Traumatic aortic injury (TAI) is a major cause of trauma-related fatalities, with the majority of the victims dying at the scene of the accident. For the few who reach the hospital, rapid diagnosis and treatment is essential in order to prevent aortic rupture. Unfortunately, the diagnosis of TAI is difficult, as clinical signs and plain radiography are poor screening methods. Helical computed tomographic angiography (CTA) has vastly improved the evaluation of TAI, and its frequent use as a screening tool has led to a reduction in the number of aortograms. This paper will provide an overview of traumatic aortic injury and the role of CTA in its diagnosis.
graduated with a BS in Biology from the Massachusetts Institute
of Technology, Boston, MA, in 1990. He received his MD in 1999
from Baylor College of Medicine, Houston, TX. He is currently
Chief Resident and a third-year Radiology Resident at Yale/New
Haven Hospital, New Haven, CT. Dr. Wu plans to complete a
Musculoskeletal Imaging Fellowship following his residency.
Traumatic aortic injury (TAI) is a major cause of
trauma-related fatalities, with the majority of the victims dying
at the scene of the accident. For the few who reach the hospital,
rapid diagnosis and treatment is essential in order to prevent
aortic rupture. Unfortunately, the diagnosis of TAI is difficult,
as clinical signs and plain radiography are poor screening
methods. Helical computed tomographic angiography (CTA) has
vastly improved the evaluation of TAI, and its frequent use as a
screening tool has led to a reduction in the number of
aortograms. This paper will provide an overview of traumatic
aortic injury and the role of CTA in its diagnosis.
More than 100,000 people sustain acute chest trauma in the
United States each year, often resulting in traumatic aortic injury
(TAI) and death.
In fact, 80% to 90% of people with TAI die at the scene of the
accident as a result of aortic rupture.
Of those who reach the hospital, 60% to 70% survive if the aortic
injury is diagnosed and treated promptly.
However, mortality increases as the time to diagnosis is prolonged.
Thirty percent of patients with untreated TAI die within the first
6 hours of arrival at the hospital, and 40% die within the first 24
If the aortic injury is never diagnosed, 90% die within 4 months.
Thus, a rapid and effective diagnostic test for TAI is
Unfortunately, the diagnosis of TAI is difficult. Physical
examination and chest radiography are of limited value, especially
in hemodynamically stable patients. Aortography is the gold
standard; however, it is not without risks and can be time
consuming. Thoracic aortography has a systemic morbidity rate of
1.7% and fatalities have been associated with catheter-induced
Computed tomographic (CT) evaluation of the thoracic aorta is a
fast, safe, and effective screening tool for TAI. Innovations in CT
technology, especially helical multidetector scanning, enable
faster scans and better z-axis resolution, which lead to the
earlier diagnosis and treatment of TAI. This paper will provide an
overview of traumatic aortic injury and the role of CT angiography
(CTA) in its diagnosis.
Overview of traumatic aortic injury
Anatomic considerations and mechanisms of injury
The descending thoracic aorta is fixed to the spine, whereas the
ascending aorta and aortic arch are fairly mobile. Most blunt
aortic injuries occur in the ascending aorta, often at the
transition between the mobile and fixed portions of the thoracic
aorta. In fact, 90% of aortic injuries occur at the aortic isthmus,
in this area of transition.
The isthmus is the portion of the aorta between the origin of the
left subclavian artery and site of attachment of the ligamentum
arteriosum. Other sites of injury include the aortic root and arch.
However, injuries at these two locations are usually more serious
and often fatal.
During a deceleration injury, such as from a motor vehicle
collision or fall, the aorta is subjected to both shearing and
bending forces. Shearing forces occur when the mobile arch
decelerates more slowly than the fixed descending aorta. Bending
forces occur when the aorta is flexed across the left pulmonary
artery and left mainstem bronchus. These bending and shearing
forces also lead to the "osseous pinch," in which the aorta is
injured as it is pinched between the anterior bony structures and
the spine during chest compression.
A review of the composition and characteristics of the aortic
wall can help in understanding aortic injuries and the signs seen
on CT (Figure 1).
The aorta is composed of three layers: intima, media, and
adventitia. The media is the middle and strongest layer, providing
most of the aorta's support and elasticity. Tears of the intima and
portions of inner media lead to intraluminal flaps and filling
defects (Figure 2). Generally, however, the contour of the aorta is
preserved, as most of the media remains intact. A pseudo-aneurysm
occurs when there is complete disruption of the intima and media,
without disruption of the adventitia. The weak adventitia bulges
outward, forming a characteristic outpouching (Figure 3). These
pseudoaneurysms can rupture when treatment is delayed.
Both intimal flaps and pseudoaneurysms can lead to emboli of
thrombus or intimal debris. Moreover, aortic dissection can occur
as the intimal flap extends longitudinally along the wall of the
Treatment of aortic injury
Aortic rupture with immediate death is the greatest concern in
TAI. Treatment consists of urgent thoracotomy with surgical repair
once the diagnosis is made. Unfortunately, surgery is associated
with significant mortality (20% to 54%) and morbidity (5% to 10%
will develop paraplegia).
Aortic cross-clamping during surgery can lead to paraplegia
secondary to under perfusion of the spinal cord.
Moreover, these patients are often poor surgical candidates as a
result of other coexisting injuries. The use of antihypertensive
medications, such as beta-blockers, improves outcome and decreases
the risk of aortic rupture.
These medications are especially important in patients with
multi-organ injuries who cannot safely undergo immediate
In the past, all patients with aortic injuries, no matter how
small, were surgically treated. However, a small number of studies
have described the nonoperative management of patients with minimal
aortic injury (MAI).
Characterized by intimal flaps of <1 cm without significant
periaortic hema-toma, MAI occurs in 10% of patients with TAI.
Such patients have been treated with antihypertensive medication
alone and closely followed-up with serial CT scans. Animal studies
have shown that arterial injuries limited to the intima and inner
media heal without intervention in a few days.
However, nonoperative management of MAI is not a universally
The few patients with untreated TAI who survive can develop
chronic pseudoaneurysms (Figure 4). Forty-two percent of patients
with chronic pseudoaneurysms develop symptoms within 5 years, 85%
within 20 years.
Such patients require surgical repair, as they remain at risk for
aortic rupture, embolism, and dissection of the aortic wall.
Diagnosis of TAI
Diagnosis of TAI is difficult. Physical examination in the
hemodynamically stable patient is of limited value, and chest
radiography (CXR) has variable sensitivity (53% to 100%) and poor
specificity (1% to 60%).
Signs of mediastinal widening, left apical cap, tracheal deviation,
and depression of the left mainstem bronchus on CXR are not
specific to patients with TAI. The positive predictive value (PPV)
for chest radiography is only 4% to 20%.
Despite these shortcomings, CXR was used for several decades as the
primary screening tool for TAI. Patients with abnormal CXR were
taken to angiography for confirmatory aortograms. Prior to the
adoption of helical CT for screening, only 10% of aortograms were
positive for aortic injury.
In 1983, Heiberg et al
used conventional CT to evaluate a small series of patients with
TAI. Based on the initial studies, conventional CT was most useful
in the detection of mediastinal hematoma (Figure 5).
If none was detected, TAI could be confidently excluded. If
mediastinal hematoma was observed, patients were sent to
angiography. Early studies showed good sensitivity, 90% to 100%,
and negative predictive value (NPV), 94% to 100% for the detection
of TAI with conventional CT. However, specificity and positive
predictive value (PPV) were poor, 19% to 45% and 0% to 50%,
These low values were due to the fact that mediastinal and
periaortic hematomas can be seen in other chest injuries, such as
sternal or spinal fractures. In fact, early studies showed that
only 14% to 56% of patients with mediastinal hematomas had TAI.
Although conventional CT was an improvement from plain radiography,
it was imperfect. A large number of patients still underwent
Long scan times precluded performing CT angiography with
conventional scanners. Moreover, suboptimal opacification of the
aorta made intimal flaps and small pseudoaneurysms difficult to
detect with conventional scanners. With the introduction of helical
CT and followed by multidetector computed tomography (MDCT), the
direct signs of aortic injury could be visualized, thereby raising
the specificity of CT in the diagnosis of TAI. Conventional CT
yields a specificity of only 19% to 45%, whereas the specificity
rises to 92% to 99% with helical CT.
Helical CT angiography is now a major screening tool for the
evaluation of TAI.
The developments in CT technology from conventional to helical
scanning, and then from single-detector CT (SDCT) to the
multidetector CT (MDCT) have led to unprecedented speed and quality
of CT imaging. Most trauma centers are currently equipped with MDCT
and routinely employ this technology in the evaluation of TAI. The
most common type of MDCT in practice is a four-channel scanner,
however, 16-channel scanners are becoming more available. The
advantages of MDCT over SDCT include shorter acquisition time,
retrospective compilation or creation of thinner slices from the
same raw data, and improved three-dimensional (3D) renderings with
Because of shorter acquisition time and the ability to reliably
image during peak vascular enhancement, smaller contrast volumes
(up to 30% less) may be used as compared with SDCT.
Prior to beginning the examination, all possible external
sources of artifact should be removed and the patient's arms should
be raised above the head. Moreover, for intubated patients, the
ventilator should be paused just prior to imaging. With both SDCT
and MDCT, the aorta must be optimally enhanced. Typically, 90 to
120 mL of nonionic contrast media with an iodine concentration of
240 to 340 mg/mL is administered using a power injector at 3 to 4
mL/sec, through a 20-gauge or larger peripheral venous catheter.
Injection through a right antecubital vein is recommended, as the
use of a left antecubital vein can result in contrast artifact in
the left brachiocephalic vein and limit evaluation of the
Following injection, an immediate saline flush of 10 mL of isotonic
solution can improve vascular enhancement profile and decrease
Using this technique, one can also decrease the contrast
requirement by up to 20%.
The scanning time can be determined using automated systems (eg,
Smartprep, GE Medical Systems, Milwaukee, WI; Care Bolus, Siemens
Medical Systems, Erlangen, Germany). Alternatively, a test
injection can be used; 20 mL of nonionic contrast material is
injected at 2.5 to 3 mL/sec and multiple sequential images are then
obtained and coupled with region of interest analysis of the aorta
in order to determine the appropriate scanning delay. In general,
the optimal delay for the thoracic aorta is 20 to 25 seconds.
With SDCT, the slice collimation and slice width are the same.
Five to 10-mm collimation with 2.5- to 5-mm reformation is commonly
used with SDCT angiography, producing limited axial images and poor
reconstructions. However, with MDCT, there is more flexibility and
the user can select the detector collimation for each study. For
the 4-channel scanners, typical collimation choices are 1 mm, 2.5
mm, or 5 mm. Five- to 2.5-mm collimation with 1-mm reformations is
commonly used when evaluating for TAI. With the 16-channel
scanners, 0.75 to 0.5 mm collimation is achievable.
Although cardiac gating is not widely used when evaluating for
TAI, electrocardiogram (EKG)-gated imaging can improve detection of
aortic injury by limiting cardiac motion artifact and improving
reconstructions. Since the heart chambers move the least during
diastole, imaging during this phase of the cardiac cycle is ideal.
Electrocardiogram-gated imaging can be divided into prospective and
retrospective gating. In prospective EKG-gating, the start of each
axial scan is triggered by the R-peak from the EKG signal, ensuring
that imaging occurs during diastole. In retrospective EKG-gating,
several axial images are obtained for every z-axis location and
only those images that correspond to diastole are utilized for
image reconstruction. Retrospective gating yields higher quality
reconstruction images compared with prospective gating; however,
the radiation dose is higher with retrospective cardiac gating.
Postprocessing of the axial slice data is an important aspect of
CT angiography. Although studies have shown that sensitivity and
specificity do not improve with reconstruction, additional images
are useful for surgical planning.
Many surgeons, accustomed to sagittal and oblique views of the
thoracic aorta, still request aorto-grams despite obvious findings
on the axial images. Two-dimensional multiplanar reformations (MPR)
in the coronal and sagittal planes are commonly performed on
studies positive for signs of TAI. Three-dimensional images can be
generated, and the quality of these images has improved with
advances in MDCT (Figures 6 and 7). The newer 16-channel scanners
allow for thinner collimation, which improves z-axis resolution and
reduces artifacts during 3D image reconstruction.
Initially, most 3D reconstructions were performed with surface
rendering or maximum intensity projection (MIP). With surface
rendering, each voxel in the data set is determined to be a part of
or not a part of the object of interest, thereby defining the
surface of the object. Once the surface of the object is
determined, the rest of the data is discarded. In MIP, each voxel
along a line from the viewer's eye is evaluated and the maximum
voxel value is used for the corresponding display pixel. Currently,
most institutions use volume rendering, as this type of
postprocessing has proven to be superior to MIP and surface
In volume rendering, the computer sums the contribution of each
voxel along a line from the viewer's eye through the data set. This
is done repeatedly in order to determine the value of each pixel in
the final display image. Therefore, the entire data set is
incorporated in the final image.
CT findings in traumatic aortic injury
CT findings suggestive of traumatic aortic injury can be divided
into indirect and direct signs.
Indirect signs of trauma include mediastinal and periaortic
hematomas, which appear as soft-tissue-attenuating material
surrounding the mediastinal structures or aorta, respectively
(Figures 5 and 8). With conventional CT scanners, only indirect
signs of TAI can be visualized. Although the indirect signs are
highly sensitive for TAI, they are not very specific, 19% to 45%.
Mediastinal and periaortic hematomas can also be seen in patients
with sternal or spine fractures but without TAI.
With helical CT and CTA, direct signs of TAI can be visualized.
The direct signs of aortic trauma are most specific and refer to
visualized defects in the aorta itself. These direct signs range
from small intraluminal filling defects to focal pseudoaneurysms to
gross aortic transection with active extravasation.
Intraluminal filling defects can be caused by small intimal flaps
or intimal thrombus. The intimal flaps are seen as small linear
low-density intraluminal filling defects (Figure 2). With more
serious injuries, the intimal flap can extend into the media or
adventitia. If the media is completely disrupted, the weak
adventitia will bulge outward producing a pseudo-aneurysm (Figures
3 and 9). If the adventitia is breached, extravasation of contrast
can occur, ranging from small leaks to gross extravasation. Gross
active extravasation is rarely seen on CT, as patients who survive
an adventitial breach are most likely hemodynamically unstable.
Intimal flaps and pseudoaneurysms can produce aortic contour
abnormalities. Best seen on sagittal reconstructions, aortic
contour abnormalities are also a direct sign of TAI (Figure 10).
Pitfalls to CTA imaging
Occasionally, the diagnosis of traumatic aortic injury on CTA
can be difficult to determine, as there are many conditions that
mimic direct and indirect signs of TAI. Prominent thymic tissue,
especially in children and young adults, can mimic mediastinal
hematoma. Motion, volume-averaging, and pulsation artifacts can be
mistaken for intimal flaps or hematomas. Cardiac motion can also
produce artifacts; which can be reduced with EKG-gated imaging.
Moreover, irregularities in the contour of the aortic wall can
appear similar to a pseudo-aneurysm. The most common aortic wall
contour abnormalities mistaken for TAI are atherosclerotic
pseudoaneuryms, prominent bronchial arteries, and ductus
Several false-positive cases on CT and aortography stem from a
normal ductus diverticulum being mistaken for a pseudo-aneurysm.
Finally, high-density contrast in the brachiocephalic vein and
superior vena cava can cause streak artifacts, limiting evaluation
of the aorta and mediastinum. These equivocal cases should go to
angiography for further evaluation.
Accuracy of CTA and aortography
In screening for TAI, sensitivity and NPV are more important
than specificity and PPV. A screening tool with 100% sensitivity
and NPV will ensure that all patients with TAI are discovered.
Missing the diagnosis of TAI is unacceptable, as the chief
consequence is aortic rupture and death.
Single-detector CT and MDCT angiography enabled visualization of
direct signs of TAI, specifically intimal flaps and
pseudoaneurysms. Studies have shown that these direct signs
identify TAI with a sensitivity of 100%, an NPV of 100%, a
specificity of 92% to 99%, and a PPV of 80% to 89%.
All patients with direct signs of injury on CTA had TAI, regardless
of whether they also had indirect signs. Most authors do not
recommend angiography if only mediastinal or periaortic hematomas
Mirvis et al
evaluated 100 patients with CT evidence of mediastinal and/or
periaortic hematomas and concluded that if hematomas were seen only
in the anterior or posterior mediastinum, TAI was very
Currently, aortography is the gold standard. However, in
comparison to CTA it is more expensive, time consuming, and
invasive. Interventional teams generally are not readily available
after normal working hours, necessitating long waiting periods or
transfer to a tertiary center for aortography. Hunt et al
showed in 144 patients with TAI that the average time from
admission to angiography was 147 minutes. Some authors argue that
if direct signs of TAI are seen on CTA, conventional angiography is
redundant and can delay treatment.
CT angiography adds only a few additional minutes to the patient
work-up, as most patients undergo imaging for other injuries.
Moreover, aortograms have serious risks, including iatrogenic
extension of intimal flaps by the guide- wire or catheter, as well
as entry of the wire into the pseudoaneurysm.
Furthermore, aortography is not 100% sensitive. Gavant et al
studied 1518 patients with nontrivial chest trauma and found
aortography to have a sensitivity of 92%, whereas the sensitivity
of helical CTA was 100%. CT has the additional benefit of being
able to diagnose other injuries. Pneumothorax, pulmonary contusion,
pericardial effusion, and rib fractures may not be seen on
aortography, but are easily seen on CT.
Aortography appears to be slightly more specific than CT, 99% to
100% for aortography versus 92% to 99% for helical CTA.
Thus, equivocal CT studies should go to aortography. However, most
authors advocate sending patients directly to surgery if direct
signs of TAI are obvious, in order to save time.
Most studies conclude that indirect signs of TAI are sensitive but
nonspecific and, therefore, should not be the sole indication for
aortography. Many centers advocate the use of aortography only when
direct signs of TAI are equivocal or large periaortic hematomas are
Management of TAI based on CTA
The main goal of CTA in aortic trauma is to diagnose all
patients with aortic injury quickly, so that surgery can be
performed prior to rupture of the pseudoaneurysm. Another goal is
to reduce the number of unnecessary aortograms, as they are
invasive and can delay treatment. Management of patients with
traumatic aortic injury depends on identifying the indirect and
direct signs of TAI on CT and knowing the appropriate next step. If
there are no indirect or direct signs of TAI, the patient is
considered to be free of aortic injury. If only indirect signs are
present, such as a mediastinal hematoma, then aortography is not
necessary. Patients with equivocal direct signs of TAI require a
confirmatory aortogram. Finally, patients with obvious direct signs
of TAI on CTA should save time by going directly to surgery.
Adherence to this pathway will hopefully save more lives and reduce
unnecessary aortography (Figure 11).
Traumatic aortic injury is a deadly disease, and patient outcome
is highly dependent on its early diagnosis and treatment. Helical
CT angiography has proven to be a very effective screening tool for
aortic injury. CT angiography is fast, accurate, and in certain
aspects, superior to aortography. Optimal care of patients with
traumatic aortic injury depends on the identification of direct and
indirect signs of aortic injury on CTA and understanding the
appropriate next step in management.
The author thanks Dr. Sanjay Saluja for guidance throughout this
project and Cathy Camputaro for assistance in generating the 3D