest X-ray is still used as the primary screening study, but has a low sensitivity, but a 98% negative predicitive value if normal.

The AP chest radiograph is one of the standard adjuncts to the primary survey in blunt trauma patients. A wide variety of signs on the chest radiograph are suggestive of traumatic aortic injury, but none are diagnostic. All are related to the identification of mediastinal haemorrhage and haematoma. This mediastinal haemorrhage is due to tears of mediastinal venous structures and as such is an indirect indicator of possible aortic injury. It does not constitute the aortic injury itself. The majority of patients with mediastinal haemorrhage do not have an aortic injury. Additionally, mediastinal haemorrhage can result from injury to the spine and surrounding structures. Thus the significance of radiographic signs for aortic injury is signficiantly decreased in the presence of vertebral trauma.

The 'funny-looking' mediastinum
While many signs of aortic injury have been reported (see below), the most sensitive indicator of blunt aortic injury remains an 'abnormal mediastinum'. When looking at the chest X-ray, a clear aortic outline from the arch down to the diaphragm is the best way to exclude significant aortic injury.


Clearly visualised aortic outline

A clear aortic knob outline has a 72% sensitivity, 47% specificity and 87% negative predictive value. When the aortic outline is not clearly seen it is impossible to exclude aortic injury on the chest film. Furhter radiographic signs are suggestive of mediastinal haemorrhage and may prompt further investigation:

Widened mediastinum
A mediastinal width of more than 8cm at the level of the aortic arch is considered abnormal and an indication for further imaging. A widened mediastinum is reported as having a 53% sensitivity, 59% specificity and 83% negative predictive value for traumatic aortic injury.

To maintain spinal precautions in blunt trauma patients, most AP chest radiographs are taken in the supine position. This will lead to fluid shifts that may cause a widened mediastinum. Some authors recommend repeating the radiograph with the patient erect, if the spine can be cleared prior to this. Around 40% of widened mediastinums will 'normalize' with the patient in the erect position.

Other less sensitive signs of mediastinal great vessel injury include depression of the left main-stem bronchus, deviation of the naso-gastric tube to the right, apical pleural haemoatoma (cap), disruption of the calcium ring in the aortic knob (broken-halo). None of these 'classic' signs have any useful sensitivity to use them as a screening for blunt aortic injury. Thus the 'funny-looking' mediastinum remains the best indicator of the need for further imaging.
 


Wide, abnormal mediastinum


Close-up.
Deviated trachea, depressed L bronchus


Angiogram of above:
Descending aorta injury


Very wide & abnormal mediastinum

Computed Tomography

As CT technology has developed it has established itself as the best screening modality for aortic injury. The sensitivity of modern CT scanners is reported at 97-100%, with a negative predictive value of 100% and specificity of 83-99%. As the newer multidetector scanners become more widespread, their increased resolution, bolus-tracking technology and improved processing software allows more and more surgeons to rely solely on the CT scan to plan operative or endovascular repair.

Exactly how CT is integrated into a hospital's protocol for the diagnosis of aortic injury will depend on the type of CT scanner, the availability of 24-hour angiography and on the perception of the thoracic surgeons on the nature and quality of the CT images.

Algorithm for evaluation of
blunt aortic injury

Most blunt aortic injuries are at the proximal descending aorta and are visible on axial CT as a pseudoaneurysm bulging anteriorly or antero-medially at the level of the left pulmonary artery. This is associated with mediastinal haemorrhage (non-enhancing) that is a result of surrounding contusion and venous injury, rather than from the aorta itself. The trachea and oesophagus may be displaced to the right. An intimal flap may be seen. If any uncontained extravasation is seen, a conservative approach is not appropriate and operation repair is indicated.

Angiography

While angiography has been the gold-standard screening modality for many years, it is being replaced by newer generations of multidetector helical CT scanners. CT scanners are generally more rapidly and widely available than interterventional radiologists and radiology suites. However the older generations of CT scanners, including single-slice helical CT, are rarely adequate for operative planning. They are also poor at identifying injuries to the great vessels. Where multi-detector CT is available, angiography is still used where the CT is equivocal or does not allow adequate visualisation of branch vessels or other surrounding structures.

Wide mediastinum
Angiogram: Descending Aortic injury

 


Descending aorta
pseudoaneurysm
(arrow)


Close-up


CT wide mediastinum


Aortic arch pseudoaneurysm


Close-up of aneurysm (arrow)

Management

As indicated in the table above, patients with aortic injury fall into two main groups. Those who have a full-thickness tear and are haemodynamically unstable from this, and those with a contained injury. Patients with a contained aortic injury may be haemodynamically unstable from haemorrhage from another organ, such as a liver or spleen injury. Haemorrhage control remains a primary priority in these patients.

If the aorta is injured, but is not the source of active haemorrhage, it should be low on the list of management priorities, after haemorrhage control and neurologic stabilization.

Most aortic injuries will need to be repaired. Some minor injuries, such as small intimal flaps or small pseudoaneurysms, have been managed entirely non-operatively. However, the natural history of these remains relatively unknown, and there are reports of delayed rupture or fistula formation many years after injury.

Pre-operative control
Most contained aortic injuries can be managed on a semi-elective basis. Patients who can not or should not be operated on immediately include:

  • Patients who need to be transferred to other facilities for definitive repair
  • Severe head injury
  • Severe pulmonary injury
  • Haemodynamically unstable patients
  • Patients who have undergone damage control procedures
  • Patients with coagulopathy, hypothermia & acidosis
  • Patients with severe medical co-morbidities
  • Patients with burns or severe sepsis.

Management of the aortic injury in these patients is to reduce the risk of rupture by controlling the blood pressure. Short-acting antihypertensive agents are used to keep the systolic blood pressure normal, ideally below 120mmHg.

Operative repair
Operative repair of aortic injury is indicated for:

  • Haemodynamic instability
  • Large-volume haemorrhage from chest tubes
  • Contrast extravasation on CT or rapidly expanding mediastinal haematoma
  • Penetrating aortic injury

Endovascular repair
In some centers, endovascular repair of thoracic aortic injury is available. This technique is still in its infancy, and long-term sequelae are, as yet unknown. However it is a useful technique for patients with multiple injuries or medical co-morbidities in whom open repair would carry an unacceptably high morbidity and mortality.


Open repair of descending aorta injury


Descending aorta injury


Endovascular stent control

References

Nagy KK, Fabian T, Rodman G. 'Guidelines for the diagnosis and management of blunt aortic injury'. EAST trauma practice guidelines committee, 2000. Available: www.east.org/tpg/chap8.pdf

Williams JS, Graff JA, Uku JM, Steinig JP. Aortic injury in vehicular trauma. Ann Thorac Surg. 1994;57:726-30

Katyal D, McLellan BA, Brenneman FD, et al. Lateral impact motor vehicle collisions: significant cause of blunt traumatic rupture of the thoracic aorta. J Trauma. 1997;42:769-72

Shkrum MJ, McClafferty KJ, Green RN, et al. Mechanisms of aortic injury in fatalities occurring in motor vehicle collisions. J Forensic Sci. 1999;44:44-56

Parmley LF, Mattingly TW, Manion WC, Jahnke EJ Jr. Nonpenetrating traumatic injury of the aorta. Circulation. 1958;17:1086-101

Mirvis SE, Bidwell JK, Buddemeyer EU, et al. Value of chest radiography in excluding traumatic aortic rupture. Radiology. 1987;163:487-93.

Schwab CW, Lawson RB, Lind JF, Garland LW. Aortic injury: comparison of supine and upright portable chest films to evaluate the widened mediastinum. Ann Emerg Med. 1984;13:896-9.

Marsh DG, Sturm JT. Traumatic aortic rupture: roentgenographic indications for angiography. Ann Thorac Surg. 1976;21:337-40.

Mirvis SE, Bidwell JK, Buddemeyer EU, et al. Imaging diagnosis of traumatic aortic rupture. A review and experience at a major trauma center. Invest Radiol. 1987;22:187-96

Marnocha KE, Maglinte DD, Woods J, et al. Mediastinal-width/chest-width ratio in blunt chest trauma: a reappraisal. AJR Am J Roentgenol. 1984;142:275-

Miller FB, Richardson JD, Thomas HA, et al. Role of CT in diagnosis of major arterial injury after blunt thoracic trauma. Surgery. 1989;106:596-602.

Dyer DS, Moore EE, Ilke DN, et al. Thoracic aortic injury: how predictive is mechanism and is chest computed tomography a reliable screening tool? A prospective study of 1,561 patients. J Trauma. 2000;48:673-82

Fabian TC, Davis KA, Gavant ML,et al. Prospective study of blunt aortic injury: helical CT is diagnostic and antihypertensive therapy reduces rupture. Ann Surg. 1998;227:666-76

Wicky S, Capasso P, Meuli R, et al. Spiral CT aortography: an efficient technique for the diagnosis of traumatic aortic injury. Eur Radiol. 1998;8:828-33

Fabian TC, Richardson JD, Croce MA,et al. Prospective study of blunt aortic injury: Multicenter Trial of the American Association for the Surgery of Trauma. J Trauma. 1997;42:374-80

Biquet JF, Dondelinger RF, Roland D. Computed tomography of thoracic aortic trauma. Eur Radiol. 1996;6:25-9

Ahrar K, Smith DC, Bansal RC, Razzouk A, Catalano RD. Angiography in blunt thoracic aortic injury. J Trauma. 1997;42:665-9

Pate JW, Gavant ML, Weiman DS, Fabian TC. Traumatic rupture of the aortic isthmus: program of selective management. World J Surg. 1999;23:59-63

Fabian TC, Davis KA, Gavant ML,et al. Prospective study of blunt aortic injury: helical CT is diagnostic and antihypertensive therapy reduces rupture. Ann Surg. 1998;227:666-76

Maggisano R, Nathens A, Alexandrova NA, et al. Traumatic rupture of the thoracic aorta: should one always operate immediately? Ann Vasc Surg. 1995;9:44-5

Fisher RG, Oria RA, Mattox KL, Whigham CJ, Pickard LR. Conservative management of aortic lacerations due to blunt trauma. J Trauma. 1990;30:1562-6

Wall MJ Jr, Soltero E. Damage control for thoracic injuries. Surg Clin North Am. 1997;77:863-78

Pate JW, Cole FH Jr, Walker WA, Fabian TC. Penetrating injuries of the aortic arch and its branches. Ann Thorac Surg. 1993;55:586-92

Doss M, Balzer J, Martens S, Wood JP, et al. Surgical versus endovascular treatment of acute thoracic aortic rupture: a single-center experience. Ann Thorac Surg. 2003;76:1465-9

Marty-Ane CH, Berthet JP, Branchereau P, Mary H, Alric P. Endovascular repair for acute traumatic rupture of the thoracic aorta. Ann Thorac Surg. 2003 Jun;75:1803-

Shim WH, Koo BK, Yoon YS, et al. Treatment of thoracic aortic dissection with stent-grafts: midterm results. J Endovasc Ther. 2002;9:817-21

CHEST TRAUMA

INITIAL EVALUATION
PNEUMOTHORAX
TENSION PNEUMO
OPEN PNEUMO
HAEMOTHORAX
CONTUSION
RIB FRACTURE / FLAIL
AORTIC INJURY
CHEST DRAINS

trauma.org 9:4, April 2004