AJR 2002; 179:458-460
© American Roentgen Ray Society
Traumatic Aortic Rupture: CT Evidence of a Dynamic Process
William C. Torreggiani1,
David Liu and
John R. Mayo
1 All authors: Department of Radiology, Vancouver General Hospital, 899 W. 12th
Ave., Vancouver, B. C., V5Z 1M9 Canada.
Received November 29, 2001;
accepted after revision January 15, 2002.
Address correspondence to J. R. Mayo.
Introduction
In the past 7 years, the introduction of single-detector helical and
multidetector CT has changed the imaging assessment of patients with suspected
traumatic aortic rupture. Multiple studies have shown that contrast-enhanced
helical CT is both sensitive and specific for the diagnosis of traumatic
aortic rupture
[1,2,3].
Surgical repair of traumatic aortic rupture is often performed after CT,
eliminating catheter aortography
[2,
4] and saving time and money.
However, articles documenting the utility of helical CT in traumatic aortic
rupture have occasionally noted a substantial difference between the extent of
aortic injury identified on preoperative contrast-enhanced CT and that found
at surgery [5]. This
observation raises questions regarding the accuracy of preoperative CT. We
report a surgically proven case of traumatic aortic rupture that showed
substantial changes in the size and configuration of the aortic injury between
two contrast-enhanced CT scans obtained during the 5-hr preoperative period.
Our case shows that traumatic aortic rupture can rapidly progress in the
preoperative period.
Case Report
A 31-year-old man was admitted to the emergency department of a community
hospital after a high-speed all-terrain-vehicle crash. Because he was
unrestrained at the time of impact, the patient was thrown from the vehicle,
sustaining substantial facial and chest trauma. He was conscious at admission
and hemodynamically stable, but he complained of severe right-sided shoulder
and chest pain.
A supine chest radiograph obtained on a portable unit at admission showed a
right pneumothorax, mild widening of the superior mediastinum, indistinctness
of the aortic knuckle, and absence of a definable aortic—pulmonary
window (Fig. 1A). After
placement of a chest tube, contrast-enhanced CT of the chest was performed to
investigate the widened mediastinum. CT was performed using a nonhelical
technique with the following parameters: 2-sec scanning time, 120 kVp, 140 mA,
10-mm collimation, and 10-mm slice spacing (contiguous slices). Images
acquired with mediastinal window settings showed circumferential enlargement
of the aortic isthmus to 2.8 cm in diameter, whereas the normal-appearing
proximal transverse aorta measured 2.2 cm in diameter
(Fig. 1B). A small adjacent
mediastinal hematoma was seen. The abnormal aortic segment showed a target
appearance of the contrast column, suggestive of a concentric aortic
dissection. Images acquired with the lung window setting showed a right-sided
chest tube in good position, with a small residual right-sided pneumothorax
and right lower lobe atelectasis. On the basis of these imaging findings and
the fact that no cardiothoracic surgeon was available at the local community
hospital, the patient was transferred by helicopter to our trauma center.
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Fig. 1A. —31-year-old man who sustained high-speed trauma. Chest
radiograph in supine anteroposterior view obtained on portable unit at first
admission shows right-sided pneumothorax (arrows), mild widening of
mediastinum, indistinctness of aortic arch, and absence of definable
aortic—pulmonary window.
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Fig. 1B. —31-year-old man who sustained high-speed trauma. Nonhelical
contrast-enhanced CT scan obtained using 10-mm collimation at level of aortic
isthmus 30 min after A shows circumferential enlargement of aortic
isthmus region and target appearance of contrast column. These changes are
believed to represent concentric dissection of aorta, with low-attenuation
ring (arrow) representing intimal flap.
|
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The patient remained stable during transfer. A repeated portable supine
chest radiograph obtained at admission to our institution, 5 hr after the
previous chest radiograph, showed marked progressive widening of the superior
mediastinum (Fig. 1C).
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Fig. 1C. —31-year-old man who sustained high-speed trauma. Chest
radiograph in supine anteroposterior view obtained on portable unit 5 hr after
A shows progressive widening of mediastinum. Chest tube has been placed
in right hemithorax, draining previously identified right-sided
pneumothorax.
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In light of the progressive mediastinal widening seen on radiography and
the atypical appearance of the aortic isthmus on the initial CT scan,
contrast-enhanced helical CT of the chest was repeated at our institution.
Parameters for the second study included single-detector section helical
acquisition, 3-mm collimation, 1.3 pitch, 120 kVp, 200 mA, 1-sec scanning
time, and image reconstruction at 1-mm spacing. Mediastinal window settings
from this study showed a pseudoaneurysm measuring 4 x 3 cm at the aortic
isthmus (Fig. 1D). Left
anterior oblique sagittal reformations through the aortic arch confirmed that
the pseudoaneurysm was located distal to the origin of the left subclavian
artery (Fig. 1E). Other
findings included enlargement of the previously identified mediastinal
hematoma, progressive atelectasis and consolidation in the right lung, and a
new left-sided pleural effusion.
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Fig. 1D. —31-year-old man who sustained high-speed trauma. Helical
contrast-enhanced CT scan obtained using 3-mm collimation at level of aortic
isthmus 5 hr after B shows focal pseudoaneurysm (arrow) of
left anterolateral aortic wall. Interval changes include increase in size of
mediastinal hematoma, development of left-sided pleural effusion, and
progressive infiltration and atelectasis in both lower lobes.
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Fig. 1E. —31-year-old man who sustained high-speed trauma. Sagittal
reformation of proximal descending aorta created from D shows
relationship of focal pseudoaneurysm (large arrows) and intimal flap
(small arrow) to origin of left subclavian artery (curved
arrow).
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On the basis of the second CT findings, the patient was immediately taken
to the operating room, where the pseudoaneurysm and surrounding extensive
mediastinal hematoma were resected. The aorta was repaired using a Dacron
(DuPont, Wilmington, DE) interposition tube graft 20 cm in diameter. The
patient made an uneventful recovery.
Discussion
Aortic injury as a result of blunt trauma is most commonly seen after
severe deceleration in high-speed motor vehicle crashes
[6,
7]. These severely injured
patients have a wide range of signs and symptoms that are seldom specific for
traumatic aortic rupture. Without diagnosis and treatment, 75% of aortic
injuries are fatal within 8 days, and 90% are fatal within 4 months
[6]. Radiographic evaluation is
paramount in making the diagnosis of aortic injury and in planning surgery.
The most commonly performed initial imaging examination for trauma patients is
chest radiography. The radiographs, usually obtained using a portable
radiography unit, provide valuable information to guide initial patient
resuscitation. However, because of its limited contrast sensitivity and its
two-dimensional imaging perspective, radiography is neither sensitive nor
specific for the diagnosis of traumatic aortic rupture
[8,
9].
In the past, catheter aortography has been used routinely in patients
suspected of having traumatic aortic rupture. The aortogram allowed diagnosis
of traumatic aortic rupture by showing the direct findings of intimal injury
or aortic pseudoaneurysm formation. It also showed the relationship of the
aortic injury to the left subclavian artery, information that is essential to
the correct placement of aortic clamps at the time of surgery. Recent
experience has shown that contrast-enhanced CT can diagnose and localize
traumatic aortic injuries sufficiently to allow surgical repair
[2,
5].
The case we have presented was unusual in that two contrast-enhanced CT
studies were performed in rapid succession during the 5-hr preoperative
period. CT was repeated because of diagnostic uncertainty about the unusual
appearance of the aortic isthmus region and the relationship of the suspected
aortic injury to the left subclavian artery seen on the initial thick-section
nonhelical CT. Obtaining the second contrast-enhanced CT scan was fortuitous
because it allowed identification of a marked change in the aortic injury. In
retrospect, we believe that the aortic injury seen on the initial CT
represented a focal concentric aortic dissection. Five hours later, when the
second scan was obtained, this injury had progressed to a large eccentric
pseudoaneurysm.
We speculate that at the time of initial trauma the anterior wall of the
aorta was injured, allowing blood to dissect within the media. This dissection
extended circumferentially around the aorta at the level of the isthmus,
producing the concentric dissection seen on the initial CT scan. During the
5-hr interval to the second CT scan, the injured anterior aortic wall
progressively dilated, producing the eccentric pseudoaneurysm. This
development changed the flow pattern within the concentric dissection,
decompressing the posterior false lumen.
In summary, it is possible that progressive aortic changes during the
preoperative period are common but not recognized because serial CT images are
not routinely obtained. This progression of injury may account for the
discrepancy in some patients between preoperative contrast-enhanced CT
findings and the findings at aortic surgery.
Acknowledgments
We thank Paul McCormack, Department of Medical Imaging, Campbell River
Hospital, for his assistance in preparing this article.
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Introduction
Case Report
