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Acute Traumatic Thoracic Aortic Injuries: Experience with 64-MDCT

¹ Both authors: Department of Radiology, Medical University of South Carolina, PO Box 250322, 169 Ashley Ave., Charleston, SC 29425.

Received October 26, 2007; accepted after revision May 23, 2008.

 
Presented at the 2007 annual meeting of the American Roentgen Ray Society, Orlando, FL.

Address correspondence to J. G. Ravenel (ravenejg{at}musc.edu).

Abstract

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OBJECTIVE. At some institutions, catheter angiography is used for confirmation of aortic injuries and equivocal MDCT findings. Because of the speed and efficiency of 64-MDCT, we believe that diagnostic catheter angiography may be obsolete. The purpose of this study was to review our experience with 64-MDCT in the evaluation of acute traumatic aortic injury (ATAI).

MATERIALS AND METHODS. The trauma registry at a level 1 trauma center was reviewed to find cases of ATAI occurring between March 1, 2005, and July 31, 2007. MDCT images were correlated with transcatheter angiograms when obtained. Surgical and clinical reports were reviewed to confirm abnormal and normal findings and the stability of the conditions of patients undergoing conservative treatment.

RESULTS. After level 1 or level 2 trauma, 1,344 patients underwent contrast-enhanced 64-MDCT. Twenty-four patients (1.79%) were found to have 25 aortic injuries. All patients had direct MDCT signs of ATAI. Ten catheter angiograms were obtained after MDCT. The presence of direct signs was confirmed in three cases. In five cases, indirect signs were found to be normal findings. In two cases, the findings remained equivocal after MDCT and conventional angiography. Fourteen patients underwent surgical repair of the aorta, six underwent conservative management, and four patients died of other injuries. No patient with equivocal or indirect findings needed surgical repair. The sensitivity of 64-MDCT was 96.0%; specificity, 99.8%; positive predictive value, 92.3%; negative predictive value, 99.9%; and accuracy, 99.8%.

CONCLUSION. Direct signs of ATAI on contrast-enhanced 64-MDCT scans do not have to be confirmed with catheter angiography. In our population, diagnostic transcatheter angiography was of limited value for clarifying equivocal or indirect MDCT findings.

Keywords: aortic injury • MDCT • trauma

Introduction

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Acute traumatic aortic injury (ATAI) is a serious outcome of blunt chest trauma; the morbidity and mortality are historically greater than 95% if the injury is left untreated [1]. Approximately 80–90% of all ATAIs are immediately fatal. With improved detection and treatment, however, patients who initially survive are more likely to undergo successful treatment [2, 3]. But even among those who reach the hospital alive and are treated, the overall mortality remains greater than 30% [4, 5]. This figure emphasizes the necessity of rapid and accurate detection and triage.

Contrast-enhanced MDCT is the preferred imaging technique for evaluation of patients with multiple trauma; injuries to several organ systems can be detected in a matter of minutes. Diagnostic confidence in the detection and exclusion of ATAI with both single-detector CT and MDCT is quite high, the negative predictive value approaching 100% in some studies [6–9]. Thus MDCT is accepted as the sole imaging test for the exclusion of ATAI [8, 10–12]. At many institutions, direct catheter angiography is reserved only for difficult cases and instances in which CT findings are equivocal [10, 11, 12–14]. Some authors [15, 16], however, continue to advocate angiography for confirmation of abnormal MDCT findings and for surgical planning, even in the face of increasing evidence that this practice may not be necessary [17]. To our knowledge, the value of 64-MDCT in the evaluation of ATAI has not been objectively evaluated. The purpose of this study was to retrospectively evaluate the effectiveness of 64-MDCT in the diagnosis of blunt ATAI.

Materials and Methods

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Our institutional review board on human research approved this study, and informed consent was waived. The trauma registry at our adult level 1 trauma center was reviewed in a HIPAA-compliant manner for diagnoses of aortic injuries in adults over a 29-month period beginning in March 2005, when a 64-MDCT system was installed in our trauma center, and ending July 31, 2007. MDCT was performed after initial evaluation and stabilization of the patient's condition at the clinical discretion of the trauma team. MDCT images were correlated with angiograms when obtained. Surgical reports were reviewed to confirm a diagnosis in the cases of patients who underwent open thoracotomy for ATAI. Clinical follow-up notes on patients with equivocal imaging findings and those who underwent nonoperative management (blood pressure control, general supportive care, and management of other injuries as needed) were used to assess stability over time. The presence of associated vascular and nonthoracic injuries was recorded.

Direct MDCT signs of ATAI were considered to be contour abnormality with pseudoaneurysm or contained rupture, vessel-wall disruption, intimal flap, luminal filling defect, and active extravasation. Minimal aortic injuries were defined as those affecting only the intima of the vessel wall [18]. Indirect signs were considered to be periaortic hematoma without evidence of direct injury and minor contour abnormalities without evidence of pseudoaneurysm or contained rupture or other direct signs. An equivocal finding was defined as one in which aortic injury could not be excluded by the interpreting radiologist, but direct and indirect signs were absent. The sensitivity, specificity, negative predictive value, positive predictive value, and accuracy of 64-MDCT were calculated.

The 64-MDCT scanner (Somatom Sensation, Siemens Medical Solutions) used had a 32 x 2 alternating focal spot that resulted in acquisition of 64 rows of data with each gantry rotation. Iodinated contrast material (140 mL iohexol, 300 mg I/mL, Omnipaque, GE Healthcare) was injected through a peripheral IV catheter at 3–4 mL/s. Data were acquired at 0.6-mm collimation from the thoracic inlet to the symphysis pubis after a standard delay of 75 seconds, according to the routine trauma protocol in our department. ECG gating was not used. The data were reconstructed at 2-mm slice thickness in the axial, coronal, and sagittal planes and submitted to our PACS. Three-dimensional workstations for the processing of raw data were available as necessary for evaluation and management but were not routinely used.

Most cases were interpreted by a thoracic radiologist, and other thoracic radiologists were available for consultation 24 hours a day in difficult cases. The results of the study were the final interpretation of the attending radiologist. Patient consent for procedures was guided by hospital policies for informed consent. The decision for further imaging and treatment was made by the trauma team in discussion with an in-house radiologist (senior resident or attending) and attending cardiothoracic surgeon when appropriate. All transcatheter angiograms were obtained by attending vascular interventional radiologists with knowledge of the MDCT findings. The ultimate management decision in all cases of indirect or direct signs of aortic injury was made by an attending cardiothoracic surgeon with experience in the management of ATAI.

View larger version (138K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 —31-year-old man with injury to aortic isthmus. Contrast-enhanced sagittal reformatted CT image shows segmental transection with contour abnormality and periaortic hematoma (arrow). Isthmus was most common location of acute traumatic aortic injury in series.

Results

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During the 29-month review period, 1,344 patients who sustained acute thoracic trauma underwent contrast-enhanced 64-MDCT. The patient demographics, associated injuries, and summary of management are shown in Table 1. Twenty-four patients (1.79%) were found to have 25 aortic injuries. The mean age of the patients with ATAI was 35.7 years (range, 18–68 years), men predominating (n = 17). The mechanism of injury was motor vehicle collision in 23 cases and fall from a 40-foot (12 m) height in one case. All 24 patients had direct signs of ATAI.

The locations of the injuries are shown in Table 2. The most common location, 19 injuries (79%), of ATAI in this series was the aortic isthmus (Fig. 1). One patient (4%) had a combined aortic root and isthmus injury (Fig. 2A, 2B, 2C). One patient had a focal intimal flap in the mid descending thoracic aorta (4%) (Fig. 3A, 3B). One patient (4%) had a traumatic intramural hematoma of the long segment of the descending thoracic aorta that manifested focal mural thrombus at follow-up (Fig. 4A, 4B, 4C). Three patients (13%) had minimal ATAI, one injury occurring at the isthmus and two injures in the distal thoracic aorta (Fig. 5).

View larger version (157K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —53-year-old man with combined acute traumatic injuries to aortic root and isthmus (Reprinted with permission from Steenburg S, Ravenel J, Ikonomidis J. Blunt traumatic injury of the ascending aorta: multidetector CT findings in two cases. Emerg Radiol 2007; 13:217–221 [19]). Axial contrast-enhanced MDCT image at level of aortic isthmus shows irregular contour of anterior descending aorta (arrows) with surrounding periaortic hematoma (arrowheads) due to transection extending along ascending aorta and main pulmonary artery. Bilateral pleural effusions and atelectasis also are present.

View larger version (172K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —53-year-old man with combined acute traumatic injuries to aortic root and isthmus (Reprinted with permission from Steenburg S, Ravenel J, Ikonomidis J. Blunt traumatic injury of the ascending aorta: multidetector CT findings in two cases. Emerg Radiol 2007; 13:217–221 [19]). Axial contrast-enhanced MDCT image at level of aortic root shows abnormal collection of contrast material immediately anterior and inferior to aortic root (arrow). No associated hemopericardium is present at this level.

View larger version (146K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —53-year-old man with combined acute traumatic injuries to aortic root and isthmus (Reprinted with permission from Steenburg S, Ravenel J, Ikonomidis J. Blunt traumatic injury of the ascending aorta: multidetector CT findings in two cases. Emerg Radiol 2007; 13:217–221 [19]). Coronal multiplanar reformation shows abnormal focal collection of contrast material at aortic root (arrow). Periaortic hematoma is remote from site of injury (arrowheads) to ascending aorta. Irregularity involving main pulmonary artery (asterisk) is due to cardiac motion artifact, not injury.)

View larger version (155K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —47-year-old woman with injury to intima of mid descending thoracic aorta. Transverse contrast-enhanced CT image shows intimal flap (arrow) within aortic lumen and minimal periaortic hematoma.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —47-year-old woman with injury to intima of mid descending thoracic aorta. Catheter angiogram shows small intimal tear (arrow). Patient was treated conservatively.

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —27-year-old woman with traumatic intramural hematoma. Contrast-enhanced CT image shows circumferential intramural hematoma (arrow) along most of descending thoracic aorta.

View larger version (193K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —27-year-old woman with traumatic intramural hematoma. Catheter angiogram in left anterior oblique projection does not show injury.

View larger version (134K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C —27-year-old woman with traumatic intramural hematoma. Contrast-enhanced CT image obtained on hospital day 10 because of distal embolic signs shows small mural thrombus (arrow), presumably due to small intimal tear.

View larger version (180K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5 —26-year-old man with minimal aortic injury at aortic hiatus. Contrast-enhanced CT image shows small mural thrombus (arrow) on left side of aorta. Patient was treated conservatively and discharged on hospital day 7.

During the study period, 10 transcatheter angiograms were obtained for evaluation of blunt thoracic trauma. All patients underwent angiography because abnormalities had been found at MDCT. In three cases, the angiographic findings confirmed the abnormal CT findings. Five angiograms were obtained because of indirect CT signs, and four showed no abnormalities (Fig. 6A, 6B). In the fifth case, MDCT had been performed for evaluation of intramural hematoma. The angiographic findings were normal, but a small intimal tear was found later at CT (Fig. 4A, 4B, 4C). Two patients with equivocal findings of ATAI were treated conservatively after angiography (Fig. 7A, 7B).

View larger version (124K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A —32-year-old man with periaortic hematoma without aortic injury. Contrast-enhanced CT image shows thoracic vertebral body burst fracture (arrowhead) with adjacent hematoma (H) but no direct signs of aortic injury. Atelectasis (arrow) adjacent to aorta mimics intimal flap.

View larger version (177K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B —32-year-old man with periaortic hematoma without aortic injury. Catheter angiogram in left anterior oblique projection shows no evidence of aortic injury. Asterisk indicates aortic isthmus.

View larger version (152K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A —49-year-old woman with 64-MDCT findings that were equivocal owing to ductus diverticulum and periaortic hematoma. Sagittal contrast-enhanced reformatted CT image shows irregular fingerlike projection with ill-defined inferior border and surrounding hematoma (arrow) arising from lesser curvature of transverse aortic arch, interpreted as equivocal but probable ductus diverticulum.

View larger version (183K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B —49-year-old woman with 64-MDCT findings that were equivocal owing to ductus diverticulum and periaortic hematoma. Right anterior oblique catheter angiogram shows fingerlike projection (arrow) from aortic isthmus.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
MDCT has become the imaging study of choice for the diagnosis and exclusion of ATAI, the sensitivity routinely exceeding 98% [6–9]. The diagnostic accuracy of CT approaches 100% when direct signs of injury are used for diagnosis, and some authors [6–9] argue that MDCT may be superior to direct catheter angiography. Despite extensive data supporting the value and accuracy of MDCT in the diagnosis of ATAI, some authors [15] do not share this opinion and continue to advocate angiography for confirmation of injuries and for surgical planning.

In this retrospective study, we examined the role of 64-MDCT in the evaluation of ATAI. We found that 64-MDCT has excellent sensitivity, specificity, negative predictive value, and accuracy in the diagnosis and exclusion of aortic injuries. Our findings support those of previous studies [8, 10–12]. The sensitivity in our study was lower than in the previous studies because we counted an aortic root injury not initially detected as a false-negative finding even though the aortic isthmus injury was detected. Thus on a per-patient basis, there were no false-negative findings.

Equivocal MDCT findings on the aorta and indirect findings alone in the setting of trauma are unusual. Equivocal findings do present a diagnostic or management challenge, however, because missing an acute aortic injury can be catastrophic. Some surgeons [15, 20] advocate direct catheter angiography in equivocal cases. These reviews and practice guidelines, however, may be outdated, and there is no evidence that this practice is efficacious. Some authors [17] suggest that in the setting of equivocal MDCT findings, angiography rarely adds information in the diagnosis of ATAI. Our findings are in keeping with that opinion. In both equivocal and indirect cases, the information from catheter angiography did not change management from nonoperative to operative. In addition, one case of intramural hematoma and minimal intimal injury according to MDCT findings was interpreted as a normal (false-negative) finding after catheter angiography and intravascular sonography.

Periaortic hematoma, an indirect sign of ATAI, is associated with a high rate of false-positive results and therefore should not be used to define an abnormal MDCT result [9, 14, 21]. Our experience supports this opinion. It is conceivable that periaortic hematoma in the absence of associated vascular injury may represent injury to the aortic adventitia. In that case, minimal aortic injury (at most) may be the source of hematoma. Evidence suggests that even when present, these lesions can be managed conservatively with imaging follow-up [18, 22]. If immediate further evaluation is needed, rather than catheter angiography, transesophageal echoaortography performed by a physician with experience in the evaluation of ATAI may be a better use of time and resources [23].

Although we believe that in most cases transcatheter angiography is not necessary, there may be a role when branch-vessel injury is suspected, when angiography is needed to evaluate and manage concomitant active bleeding at other sites, and in the planning of endovascular management of ATAI. Ultimately, the utility of diagnostic catheter angiography in the setting of suspected ATAI may be better elucidated through pooled data from multiple trauma centers or a meta-analysis of existing data.

We are aware of several limitations of this study. First, it was a single-center retrospective study with a relatively limited number of aortic injuries and catheter angiograms. Second, our MDCT trauma protocol calls for a standard delay of 75 seconds; therefore, images were not obtained at peak systemic arterial enhancement. It is conceivable that owing to less than maximal enhancement of the aorta, subtle intimal injuries might not have been detected. Third, the patients with normal CT findings did not undergo follow-up imaging. We are unaware of any missed aortic injuries during the follow-up period.

Calculations of sensitivity, specificity, and accuracy for this study should be viewed with the knowledge that not every patient underwent the same reference standard examination. In all cases clinical judgment determined the course of treatment, and indirect signs were characterized as false-positive MDCT findings even though they did not lead to inappropriate therapy. Most important, all cases necessitating surgical management were identified prospectively at MDCT.

Patients with direct 64-MDCT signs of ATAI need no further imaging evaluation and can go directly to surgery. Direct catheter angiography in cases of equivocal and indirect findings is unlikely to yield additional useful information. Strategies including conservative management; transesophageal echoaortography; MDCT follow-up, perhaps with cardiac gating to evaluate the aortic root in selected cases; or a combination of these methods should be used instead of catheter angiography.

References

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