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Published online before print February 1, 2006, 10.1148/radiol.2383041528
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(Radiology 2006;238:841-852.)
© RSNA, 2006

Emergency Radiology

Suspected Aortic Dissection and Other Aortic Disorders: Multi–Detector Row CT in 373 Cases in the Emergency Setting1

Robert G. Hayter, BS, James T. Rhea, MD, Andrew Small, MD, Faranak S. Tafazoli, MD and Robert A. Novelline, MD

1 From the Department of Radiology, Massachusetts General Hospital and Harvard Medical School, 107 Avenue Louis Pasteur, Room 185, Boston, MA 02115. Received September 3, 2004; revision requested November 3; revision received March 11, 2005; accepted April 15; final version accepted July 27. Address correspondence to R.G.H. (e-mail: robert_hayter{at}student.hms.harvard.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Purpose: To retrospectively review the authors' experience with multi–detector row computed tomography (CT) for detection of aortic dissection in the emergency setting.

Materials and Methods: The investigation was institutional review board approved, did not require informed patient consent, and was HIPAA compliant. In 373 clinical evaluations in the emergency setting, 365 patients suspected of having aortic dissection and/or other aortic disorders underwent multidetector CT. Criteria for acute aortic disorder were confirmed by using surgical and pathologic diagnoses or findings at clinical follow-up and any subsequent imaging as the reference standard. Positive cases were characterized according to type of disorder interpreted. Resulting sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated by using two-way contingency tables. All cases found to be negative for acute aortic disorders were grouped according to alternative CT findings.

Results: Sixty-seven (18.0%) of the 373 cases were interpreted as positive for acute aortic disorder. One hundred twelve acute aortic disorders were identified in these 67 cases: 23 acute aortic dissections, 14 acute aortic intramural hematomas, 20 acute penetrating aortic ulcers, 44 new or enlarging aortic aneurysms, and 11 acute aortic ruptures. Three hundred five (81.8%) cases were interpreted as negative for acute aortic disorder. In 48 negative cases, multidetector CT depicted alternative findings that accounted for the clinical presentation. Of these, three included both acute aortic disorders and alternative findings, and 45 included only alternative findings. One (0.3%) case was indeterminate for acute aortic disorder. Overall, 112 findings were interpreted as positive for acute aortic disorder, an alternative finding, or both at CT. No interpretations were false-positive, one was false-negative, 67 were true-positive, and 304 were true-negative. Sensitivity, specificity, PPV, NPV, and accuracy were 99% (67 of 68), 100% (304 of 304), 100% (67 of 67), 99.7% (304 of 305), and 99.5% (371 of 373), respectively.

Conclusion: The positivity rate for acute aortic dissection or other acute aortic disorder in 373 cases examined at multi–detector row CT was 18.0%.

© RSNA, 2006


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Acute aortic dissection, acute aortic intramural hematoma, and acute penetrating aortic ulcer are life-threatening disorders (1). The clinical diagnosis of aortic dissection and other aortic disorders remains challenging, however, because the patient's symptoms can vary markedly according to the organ systems affected. The true incidence of aortic dissection is unknown because as many as one-third of cases are not diagnosed (2). Investigators have calculated an incidence of five to 27 cases per million people per year, making this condition the most common aortic disorder requiring surgery (2–4). The peak incidence of aortic dissection occurs during the 6th and 7th decades of life, with a 3:1 male-to-female predominance (5).

Aortic dissection is associated with several reported risk factors, the most important of which are hypertension and medial degeneration of the aortic wall (6,7). Aortic intramural hematoma, a disorder differentiated from aortic dissection by the lack of both a detectable intimomedial flap and direct flow communication between the true and false lumina, has an estimated prevalence of 5%–20% of all acute aortic disorders identified at presentation (8). Penetrating aortic ulceration, a disorder associated with increased risk of progression to acute aortic rupture and other acute aortic disorders, has an unknown independent prevalence but has been reported in association with 2.3% of cases of suspected aortic dissection and is associated with 52% of aortic intramural hematomas (9,10). A delayed or missed diagnosis of acute aortic dissection, and possibly acute aortic intramural hematoma, when untreated, is associated with a mortality rate of greater than 1% per hour during the first 24 hours after onset and of 80% by 2 weeks (11,12).

A variety of imaging modalities have been used to diagnose acute aortic disorders, including conventional aortography, ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging. The accuracy and ease of performing multi–detector row CT in patients in emergency settings who have presentations suggestive of aortic dissection or other aortic disorders have made this examination the first choice of referring physicians at our hospital. Thus, the purpose of our investigation was to retrospectively review our experience in using an aortic dissection multi–detector row CT protocol in the emergency setting.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
The investigation was approved by our hospital's institutional review board. Informed patient consent was not required for our retrospective investigation, which was Health Insurance Portability and Accountability Act compliant. Unless otherwise stated, the data retrieval and analysis procedures were performed by one author (R.G.H.).

Patients and Imaging
We retrospectively reviewed the data for patients who had not experienced trauma but were suspected of having aortic dissection and/or other aortic disorders and underwent multi–detector row CT in the large urban emergency department of Massachusetts General Hospital between January 1, 2002, and June 30, 2003. The aortic dissection multi–detector row CT protocol included the acquisition of nonenhanced and contrast material–enhanced chest, abdominal, and pelvic images and was performed by using a GE LightSpeed multi–detector row scanner (GE Medical Systems, Milwaukee, Wis). The acquisition of nonenhanced CT images for visualization of the hyperattenuating crescentic hematoma produced by aortic intramural hematomas was followed by the acquisition of contrast-enhanced transverse CT images from the lung apices to the acetabular roof for visualization of the classic intimomedial flap. Initial transverse CT scanning was performed by using a detector configuration of 4 x 2.5 mm in the high-speed mode with a pitch of 6 and a table speed of 30 mm per rotation, which yielded 7.5-mm nonenhanced images with 7.5-mm spacing. Iodinated contrast material was then injected intravenously through an 18-gauge catheter at a rate of 3–4 mL/sec (total injected, 100–120 mL). After a 25–35-second injection delay, transverse scanning was performed by using a detector configuration of 4 x 2.5 mm in the high-speed mode with a pitch of 6 and a table speed of 15 mm per rotation, which yielded 3.75-mm contrast-enhanced images with 3.0-mm spacing.

In cases positive for acute aortic disorder, additional 2-minute-delay scanning was performed by using a detector configuration of 4 x 2.5 mm in the high-speed mode with a pitch of 6 and a table speed of 15 mm per rotation. This examination yielded 7.5-mm contrast-enhanced images with 7.5-mm spacing, which were used to differentiate the initial slow blood flow in the false lumen from the potential free blood flow between the true and false lumina.

All examinations included routine coronal and sagittal aortic reformations from the initial contrast-enhanced image. Coronal and sagittal reformations were generated from 2.5-mm sections with 2-mm spacing. In the positive cases, a three-dimensional reformation of the aorta was generated from 2.5-mm sections with 2-mm spacing on a separate workstation (Vital Images Vitrea; Vital Images, Plymouth, Minn). All images were reviewed on a picture archiving and communications system by using AGFA workstations (AGFA, Mortsel, Belgium). All multi–detector row CT cases were interpreted at the time of image acquisition and most often by eight board-certified staff emergency radiologists (J.T.R., R.A.N.) with 1–30 years postresidency experience. Some images were interpreted by junior members of other divisions of our main radiology department.

We identified the patient cohort from the radiology computer database (Folio Views 4.2; Folio, division of Open Market, Provo, Utah) by using key words related to CT and aortic dissection in patients without trauma in the emergency setting. Inpatients were excluded. Once the patient cohort was identified, it was cross-referenced against the cohort listed in a separate emergency department multi–detector row CT database for accuracy and completeness to ensure that all cases had been identified by the authors (R.G.H., A.S., and F.S.T. independently; final review by R.G.H.).

During the period from January 1, 2002, to June 30, 2003, a total of 373 emergency department cases were evaluated for suspected aortic dissection and other aortic disorders with multi–detector row CT. These were the cases of 373 aortic dissection multi–detector row CT examinations performed in 365 patients for 373 separate clinical evaluations. Of these 365 patients, 204 (55.9%) were male and 161 (44.1%) were female. The mean ages of the male and female patients were 61.0 years ± 16.2 (standard deviation) and 69.1 years ± 16.6, respectively. The overall mean age was 64.6 years ± 16.8 (range, 21.7–96.0 years).

By using the hospital database (Clinical Application Suite [CAS]; Partners Healthcare Systems, Boston, Mass), we retrieved additional information about the patients during their hospital admission for categorization and accuracy analysis (performed by all authors). This additional information included clinical history, other imaging examination results, surgery reports, pathology reports, electrocardiographic reports, and clinical follow-up results.

The cases of four multi–detector row CT examinations (three chest, one abdominal-pelvic) performed for other clinically suspected problems with associated findings of acute aortic disorder were not included in our series of suspected aortic dissection and other aortic disorders. The cases of 16 multi–detector row CT examinations determined to be inadequate on the basis of the scanning protocol or the final images obtained also were not included in our investigation. All 16 of these cases involved requests for the aortic dissection multi–detector row CT protocol.

Definitions
Positive case was defined as the diagnosis of acute aortic dissection, acute aortic intramural hematoma, acute penetrating aortic ulcer, new or enlarging aortic aneurysm, or acute aortic rupture. Positive cases were identified by using multi–detector row CT, aortography, MR angiography, transesophageal echocardiography (TEE), or transthoracic echocardiography. Acute aortic dissections, acute aortic intramural hematomas, and acute penetrating aortic ulcers were defined as acute aortic disorders, according to published imaging findings criteria, when they were associated with less than 2 weeks of symptoms at the time of scanning or changed findings on multi–detector row CT images compared with findings on previously obtained images (13–16). New or enlarging aortic aneurysms were defined as acute aortic disorders without associated findings on previously obtained images, thoracic aortic dilatations 5 cm in diameter or larger, or abdominal aortic dilatations 3 cm in diameter or larger. Acute aortic ruptures were defined as acute aortic disorders in association with extravasation of contrast material or blood identified beyond the adventitia or within the pericardial sac.

Chronic aortic dissections, aortic intramural hematomas, and penetrating aortic ulcers were defined as aortic disorders associated with more than 2 weeks of symptoms at the time of scanning (13,15). Stable aortic dissections, aortic intramural hematomas, and penetrating aortic ulcers were defined either as aortic disorders associated with unchanged findings on multi–detector row CT images compared with findings on previously obtained images or on the basis of the finding of a calcified outer wall in the false lumen (17,18). Neither chronic nor stable aortic disorders were included in our investigation cohort of 373 cases. The criteria for acute aortic disorder were confirmed by using "hard" data, including surgical and pathologic diagnoses, or "soft" data, including findings at clinical follow-up and any subsequent imaging, as the reference standard.

Data and Statistical Analyses
Review of the retrieved multi–detector row CT and hospital course information included categorization and accuracy analyses of the clinical presentations, medical histories, positive and negative cases, alternative and indeterminate findings, initial imaging modality used, other reported imaging examination findings, diagnoses at discharge, reported electrocardiographic findings, reported radiographic findings, and clinical follow-up results. For all cases that were difficult to interpret on the basis of the examination reports and medical records alone, images were reviewed independently by two authors (J.T.R., R.A.N.), who each had 30 years experience with CT in the emergency radiology setting. P values for differences among the acute aortic disorder categories described were not calculated, because there was an insufficient number of cases in each positive-finding group to demonstrate any potential statistical significance.

For accuracy analysis, multi–detector row CT findings were compared with available aortographic, MR angiographic, TEE, transthoracic echocardiographic, surgical, and pathologic findings; with the discharge diagnoses; and with clinical follow-up findings. The resulting sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the aortic dissection multi–detector row CT protocol were calculated by using two-way contingency table analysis. The one multi–detector row CT case interpreted as indeterminate was not included in this analysis. This exclusion decreased the sample size from 373 to 372 cases for two-way contingency table analysis. All cases found to be negative for acute aortic disorders were grouped (by A.S) according to the alternative findings identified at multi–detector row CT.

A cost comparison of aortic dissection multi–detector row CT and aortography was performed by two authors (R.G.H., J.T.R.) in consensus. To compare costs, the actual hospital costs associated with performing aortic dissection multi–detector row CT and aortography were calculated. Cost data were retrieved from the hospital cost database (Sunrise Decision Support Manager [SDSM], version 5.1.02; Eclipsys, Boca Raton, Fla).

The costs incurred by the hospital in performing multi–detector row CT were calculated as follows: The multi–detector row CT actual hospital cost included the actual variable direct cost per multi–detector row CT examination, the actual fixed direct cost per unit, and the actual fixed indirect cost per unit, where the total cost equaled the total actual cost per unit (in the aortic dissection multi–detector row CT protocol). The multi–detector row CT actual hospital cost per examination was then multiplied by the number of cases of suspected aortic dissection and other aortic disorders (n = 373). The actual cost was rounded to the nearest U.S. dollar by using the arithmetic rounding algorithm. The potential cost that the hospital would have incurred if aortography had been performed was calculated by using the same method. The costs for aortic dissection multi–detector row CT and aortography were compared, and the difference was calculated.

The actual hospital cost associated with performing aortic dissection multi–detector row CT, given the current positivity rate (18.0%), was calculated by R. G. Hayter and J. T. Rhea in consensus. The hospital cost per positive multi–detector row CT case was calculated as follows: The product obtained by multiplying the multi–detector row CT actual hospital cost by the 373 cases in the identified cohort was divided by the number of positive acute aortic disorder cases (n = 67). The potential cost per positive case that the hospital would have incurred if aortography had been performed was calculated by using the same method. The costs for positive-result aortic dissection multi–detector row CT and positive-result aortography—if aortography was the primary imaging method—were compared, and the difference was calculated.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Overall Clinical Presentations
Clinical presentations were highly variable. In the 373 cases, there were seven groups of symptoms and signs: chest pain in 217 (58.2%), back pain in 162 (43.4%), abdominal pain in 54 (14.5%), syncope in 10 (2.7%), shortness of breath in 21 (5.6%), unequal blood pressure in the arms in five (1.3%), and miscellaneous symptoms in 19 (5.1%) cases.

History of Aortic Aneurysm
Thirty-eight (10.2%) cases involved histories of a total 54 aortic aneurysms: 13 ascending thoracic, 12 descending thoracic, and 29 abdominal aortic aneurysms. Twenty-two (5.9%) cases involved 23 prior aortic aneurysm repairs: seven cases of aortic aneurysm repair in the ascending thoracic aorta, one case in the descending thoracic aorta, and 15 cases in the abdominal aorta. Nine (2.4%) cases involved a history of type A aortic dissection repair. Only one (0.3%) case involved a history of type B aortic dissection repair. Sixteen (4.3%) cases involved a history of aortic valve replacement.

Positive and Negative Interpretation Findings
Of 373 cases evaluated for suspected aortic dissection and other aortic disorders with multi–detector row CT, 67 (18.0%) were interpreted as positive for acute aortic disorder (Table 1). One hundred twelve acute aortic disorders were identified in these 67 cases: 23 acute aortic dissections, 14 acute aortic intramural hematomas, 20 acute penetrating aortic ulcers, 44 new or enlarging aortic aneurysms, and 11 acute aortic ruptures. Three hundred five cases were interpreted as negative for acute aortic disorder. In 48 (12.9% of total 373 cases) negative cases, multi–detector row CT depicted alternative findings that accounted for the clinical presentation. In three (0.8% of total 373 cases) of these 48 cases, there were both acute aortic disorders and alternative findings, and in 45 (12.1% of total 373 cases), there were only alternative findings. One (0.3%) case was interpreted as indeterminate for acute aortic disorder. Overall, 112 (30.0%) cases were interpreted to be positive for acute aortic disorder, an alternative finding, or both at multi–detector row CT.


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  		Table 1. Multi–Detector Row CT Interpretation of 373 Cases of Suspected Aortic Dissection and Other Aortic Disorders

 
Imaging Examinations
The initial imaging modality was multi–detector row CT in 367 (98.4%) cases and cardiac US in six (1.6%). Only four (1.1%) cases were evaluated with aortography during hospital admission. In addition, MR angiography was performed in 15 (4.0%); TEE, in 36 (9.7%); and transthoracic echocardiography, in 117 (31.4%) cases. Among these additional imaging examinations performed during the patients' hospitalization, one TEE examination yielded results that were crucial in making the final diagnosis: acute aortic intramural hematoma that was missed at multi–detector row CT. However, the TEE results may have been false-positive. Nonetheless, the diagnosis made by using TEE did not lead to a change in the patient's treatment, and surgery was not required.

In the one case interpreted as indeterminate at multi–detector row CT, no acute aortic disorder was found at follow-up TEE. In this case, there were findings of an abnormal flap of tissue in the aortic root that could not be differentiated as either a prominent valve leaflet or a small acute aortic dissection. Follow-up TEE results revealed the multi–detector row CT findings to be thickened aortic leaflets with Lambl excrescence. Clinical and imaging follow-up for up to 18 months after the presentations revealed no additional cases of acute aortic disorder and either confirmed or did not alter the initial multi–detector row CT interpretations.

Statistical Findings
Of 372 aortic dissection multi–detector row CT case interpretations, none were false-positive, one was false-negative, 67 were true-positive, and 304 were true-negative (Table 2). Sensitivity was 99%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 99.7%. Overall accuracy was 99.5%.


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  		Table 2. Accuracy of Multi–Detector Row CT in Diagnosis of Acute Aortic Dissection and Other Acute Aortic Disorders in 372 Cases

 
Other Findings and Analyses
Among the 373 cases evaluated for suspected aortic dissection and other aortic disorders, there were 48 (12.9%) cases involving 10 alternative findings at multi–detector row CT that likely accounted for the patients' presenting symptoms and signs (Table 3). The most frequent alternative findings were acute cholecystitis and other biliary conditions, which were identified in 12 (3.2%) cases. Several clinically important alternative findings also were identified at multi–detector row CT and included lung cancer, a perforated gastric ulcer, pancreatic cancer, a superior mesenteric artery embolus, mesenteric ischemia, and a perforated viscus.


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  		Table 3. Alternative Findings Identified with Aortic Dissection Multi–Detector Row CT Protocol

 
The use of multi–detector row CT enabled the temporal analysis of cases positive for acute aortic disorder. Nine (2.4%) cases of aortic dissection, aortic intramural hematoma, or penetrating aortic ulcer were interpreted as chronic or stable.

Types of Acute Aortic Disorders
In the 67 cases of acute aortic disorder, 23 (34%) acute aortic dissections, 14 (21%) acute aortic intramural hematomas, and 20 (30%) acute penetrating aortic ulcers were detected (Table 4). Each of these cases was further classified according to the Stanford-Daily, DeBakey, and variant (less common) systems (19). With use of the Stanford-Daily classification system, 13 (19%) of the 67 cases were type A and 10 (15%) were type B acute aortic dissections (Figs 1, 2), one (2%) case was type A and 13 (19%) were type B acute aortic intramural hematomas, and three (5%) cases were type A and 17 (25%) were type B acute penetrating aortic ulcers.


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  		Table 4. Characteristics of 67 Cases Positive for Acute Aortic Disorder at Aortic Dissection Multi–Detector Row CT

 

Figure 1
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  		Figure 1a: Contrast-enhanced multidetector CT images in 76-year-old man with type A acute aortic dissection. (a) Transverse image obtained at pulmonary artery level shows false lumina (F) in right lateral aspect of ascending aorta and in posterior position in descending aorta. Delayed contrast material filling and thrombosis are seen in ascending aorta false lumen. Thrombosis is seen in descending aorta false lumen. The true lumina (T) are well opacified. (b) Sagittal reformation shows false lumina (F) in anterior aspect of ascending aorta and in posterior position in descending aorta. The true lumen (T) is well opacified. (c) Transverse image obtained at superior pulmonary vein level shows proximal origin of dissection flap (arrow) in ascending aorta.

 

Figure 1
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  		Figure 1b: Contrast-enhanced multidetector CT images in 76-year-old man with type A acute aortic dissection. (a) Transverse image obtained at pulmonary artery level shows false lumina (F) in right lateral aspect of ascending aorta and in posterior position in descending aorta. Delayed contrast material filling and thrombosis are seen in ascending aorta false lumen. Thrombosis is seen in descending aorta false lumen. The true lumina (T) are well opacified. (b) Sagittal reformation shows false lumina (F) in anterior aspect of ascending aorta and in posterior position in descending aorta. The true lumen (T) is well opacified. (c) Transverse image obtained at superior pulmonary vein level shows proximal origin of dissection flap (arrow) in ascending aorta.

 

Figure 1
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  		Figure 1c: Contrast-enhanced multidetector CT images in 76-year-old man with type A acute aortic dissection. (a) Transverse image obtained at pulmonary artery level shows false lumina (F) in right lateral aspect of ascending aorta and in posterior position in descending aorta. Delayed contrast material filling and thrombosis are seen in ascending aorta false lumen. Thrombosis is seen in descending aorta false lumen. The true lumina (T) are well opacified. (b) Sagittal reformation shows false lumina (F) in anterior aspect of ascending aorta and in posterior position in descending aorta. The true lumen (T) is well opacified. (c) Transverse image obtained at superior pulmonary vein level shows proximal origin of dissection flap (arrow) in ascending aorta.

 

Figure 2
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  		Figure 2a: Contrast-enhanced multidetector CT images in 31-year-old man with Marfan syndrome and type B acute aortic dissection. (a) Transverse image obtained at aortic arch level shows intima (arrow) surrounding a communicating posterior false lumen in proximal descending aorta. (b) Coronal reformation shows distal extent of intimomedial flap (arrow). (c) Sagittal reformation shows proximal intimomedial flap (arrow) in proximal descending thoracic aorta originating immediately distal to origin of left subclavian artery. True (T) and false (F) lumina are well opacified and show a communicating aortic dissection.

 

Figure 2
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  		Figure 2b: Contrast-enhanced multidetector CT images in 31-year-old man with Marfan syndrome and type B acute aortic dissection. (a) Transverse image obtained at aortic arch level shows intima (arrow) surrounding a communicating posterior false lumen in proximal descending aorta. (b) Coronal reformation shows distal extent of intimomedial flap (arrow). (c) Sagittal reformation shows proximal intimomedial flap (arrow) in proximal descending thoracic aorta originating immediately distal to origin of left subclavian artery. True (T) and false (F) lumina are well opacified and show a communicating aortic dissection.

 

Figure 2
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  		Figure 2c: Contrast-enhanced multidetector CT images in 31-year-old man with Marfan syndrome and type B acute aortic dissection. (a) Transverse image obtained at aortic arch level shows intima (arrow) surrounding a communicating posterior false lumen in proximal descending aorta. (b) Coronal reformation shows distal extent of intimomedial flap (arrow). (c) Sagittal reformation shows proximal intimomedial flap (arrow) in proximal descending thoracic aorta originating immediately distal to origin of left subclavian artery. True (T) and false (F) lumina are well opacified and show a communicating aortic dissection.

 
Type A versus Type B Aortic Disorders
For the 67 cases positive for acute aortic disorder at multi–detector row CT, further analyses of the clinical presentations, medical histories, and examination results were performed. In these cases, the mean ages were 71.6 years ± 11.0 (standard deviation) for patients with Stanford-Daily type A disorders, 73.2 years ± 16.1 for patients with type B disorders, 75.7 years ± 9.8 for patients with new or enlarging aortic aneurysms, and 76.0 years ± 9.5 for patients with acute aortic ruptures. Of 17 cases of type A disorder, 13 (77%) involved male and four (24%) involved female patients. Of 32 cases of type B disorder, 10 (31%) involved male and 22 (69%) involved female patients. Of 44 cases of new or enlarging aortic aneurysm, 22 (50%) involved male and 22 (50%) involved female patients. Of 11 cases of acute aortic rupture, seven (64%) involved male and four (36%) involved female patients.

A history of aortic aneurysm and hypertension was frequent among the cases of acute aortic disorder. Ascending thoracic aortic aneurysms were present in three (18%) of 17 cases of type A disorder, one (3%) of 32 cases of type B disorder, four (9%) of 44 cases of new or enlarging aortic aneurysm, and two (18%) of 11 cases of acute aortic rupture. Descending thoracic aortic aneurysms were present in two (12%) cases of type A disorder, five (16%) cases of type B disorder, five (11%) cases of new or enlarging aortic aneurysm, and three (27%) cases of acute aortic rupture. Abdominal aortic aneurysms were present in five (29%) cases of type A disorder, nine (28%) cases of type B disorder, 10 (23%) cases of new or enlarging aortic aneurysm, and six (55%) cases of acute aortic rupture.

There was a history of ascending thoracic aortic aneurysm repair in six (19%) of 32 cases of type B disorder and in two (5%) of 44 cases of new or enlarging aortic aneurysms. Descending thoracic aortic aneurysm repair was present in one (3%) case of type B disorder. Abdominal aortic aneurysm repair was present in two (12%) of 17 cases of type A disorder, three (9%) cases of type B disorder, seven (16%) of 44 cases of new or enlarging aortic aneurysms, and one (9%) of 11 cases of acute aortic rupture. There was a history of type A aortic dissection repair in one (6%) case of type A disorder and in two (5%) cases of new or enlarging aortic aneurysm. There were no cases of acute aortic disorder associated with type B aortic dissection repair. There was a history of aortic valve repair in one (6%) case of type A disorder, in five (16%) cases of type B disorder, and in two (5%) cases of new or enlarging aortic aneurysm.

Marfan syndrome was present in three (9%) of 32 cases of type B disorder. No case of acute aortic disorder involved a history of Ehlers-Danlos syndrome. Hypertension was present in 12 (71%) of 17 cases of type A disorder, 21 (66%) cases of type B disorder, 30 (68%) of 44 cases of new or enlarging aortic aneurysm, and eight (73%) of 11 cases of acute aortic rupture. Diabetes mellitus was present in one (6%) case of type A disorder, two (6%) cases of type B disorder, four (9%) cases of new or enlarging aortic aneurysm, and one (9%) case of acute aortic rupture. No case of acute aortic dissection or acute aortic intramural hematoma involved a history of bicuspid or unicommissural aortic valves.

Presenting Symptoms of Acute Aortic Disorder
Symptoms of acute aortic disorder at presentation were variable. Chest pain was present in 11 (65%) of 17 cases of type A disorder, 11 (34%) of 32 cases of type B disorder, 22 (50%) of 44 cases of new or enlarging aortic aneurysm, and nine (82%) of 11 cases of acute aortic rupture. Back pain was present in four (24%) cases of type A disorder, 12 (38%) cases of type B disorder, 16 (36%) cases of new or enlarging aortic aneurysm, and one (9%) case of acute aortic rupture. Abdominal pain was present in three (18%) cases of type A disorder, 11 (34%) cases of type B disorder, 12 (27%) cases of new or enlarging aortic aneurysm, and four (36%) cases of acute aortic rupture. Syncope was present in one case each of type B disorder (3%), new or enlarging aortic aneurysm (2%), and acute aortic rupture (9%). Shortness of breath was present in three (18%) cases of type A disorder, one (3%) case of type B disorder, and two (5%) cases of new or enlarging aortic aneurysm. Miscellaneous symptoms were present in one (6%) case of type A disorder, three (9%) cases of type B disorder, and three (7%) cases of new or enlarging aortic aneurysm. The textbook symptom of tearing chest pain was not present in any of the acute aortic disorder cases.

Blood Pressure and Electrocardiographic Findings
Blood pressure at presentation tended to be normal to high systolic in the acute aortic disorder cases. In the 12 cases of type A disorder with available blood pressure data, no systolic blood pressure measurements were 80 mm Hg or lower, one (8%) measurement was in the 81–99 mm Hg range, seven (58%) measurements were 100–139 mm Hg, and four (33%) measurements were 140 mm Hg or higher. In the 23 cases of type B disorder with available data, there was one (4%) systolic blood pressure measurement in the 80 mm Hg or lower category, one (4%) measurement in the 81–99 mm Hg range, eight (35%) measurements of 100–139 mm Hg, and 13 (57%) measurements of 140 mm Hg or higher. In the 31 cases of new or enlarging aortic aneurysm with available data, there were no systolic blood pressure measurements of 80 mm Hg or lower, two (7%) measurements of 81–99 mm Hg, 14 (45%) measurements of 100–139 mm Hg, and 15 (48%) measurements of 140 mm Hg or higher. In the eight cases of acute aortic rupture with available data, there were no systolic blood pressure measurements of 80 mm Hg or lower, two (25%) measurements of 81–99 mm Hg, four (50%) measurements of 100–139 mm Hg, and two (25%) measurements of 140 mm Hg or higher. There were only two (of 44 [5%]) cases of unequal blood pressure in the arms, and both were positive for new or enlarging aortic aneurysm, with no acute aortic dissections or acute aortic intramural hematomas.

Electrocardiographic findings in the acute aortic disorder cases were variable. The two most frequent electrocardiographic findings were nonspecific ST-T wave interval changes and old Q waves. Nonspecific ST-T wave interval changes were present in 14 (82%) of 17 cases of type A disorder, 17 (53%) of 32 cases of type B disorder, 22 (50%) of 44 cases of new or enlarging aortic aneurysm, and eight (73%) of 11 cases of acute aortic rupture. Old Q waves were present in three (18%) cases of type A disorder, eight (25%) cases of type B disorder, eight (18%) cases of new or enlarging aortic aneurysm, and three (27%) cases of acute aortic rupture.

Radiographic Findings
There was no consistent pattern of radiographic findings in the acute aortic disorder cases. A widened mediastinum was present in eight (47%) of 17 cases of type A disorder, four (13%) of 32 cases of type B disorder, four (9%) of 44 cases of new or enlarging aortic aneurysm, and seven (64%) of 11 cases of acute aortic rupture. Cardiac silhouette enlargement was present in four (24%) cases of type A disorder, seven (22%) cases of type B disorder, six (14%) cases of new or enlarging aortic aneurysm, and three (27%) cases of acute aortic rupture. Thoracic aortic ectasia was present in three (18%) cases of type A disorder, six (19%) cases of type B disorder, 10 (23%) cases of new or enlarging aortic aneurysm, and three (27%) cases of acute aortic rupture. A tortuous aorta was present in three (18%) cases of type A disorder, five (16%) cases of type B disorder, 12 (27%) cases of new or enlarging aortic aneurysm, and one (9%) case of acute aortic rupture. Pleural effusion was present in six (35%) cases of type A disorder, four (13%) cases of type B disorder, 10 (23%) cases of new or enlarging aortic aneurysm, and six (55%) cases of acute aortic rupture.

Aortic calcification, displacement of the aorta, displacement of the mediastinum, and intimal calcification were rare findings. Absence of a widened mediastinum and absence of thoracic aortic ectasia were frequent negative findings. A widened mediastinum was absent in seven (41%) of 17 cases of type A disorder, 16 (50%) of 32 cases of type B disorder, 30 (68%) of 44 cases of new or enlarging aortic aneurysm, and three (27%) of 11 cases of acute aortic rupture. Thoracic aortic ectasia was absent in 12 (71%) cases of type A disorder, 14 (44%) cases of type B disorder, 24 (55%) cases of new or enlarging aortic aneurysm, and seven (64%) cases of acute aortic rupture.

Treatments and Outcomes
Emergent surgical repair of the aorta was most frequent in the cases of type A disorder and acute aortic rupture, as expected. Surgical repair was performed in 11 (65%) of 17 cases of type A disorder, six (19%) of 32 cases of type B disorder, 10 (23%) of 44 cases of new or enlarging aortic aneurysm, and 10 (91%) of 11 cases of acute aortic rupture.

The most frequent outcome in the cases of acute aortic disorder was stable discharge to either home or a rehabilitation facility. The patient was discharged in stable condition in 14 (82%) of 17 cases of type A disorder, 26 (81%) of 32 cases of type B disorder, 41 (93%) of 44 cases of new or enlarging aortic aneurysm, and eight (73%) of 11 cases of acute aortic rupture. The patient died of an acute aortic disorder during hospitalization in two (12%) cases of type A disorder, two (6%) cases of type B disorder, no cases of new or enlarging aortic aneurysm, and three (27%) cases of acute aortic rupture. The overall mortality rate for the 67 cases of acute aortic disorder was 6% (four cases).

Cost Calculations
The actual hospital cost of an aortic dissection multi–detector row CT examination was $314.18. This cost represents the true cost incurred by the hospital—not the billed charges. On the basis of these data, the total actual hospital cost of performing multi–detector row CT in the 373 cases of suspected aortic dissection and other aortic disorders was $117 189 compared with the actual hospital cost of $709 670 that would have incurred if aortography had been performed (Table 5). According to these data, using multi–detector row CT to evaluate 373 cases of suspected acute aortic disorder yields a cost savings of $592 481.


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  		Table 5. Hospital Costs Associated with Diagnosis of Acute Aortic Disorder

 
The total cost of identifying a case positive for acute aortic disorder with multi–detector row CT was $1749 (Table 5). The total cost of identifying a case positive for acute aortic disorder with aortography would have been $10 592. According to these data, using multi–detector row CT to identify patients with findings positive for acute aortic disorder yielded a cost savings of $8843.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
Aortic dissections are classified by using three systems. In 1964, DeBakey et al (20,21) classified aortic dissection into three types on the basis of the anatomic location of the abnormality: Type 1 aortic dissection involves both the ascending and the descending aorta. Type 2 is confined to the ascending aorta and extends to the origin of the brachiocephalic artery. Type 3 is confined to the descending aorta, beginning at the origin of the left subclavian artery, and proceeds distally. Currently, however, aortic dissections, aortic intramural hematomas, and penetrating aortic ulcers are more commonly classified into two types—A and B—by using the Stanford-Daily system developed at Stanford University in 1970 (13,22,23). Type A involves the region of the ascending aorta and beyond. Type B is confined to the descending aorta, beginning at the origin of the left subclavian artery, and proceeds distally (equivalent to DeBakey type 3). The Stanford-Daily classification system serves as the basis for management—namely, surgery for type A and nonsurgical therapy for type B aortic dissections, aortic intramural hematomas, and penetrating aortic ulcers (1,8,22,24,25).

With use of a variant classification system proposed by Svensson et al (19) in 1999, the variants of aortic dissection are described in relation to the form of injury to the aortic wall rather than in relation to the site of the intimal tear or the extent of the aorta involved. The variant classification system represents an attempt to describe the pathologic origins of acute aortic disorders at presentation, with an emphasis on the difficult-to-diagnose—but no less clinically important—class 3 disorders. The variant system includes five classes of disorders: Class 1 includes classic aortic dissections, with separation of the intima from the media and the creation of an intimomedial flap and dual lumina. Class 2 includes aortic intramural hematomas, with separation of the intima from the media without an intraluminal tear or flap. Class 3 includes subtle aortic intimal tears with an eccentric bulge and without hematoma. Class 4 includes atherosclerotic penetrating aortic ulcers that usually penetrate to the adventitia with localized hematoma. Class 5 includes iatrogenic or traumatic aortic dissections.

Aortic dissections and penetrating aortic ulcers generally have been diagnosed by using conventional aortography (5,9). Aortography reportedly has 88% sensitivity, 94% specificity, a 96% positive predictive value, and an 84% negative predictive value for detection of aortic dissection and is 83% sensitive for detection of penetrating aortic ulcers. However, aortography may not be able to depict aortic intramural hematomas or many of the other potential alternative findings (22,26). Aortography is also expensive, time-consuming, and associated with higher morbidity compared with other imaging modalities (26).

The diagnosis of aortic dissection is now far less complicated and less labor-intensive. For primary imaging in cases of suspected acute aortic disorder, aortography has been replaced by CT, MR imaging, or US. These imaging modalities have benefits and limitations, however. CT is readily available in most emergency departments. Compared with using the older-model single–detector row helical CT scanners, using multi–detector row CT scanners has led to dramatically increased speed and spatial resolution in aortic imaging. The (to our knowledge) most recent published data on CT show it to have 100% sensitivity and specificity for detection of aortic dissection and aortic intramural hematoma (25,27–29), similar to the respective values of 99% and 100% for multi–detector row CT achieved in this investigation. Other published data show CT to have 65% sensitivity for detection of penetrating aortic ulcers (22). These data demonstrate that aortic dissection CT protocols are more than adequately reliable for the detection of true aortic dissection and other aortic disorders.

US techniques—TEE more than transthoracic echocardiography—have been investigated extensively for the diagnosis of aortic dissection, aortic intramural hematoma, and penetrating aortic ulcer. Although transthoracic echocardiography can be performed at the bedside, it has low sensitivity for detection of type A (60%–80%) and type B (50%) aortic dissections and 90% specificity for detection of both types (30,31). TEE also is a portable procedure, but it requires esophageal intubation to yield a sensitivity of 97%–99% and, with the addition of M-mode imaging, a specificity of 99%–100% in the detection of aortic dissection (32–34). TEE has a sensitivity of 90%–100% and a specificity of 91%–100% for detection of aortic intramural hematomas and a sensitivity of 61%–83% for detection of penetrating aortic ulcers (22,33,35–37). TEE, when performed in awake patients, however, has been shown to lead to increased systolic blood pressure and consequently an increased risk for acute aortic rupture in 77% of cases (38). It is important to note, however, that not all cardiac and vascular surgeons feel confident in performing surgery on the basis of TEE findings alone (39).

MR imaging is currently considered an accurate noninvasive technique for examining patients suspected of having aortic dissection, aortic intramural hematoma, or penetrating aortic ulcer. Although MR imaging has high sensitivity (95%–100%) and high specificity (94%–98%) for detection of aortic dissection, a sensitivity of 100% for detection of aortic intramural hematoma, and a sensitivity of 86% for detection of penetrating aortic ulcer, it has serious limitations (22,23,29,30,40,41). Most important, the MR examination requires approximately 30 minutes, compared with the 30 seconds required for multi–detector row CT, for image acquisition in a rather limited-access environment and thus may create a high-risk situation in patients suspected of having aortic dissection and other aortic disorders, who may be unstable. In addition, MR imaging is more expensive than CT. Also, MR imaging is not readily available in many emergency departments in the United States; this factor further limits its potential role in the diagnosis of aortic dissection and other aortic disorders in the acute setting.

Currently, in the common diagnostic work-up of patients suspected of having aortic dissection or other aortic disorders, as is proper, the pretest probability (of having aortic dissection and/or other aortic disorder) and the patient's stability and renal function are taken into account before the imaging modality (or modalities) is chosen. Aortography is rarely a part of the primary diagnostic work-up of aortic dissection and other aortic disorders. The current role of aortography is that of a potential adjunctive examination for use in the event that the primary imaging examination yields inconclusive results and more detailed information is necessary (42). However, other noninvasive imaging modalities also may serve in this role (31,43).

CT—preferably multi–detector row CT—is now the primary imaging modality commonly used when aortic dissection and/or other aortic disorders are suspected. Exceptions to this standard arise when patient instability, poor renal function, and/or allergy to iodinated contrast material prohibits the use of CT. When the patient in the emergency setting is too unstable to withstand being inside the CT scanner for even a brief period or when the CT scanner itself is unavailable, TEE is often the alternative imaging examination (42). In this scenario, the time spent performing imaging is minimized because the patient is imaged in a portable manner in as little as 5 minutes while in a state of general anesthesia in the emergency department or operating room. However, TEE requires a skilled operator to achieve proper safety levels and high diagnostic value (43).

Transthoracic echocardiography, an alternative choice for bedside imaging, has too low a sensitivity for detection of aortic dissection and other aortic disorders and thus has poor prognostic value and is more suitable for the diagnosis of potential cardiac complications (43). However, MR angiography offers an alternative approach for patients in emergency settings who are unable to tolerate intravenous contrast material owing to impaired renal function or iodinated contrast material allergy (42).

Acute aortic dissection and other acute aortic disorders are life-threatening diseases that require timely and accurate diagnoses in patients with emergent conditions. The described aortic dissection CT examination performed in the emergency setting has proved to be quick, reliable, and appropriate for use in patients suspected of having acute aortic disorders. Other options for detecting these disorders exist and include TEE, MR angiography, and aortography; however, each of these alternative modalities has a limitation not associated with CT.

Aortography, the previous reference standard for the diagnosis of aortic dissection and other aortic disorders, is more invasive, expensive, time-consuming, and labor-intensive than CT. Although aortography has reliable sensitivity and specificity for detection of aortic disorders, with the exception of aortic intramural hematoma, it cannot depict many of the other potential alternative findings. In this clinical series, aortography was rarely used.

With the advent of the described aortic dissection multi–detector row CT protocol, physicians have a highly sensitive and specific imaging modality that enables them to quickly diagnose aortic dissection and other aortic disorders in patients in the emergency setting. In the current investigation, 18% of 373 emergent cases of suspected aortic dissection and other aortic disorders were found to be positive for acute aortic disorder with multi–detector row CT. This positivity rate provides evidence that the screening of patients in the emergency setting prior to multi–detector row CT is adequate. Furthermore, the imaging cost savings per positive acute aortic disorder diagnosis is $8843 when CT is compared with aortography. Overall, 30% of emergency cases were interpreted to be positive for acute aortic disorder, an alternative finding, or both with multi–detector row CT. Thus, multi–detector row CT should be considered the imaging modality of choice for patients who are clinically stable enough to undergo the examination.

The three primary limitations of our investigation included the limited application of the data to other populations that may have different incidences of aortic dissection, the lack of a clear definition of what may constitute increased use of the aortic dissection multi–detector row CT protocol, and the retrospective design. In the setting of life-threatening conditions such as acute aortic disorder, the positivity rate of 18%, when compared with the accepted positivity rate of 1% for detection of traumatic aortic injury with CT, suggests that the described aortic dissection multi–detector row CT protocol is not overused (44,45). We found no reliable data derived from the presenting symptoms and signs, radiographic findings, or electrocardiographic findings in the cohort of patients with positive findings to aid in the further screening of patients suspected of having acute aortic dissection or other acute aortic disorders before they undergo multi–detector row CT. Therefore, the physician must keep a high clinical index of suspicion for aortic dissection and other aortic disorders in patients in emergency settings because multi–detector row CT can enable a rapid and accurate diagnosis of any acute aortic disorder.


   FOOTNOTES
 

Abbreviations: TEE = transesophageal echocardiography

Authors stated no financial relationship to disclose.

Author contributions: Guarantor of integrity of entire study, R.G.H.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, R.G.H.; clinical studies, R.G.H.; statistical analysis, R.G.H.; and manuscript editing, R.G.H., J.T.R., R.A.N.


   References
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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

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