Current issues of ACP Journal Club are published in Annals of Internal Medicine


Diagnosis

Magnetic resonance imaging: computed tomography, and transesophageal color-flow Doppler echocardiography were sensitive and specific for diagnosing thoracic aortic dissection

ACP J Club. 1993 May-June;118:87. doi:10.7326/ACPJC-1993-118-3-087


Source Citation

Nienaber CA, von Kodolitsch Y, Nicolas V, et al. The diagnosis of thoracic aortic dissection by noninvasive imaging procedures. N Engl J Med. 1993 Jan 7;328:1-9.


Abstract

Objective

To determine the accuracy of magnetic resonance imaging (MRI), transthoracic and transesophageal color-flow Doppler echocardiography (TTE and TEE), and contrast-enhanced x-ray computed tomography (CT) in diagnosing thoracic aorta dissection.

Design

Blinded comparison of MRI, TTE, TEE, and CT results with intraoperative findings, autopsy findings, and the results of contrast angiography.

Setting

2 medical centers in Germany.

Patients

110 consecutive patients (mean age 54 y, 70 men) referred for suspected dissection of the thoracic aorta. Patients with chronic dissections were excluded.

Description of tests and diagnostic standard

TTE was done in all patients. In 70 patients TEE with optional color-flow Doppler mapping was done. With TTE and TEE a diagnosis of dissection was confirmed by the presence of 2 vascular lumens separated by an intimal flap. Third-generation CT scanners were used in 79 patients. An abrupt transition to a larger lumen at the origin of a side branch, the visualization of a dissecting membrane, or the presence of a poorly opacified crescent portion of the aorta was considered diagnostic. 105 patients had MRI with a whole-body magnet. An aortic-wall dissection was diagnosed if there were 2 separated lumens. The diagnostic standard was conventional or digital contrast angiography (64 patients, an intimal flap or a double lumen was considered diagnostic), intraoperative findings (62 patients), and autopsy findings (7 patients).

Main outcome measures

Sensitivity and specificity of each imaging technique.

Main results

There were 24 acute and 8 subacute type A aortic dissections and 11 acute and 19 subacute type B dissections. The sensitivities and specifities of MRI, TEE, and CT are presented in the Table. For TTE, the sensitivity was 59.3% and the specificity was 83.0%. MRI and CT were the most specific methods for excluding a dissection involving the ascending aorta. MRI and TEE were highly reliable in identifying an entry site and aortic regurgitation. Thrombus formation was best detected by CT, TEE, and MRI.

Conclusions

Magnetic resonance imaging and transesophageal color-flow Doppler echocardiography were highly sensitive and specific in diagnosing thoracic aortic dissection. The imaging techniques of contrast-enhanced computed tomography and transthoracic color-flow Doppler echocardiography were not as sensitive.

Source of funding: Not stated.

For article reprint: Dr. C.A. Nienaber, Department of Internal Medicine II, Division of Cardiology, Universitäts-Krankenhaus Eppendorf, Martinistrasse 52, D-2000 Hamburg 20, Germany. FAX 4940-4717-2438.


Table. Estimated test characteristics for detecting thoracic aortic dissection*

Test Sensitivity (95% CI) Specificity (CI) +LR -LR
Magnetic resonance imaging 98.3% (90.9 to 100.0) 97.8% (88.5 to 100.0) 45.22 0.02
Transesophageal Doppler echocardiography 97.7% (88.0 to 100.0) 76.9% (56.4 to 91.0) 4.23 0.03
Computed tomography 93.8% (82.8 to 98.7) 87.1% (70.2 to 96.4) 7.27 0.07

*+LR = likelihood ratio for the presense of the disease if the test is positive; -LR = likelihood ratio if the test is negative. Both calculated from data in article.


Commentary

The article by Nienaber and colleagues expands on the previous work done by the group comparing MRI with TEE in the diagnoses of aortic dissection (1). Their findings indicate that the greatest sensitivity and specificity are with MRI. TEE, however, still comes out as an excellent diagnostic method. The TEE study was done with a single-plane scope. With the increasing availability of bi- and omniplane studies, I expect that these numbers will become more similar. Omniplane TEE is superior for visualization of the aorta and will increase sensitivity and specificity of the procedure.

In the same issue of the New England Journal of Medicine, Cigarroa and colleagues (2) review the technologies currently available—MRI, TEE, CT, and aortography. The conclusions are similar to my own regarding the challenge facing the clinician. These procedures are complementary to a good history and physical examination. The best diagnostic tool for the patient presenting with chest pain, in whom the diagnosis of aortic dissection is suspect, is the one that gives the correct answer most often and most efficiently in your particular institution. Observer training is critical whether one is looking at MRI or TEE. Time is probably on the side of TEE because frequently a transthoracic echo is readily available, and a TEE is an obvious next step. MRI is also very accurate, but the initial technology is far more costly; in addition, the procedure takes longer and is more difficult with unstable patients. For the community hospital, TEE or CT is more likely to be available and can be used effectively as long as the observer is confident of his or her skills and understanding of what is abnormal. My own experience suggests that the changes are often subtle, especially with chronic dissection.

Dennis DeSilvey, MD
University of VirginiaCharlottesville, Virginia, USA


References

1. Nienaber CA, Spielmann RP, von Kodolitsch Y, et al. Diagnosis of thoracic aortic dissection. Magnetic resonance imaging versus transesophageal echocardiography. Circulation. 1992;85:434-47.

2. 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.