Correspondence
The Diagnosis of Thoracic Aortic Dissection by Noninvasive Imaging Procedures
N Engl J Med 1993; 328:1637-1638June 3, 1993
- Article
To the Editor:
The paper by Nienaber et al.1 and the review article by Cigarroa et al.2 (Jan. 7 issue) on diagnosing thoracic aortic dissection demonstrate the problems of evaluating rapidly developing imaging techniques. Progress in computed tomographic (CT) scanning and magnetic resonance imaging (MRI) is so rapid that the results of studies carried out over a five-year period1 or reported in the late 1970s and 1980s do not reflect the best current standards of clinical imaging.
The CT technique used by Nienaber et al.1 was satisfactory for the older scanner (Somatom II) used in their study but not for the newer scanner (Somatom Plus) used later in the study. Their CT technique is outdated for two reasons. The use of 2-cm distances between tomographic scans leaves gaps and may lead one to miss subtle intimal flaps. Scanning times of 5 to 15 minutes are too long and prevent optimal contrast enhancement, even with large doses of contrast material, leading to lower test sensitivity. Spiral CT and ultrafast CT allow rapid imaging of the thoracic aorta (typically within 32 seconds) after a single bolus injection of contrast medium3. This allows imaging at peak contrast enhancement, so that subtle flaps and dissection entry sites can be recognized. With faster CT imaging, it is possible to see the relations of flaps to the origins of the coronary arteries. The study can be conducted in less than five minutes, providing a definitive, reproducible screening examination suitable for critically ill patients.
Even an older CT scanner used appropriately with an understanding of its limitations is of value and can be used during resuscitation and, if necessary, concurrently with transthoracic echocardiography. Transthoracic echocardiography and conventional CT have complementary strengths and together can rapidly provide accurate and comprehensive diagnosis of aortic dissection as well as information on ventricular function, hemopericardium, and aortic regurgitation4.
CT has further advantages in detecting coronary calcification. Most patients with acute dissection do not need coronary angiography, but there is often concern about coronary artery disease, especially in the elderly. CT, especially fast CT, is an accurate method of detecting coronary calcification, providing a guide to the likelihood of clinically important coronary disease.
MRI is also changing rapidly with the development of fast angiographic techniques for conventional MRI scanners. Breath-holding and cineangiographic techniques allow comprehensive evaluation of the entire thoracic aorta, its major branches, the aortic valve, and ventricular function in a shorter time than that suggested in previous reports5.
5 ReferencesGeorge Hartnell, F.R.C.R.
Philip Costello, M.D.
Deaconess Hospital, Boston, MA 022151
Nienaber CA ,von Kodolitsch Y ,Nicolas V , et al. The diagnosis of thoracic aortic dissection by noninvasive imaging procedures. N Engl J Med 1993;328:1-9
Full Text | Web of Science | Medline2
Cigarroa JE ,Isselbacher EM ,DeSanctis RW ,Eagle KA . Diagnostic imaging in the evaluation of suspected aortic dissection -- old standards and new directions. N Engl J Med 1993;328:35-43
Full Text | Web of Science | Medline3
Costello P ,Ecker CP ,Tello R ,Hartnell GG . Assessment of the thoracic aorta by spiral CT. AJR Am J Roentgenol 1992;158:1127-1130
Web of Science | Medline4
Tottle AJ ,Wilde RPH ,Hartnell GG ,Wisheart JD . Diagnosis of acute thoracic aortic dissection using combined echocardiography and computed tomography. Clin Radiol 1992;45:104-108
CrossRef | Web of Science | Medline5
Hartnell GG ,Finn JP ,Zenni M ,Dupuy D ,Longmaid HE . Magnetic resonance angiography in assessment of the thoracic aorta: comparison with standard MR and non-MR techniques. Radiology 1992;185:227-227
Web of Science
To the Editor:
Although we generally agree with Nienaber et al. that MRI and transesophageal echocardiography (TEE) are both excellent techniques, the relatively low specificity of TEE reported in this study differs from our own experience (in 94 patients with suspected aortic dissections, the specificity was 100 percent) and that of others. For example, Erbel et al.1 reported only two false positive results on TEE in 164 patients with suspected aortic dissection (specificity, 98 percent). Ballal et al. cited data on 61 patients with suspected aortic dissection and found no false positive results (specificity, 100 percent)2. How do Nienaber et al. explain the relatively low specificity of TEE in their study?
2 ReferencesSteven A. Goldstein, M.D.
Joseph Lindsay, Jr., M.D.
Ramachandran Vasan, M.D.
Washington Hospital Center, Washington, DC 200101
Erbel R ,Engberding R ,Daniel W ,Roelandt J ,Visser C ,Rennollet H . Echocardiography in diagnosis of aortic dissection. Lancet 1989;1:457-461
CrossRef | Web of Science | Medline2
Ballal RS ,Nanda NC ,Gatewood R , et al. Usefulness of transesophageal echocardiography in assessment of aortic dissection. Circulation 1991;84:1903-1914
Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: Goldstein et al. address the intriguing issue of the relatively low specificity of TEE reported in our series,1 as compared with their own experience and the literature2,3. We concede that a learning-curve phenomenon and improving techniques over the past five years may have affected the specificity of TEE in our study. More importantly, however, the assessment of specificity in the literature deserves a closer look. Our data were based on blinded, prospective analysis of images; in contrast, Ballal et al. derived their specificity of 100 percent from data on 27 patients known to have no dissection, 8 of whom were even studied by biplane TEE. Moreover, with one exception, none of their patients had any clinical symptoms of aortic dissection2. The studies by both Ballal et al.2 and Erbel et al.3 were not designed to assess the specificity of TEE in a prospective fashion; data were obtained either on selected patients with known diagnoses or by an unblinded approach. Thus, the lower specificity of TEE in our study is not surprising. However, specificity can be improved by the use of an additional criterion, such as a Doppler flow signal in both lumens, to separate “definite” from “probable” dissections, as suggested by Cigarroa et al.4.; according to this criterion, none of our false positive findings would have been categorized as a definite dissection5. For probable dissections, a second independent noninvasive procedure may then be justified.
We fully support Hartnell and Costello's emphasis on the ongoing evolution of CT scanning, especially with the advent of spiral CT. According to their pictorial essay,6 even subtle abnormalities can be identified with higher precision. Unfortunately, however, we did not have the opportunity to use spiral CT until 1992, in the closing phase of our study,5 but we are currently analyzing the diagnostic performance of spiral CT in a controlled fashion. Ultrafast CT, at present technically demanding and available at only a few institutions in the United States and Europe, cannot realistically be considered a routine clinical tool. In addition, the clinical importance of coronary calcifications on ultrafast CT as an indicator of the severity of coronary stenosis is far from proved, and the effect on the management of aortic dissection is unknown. Finally, Hartnell and Costello suggest the combined use of conventional CT and transthoracic echocardiography as an alternative to gain diagnostic strength; this concept appears similar to that behind the combined use of spin-echo MRI and Doppler echocardiography, but without the option of the free choice of imaging planes and with the need for contrast medium5. At present, the image quality provided by MRI angiography of the ascending aorta and arch vessels is still poor owing to image degradation from pulsation; we agree, however, that fast MRI angiography may offer great potential in the future, further supporting our idea of the use of a single noninvasive diagnostic test in the investigation of suspected dissection of the thoracic aorta.
6 ReferencesChristoph A. Nienaber, M.D.
Universitats-Krankenhaus Eppendorf, 2000 Hamburg 20, GermanyRolf P. Spielmann, M.D., Ph.D.
Christian-Albrechts-Universitat, 2300 Kiel, Germany1
Nienaber CA ,Spielmann RP ,von Kodolitsch Y , et al. Diagnosis of thoracic aortic dissection: magnetic resonance imaging versus transesophageal echocardiography. Circulation 1992;85:434-447
Web of Science | Medline2
Ballal RS ,Nanda NC ,Gatewood R , et al. Usefulness of transesophageal echocardiography in assessment of aortic dissection. Circulation 1991;84:1903-1914
Web of Science | Medline3
Erbel R ,Engberding R ,Daniel W ,Roelandt J ,Visser C ,Rennollet H . Echocardiography in diagnosis of aortic dissection. Lancet 1989;1:457-461
CrossRef | Web of Science | Medline4
Cigarroa JE ,Isselbacher EM ,DeSanctis RW ,Eagle KA . Diagnostic imaging in the evaluation of suspected aortic dissection -- old standards and new directions. N Engl J Med 1993;328:35-43
Full Text | Web of Science | Medline5
Nienaber CA ,von Kodolitsch Y ,Nicolas V , et al. The diagnosis of thoracic aortic dissection by noninvasive imaging procedures. N Engl J Med 1993;328:1-9
Full Text | Web of Science | Medline6
Costello P ,Ecker CP ,Tello R ,Hartnell GG . Assessment of the thoracic aorta by spiral CT. AJR Am J Roentgenol 1992;158:1127-1130
Web of Science | Medline
Author/Editor Response
Although spiral CT and ultrafast CT scanners with rapid imaging enhance spatial resolution relative to older scanners and are likely to be more accurate than newer scanners, one cannot claim that they provide a “definitive, reproducible screening examination” until a large prospective study of patients with suspected aortic dissection has been performed. Moreover, these newer CT scanners are still unable to provide data on entry site, reentry site, branch-vessel involvement, aortic insufficiency, or coronary-artery involvement -- information that many surgeons request before surgery. Therefore, even though CT may be an accurate method of screening for aortic dissection, an additional diagnostic study will often be required to define anatomy further in surgical candidates. Although we agree with Hartnell and Costello that transthoracic echocardiography provides information complementary to that obtained with CT in many cases, there are no data confirming that this combined approach will increase the sensitivity over that of CT alone.
Given the current data in the literature, as reviewed by Cigarroa et al., we maintain that MRI and TEE remain the diagnostic studies of choice in suspected cases of aortic dissection. Therefore, any other approach, such as spiral or ultrafast CT, should be compared prospectively with MRI and TEE.
Joaquin E. Cigarroa, M.D.
Kim A. Eagle, M.D.
Eric M. Isselbacher, M.D.
Massachusetts General Hospital, Boston, MA 02114- Citing Articles (4)
Citing Articles
1
Cyrus J. Parsa, G. Chad Hughes. (2009) Surgical Options to Contend with Thoracic Aortic Pathology. Seminars in Roentgenology 44:1, 29-51
CrossRef2
Marvin D. Atkins, James H. Black, Richard P. Cambria. (2006) Aortic dissection: Perspectives in the era of stent-graft repair. Journal of Vascular Surgery 43:2, A30-A43
CrossRef3
Fusako Sato, Tetsuya Kitamura, Mariko Kongo, Tsutomu Okinaka, Kazuko Onishi, Masaaki Ito, Naoki Isaka, Takeshi Nakano. (2005) Newly Diagnosed Acute Aortic Dissection. International Heart Journal 46:6, 1083-1098
CrossRef4
(1995) Transesophageal Echocardiography. New England Journal of Medicine 333:17, 1153-1154
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