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Aortic Stenosis: Spectrum of Diseases Depicted at Multisection CT¹

¹ From the Institut de Diagnòstic per la Imatge (C.S., M.P.L., E.C.) and the Department of Radiology (S.Q., R.B., A.A.C.), Vall d’Hebron Teaching Hospital, Passeig Vall d’Hebron 119–129, 08035 Barcelona, Spain. Presented as an education exhibit at the 2002 RSNA scientific assembly. Received February 7, 2003; revision requested March 18; final revision received May 20; accepted May 22. Address correspondence to C.S. (e-mail: sebastia@hg.vhebron.es).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

 
Aortic stenosis, or narrowing of the aortic lumen, has many causes. It may originate in coarctation or pseudocoarctation of the aorta, midaortic dysplastic syndrome, atherosclerosis, Takayasu arteritis, aortic dissection, or various intraaortic and periaortic diseases or as a result of aortic surgical repair. The impedance of blood flow through the stenotic segment may lead to the development of various collateral arterial pathways, according to the location of stenosis. Aortography is the standard technique for evaluating aortic stenosis; however, helical computed tomography (CT), particularly multisection CT, may provide additional information or in some cases may be used instead of arteriography. Multisection CT can depict the aorta and thoracoabdominal collateral pathways in less than 1 minute and provide high-quality arterial-phase imaging data suitable for multiple two-dimensional and three-dimensional reformations. To produce a useful differential diagnosis, the imaging specialist must be able to recognize the type of stenosis and the configuration of collateral circulatory pathways.

© RSNA, 2003

Index Terms: Aorta, stenosis or obstruction, 56.151 • Aorta, CT, 56.1211

	LEARNING OBJECTIVES FOR TEST 4

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

 
After reading this article and taking the test, the reader will be able to:

• Describe the common causes of aortic stenosis.
  
• Identify various types of aortic stenosis and collateral arterial pathways on multisection CT images.
  
• Discuss applications of multisection CT for evaluation of aortic stenosis.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

 
Aortic stenosis, or narrowing of the aortic lumen, has several causes. Aortic stenosis in the descending thoracic aorta and in the abdominal aorta has been well described in the literature, but stenosis in the ascending aorta (excluding aortic valve stenosis and supravalvular stenosis in Williams syndrome) is not as widely reported. The site of aortic stenosis varies according to the disease or condition that caused the stenosis. Stenosis of the proximal descending thoracic aorta is typical of congenital coarctation, stenosis of the thoracoabdominal aortic junction occurs in dysplastic midaortic syndrome, and stenosis of the abdominal aorta is often secondary to atherosclerosis. In Takayasu arteritis—aortic dissection due to intraaortic and periaortic diseases or aortic stenosis—stenosis can occur in any part of the vessel. Aortic stenosis also may occur as a result of surgery. The obstruction of blood flow through the stenotic segment may lead to the development of collateral arterial pathways, depending on the level of stenosis.

Aortography is the standard technique for evaluating aortic stenosis; however, helical computed tomography (CT), particularly multisection CT, may provide additional information or in some cases may be used instead of arteriography. Multisection CT can depict the aorta and thoracoabdominal collateral pathways in less than 1 minute and provide high-quality arterial-phase imaging data suitable for multiple two-dimensional and three-dimensional reformations. To make optimal use of this technique, the imaging specialist must become familiar with the characteristic appearance of aortic stenoses and collateral pathways on multisection CT images.

	Multisection CT Scanning

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

 
Our department uses a Twin II Plus scanner acquired in May 1995 (Elscint, Haifa, Israel) and an MX-8000 scanner (Philips Medical Systems, Haifa, Israel) acquired in March 2001. The images of thoracoabdominal stenosis that accompany this article were obtained with use of these scanners. The protocol for evaluation of the aorta with multisection CT at our institution begins in all cases with unenhanced scanning of the thoracoabdominal cavity, from the pulmonary apex to the pubic symphysis, in contiguous 10-mm sections. Subsequently, 100 mL of nonionic contrast material is administered through a right antecubital vein at a flow rate of 3 mL/sec. After a delay of 20–25 seconds from initiation of the bolus injection, contrast-enhanced helical CT is performed. Different scanning parameters are used with the different scanners. The Twin II Plus scanning parameters are as follows: number of detector rows, two; section collimation, 5 mm; rotation time, 1 second; pitch, 1.5; section width, 5.5 mm; table feed, 15 mm per rotation; and reconstruction increment, 3 mm. The MX-8000 scanning parameters are as follows: number of detector rows, four; section collimation, 2.5 mm; rotation time, 0.7 second; pitch, 3.5; section width, 3.2 mm; table feed, 16 mm per second; and reconstruction increment, 1.6 mm.

Two-dimensional and three-dimensional reformation is performed in all cases by means of maximum-intensity projection, shaded surface display, and volume rendering techniques.

The most useful reformations for visualizing the various aspects of the thoracic aorta are coronal (for the ascending and descending aorta), sagittal oblique (for the aortic arch), and sagittal curved oblique (for the supraaortic trunks). We do not routinely use maximum-intensity projection or shaded surface display images for visualizing the thoracic aorta, because of the difficulty of deleting the bones of the thoracic cage. Clipped volume-rendered images from which the thoracic cage has been omitted are more useful for detecting thoracic aortic stenosis.

The most useful images for visualizing the abdominal aorta are curved coronal images showing the abdominal aorta, the iliac system, and the renal arteries, and curved sagittal images showing the abdominal aorta, the celiac trunk, and the superior and inferior mesenteric arteries. Maximum-intensity projection, shaded surface display, and volume-rendered images in various planes also may be used.

	Causes of Aortic Stenosis

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

 
Coarctation of the Aorta
Coarctation of the aorta is a congenital obstructive anomaly of the aortic lumen. Coarctation typically occurs in the aortic isthmus, between the left subclavian artery and the ductus. More than half of cases show tubular hypoplasia of the transverse portion of the aortic arch with dilatation of the supraaortic vessels. Coarctation-associated lesions include ventricular septal defect and bi-cuspid aortic valve; aneurysms of the ascending aorta, ductus, intercostal arteries, and circle of Willis; stenosis of the left subclavian artery; and aberrant right subclavian artery (1).

The diagnosis and treatment of aortic coarctation are based on clinical, echocardiographic, and aortographic findings (2). Aortography provides the highest-resolution depiction of the coarctated segment and the aortic arch vessels; it also allows measurement of the gradient across the coarctation, visualization of collateral vessels, and assess-ment for additional cardiac malformations (3). Echocardiography cannot depict collateral vessels. Multisection CT directly depicts both the stenosis and collateral circulatory pathways (Fig 1a, 1b) but is not useful for visualizing the aortic gradient, patent ductus, or small cardiac malformations (4). Nevertheless, multisection CT is useful for planning stent-graft implantation and for postoperative follow-up examination (5,6).

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Congenital aortic coarctation. (a, b) Left lateral (a) and frontal (b) volume-rendered images show aortic narrowing below the left subclavian artery (large arrow). Elongation of the supraaortic vessels also is visible (small arrow in a). (c) Contrast-enhanced axial CT scan shows enlarged internal mammary arteries (large arrows), intercostal arteries (small arrows), and descending scapular arteries (arrowheads). (d, e) Left lateral volume-rendered images show the internal mammary artery (arrowheads in d), the intercostal arteries (arrows in e), and the descending scapular arteries (arrowheads in e).

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Congenital aortic coarctation. (a, b) Left lateral (a) and frontal (b) volume-rendered images show aortic narrowing below the left subclavian artery (large arrow). Elongation of the supraaortic vessels also is visible (small arrow in a). (c) Contrast-enhanced axial CT scan shows enlarged internal mammary arteries (large arrows), intercostal arteries (small arrows), and descending scapular arteries (arrowheads). (d, e) Left lateral volume-rendered images show the internal mammary artery (arrowheads in d), the intercostal arteries (arrows in e), and the descending scapular arteries (arrowheads in e).

View larger version (78K): [in this window] [in a new window] [Download PPT slide]   Figure 1c.  Congenital aortic coarctation. (a, b) Left lateral (a) and frontal (b) volume-rendered images show aortic narrowing below the left subclavian artery (large arrow). Elongation of the supraaortic vessels also is visible (small arrow in a). (c) Contrast-enhanced axial CT scan shows enlarged internal mammary arteries (large arrows), intercostal arteries (small arrows), and descending scapular arteries (arrowheads). (d, e) Left lateral volume-rendered images show the internal mammary artery (arrowheads in d), the intercostal arteries (arrows in e), and the descending scapular arteries (arrowheads in e).

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 1d.  Congenital aortic coarctation. (a, b) Left lateral (a) and frontal (b) volume-rendered images show aortic narrowing below the left subclavian artery (large arrow). Elongation of the supraaortic vessels also is visible (small arrow in a). (c) Contrast-enhanced axial CT scan shows enlarged internal mammary arteries (large arrows), intercostal arteries (small arrows), and descending scapular arteries (arrowheads). (d, e) Left lateral volume-rendered images show the internal mammary artery (arrowheads in d), the intercostal arteries (arrows in e), and the descending scapular arteries (arrowheads in e).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 1e.  Congenital aortic coarctation. (a, b) Left lateral (a) and frontal (b) volume-rendered images show aortic narrowing below the left subclavian artery (large arrow). Elongation of the supraaortic vessels also is visible (small arrow in a). (c) Contrast-enhanced axial CT scan shows enlarged internal mammary arteries (large arrows), intercostal arteries (small arrows), and descending scapular arteries (arrowheads). (d, e) Left lateral volume-rendered images show the internal mammary artery (arrowheads in d), the intercostal arteries (arrows in e), and the descending scapular arteries (arrowheads in e).

View larger version (84K): [in this window] [in a new window] [Download PPT slide]   Figure 2.  Diagram of systemic thoracic (A and B), thoracoabdominal (B), and abdominal (C and D) collateral pathways in cases of aortic stenosis. In A, the thoracoacromial and descending scapular arteries (arising from the subclavian arteries) supply the poststenotic descending thoracic aorta with retrograde flow via the intercostal arteries. In B, the internal mammary arteries (arising from the subclavian arteries) connect both with the descending thoracic aorta via the intercostal arteries and with the external iliac arteries via the superior and inferior abdominal epigastric arteries. In C, the inferior intercostal arteries supply the external iliac arteries through the superficial and deep iliac circumflex arteries. In D, the lumbar arteries supply the internal iliac arteries via the inferior gluteal arteries.

2. Subclavian artery thyrocervical and costocervical trunks thoracoacromial and descending scapular arteries postcoarctation descending thoracic aorta.

3. Subclavian artery vertebral artery anterior spinal artery intercostal arteries postcoarctation descending thoracic aorta.

Pseudocoarctation
Pseudocoarctation of the aortic arch is a rare congenital anomaly characterized by one or more stenoses of the descending thoracic aorta immediately distal to the origin of the left subclavian artery. This condition is differentiated from true coarctation of the aorta by the absence of significant hemodynamic obstruction; the stenosis instead produces elongation of the aorta. Kinking and buckling are often used to describe the radiologic appearance of the aortic arch in patients with this condition (7). Pseudocoarctation is usually asymptomatic and benign, but aneurysmal dilatations may develop in the affected areas and must be monitored and treated. Multisection CT can help physicians detect pseudocoarctation in asymptomatic patients, especially in adults, by depicting the multiple small stenoses and aneurysms that are pathognomonic of this disease. In children, however, aortography is mandatory to rule out significant hemodynamic stenosis. Multisection CT is also useful in the follow-up of this disease to control aneurysmal dilatation (Fig 3).

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  Aortic pseudocoarctation. Contrast-enhanced axial CT scan (a) and curved reformatted image (b) of the aortic arch depict multiple calcified aneurysms (large arrows) and stenoses (small arrows).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  Aortic pseudocoarctation. Contrast-enhanced axial CT scan (a) and curved reformatted image (b) of the aortic arch depict multiple calcified aneurysms (large arrows) and stenoses (small arrows).

Multisection CT can be used to determine the location and extent of stenosis in the middle part of the aorta and its associated visceral branches, as well as the presence of collateral circulation (Fig 4). This modality is also useful for postoperative follow-up (Fig 5). However, midaorticdysplastic syndrome cannot be distinguished from late-phase type II Takayasu arteritis on the basis of radiologic findings alone. The two disease entities can be differentiated only by histopathologic exclusion of inflammatory change, which is present in Takayasu arteritis but not in midaortic dysplastic syndrome (9).

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Midaortic dysplastic syndrome in an 18-year-old man with hypertension and weak femoral pulses. (a) Lateral volume-rendered image depicts calcification and stenosis of the thoracoabdominal aorta (large arrow). The area of stenosis includes the ostium of the celiac trunk and superior mesenteric artery (small arrows). (b) Frontal volume-rendered image shows stenoses of the aorta (large arrow) and of the right and left renal arteries (small arrows). Note the meandering mesenteric artery (arrowhead). (c) Contrast-enhanced axial CT section depicts thrombosis and calcification of the retrocrural aorta (large arrow) and enlarged epigastric (small arrows) and intercostal (arrowheads) arteries. (d) Contrast-enhanced axial CT section shows collateral circulation in the anterior abdominal wall (arrows) and the meandering mesenteric artery (arrowhead). Note the hypoplastic abdominal aorta. (e) Frontal volume-rendered image of the anterior thoracoabdominal wall shows enlarged internal mammary arteries (large arrows) that communicate with the epigastric arteries (small arrows).

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Midaortic dysplastic syndrome in an 18-year-old man with hypertension and weak femoral pulses. (a) Lateral volume-rendered image depicts calcification and stenosis of the thoracoabdominal aorta (large arrow). The area of stenosis includes the ostium of the celiac trunk and superior mesenteric artery (small arrows). (b) Frontal volume-rendered image shows stenoses of the aorta (large arrow) and of the right and left renal arteries (small arrows). Note the meandering mesenteric artery (arrowhead). (c) Contrast-enhanced axial CT section depicts thrombosis and calcification of the retrocrural aorta (large arrow) and enlarged epigastric (small arrows) and intercostal (arrowheads) arteries. (d) Contrast-enhanced axial CT section shows collateral circulation in the anterior abdominal wall (arrows) and the meandering mesenteric artery (arrowhead). Note the hypoplastic abdominal aorta. (e) Frontal volume-rendered image of the anterior thoracoabdominal wall shows enlarged internal mammary arteries (large arrows) that communicate with the epigastric arteries (small arrows).

View larger version (103K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.  Midaortic dysplastic syndrome in an 18-year-old man with hypertension and weak femoral pulses. (a) Lateral volume-rendered image depicts calcification and stenosis of the thoracoabdominal aorta (large arrow). The area of stenosis includes the ostium of the celiac trunk and superior mesenteric artery (small arrows). (b) Frontal volume-rendered image shows stenoses of the aorta (large arrow) and of the right and left renal arteries (small arrows). Note the meandering mesenteric artery (arrowhead). (c) Contrast-enhanced axial CT section depicts thrombosis and calcification of the retrocrural aorta (large arrow) and enlarged epigastric (small arrows) and intercostal (arrowheads) arteries. (d) Contrast-enhanced axial CT section shows collateral circulation in the anterior abdominal wall (arrows) and the meandering mesenteric artery (arrowhead). Note the hypoplastic abdominal aorta. (e) Frontal volume-rendered image of the anterior thoracoabdominal wall shows enlarged internal mammary arteries (large arrows) that communicate with the epigastric arteries (small arrows).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 4d.  Midaortic dysplastic syndrome in an 18-year-old man with hypertension and weak femoral pulses. (a) Lateral volume-rendered image depicts calcification and stenosis of the thoracoabdominal aorta (large arrow). The area of stenosis includes the ostium of the celiac trunk and superior mesenteric artery (small arrows). (b) Frontal volume-rendered image shows stenoses of the aorta (large arrow) and of the right and left renal arteries (small arrows). Note the meandering mesenteric artery (arrowhead). (c) Contrast-enhanced axial CT section depicts thrombosis and calcification of the retrocrural aorta (large arrow) and enlarged epigastric (small arrows) and intercostal (arrowheads) arteries. (d) Contrast-enhanced axial CT section shows collateral circulation in the anterior abdominal wall (arrows) and the meandering mesenteric artery (arrowhead). Note the hypoplastic abdominal aorta. (e) Frontal volume-rendered image of the anterior thoracoabdominal wall shows enlarged internal mammary arteries (large arrows) that communicate with the epigastric arteries (small arrows).

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 4e.  Midaortic dysplastic syndrome in an 18-year-old man with hypertension and weak femoral pulses. (a) Lateral volume-rendered image depicts calcification and stenosis of the thoracoabdominal aorta (large arrow). The area of stenosis includes the ostium of the celiac trunk and superior mesenteric artery (small arrows). (b) Frontal volume-rendered image shows stenoses of the aorta (large arrow) and of the right and left renal arteries (small arrows). Note the meandering mesenteric artery (arrowhead). (c) Contrast-enhanced axial CT section depicts thrombosis and calcification of the retrocrural aorta (large arrow) and enlarged epigastric (small arrows) and intercostal (arrowheads) arteries. (d) Contrast-enhanced axial CT section shows collateral circulation in the anterior abdominal wall (arrows) and the meandering mesenteric artery (arrowhead). Note the hypoplastic abdominal aorta. (e) Frontal volume-rendered image of the anterior thoracoabdominal wall shows enlarged internal mammary arteries (large arrows) that communicate with the epigastric arteries (small arrows).

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Coronal volume-rendered images obtained in a 25-year-old man at follow-up after surgery for midaortic dysplastic syndrome. Note the long, narrowed aorta in a (small arrows) and the left-sided aortic bypass with stenosis at the lower end (arrowhead). The superior mesenteric aorta was also stenotic (not shown). A meandering mesenteric artery (large arrow) connects the inferior and superior mesenteric arteries. The extraanatomic left-sided aortic bypass (arrows) and a surgically implanted endoprosthesis (arrowhead) are visible in b.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Coronal volume-rendered images obtained in a 25-year-old man at follow-up after surgery for midaortic dysplastic syndrome. Note the long, narrowed aorta in a (small arrows) and the left-sided aortic bypass with stenosis at the lower end (arrowhead). The superior mesenteric aorta was also stenotic (not shown). A meandering mesenteric artery (large arrow) connects the inferior and superior mesenteric arteries. The extraanatomic left-sided aortic bypass (arrows) and a surgically implanted endoprosthesis (arrowhead) are visible in b.

When the celiac trunk or superior mesenteric artery is obstructed, retrograde flow comes through the superior and inferior mesenteric arteries (Fig 6, A and B) by the following pathway: inferior mesenteric artery meandering mesenteric artery superior mesenteric artery pancreaticoduodenal arcades celiac trunk.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 6.  Diagram of visceral (A and B) and visceral-systemic (C) abdominal collateral pathways. The celiac trunk and superior mesenteric artery can supply each other with bidirectional blood flow (A). The superior and inferior mesenteric arteries also can supply each other bidirectionally through the Riolano arcade (ie, the meandering mesenteric artery) (B). The inferior mesenteric artery can supply blood to the internal iliac artery via the hemorrhoidal plexus (C).

Aortoiliac Occlusive Disease
Severe atherosclerotic disease of the iliac arteries or aorta may result in stenosis or occlusion of the aorta below the renal arteries. Complete obliteration of the aortic bifurcation is called Leriche syndrome. This term describes a complex of clinical symptoms (eg, claudication, decreased femoral pulses) attributed to obstruction of the infrarenal aorta (11).

At our institution, the following additional descriptors are used to differentiate among occurrences of infrarenal atherosclerotic occlusion (11): juxtarenal, or within 5 mm of the lower renal arterial origin; infrarenal, or cephalic to the origin of the inferior mesenteric artery; and inframesenteric, or caudal to the origin of the inferior mesenteric artery.

Multisection CT can be used to evaluate the location of aortic stenosis and occlusion, the pres-ence of concomitant occlusive disease affecting visceral arteries, the type and extent of collateralization, and the level of the most proximal and distal arterial segments amenable to stent-graft placement.

A large network of parietal and visceral vessels may be recruited to bypass any segment of the aortoiliac arterial system by means of the formation of collateral channels (Figs 7, 8) (11). In abdominal aortoiliac stenosis and occlusion, the most commonly occurring collateral pathways to the lower extremities are as follows (10,12) (Fig 2, C and D; Fig 6, B and C):

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Total occlusion of the infrarenal abdominal aorta. (a) Contrast-enhanced axial CT scan shows a totally occluded infrarenal abdominal aorta (large arrow). Note the enlarged pancreaticoduodenal arcades (small arrows) and epigastric arteries (arrowheads). (b) Lateral volume-rendered image shows complete thrombosis of the infrarenal abdominal aorta and occlusion of the celiac trunk and superior mesenteric artery (large arrows). Note the patency of the inferior mesenteric artery (arrowhead) and the enlarged epigastric arteries in the abdominal wall (small arrows).

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Total occlusion of the infrarenal abdominal aorta. (a) Contrast-enhanced axial CT scan shows a totally occluded infrarenal abdominal aorta (large arrow). Note the enlarged pancreaticoduodenal arcades (small arrows) and epigastric arteries (arrowheads). (b) Lateral volume-rendered image shows complete thrombosis of the infrarenal abdominal aorta and occlusion of the celiac trunk and superior mesenteric artery (large arrows). Note the patency of the inferior mesenteric artery (arrowhead) and the enlarged epigastric arteries in the abdominal wall (small arrows).

View larger version (152K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Total occlusion of the infrarenal abdominal aorta. (a) Sagittal reformatted image of the abdominal aorta depicts calcification and mural thrombosis (arrows). (b) Contrast-enhanced axial CT scan shows collateral circulation, epigastric arteries (large white arrows), circumflex arteries (small white arrows), an enlarged inferior mesenteric artery (arrowhead), and enlarged lumbar arteries (black arrows). (c) Sagittal maximum-intensity projection image shows enlarged epigastric arteries in the abdominal wall (arrows) and retrograde flow in the inferior mesenteric artery (arrowhead). (d) Coronal volume-rendered image shows a collateral pathway proceeding from the subcostal arteries through the circumflex arteries to the external iliac artery (arrows). Note the enlarged inferior mesenteric artery (arrowhead).

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Total occlusion of the infrarenal abdominal aorta. (a) Sagittal reformatted image of the abdominal aorta depicts calcification and mural thrombosis (arrows). (b) Contrast-enhanced axial CT scan shows collateral circulation, epigastric arteries (large white arrows), circumflex arteries (small white arrows), an enlarged inferior mesenteric artery (arrowhead), and enlarged lumbar arteries (black arrows). (c) Sagittal maximum-intensity projection image shows enlarged epigastric arteries in the abdominal wall (arrows) and retrograde flow in the inferior mesenteric artery (arrowhead). (d) Coronal volume-rendered image shows a collateral pathway proceeding from the subcostal arteries through the circumflex arteries to the external iliac artery (arrows). Note the enlarged inferior mesenteric artery (arrowhead).

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.  Total occlusion of the infrarenal abdominal aorta. (a) Sagittal reformatted image of the abdominal aorta depicts calcification and mural thrombosis (arrows). (b) Contrast-enhanced axial CT scan shows collateral circulation, epigastric arteries (large white arrows), circumflex arteries (small white arrows), an enlarged inferior mesenteric artery (arrowhead), and enlarged lumbar arteries (black arrows). (c) Sagittal maximum-intensity projection image shows enlarged epigastric arteries in the abdominal wall (arrows) and retrograde flow in the inferior mesenteric artery (arrowhead). (d) Coronal volume-rendered image shows a collateral pathway proceeding from the subcostal arteries through the circumflex arteries to the external iliac artery (arrows). Note the enlarged inferior mesenteric artery (arrowhead).

View larger version (172K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.  Total occlusion of the infrarenal abdominal aorta. (a) Sagittal reformatted image of the abdominal aorta depicts calcification and mural thrombosis (arrows). (b) Contrast-enhanced axial CT scan shows collateral circulation, epigastric arteries (large white arrows), circumflex arteries (small white arrows), an enlarged inferior mesenteric artery (arrowhead), and enlarged lumbar arteries (black arrows). (c) Sagittal maximum-intensity projection image shows enlarged epigastric arteries in the abdominal wall (arrows) and retrograde flow in the inferior mesenteric artery (arrowhead). (d) Coronal volume-rendered image shows a collateral pathway proceeding from the subcostal arteries through the circumflex arteries to the external iliac artery (arrows). Note the enlarged inferior mesenteric artery (arrowhead).

2. Intercostal, subcostal, and lumbar arteries superior gluteal and iliolumbar arteries internal iliac arteries external iliac arteries.

3. Intercostal, subcostal, and lumbar arteries circumflex arteries external iliac arteries.

Chronic Vasculitis
Various types of vasculitis produce aneurysms in many portions of the aorta and its branches, but Takayasu arteritis is the only type of aortitis that produces stenosis in the thoracic aorta (13).

Takayasu arteritis is a well-known systemic disease that affects the aorta and its major branches as well as the pulmonary artery. In the early phase of the disease, known as the systemic or prepulseless phase, CT scans and magnetic resonance images depict mural thickening and contrast enhancement—changes that cannot be assessed by arteriography (14). Mural thickness decreases after steroid therapy. If transmural fibrosis is left untreated, chronic changes may ensue, including stenosis, occlusion, mural calcification, intraluminal thrombus, or aneurysmal dila-tation of the aorta and its branches. This stage of the disease is called the late or occlusive phase. Multisection CT is more effective than arteriography in depicting mural calcification and intraluminal thrombus, and it can be used to evaluate the supraaortic vessels, the thoracoabdominal aorta and its visceral branches, and the pulmonary artery in a single imaging session. Multisection CT is also useful for diagnosing chronic vasculitis and performing postoperative follow-up (Fig 9) (15,16).

View larger version (91K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Takayasu arteritis. (a, b) Contrast-enhanced axial CT images of the lower thoracic aorta and upper abdominal aorta depict stenosis with mural calcification (arrows in a) and small aneurysms (arrow in b). (c) Sagittal volume-rendered image shows the stenotic segment in the lower thoracic aorta (arrows).

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Takayasu arteritis. (a, b) Contrast-enhanced axial CT images of the lower thoracic aorta and upper abdominal aorta depict stenosis with mural calcification (arrows in a) and small aneurysms (arrow in b). (c) Sagittal volume-rendered image shows the stenotic segment in the lower thoracic aorta (arrows).

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.  Takayasu arteritis. (a, b) Contrast-enhanced axial CT images of the lower thoracic aorta and upper abdominal aorta depict stenosis with mural calcification (arrows in a) and small aneurysms (arrow in b). (c) Sagittal volume-rendered image shows the stenotic segment in the lower thoracic aorta (arrows).

Aortic Dissection
In aortic dissection, the intimal layer of the aortic wall is detached and the aortic lumen separates into two parts, the true lumen and the false lumen. When the two lumina communicate and their pressures are equal, no ischemic changes occur. In some cases, however, the false lumen has an entrance but no exit, and it becomes thrombosed (Fig 10). In such cases, when the true lumen is very narrow, ischemic changes may occur (18). The flap also may have an ischemic configuration due to compression of the low-pressure true lumen by the high-pressure false lumen (19). Multisection CT may be used to examine the entire aorta in the arterial phase, from the supraaortic vessels to the femoral arteries, to evaluate the extent and configuration of the flap, the presence or absence of contrast material in the two lumina, and associated ischemic signs. True lumen collapse may occur, necessitating fenestration or stent-graft placement (20).

View larger version (152K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Aortic dissection. (a) Contrast-enhanced axial CT image depicts a dissected aorta with a thrombosed false lumen (large arrow) and a small, enhanced true lumen (small arrow). The thrombosed false lumen compresses the celiac trunk ostium. Note the right kidney infarction due to a thrombosed renal artery (not shown). (b) Curved coronal reformatted image of the descending thoracic aorta depicts the thrombosed false lumen (large arrow) and stenotic true lumen (small arrow).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Aortic dissection. (a) Contrast-enhanced axial CT image depicts a dissected aorta with a thrombosed false lumen (large arrow) and a small, enhanced true lumen (small arrow). The thrombosed false lumen compresses the celiac trunk ostium. Note the right kidney infarction due to a thrombosed renal artery (not shown). (b) Curved coronal reformatted image of the descending thoracic aorta depicts the thrombosed false lumen (large arrow) and stenotic true lumen (small arrow).

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Aortic stenosis in a 42-year-old man who had undergone surgical repair of aortic coarctation in childhood and whose symptoms at the time of scanning included hypertension and weak femoral pulses. (a, b) Contrast-enhanced axial CT images of the thoracic aorta show a calcified prosthesis (large arrow) in the proximal descending thoracic aorta. The prosthesis has become detached from the left wall, producing partial aortic thrombosis and stenosis (small arrow in b). Note the enlarged internal mammary arteries (arrowheads in a). (c) Sagittal oblique reformatted image of the thoracic aorta shows movement of the aortic stent-graft (large arrow) and secondary aortic stenosis (small arrow).

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Aortic stenosis in a 42-year-old man who had undergone surgical repair of aortic coarctation in childhood and whose symptoms at the time of scanning included hypertension and weak femoral pulses. (a, b) Contrast-enhanced axial CT images of the thoracic aorta show a calcified prosthesis (large arrow) in the proximal descending thoracic aorta. The prosthesis has become detached from the left wall, producing partial aortic thrombosis and stenosis (small arrow in b). Note the enlarged internal mammary arteries (arrowheads in a). (c) Sagittal oblique reformatted image of the thoracic aorta shows movement of the aortic stent-graft (large arrow) and secondary aortic stenosis (small arrow).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 11c.  Aortic stenosis in a 42-year-old man who had undergone surgical repair of aortic coarctation in childhood and whose symptoms at the time of scanning included hypertension and weak femoral pulses. (a, b) Contrast-enhanced axial CT images of the thoracic aorta show a calcified prosthesis (large arrow) in the proximal descending thoracic aorta. The prosthesis has become detached from the left wall, producing partial aortic thrombosis and stenosis (small arrow in b). Note the enlarged internal mammary arteries (arrowheads in a). (c) Sagittal oblique reformatted image of the thoracic aorta shows movement of the aortic stent-graft (large arrow) and secondary aortic stenosis (small arrow).

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.  Axillobifemoral bypass stenosis. (a, b) Axial CT images depict a subcutaneous axillobifemoral bypass (arrow in a) and a fluid collection from infection (arrow in b) surrounding and compressing the extraanatomic graft. (c, d) Lateral volume-rendered images of the axillobifemoral bypass show several mild stenoses and one severe stenosis (arrow) due to the periprosthetic fluid collection. Note the absence of enhancement in the infrarenal aorta in d, a result of thrombosis.

View larger version (148K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.  Axillobifemoral bypass stenosis. (a, b) Axial CT images depict a subcutaneous axillobifemoral bypass (arrow in a) and a fluid collection from infection (arrow in b) surrounding and compressing the extraanatomic graft. (c, d) Lateral volume-rendered images of the axillobifemoral bypass show several mild stenoses and one severe stenosis (arrow) due to the periprosthetic fluid collection. Note the absence of enhancement in the infrarenal aorta in d, a result of thrombosis.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 12c.  Axillobifemoral bypass stenosis. (a, b) Axial CT images depict a subcutaneous axillobifemoral bypass (arrow in a) and a fluid collection from infection (arrow in b) surrounding and compressing the extraanatomic graft. (c, d) Lateral volume-rendered images of the axillobifemoral bypass show several mild stenoses and one severe stenosis (arrow) due to the periprosthetic fluid collection. Note the absence of enhancement in the infrarenal aorta in d, a result of thrombosis.

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 12d.  Axillobifemoral bypass stenosis. (a, b) Axial CT images depict a subcutaneous axillobifemoral bypass (arrow in a) and a fluid collection from infection (arrow in b) surrounding and compressing the extraanatomic graft. (c, d) Lateral volume-rendered images of the axillobifemoral bypass show several mild stenoses and one severe stenosis (arrow) due to the periprosthetic fluid collection. Note the absence of enhancement in the infrarenal aorta in d, a result of thrombosis.

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.  Abdominal aortic stenosis due to retroperitoneal fibrosis. (a) Contrast-enhanced axial CT image shows an irregular mass (white arrows) around the abdominal aorta, producing severe aortic narrowing (black arrow). (b, c) Coronal (b) and sagittal (c) reformatted images of the abdominal aorta demonstrate severe aortic stenosis (black arrow) secondary to retroperitoneal fibrosis (white arrows).

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.  Abdominal aortic stenosis due to retroperitoneal fibrosis. (a) Contrast-enhanced axial CT image shows an irregular mass (white arrows) around the abdominal aorta, producing severe aortic narrowing (black arrow). (b, c) Coronal (b) and sagittal (c) reformatted images of the abdominal aorta demonstrate severe aortic stenosis (black arrow) secondary to retroperitoneal fibrosis (white arrows).

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 13c.  Abdominal aortic stenosis due to retroperitoneal fibrosis. (a) Contrast-enhanced axial CT image shows an irregular mass (white arrows) around the abdominal aorta, producing severe aortic narrowing (black arrow). (b, c) Coronal (b) and sagittal (c) reformatted images of the abdominal aorta demonstrate severe aortic stenosis (black arrow) secondary to retroperitoneal fibrosis (white arrows).

	Conclusion

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

	References

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Multisection CT Scanning Causes of Aortic Stenosis Conclusion References

 

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