Tortuosity of the Descending Thoracic Aorta Simulating Dissection on Transesophageal Echocardiography

Transcription

1 CASE REPORTS Tortuosity of the Descending Thoracic Aorta Simulating Dissection on Transesophageal Echocardiography Edward S. Katz, MD, Robert M. Applebaum, MD, James P. Earls, MD, Glenn Krinsky, MD, Jeffrey Weinreb, MD, and Itzhak Kronzon, MD, New York, New York In an 80-year-old patient with syncope, a markedly tortuous descending thoracic aorta produced images on transesophageal echocardiography which were suggestive of an intimal flap caused by dissection. A magnetic resonance aortogram dearly showed that the transesophageal echocardiogram was a false positive. In addition, multiplanar reconstructed images of the magnetic resonance aortogram through the tortuous de- scending thoracic aorta could reproduce images similar to that seen by transesophageal echocardiography. Because transesophageal echocardiography has become a popular imaging modality for the detection of aortic dissection, it is essential for echocardiographers to be aware of possible pitfalls which may create false positive findings. (J Am Soc Echocardiogr 1997;10:83-7.) Clinical suspicion of thoracic aortic dissection requires accurate and immediate diagnostic evaluation. Recently, magnetic resonance imaging (MRI) and transesophageal echocardiography (TEE) have emerged as the preferred imaging modalities.l-7 In this report, we present a case in which an unusually tortuous descending thoracic aorta gave rise to images on multiplanar TEE that were highly suggestive of an intimal flap. Subsequently, MRI demonstrated the false positivity of this TEE finding and clearly delineated how a markedly tortuous aorta can be a diagnostic pitfall in the diagnosis of an intimal flap on TEE. CASE REPORT An 80-year-old woman presented to our institution after a syncopal episode during which she sustained a right tibial fracture. The patient reported a sudden loss of consciousness while walking to her bathroom. She described no prior dizziness, palpitation, chest pain, shortness of breath, headache, visual disturbances, or aura. She awoke fully oriented with no loss of continence or tongue biting. The patient denied any history of myocardial infarction, angina, paroxysmal nocturnal dyspnea, orthopnea, syncope, dizziness, or seizure disorder. Her medical history was significant only for a 10-year history of hypertension, for which she was treated with enalapril. From the Department of Medicine, Cardiology Section, and Department of Radiology, New York University School of Medicine. Reprint requests: Edward S. Katz, MD, New York University School of Medicine, 550 First Ave., New York, NY Copyright by the American Society of Echocardiography /97 $ /4/76028 On physical examination, the patient appeared to be well and in no acute distress. Her blood pressure was 140/90 mm Hg in both upper extremities and she had a pulse of 80 beats/minute. Her neck examination revealed normal carotid upstrokes with no bruits, thyromegaly, or jugular venous distension. On cardiac examination, the point of maximal impulse was not displaced. The heart sounds were normal, and a 3/6 systolic murmur as well as a 2/4 diastolic murmur were best audible at the left sternal border. The lungs were clear to auscultation and percussion. Her extremities were without cyanosis, clubbing, or edema. The pulses were 2 + to the dorsalis pedis and equal bilaterally. Laboratory data included normal values for the serum chemistry analyses, a hematocrit value of 38%, and normal levels ofcreatine phosphokinase isoenzymes. An electrocardiogram revealed normal sinus rhythm, right bundle branch block, and a left anterior hemiblock. A chest radiograph showed a widened mediastinum, normal heart size, and clear lung fields. A His bundle electrogram revealed normal atrioventricular nodal conduction and a normal infranodal HIS-ventricular (H-V) time. Programmed ventricular stimulation did not induce ventricular tachycardia. A transthoracic echocardiogram revealed a dilated aortic root and ascending aorta (5.0 cm in diameter), moderate aortic insufficiency, and normal left ventricular systolic function. Because of these findings, a widened mediastinum on the chest radiograph, and the syncopal episode, TEE was performed to exclude an aortic dissection. This TEE study confirmed a dilated aortic root and ascending aorta (5.0 cm) with no evidence of an intimal flap in this area. Examination of the descending thoracic aorta revealed a markedly tortuous aorta. At one level 8 cm distal to the aortic arch, the descending thoracic aorta appeared elongated on the transverse imaging plane (instead of the usual circular appearance) because of the horizontal orientation of the tortuous aorta at this level. A linear echodensity suggestive of an intimal flap was seen tra- 83

2 84 Katz et al. January-February 1997 Figure 1 Multiplanar transesophageal echocardiogram of the descending thoracic aorta 8 cm distal to the aortic arch. A, Transverse imaging plane. A linear echodensity can be seen traversing the lumen (small arrows). The aorta appears to be elongated rather than having the typical circular appearance, suggesting tortuosity. B, Sagittal or vertical imaging plane. Again, on this plane a thickened linear echodensity can be seen traversing the aorta (small arroms). versing the aortic lumen only at this level (Figure 1A), which also was visualized by multiple imaging (Figure 1B). No Doppler flow disturbance was noted. To further define this finding, MRI was performed (Figures 2 and 3). The MRI study demonstrated marked curvature of the descending thoracic aorta but no evidence of dissection. Axial and sagittal reconstructions of the magnetic resonance aortogram were able to reproduce images of the thoracic aorta corresponding to those obtained by multiplanar TEE. The magnetic resonance images clearly demonstrated that the redundant aortic wall, caused by the aorta folding back on itself, had produced images resembling an intimal flap on TEE. DISCUSSION Aortic dissection may be a life-threatening condition that requires a prompt and accurate diagnosis so that therapy can be initiated to optimize chances of a favorable clinical outcome. Contrast aortography was for many years the only accurate method of diagnosing thoracic aortic aneurysms and offered the additional advantages of visualization of branch vessels, proximal coronary arteries, and aortic insufficiency. The procedure, however, carried with it the significant risks of procedural complications

3 Volume 10 Number I Katz et al. 85 Figure 2 Magnetic resonance aortogram. A, Maximal intensity projection (MIP) of a threedimensional fast imaging with steady-state precession (FISP) gadolinium enhanced magnetic resonance aortogram demonstrates marked curvature of the descending thoracic aorta. The angled axial imaging plane represented by the arrow is reconstructed in Figure 2B. B, Multiplanar reconstructed (MPR) image through the thoracic aorta. The plane corresponds to the approximate horizontal plane obtained on the transesophageal echocardiogram. This image demonstrates the redundant aortic wall (small arrows) that resembles an intimal flap on the transesophageal echocardiogram (see Figure 1A). ALl, Ascending aorta; DA, descending thoracic aorta. and administration of an intravenous contrast agent, and had diagnostic shortcomings.1 Contrast enhanced computed tomography scanning in some studies had been found to have a somewhat lower diagnostic sensitivity for thoracic aortic dissections. It also carried with it the inherent risk of administering an intravenous contrast agent, and was unable to reliably identify aortic insufficiency, involvement of branch vessels, or to delineate the coronary arteries. ~,2 Magnetic resonance imaging has been shown to have the highest diagnostic sensitivity. In two prospective studies by Nienaber et al. 2,3 of patients with clinically suspected thoracic aortic dissection, the diagnostic sensitivity and specificity of MRI both were 98% to 100%. Magnetic resonance imaging, however, also has its shortcomings. The test may be time consuming and not readily available. The test also cannot be performed on patients with pacemakers, vascular clips, or claustrophobic tendencies. In addition, many patients with aortic dissections are hemodynamically unstable, making intensive monitoring impractical while the patient is lying on an MRI table for a prolonged period. For these reasons, TEE has emerged as a popular technique for diagnosing suspected thoracic aortic dissections. Its high diagnostic sensitivity, portability, availability, and cost effectiveness have made it a practical and effective modality. In addition, TEE is able to assess other cardiac variables (such as ventricular and valvular function, pericardial effusion, and proximal coronary arteries), and identify the entry sites of dissections 6-8. Although the diagnostic sensitivity of TEE approaches that of MRI, the lower specificity (68% and 77%, as reported in the two studies by Nienaber et al.)

4 86 Katz et al. January-February 1997 Figure 3 Sagittal MPR of the three-dimensional FISP aortogram demonstrates a tortuous, redundant thoracic aorta. This imaging plane was obtained in the sagittal vertical transesophageal echocardiogram image (see Figure 1B). AA, Ascending aorta; DA, descending thoracic aorta. has raised concerns about false positive test results. 2,3 Almost all of the false positive results in these studies were confined to misinterpretations of intimal flaps in the ascending aorta caused by artifactual reverberations and calcified atheromas that produce echo images resembling an intimal flap. It should be noted, however, that these studies were performed with monoplanar TEE. Biplanar and multiplanar TEE techniques are able to examine a larger extent of the ascending aorta. In addition, misinterpretation of these artifacts would be minimized because the intimal flap would have to be verified in more than one plane. In the current report, we describe an unusual case in which a tortuous aorta curving back on itself produced an image resembling an intimal flap on TEE. To our knowledge, this cause of a false positive TEE examination result has not been previously described. Several clues, however, are present on the TEE examination that should raise suspicion about the true nature of the image. First, the 'intimal flap' was unusually thickened. Second, the flap was seen in only one localized segment of the aorta, an area of the descending thoracic aorta that appeared elongated rather than circular on a horizontal imaging plane, suggestive of a markedly tortuous aorta. Third, no frank flow disturbance (that is, flow stasis or thrombus in a false lumen) or communication sites were identified. For institutions regarding TEE as the primary diagnostic test for aortic dissection, it is essential for experienced echocardiographers to be familiar with all possible reasons for false positive examination results. In cases where these questions exist, TEE and MRI may be indicated as complementary examinations. REFERENCES 1. Cigarroa JE, Isselbacher EM, DeSanctis RW, Eagle KA. Diagnostic imaging in the evaluation of suspected aortic dissection. N Engl J Med 1993;328: Nienaber CA, von Kodolitsch YV, Nicolas V, et al. The diagnosis of thoracic aortic dissection by noninvasive imaging procedures. N Engl J Med 1993;328: Nienaber CA, Spielmann RP, von Kodolitsch YV, et al. Diagnosis of thoracic aortic dissection, magnetic resonance imaging

5 Journal of the American Socict T of Echocardiography Volume 10 Number 1 Katz et al. 87 versus transesophageal echocardiography. Circulation 1992; 85: Laissy JP, Blanc F, Soyer P, et al. Thoracic aortic dissection: diagnosis with transesophageal echocardiography versus MR imaging. Radiology 1995;194: Kerstig SommerhoffBA, Higgins CB, White RD, Sommerhofl" CP, Lipton MJ. Aortic dissection: sensitivit 3, and specifici~, of MR imaging. Radiology, 1988;166: Erbel R, Engberding 1<, Daniel W. Echocardiography in the diagnosis of aortic dissection. Lancet 1989;1: Ballal RS, Nanda NC, Gatewood R. Usefulness oftransesophageal echocardiography in assessment of aortic dissection. Circulation 1991;84: Hashimoto S, Kumada T, Oskada G. Assessment oftransesophageal Doppler echocardiography in dissecting aortic aneurysms. l Am Coil Cardiol 1989;14: Bound volumes available to subscribers Bound volumes of the Journal of the American Society of Echocardiography are available to subscribers (only) for the 1997 issues from the Publisher at a cost of $72.00 for domestic, $89.88 Canadian, and $84.00 for international subscribers for Vol. 10 (January-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. The binding is durable buckram with the Journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, Westline Industrial Dr., St. Louis, MO , USA; telephone (800) , ext. 4351, or (314) Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular Journal subscription.