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Pitfalls in the Diagnosis of Thoracic Aortic Dissection at CT Angiography¹

¹ From the Department of Radiological Sciences, UCLA Medical Center, 10833 Le Conte Ave, Los Angeles, CA 90095-1721. Recipient of a Certificate of Merit award for a scientific exhibit at the 1998 RSNA scientific assembly. Received February 26, 1999; revision requested May 17 and received July 1; accepted July 8. Address reprint requests to P.B. (e-mail: pbatra@mednet.ucla.edu).

View larger version (131K): [in a new window]   Figure 1a.   Stanford type B aortic dissection originating immediately distal to the left subclavian artery in an 89-year-old man. (a) Axial contrast-enhanced helical CT scan shows a linear area of low attenuation in the descending thoracic aorta (arrow) that represents an intimal flap separating the true and false lumen. (b) Sagittal oblique reformatted image of the thoracic aorta demonstrates the intimal flap (arrows) beginning just distal to the origin of the left subclavian artery.

View larger version (147K): [in a new window]   Figure 1b.   Stanford type B aortic dissection originating immediately distal to the left subclavian artery in an 89-year-old man. (a) Axial contrast-enhanced helical CT scan shows a linear area of low attenuation in the descending thoracic aorta (arrow) that represents an intimal flap separating the true and false lumen. (b) Sagittal oblique reformatted image of the thoracic aorta demonstrates the intimal flap (arrows) beginning just distal to the origin of the left subclavian artery.

View larger version (129K): [in a new window]   Figure 2a.    Poor visualization of an intimal flap due to improper timing of contrast material administration. (a) Axial contrast-enhanced helical CT scan shows suboptimal aortic enhancement with poor visualization of an intimal flap (arrow), which may result in a false-negative diagnosis. (b) On an axial contrast-enhanced helical CT scan obtained with better synchronization of contrast material administration and image acquisition, the intimal flap (arrow) is easily identified in the well-enhanced aorta.

View larger version (127K): [in a new window]   Figure 2b.    Poor visualization of an intimal flap due to improper timing of contrast material administration. (a) Axial contrast-enhanced helical CT scan shows suboptimal aortic enhancement with poor visualization of an intimal flap (arrow), which may result in a false-negative diagnosis. (b) On an axial contrast-enhanced helical CT scan obtained with better synchronization of contrast material administration and image acquisition, the intimal flap (arrow) is easily identified in the well-enhanced aorta.

View larger version (119K): [in a new window]   Figure 3.   Streak artifact caused by a pacemaker lead. Axial contrast-enhanced helical CT scan shows two linear areas of low attenuation crossing the ascending aorta and simulating intimal flaps (arrows). These streak artifacts radiate from a pacemaker lead located on the right anterior chest wall (arrowhead).

View larger version (136K): [in a new window]   Figure 4.   Streak artifact caused by suboptimal arm positioning. Axial contrast-enhanced helical CT scan obtained at the level of the main pulmonary artery demonstrates a horizontal linear area of low attenuation in the descending thoracic aorta simulating an intimal flap (arrow). The patient was unable to elevate his arms and was scanned with his arms at his sides. Beam hardening caused by the arms produced the numerous artifacts seen along the posterior thorax.

View larger version (76K): [in a new window]   Figure 5a.   Streak artifact caused by contrast material in the right pulmonary artery. (a) Axial contrast-enhanced helical CT scan obtained at the level of the main pulmonary artery demonstrates a semilunar streak artifact along the posterior aspect of the ascending thoracic aorta simulating an intimal flap (arrow). (b) Axial contrast-enhanced helical CT scan obtained with optimal window width and level settings better demonstrates the aortic lumen and wall. Multiple streak artifacts are also more readily seen (arrows).

View larger version (91K): [in a new window]   Figure 5b.   Streak artifact caused by contrast material in the right pulmonary artery. (a) Axial contrast-enhanced helical CT scan obtained at the level of the main pulmonary artery demonstrates a semilunar streak artifact along the posterior aspect of the ascending thoracic aorta simulating an intimal flap (arrow). (b) Axial contrast-enhanced helical CT scan obtained with optimal window width and level settings better demonstrates the aortic lumen and wall. Multiple streak artifacts are also more readily seen (arrows).

View larger version (120K): [in a new window]   Figure 6a.   Streak artifact caused by cardiac motion. (a) Axial contrast-enhanced helical CT scan shows a linear area of low attenuation in the descending thoracic aorta simulating an intimal flap (arrow). This artifact was not present on adjacent sections (not shown). (b) Axial contrast-enhanced helical CT scan obtained in a different patient shows a streak artifact in the descending aorta (arrow) resembling differential filling of the true and false lumen seen in aortic dissection. High-contrast interfaces between left ventricular wall motion and the adjacent lung generate artifacts that project across the descending aorta and may simulate an intimal flap or double lumina.

View larger version (160K): [in a new window]   Figure 6b.   Streak artifact caused by cardiac motion. (a) Axial contrast-enhanced helical CT scan shows a linear area of low attenuation in the descending thoracic aorta simulating an intimal flap (arrow). This artifact was not present on adjacent sections (not shown). (b) Axial contrast-enhanced helical CT scan obtained in a different patient shows a streak artifact in the descending aorta (arrow) resembling differential filling of the true and false lumen seen in aortic dissection. High-contrast interfaces between left ventricular wall motion and the adjacent lung generate artifacts that project across the descending aorta and may simulate an intimal flap or double lumina.

View larger version (86K): [in a new window]   Figure 7a.   Origins of the brachiocephalic artery and left common carotid artery mimicking dissection. (a) Axial contrast-enhanced CT scan shows a linear area of low attenuation in a great vessel adjacent to the aortic arch simulating an intimal flap (arrow). (b) Contrast-enhanced CT scan obtained cephalad to a shows that this area represents the walls of the brachiocephalic (arrow) and left common carotid (arrowhead) arteries originating from the aortic arch.

View larger version (83K): [in a new window]   Figure 7b.   Origins of the brachiocephalic artery and left common carotid artery mimicking dissection. (a) Axial contrast-enhanced CT scan shows a linear area of low attenuation in a great vessel adjacent to the aortic arch simulating an intimal flap (arrow). (b) Contrast-enhanced CT scan obtained cephalad to a shows that this area represents the walls of the brachiocephalic (arrow) and left common carotid (arrowhead) arteries originating from the aortic arch.

View larger version (96K): [in a new window]   Figure 8.   Left brachiocephalic vein simulating aortic dissection. Axial contrast-enhanced electron beam CT scan obtained at the level of the left pulmonary artery demonstrates a semilunar area of high attenuation anterior to the ascending aorta (arrow). The normal aortic wall between the left brachiocephalic vein and the ascending thoracic aorta simulates an intimal flap. Note that the left brachiocephalic vein is isoattenuating relative to the superior vena cava and hyperattenuating relative to the aorta. The contrast material was administered via a left antecubital vein.

View larger version (87K): [in a new window]   Figure 9.   Left brachiocephalic vein mimicking aortic dissection. Axial contrast-enhanced helical CT scan demonstrates a curvilinear area of low attenuation anterior to the ascending aorta (arrow), which adjacent sections (not shown) helped confirm as a low-positioned brachiocephalic vein. The contrast material was administered via a right antecubital vein; consequently, the unenhanced left brachiocephalic vein could be misinterpreted as a false lumen.

View larger version (131K): [in a new window]   Figure 10a.   Left superior intercostal vein mimicking a double lumen. (a) Axial contrast-enhanced helical CT scan demonstrates an enhancing structure alongside the aortic arch simulating aortic dissection (arrows). (b) On an axial contrast-enhanced helical CT scan obtained cephalad to a, the structure is seen terminating in the left brachiocephalic vein (arrowhead), a finding that confirms the structure to be the left superior intercostal vein.

View larger version (118K): [in a new window]   Figure 10b.   Left superior intercostal vein mimicking a double lumen. (a) Axial contrast-enhanced helical CT scan demonstrates an enhancing structure alongside the aortic arch simulating aortic dissection (arrows). (b) On an axial contrast-enhanced helical CT scan obtained cephalad to a, the structure is seen terminating in the left brachiocephalic vein (arrowhead), a finding that confirms the structure to be the left superior intercostal vein.

View larger version (99K): [in a new window]   Figure 11a.   Left superior intercostal vein mimicking a double lumen. Adjacent axial contrast-enhanced helical CT scans obtained at the level of the aortic arch demonstrate an enhancing structure lateral to the aortic arch in the expected location of the left superior intercostal vein (arrowhead).

View larger version (100K): [in a new window]   Figure 11b.   Left superior intercostal vein mimicking a double lumen. Adjacent axial contrast-enhanced helical CT scans obtained at the level of the aortic arch demonstrate an enhancing structure lateral to the aortic arch in the expected location of the left superior intercostal vein (arrowhead).

View larger version (112K): [in a new window]   Figure 12a.   Left inferior pulmonary vein simulating a double lumen. (a) Axial contrast-enhanced helical CT scan obtained at the level of the left atrium demonstrates a curvilinear area of high attenuation lateral to the descending aorta (arrow). (b) Axial contrast-enhanced helical CT scan obtained cephalad to a reveals that this high-attenuation area is contiguous with the left inferior pulmonary vein (arrowhead).

View larger version (119K): [in a new window]   Figure 12b.   Left inferior pulmonary vein simulating a double lumen. (a) Axial contrast-enhanced helical CT scan obtained at the level of the left atrium demonstrates a curvilinear area of high attenuation lateral to the descending aorta (arrow). (b) Axial contrast-enhanced helical CT scan obtained cephalad to a reveals that this high-attenuation area is contiguous with the left inferior pulmonary vein (arrowhead).

View larger version (115K): [in a new window]   Figure 13.   Superior pericardial recess mimicking aortic dissection. Axial contrast-enhanced helical CT scan shows a semilunar area of low attenuation abutting the posterior aspect of the ascending thoracic aorta (arrow), a finding that can be misinterpreted as a false lumen. Note also the crescentic area of high attenuation representing the left brachiocephalic vein coursing anterolateral to the ascending thoracic aorta and mimicking dissection (arrowhead).

View larger version (136K): [in a new window]   Figure 14.   Right atrial appendage simulating aortic dissection. Axial contrast-enhanced helical CT scan obtained near the aortic root demonstrates a crescentic enhancing structure anterior to the aorta (arrow) simulating the double aortic lumina seen in dissection. CT scans obtained more caudad (not shown) revealed this structure to be a right atrial appendage contiguous with the right atrium. Note also the atelectasis in the left lower lobe adjacent to the descending thoracic aorta (arrowhead).

View larger version (129K): [in a new window]   Figure 15a.   Residual thymus mimicking a false lumen. (a) Axial contrast-enhanced helical CT scan obtained at the level of the aortic arch demonstrates an area of soft-tissue attenuation anterior to the aorta (arrow), a finding that can be misinterpreted as a false lumen. (b) Axial contrast-enhanced helical CT scan obtained cephalad to a demonstrates the triangular configuration of this finding (arrowhead), which is consistent with residual thymus given the young age of the patient.

View larger version (135K): [in a new window]   Figure 15b.   Residual thymus mimicking a false lumen. (a) Axial contrast-enhanced helical CT scan obtained at the level of the aortic arch demonstrates an area of soft-tissue attenuation anterior to the aorta (arrow), a finding that can be misinterpreted as a false lumen. (b) Axial contrast-enhanced helical CT scan obtained cephalad to a demonstrates the triangular configuration of this finding (arrowhead), which is consistent with residual thymus given the young age of the patient.

View larger version (113K): [in a new window]   Figure 16a.   Atelectasis mimicking Stanford type B dissection. (a) Axial contrast-enhanced helical CT scan obtained at the level of the main pulmonary artery demonstrates a crescentic area of enhancement posterolateral to the descending thoracic aorta (arrowhead). The normal aortic wall between the contrast material-filled aortic lumen and the atelectatic lung is seen as a thin linear area of low attenuation resembling an intimal flap (arrow). A similar appearance results when thickened pleura abuts the descending thoracic aorta. (b) Axial contrast-enhanced helical CT scan obtained with lung windowing helps confirm the presence of atelectasis in the left lower lobe (arrowhead). Note that a subsegmental bronchus leads into the atelectatic lung, producing an air bronchogram (arrow).

View larger version (122K): [in a new window]   Figure 16b.   Atelectasis mimicking Stanford type B dissection. (a) Axial contrast-enhanced helical CT scan obtained at the level of the main pulmonary artery demonstrates a crescentic area of enhancement posterolateral to the descending thoracic aorta (arrowhead). The normal aortic wall between the contrast material-filled aortic lumen and the atelectatic lung is seen as a thin linear area of low attenuation resembling an intimal flap (arrow). A similar appearance results when thickened pleura abuts the descending thoracic aorta. (b) Axial contrast-enhanced helical CT scan obtained with lung windowing helps confirm the presence of atelectasis in the left lower lobe (arrowhead). Note that a subsegmental bronchus leads into the atelectatic lung, producing an air bronchogram (arrow).

View larger version (139K): [in a new window]   Figure 17a.   Pleural effusion simulating aortic dissection. (a) Axial contrast-enhanced helical CT scan obtained at the level of the midheart demonstrates a region of low attenuation along the left lateral aspect of the descending thoracic aorta simulating a false lumen (arrow). Note also the atelectasis in the left lower lobe (*). (b) Axial contrast-enhanced helical CT scan obtained cephalad to a at the level of the aortic root shows this low-attenuation region to be contiguous with pleural fluid (arrows), a finding that confirms the presence of pleural effusion.

View larger version (137K): [in a new window]   Figure 17b.   Pleural effusion simulating aortic dissection. (a) Axial contrast-enhanced helical CT scan obtained at the level of the midheart demonstrates a region of low attenuation along the left lateral aspect of the descending thoracic aorta simulating a false lumen (arrow). Note also the atelectasis in the left lower lobe (*). (b) Axial contrast-enhanced helical CT scan obtained cephalad to a at the level of the aortic root shows this low-attenuation region to be contiguous with pleural fluid (arrows), a finding that confirms the presence of pleural effusion.

View larger version (123K): [in a new window]   Figure 18a.   Aortic motion artifact simulating aortic dissection. (a) Axial contrast-enhanced helical CT scan obtained at the aortic root shows a curvilinear area of low attenuation along the left anterior and right posterior aspects of the ascending aorta (arrows). (b) Axial contrast-enhanced helical CT scan obtained at the aortic root in a different patient demonstrates a low-attenuation interface along the left and right lateral aspects of the aorta simulating an intimal flap (arrows).

View larger version (115K): [in a new window]   Figure 18b.   Aortic motion artifact simulating aortic dissection. (a) Axial contrast-enhanced helical CT scan obtained at the aortic root shows a curvilinear area of low attenuation along the left anterior and right posterior aspects of the ascending aorta (arrows). (b) Axial contrast-enhanced helical CT scan obtained at the aortic root in a different patient demonstrates a low-attenuation interface along the left and right lateral aspects of the aorta simulating an intimal flap (arrows).

View larger version (94K): [in a new window]   Figure 19a.   Aortic valve cusps simulating intimal flaps. (a) Axial contrast-enhanced electron beam CT scan shows a curvilinear area of low attenuation along the left lateral aspect of the aortic root simulating an intimal flap (arrow). (b) Axial contrast-enhanced electron beam CT scan obtained caudad to a reveals that the low-attenuation area does not represent an intimal flap but the semilunar cusp of the aortic valve.

View larger version (97K): [in a new window]   Figure 19b.   Aortic valve cusps simulating intimal flaps. (a) Axial contrast-enhanced electron beam CT scan shows a curvilinear area of low attenuation along the left lateral aspect of the aortic root simulating an intimal flap (arrow). (b) Axial contrast-enhanced electron beam CT scan obtained caudad to a reveals that the low-attenuation area does not represent an intimal flap but the semilunar cusp of the aortic valve.

View larger version (136K): [in a new window]   Figure 20.   Ductus diverticulum simulating aortic dissection. Sagittal oblique reformatted CT scan demonstrates a focal bulge at the anteromedial aspect of the aortic isthmus. Note the smooth margins and the typical gentle obtuse angles formed by the ductus diverticulum and the aortic wall (arrow). The diverticulum was difficult to diagnose on axial CT scans. In contrast, false aneurysms occurring with aortic dissection are of variable size and shape, have sharp margins, and often contain an intimal flap.

View larger version (125K): [in a new window]   Figure 21.   Aneurysmal dilatation of the aorta with intraluminal thrombus. Axial contrast-enhanced helical CT scan obtained at the level of the aortic arch demonstrates a mildly dilated, enhanced, atherosclerotic aorta containing an intraluminal thrombus. Note the dense calcification at the periphery of the aorta (arrowhead); in true dissection, calcification is inwardly displaced.

View larger version (141K): [in a new window]   Figure 22.   Atherosclerotic penetrating ulcer. Axial contrast-enhanced helical CT scan shows an atherosclerotic ulcer (straight solid arrow) surrounded by intramural hematoma (open arrow) beneath the calcified intima (curved solid arrow).