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DOI: 10.1148/rg.264055082
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RadioGraphics 2006;26:981-992
© RSNA, 2006

EDUCATION EXHIBIT

MR Angiographic Evaluation of Complications in Surgically Treated Type A Aortic Dissection1

Àngela García, MD, Joaquín Ferreirós, MD, PhD, Mónica Santamaría, MD, Ana Bustos, MD, José Luis Abades, MD and Nuria Santamaría, MD

1 From the Department of Diagnostic Imaging, Hospital Clínico San Carlos, Universidad Complutense, c/o Profesor Martín Lagos s/n, 28040 Madrid, Spain. Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received April 4, 2005; revision requested June 20 and received August 22; accepted August 26. All authors have no financial relationships to disclose. Address correspondence to A.G.P. (e-mail: angelagpalvarez{at}gmail.com).


   Abstract
Top
 Abstract
Introduction
 Surgical Procedures and...
 Postsurgical Complications
 Conclusions
 References
 
Thoracic aortic dissection is a life-threatening disease with a high mortality rate and an elevated incidence of early and long-term complications. Advances in surgical treatment of ascending (Stanford type A) aortic dissection have helped improve patient survival, but follow-up imaging is critically important for the identification of postsurgical complications. Gadolinium-enhanced three-dimensional (3D) magnetic resonance (MR) angiography, along with multisection computed tomography, is the technique of choice for this purpose. For accurate assessment of 3D MR angiograms, it is important to know what surgical procedure was performed and to be familiar with the appearance of the normal postsurgical anatomy. A thorough understanding of potential postsurgical complications also is essential. Some complications (eg, formation of a periprosthetic hematoma or pseudoaneurysm, stenosis in a graft anastomosis) may derive from the prosthesis. Complications also may occur in the remnant of the native aorta, where persistent dissection distal to the prosthesis is common and may result in false channel thrombosis or aneurysmatic dilatation with collapse of the true lumen. Residual dissection that involves the supra-aortic trunks or the visceral aortic branches may produce neurologic effects or renal and mesenteric ischemia, respectively.

© RSNA, 2006


   Introduction
Top
 Abstract
 Introduction
Surgical Procedures and...
 Postsurgical Complications
 Conclusions
 References
 
Cardiovascular disease is the leading cause of death in occidental societies, and diseases of the aorta contribute to the high overall cardiovascular mortality. Thoracic aortic dissection, in particular, is associated with high early and long-term mortality rates (1,2).

Pain is the most common symptom of aortic dissection. However, a wide range of clinical manifestations (eg, myocardial ischemia, stroke, or renal or mesenteric ischemia with abdominal pain) may occur as a result of dissection, depending on the aortic branches affected. Familiarity with the complete spectrum of possible clinical manifestations is important for accurate and rapid diagnosis and effective management. Computed tomography (CT), magnetic resonance (MR) imaging, and transesophageal echocardiography are all fairly accurate modalities for diagnosis of aortic dissection. The choice of diagnostic imaging modality depends on the availability of imaging equipment and staff expertise (2). In general, acute aortic syndrome now can be better and more quickly diagnosed with multisection CT than with single-section helical CT (3).

In the classic DeBakey system for classifying aortic dissection, three types are recognized: Type I dissection involves the entire aorta, type II affects the ascending aorta, and in type III only the descending aorta is affected. The Stanford classification system includes only two types: type A, which involves the ascending aorta regardless of the site of the proximal intimal tear, and type B, which involves the part of the aorta distal to the origin of the left subclavian artery (4). The Stan-ford system of classifying aortic dissection according to the presence or absence of involvement of the ascending aorta has replaced the DeBakey system because it better reflects the dichotomy in treatment: Stanford type A aortic dissection usually requires surgical treatment, whereas type B dissection is treated with medication unless complications are present (3).

Early surgical intervention is indicated for all patients with type A aortic dissection. Advances in surgical treatment of ascending aortic dissection have helped improve patient survival. Follow-up imaging for detection of postsurgical complications is critically important, and it can be performed with multisection CT or gadolinium-enhanced three-dimensional (3D) MR angiography. Multisection CT is faster and provides higher spatial resolution than 3D MR angiography; however, the CT examination involves the use of a potentially nephrotoxic intravenous contrast medium and ionizing radiation. Because of its relative safety, gadolinium-enhanced 3D MR angiography is often performed for follow-up of patients who have undergone surgery for type A aortic dissection, especially young adults, patients in whom multiple follow-up imaging examinations are necessary, and patients with renal failure. To accurately access MR angiograms, the radiologist must know the type of surgical procedure performed and the normal appearance of the postsurgical anatomy at MR angiography.

Also essential is a thorough understanding of the post-surgical complications that may arise in or near the prosthesis or in the remaining native aorta, especially since persistent aortic dissection distal to the prosthesis is common.

In this article, the normal anatomic appearance at gadolinium-enhanced 3D MR angiography after the most common surgical procedures for type A dissection (including prosthetic replacement of the supracoronary ascending aorta, the Bentall procedure, and replacement of the aortic arch) is described. Postsurgical complications that may occur in or near the prosthesis (eg, hematoma and pseudoaneurysm formation, anastomotic stenosis) or in the native aorta or its branches (eg, proximal aortic dissection, supra-aortic or visceral branch involvement, true lumen collapse, false channel thrombosis, false lumen pseudoaneurysm) are discussed.


   Surgical Procedures and Postsurgical Appearance
Top
 Abstract
 Introduction
 Surgical Procedures and...
Postsurgical Complications
 Conclusions
 References
 
Surgical intervention is indicated in all patients with type A acute aortic dissection except those with preexisting diseases because of which open surgery cannot be performed. The aim of surgical therapy is to prevent aortic rupture and pericardial effusion (which may lead to cardiac tamponade), acute aortic regurgitation and heart failure, myocardial and visceral ischemia, and death (1,5). The surgical objective is the complete exclusion of the entire dissected aorta. There are many techniques for surgical repair of aortic dissection, and the best technique has yet to be determined (2).

Dissection of the ascending aorta can be repaired by inserting a synthetic graft of polyester textile fiber between the coronary ostia and the proximal aortic arch (Fig 1).


Figure 1
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  		Figure 1a.  Prosthetic replacement of the ascending aorta. (a) Diagram shows a prosthetic tube used to replace the supracoronary ascending aorta. (b) Maximum intensity projection image from gadolinium-enhanced 3D MR angiography shows the prosthetic replacement in a 50-year-old man.

 

Figure 1
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  		Figure 1b.  Prosthetic replacement of the ascending aorta. (a) Diagram shows a prosthetic tube used to replace the supracoronary ascending aorta. (b) Maximum intensity projection image from gadolinium-enhanced 3D MR angiography shows the prosthetic replacement in a 50-year-old man.

 
In patients with a previously ectatic proximal aorta (eg, most patients with Marfan syndrome) or aortic regurgitation, replacement of both the ascending aorta and the aortic valve and reimplantation of the coronary arteries are necessary. The most common method, first described by Bentall and De Bono (6), consists of replacement of the entire ascending aorta and the aortic valve with a valve-equipped prosthesis, as well as reimplantation of the coronary arteries onto the graft (Fig 2). However, during long-term follow-up after surgical treatment with this technique, a high incidence of bleeding near coronary sutures and aneurysmatic dilatation of coronary arteries were found (7). To avoid this complication, various modifications of the Bentall procedure have been devised. For example, in the Cabrol procedure (8), a composite graft that includes an aortic valve and a synthetic tube made of polyester textile fiber is implanted in place of the dissected ascending aorta, and an additional prosthetic conduit that interconnects the coronary ostia is anastomosed directly to the aortic graft (Fig 3a). The native aortic wall then is wrapped around the aortic graft, and another shunt is created between the wall and the right atrium to decompress a potentially tense perigraft space and prevent aneurys-matic dilatation of the wall (Fig 3b, 3c).


Figure 2
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  		Figure 2a.  Bentall procedure. (a) Schematic shows the replacement of the entire ascending aorta and aortic valve with a valve-equipped prosthesis and the reimplantation of the coronary arteries onto the graft. The native aorta is either resected or wrapped around the prosthesis. (b) Maximum intensity projection image from gadolinium-enhanced 3D MR angiography in a 60-year-old man after a Bentall procedure shows the anastomoses of the coronary arteries to the prosthesis (arrowheads).

 

Figure 2
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  		Figure 2b.  Bentall procedure. (a) Schematic shows the replacement of the entire ascending aorta and aortic valve with a valve-equipped prosthesis and the reimplantation of the coronary arteries onto the graft. The native aorta is either resected or wrapped around the prosthesis. (b) Maximum intensity projection image from gadolinium-enhanced 3D MR angiography in a 60-year-old man after a Bentall procedure shows the anastomoses of the coronary arteries to the prosthesis (arrowheads).

 

Figure 3
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  		Figure 3a.  Cabrol procedure. (a) Diagram shows a Cabrol-type interostial conduit, which is routed behind the aortic prosthesis and anastomosed to an opening in it (arrow). (b, c) Schematics show a direct Cabrol shunt (b) between the perigraft space (PS) and the right atrial appendage (RA) and an indirect shunt (c) created by using a prosthetic tube. AO = aortic graft, RV = right ventricle.

 

Figure 3
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  		Figure 3b.  Cabrol procedure. (a) Diagram shows a Cabrol-type interostial conduit, which is routed behind the aortic prosthesis and anastomosed to an opening in it (arrow). (b, c) Schematics show a direct Cabrol shunt (b) between the perigraft space (PS) and the right atrial appendage (RA) and an indirect shunt (c) created by using a prosthetic tube. AO = aortic graft, RV = right ventricle.

 

Figure 3
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  		Figure 3c.  Cabrol procedure. (a) Diagram shows a Cabrol-type interostial conduit, which is routed behind the aortic prosthesis and anastomosed to an opening in it (arrow). (b, c) Schematics show a direct Cabrol shunt (b) between the perigraft space (PS) and the right atrial appendage (RA) and an indirect shunt (c) created by using a prosthetic tube. AO = aortic graft, RV = right ventricle.

 
If there are any intimal tears in the aortic arch, replacement of the entire ascending aorta and aortic arch and reimplantation of the supra-aortic trunks may be required (Fig 4a). If the dissection also affects the descending aorta or is accompanied by a preexisting aortic aneurysm, an elephant trunk–like extension of the aortic arch prosthesis may be used (9). This technique greatly facilitates subsequent surgical procedures in the descending aorta: The graft is not immediately anastomosed to the descending aorta according to convention but, instead, projects freely into the lumen of the descending aorta, like an elephant’s trunk (10). In a second step, the free end of the graft may be connected directly to the distal part of the descending aorta or extended by means of another tubular prosthesis or an endovascular stent-graft (5) (Fig 4b, 4c). This last procedure is necessary because of the difficulty of a surgical approach to the descending aorta by means of a median sternotomy.


Figure 4
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  		Figure 4a.  Replacements of the aortic arch and descending aorta. (a, b) Schematics show a prosthetic replacement of the aortic arch (a) and an elephant trunk–like extension distal to a prosthetic replacement of the proximal descending aorta (b). (c) Sagittal gadolinium-enhanced 3D MR angiogram in a 47-year-old woman shows prosthetic replacements of the supracoronary aorta and aortic arch, with an elephant trunk–like extension (arrow) of the native descending thoracic aorta.

 

Figure 4
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  		Figure 4b.  Replacements of the aortic arch and descending aorta. (a, b) Schematics show a prosthetic replacement of the aortic arch (a) and an elephant trunk–like extension distal to a prosthetic replacement of the proximal descending aorta (b). (c) Sagittal gadolinium-enhanced 3D MR angiogram in a 47-year-old woman shows prosthetic replacements of the supracoronary aorta and aortic arch, with an elephant trunk–like extension (arrow) of the native descending thoracic aorta.

 

Figure 4
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  		Figure 4c.  Replacements of the aortic arch and descending aorta. (a, b) Schematics show a prosthetic replacement of the aortic arch (a) and an elephant trunk–like extension distal to a prosthetic replacement of the proximal descending aorta (b). (c) Sagittal gadolinium-enhanced 3D MR angiogram in a 47-year-old woman shows prosthetic replacements of the supracoronary aorta and aortic arch, with an elephant trunk–like extension (arrow) of the native descending thoracic aorta.

 
Because prosthetic valve implantation is associated with postsurgical complications such as thromboembolism as well as with bleeding due to anticoagulation therapy, aortic valve–sparing techniques have been developed for use in selected patients. In 1992, David and Feindel reported the use of one such technique to treat aortic insufficiency without valve replacement in patients in whom the native valve leaflets were anatomically normal (11).

All of these techniques involve the placement of either an interposition graft or an inclusion graft. The procedure for interposition graft placement consists of resection of the damaged aortic wall and creation of an end-to-end anastomosis. The procedure for inclusion graft placement involves wrapping of the graft in the remnant of the diseased aorta, a procedure that creates a space between the graft and the aortic wall. This peri-graft space may contain a thrombus, flowing blood, or both (12).


   Postsurgical Complications
Top
 Abstract
 Introduction
 Surgical Procedures and...
 Postsurgical Complications
Conclusions
 References
 
Because of its safety and reproducibility, MR imaging is one of the modalities most often used for follow-up imaging of patients after surgical treatment of acute aortic dissection (1). The aim of imaging is to exclude potential complications and to document the baseline appearance for future comparison (10).

Prosthesis-related Complications
Anastomotic Stenosis.— In the follow-up of postsurgical type A aortic dissection, it is important to evaluate the periprosthetic area and both the distal and proximal parts of the anastomosis. A slight narrowing of the lumen usually can be observed near sutures (13), and sometimes the aortic lumen at the anastomosis is compromised (Fig 5). Three-dimensional gadolinium-enhanced MR angiography can help determine the luminal diameters of the native aorta and the prosthesis and help detect blood flow within the graft.


Figure 5
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  		Figure 5a.  Stenosis of a distal anastomosis in a 56-year-old-man 1 month after a Bentall procedure. (a) Axial gadolinium-enhanced 3D MR angiogram shows narrowing of the aortic lumen at the level of the distal anastomosis (*). (b) Sagittal 3D MR angiogram from the same examination shows a circumferential stenosis (white arrows) in the area of the distal anastomosis, a residual dissection that involves the brachio-cephalic artery (black arrows), and a hypointense periprosthetic hematoma (x).

 

Figure 5
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  		Figure 5b.  Stenosis of a distal anastomosis in a 56-year-old-man 1 month after a Bentall procedure. (a) Axial gadolinium-enhanced 3D MR angiogram shows narrowing of the aortic lumen at the level of the distal anastomosis (*). (b) Sagittal 3D MR angiogram from the same examination shows a circumferential stenosis (white arrows) in the area of the distal anastomosis, a residual dissection that involves the brachio-cephalic artery (black arrows), and a hypointense periprosthetic hematoma (x).

 
Periprosthetic Hematoma.— Gaubert et al (13) found that a uniform concentric thickening of the lumen near the graft, provided it did not exceed a thickness of 10 mm, was part of the normal postsurgical appearance. Pathologic collections such as periprosthetic hematomas usually are asymmetric, may appear heterogeneous on spin-echo (SE) MR images, and characteristically do not show enhancement at gadolinium-enhanced 3D MR angiography (Fig 6). Mesana et al (14) analyzed the volume and thickness of periprosthetic hematomas and found that these parameters, at the first MR imaging examination after surgery, had predictive value; if the thickness of a periprosthetic hematoma was greater than 15 mm at the first postoperative MR imaging examination, the patient was at risk for a pseudoaneurysm. Similar results have been observed in other studies (15).


Figure 6
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  		Figure 6a.  Progression of a periprosthetic hematoma to a pseudoaneurysm in a 44-year-old woman. (a) Axial T1-weighted SE image obtained 2 months after prosthetic replacement of the aortic valve and the ascending aorta shows a large periprosthetic hematoma (*) and residual dissection of the descending aorta (arrow). (b) Axial T1-weighted SE image obtained 2 years later shows a hyperintense persistent hematoma (*) and an increased diameter of the false lumen (x) with partial thrombosis (arrowhead) in the descending aorta. (c) Axial gadolinium-enhanced 3D MR angiogram shows the unenhanced hematoma (*) and a small gadolinium-enhanced pseudoaneurysm (arrow) indicative of dehiscence of the proximal anastomosis. Moderate contrast enhancement at the center of the false lumen indicates slow flow (x), and a lack of enhancement at the periphery confirms partial thrombosis (arrowhead).

 

Figure 6
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  		Figure 6b.  Progression of a periprosthetic hematoma to a pseudoaneurysm in a 44-year-old woman. (a) Axial T1-weighted SE image obtained 2 months after prosthetic replacement of the aortic valve and the ascending aorta shows a large periprosthetic hematoma (*) and residual dissection of the descending aorta (arrow). (b) Axial T1-weighted SE image obtained 2 years later shows a hyperintense persistent hematoma (*) and an increased diameter of the false lumen (x) with partial thrombosis (arrowhead) in the descending aorta. (c) Axial gadolinium-enhanced 3D MR angiogram shows the unenhanced hematoma (*) and a small gadolinium-enhanced pseudoaneurysm (arrow) indicative of dehiscence of the proximal anastomosis. Moderate contrast enhancement at the center of the false lumen indicates slow flow (x), and a lack of enhancement at the periphery confirms partial thrombosis (arrowhead).

 

Figure 6
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  		Figure 6c.  Progression of a periprosthetic hematoma to a pseudoaneurysm in a 44-year-old woman. (a) Axial T1-weighted SE image obtained 2 months after prosthetic replacement of the aortic valve and the ascending aorta shows a large periprosthetic hematoma (*) and residual dissection of the descending aorta (arrow). (b) Axial T1-weighted SE image obtained 2 years later shows a hyperintense persistent hematoma (*) and an increased diameter of the false lumen (x) with partial thrombosis (arrowhead) in the descending aorta. (c) Axial gadolinium-enhanced 3D MR angiogram shows the unenhanced hematoma (*) and a small gadolinium-enhanced pseudoaneurysm (arrow) indicative of dehiscence of the proximal anastomosis. Moderate contrast enhancement at the center of the false lumen indicates slow flow (x), and a lack of enhancement at the periphery confirms partial thrombosis (arrowhead).

 
Periprosthetic Pseudoaneurysm.— Pseudoaneurysm formation has been identified as a major complication of graft interposition techniques. It usually results from partial dehiscence of a suture line, either the proximal line (Fig 7) or the distal one (Fig 8). In addition, substantial perigraft flow with the MR imaging characteristics of a pseudoaneurysm (Fig 9) may result from leakage created by needle holes, even with an intact suture line (12). Patients who have undergone a Cabrol procedure (8) may have a small amount of perigraft flow, without progression to a larger pseudoaneurysm formation, because of the shunt created between the wrapped aortic sac and the right atrium.


Figure 7
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  		Figure 7a.  Periprosthetic pseudoaneurysm in a 56-year-old man after a Bentall procedure. Axial T1-weighted SE image (a) and axial gadolinium-enhanced 3D MR angiogram (b) show a pseudoaneurysm anterior and lateral to the prosthesis, a finding suggestive of suture dehiscence at the proximal anastomosis (*).

 

Figure 7
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  		Figure 7b.  Periprosthetic pseudoaneurysm in a 56-year-old man after a Bentall procedure. Axial T1-weighted SE image (a) and axial gadolinium-enhanced 3D MR angiogram (b) show a pseudoaneurysm anterior and lateral to the prosthesis, a finding suggestive of suture dehiscence at the proximal anastomosis (*).

 

Figure 8
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  		Figure 8a.  Pseudoaneurysm in a 58-year-old man 6 months after prosthetic replacement of the aortic valve and the ascending aorta. Sagittal (a), axial (b), and coronal (c) gadolinium-enhanced 3D MR angiograms demonstrate a pseudoaneurysm (*) caused by disruption of the distal anastomosis. The pseudoaneurysm extends to the origin of the brachiocephalic artery. Follow-up MR angiography 5 months later showed no significant changes.

 

Figure 8
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  		Figure 8b.  Pseudoaneurysm in a 58-year-old man 6 months after prosthetic replacement of the aortic valve and the ascending aorta. Sagittal (a), axial (b), and coronal (c) gadolinium-enhanced 3D MR angiograms demonstrate a pseudoaneurysm (*) caused by disruption of the distal anastomosis. The pseudoaneurysm extends to the origin of the brachiocephalic artery. Follow-up MR angiography 5 months later showed no significant changes.

 

Figure 8
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  		Figure 8c.  Pseudoaneurysm in a 58-year-old man 6 months after prosthetic replacement of the aortic valve and the ascending aorta. Sagittal (a), axial (b), and coronal (c) gadolinium-enhanced 3D MR angiograms demonstrate a pseudoaneurysm (*) caused by disruption of the distal anastomosis. The pseudoaneurysm extends to the origin of the brachiocephalic artery. Follow-up MR angiography 5 months later showed no significant changes.

 

Figure 9
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  		Figure 9a.  Pseudoaneurysm around an aortic prosthesis wrapped in the native aorta in a 60-year-old man. (a) Axial T1-weighted SE image depicts blood flow (*) between the anterior native aorta and the prosthesis, as well as a hyperintense periprosthetic hematoma. (b, c) Axial (b) and sagittal (c) gadolinium-enhanced 3D MR angiograms show a partial rim of contrast enhancement (*) around the prosthesis, a finding indicative of pseudoaneurysm.

 

Figure 9
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  		Figure 9b.  Pseudoaneurysm around an aortic prosthesis wrapped in the native aorta in a 60-year-old man. (a) Axial T1-weighted SE image depicts blood flow (*) between the anterior native aorta and the prosthesis, as well as a hyperintense periprosthetic hematoma. (b, c) Axial (b) and sagittal (c) gadolinium-enhanced 3D MR angiograms show a partial rim of contrast enhancement (*) around the prosthesis, a finding indicative of pseudoaneurysm.

 

Figure 9
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  		Figure 9c.  Pseudoaneurysm around an aortic prosthesis wrapped in the native aorta in a 60-year-old man. (a) Axial T1-weighted SE image depicts blood flow (*) between the anterior native aorta and the prosthesis, as well as a hyperintense periprosthetic hematoma. (b, c) Axial (b) and sagittal (c) gadolinium-enhanced 3D MR angiograms show a partial rim of contrast enhancement (*) around the prosthesis, a finding indicative of pseudoaneurysm.

 
Perigraft thickening can be readily detected with SE sequences. However, on SE images, the signal void due to blood flow around the graft, a finding that indicates pseudoaneurysm formation, may be absent in the presence of slow or turbulent flow. If this occurs, it may be difficult or impossible to differentiate between perigraft flow and a thrombus. In such a case, a pseudoneurysm can be differentiated from a perisprosthetic hematoma on the basis of gadolinium-enhanced 3D MR angiograms with high-signal-intensity areas that are indicative of perigraft flow (16).

Complications in the Native Aorta
Persistent Residual Dissection.— A patent distal false lumen with demonstrable blood flow has been found in 80% of patients with aortic dissection after surgical replacement of the ascending aorta (17).

False Lumen Thrombosis.— The false lumen may contain persistent blood flow due to distal intimal tears or blood flow from principal aortic branches that communicate with or originate from the false channel. The development of thrombosis within the false channel could compromise blood flow in vessels that communicate with the false channel (Fig 10) and may result in cerebral, spinal, mesenteric, or renal ischemia. Gadolinium-enhanced 3D MR angiography can be used to evaluate the blood flow through these vessels and demonstrate complications such as arterial stenosis and thrombosis.


Figure 10
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  		Figure 10a.  False lumen thrombosis in a 44-year-old woman with a prosthetic replacement of the aortic valve and the ascending aorta. (a) Axial gadolinium-enhanced fast spoiled gradient-recalled image shows residual dissection with high signal intensity due to blood flow in both the true and the false lumen (*). (b) Axial gadolinium-enhanced fast spoiled gradient-recalled image obtained at the same level 1 year later shows a lack of enhancement in the false channel (*), a finding indicative of thrombosis. (c, d) Axial gadolinium-enhanced fast spoiled gradient-recalled image (c), at a lower level than a and b, and coronal gadolinium-enhanced 3D MR angiogram (d) show blood flow in the false lumen (arrows). The flow originated from a distal reentry point in the left common iliac artery.

 

Figure 10
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  		Figure 10b.  False lumen thrombosis in a 44-year-old woman with a prosthetic replacement of the aortic valve and the ascending aorta. (a) Axial gadolinium-enhanced fast spoiled gradient-recalled image shows residual dissection with high signal intensity due to blood flow in both the true and the false lumen (*). (b) Axial gadolinium-enhanced fast spoiled gradient-recalled image obtained at the same level 1 year later shows a lack of enhancement in the false channel (*), a finding indicative of thrombosis. (c, d) Axial gadolinium-enhanced fast spoiled gradient-recalled image (c), at a lower level than a and b, and coronal gadolinium-enhanced 3D MR angiogram (d) show blood flow in the false lumen (arrows). The flow originated from a distal reentry point in the left common iliac artery.

 

Figure 10
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  		Figure 10c.  False lumen thrombosis in a 44-year-old woman with a prosthetic replacement of the aortic valve and the ascending aorta. (a) Axial gadolinium-enhanced fast spoiled gradient-recalled image shows residual dissection with high signal intensity due to blood flow in both the true and the false lumen (*). (b) Axial gadolinium-enhanced fast spoiled gradient-recalled image obtained at the same level 1 year later shows a lack of enhancement in the false channel (*), a finding indicative of thrombosis. (c, d) Axial gadolinium-enhanced fast spoiled gradient-recalled image (c), at a lower level than a and b, and coronal gadolinium-enhanced 3D MR angiogram (d) show blood flow in the false lumen (arrows). The flow originated from a distal reentry point in the left common iliac artery.

 

Figure 10
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  		Figure 10d.  False lumen thrombosis in a 44-year-old woman with a prosthetic replacement of the aortic valve and the ascending aorta. (a) Axial gadolinium-enhanced fast spoiled gradient-recalled image shows residual dissection with high signal intensity due to blood flow in both the true and the false lumen (*). (b) Axial gadolinium-enhanced fast spoiled gradient-recalled image obtained at the same level 1 year later shows a lack of enhancement in the false channel (*), a finding indicative of thrombosis. (c, d) Axial gadolinium-enhanced fast spoiled gradient-recalled image (c), at a lower level than a and b, and coronal gadolinium-enhanced 3D MR angiogram (d) show blood flow in the false lumen (arrows). The flow originated from a distal reentry point in the left common iliac artery.

 
False Lumen Dilatation.— The major problem in a patent false lumen is progressive dilatation, which often is followed by the collapse of the true lumen (Fig 11) and, potentially, late aortic rupture (18). Dilatation of the false lumen is facilitated by the poor condition of the aortic wall, which is weakened by dissection (13).


Figure 11
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  		Figure 11a.  True lumen collapse in a 26-year-old woman with Marfan syndrome who underwent a prosthetic replacement of the aortic valve and the ascending aorta in the 7th month of pregnancy. (a) Axial T1-weighted SE image shows residual dissection distal to the prosthesis (arrow). (b) Coronal T1-weighted SE image shows dilatation of the aortic sinuses (arrows). (c) Axial gadolinium-enhanced 3D MR angiogram at the level of the renal arteries shows a narrow true lumen, a wide false channel, and the site of communication between the two (*). (d) Maximum intensity projection image from the same examination as c shows the narrow true lumen (x).

 

Figure 11
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  		Figure 11b.  True lumen collapse in a 26-year-old woman with Marfan syndrome who underwent a prosthetic replacement of the aortic valve and the ascending aorta in the 7th month of pregnancy. (a) Axial T1-weighted SE image shows residual dissection distal to the prosthesis (arrow). (b) Coronal T1-weighted SE image shows dilatation of the aortic sinuses (arrows). (c) Axial gadolinium-enhanced 3D MR angiogram at the level of the renal arteries shows a narrow true lumen, a wide false channel, and the site of communication between the two (*). (d) Maximum intensity projection image from the same examination as c shows the narrow true lumen (x).

 

Figure 11
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  		Figure 11c.  True lumen collapse in a 26-year-old woman with Marfan syndrome who underwent a prosthetic replacement of the aortic valve and the ascending aorta in the 7th month of pregnancy. (a) Axial T1-weighted SE image shows residual dissection distal to the prosthesis (arrow). (b) Coronal T1-weighted SE image shows dilatation of the aortic sinuses (arrows). (c) Axial gadolinium-enhanced 3D MR angiogram at the level of the renal arteries shows a narrow true lumen, a wide false channel, and the site of communication between the two (*). (d) Maximum intensity projection image from the same examination as c shows the narrow true lumen (x).

 

Figure 11
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  		Figure 11d.  True lumen collapse in a 26-year-old woman with Marfan syndrome who underwent a prosthetic replacement of the aortic valve and the ascending aorta in the 7th month of pregnancy. (a) Axial T1-weighted SE image shows residual dissection distal to the prosthesis (arrow). (b) Coronal T1-weighted SE image shows dilatation of the aortic sinuses (arrows). (c) Axial gadolinium-enhanced 3D MR angiogram at the level of the renal arteries shows a narrow true lumen, a wide false channel, and the site of communication between the two (*). (d) Maximum intensity projection image from the same examination as c shows the narrow true lumen (x).

 
Gadolinium-enhanced 3D MR angiography can be used for follow-up imaging to detect persistent blood flow and thrombosis in the false channel and to define additional intimal tears. In addition, the 3D MR angiograms may be used to measure the diameter of the false lumen and thereby enable early detection of aneurysm formation (Fig 12).


Figure 12
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  		Figure 12a.  Aneurysmatic dilatation of the false channel and collapse of the true lumen. (a, b) Axial T1-weighted SE MR image (a) and sagittal oblique gadolinium-enhanced 3D MR angiogram (b) in a 46-year-old man with a prosthetic replacement of the ascending aorta show dilatation and partial thrombosis of the aortic false channel (x). A point of communication between the true lumen and the false channel also is depicted (arrow in b). (c, d) Axial (c) and coronal oblique (d) gadolinium-enhanced 3D MR angiograms in a 58-year-old man (same patient as Figure 9) with true lumen collapse show dilatation of the false channel along the abdominal aorta (*). (e) Photograph of an autopsy specimen from a patient who died several years after aortic replacement shows aneurysmatic dilatation and endothelialization of the false channel (arrowheads).

 

Figure 12
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  		Figure 12b.  Aneurysmatic dilatation of the false channel and collapse of the true lumen. (a, b) Axial T1-weighted SE MR image (a) and sagittal oblique gadolinium-enhanced 3D MR angiogram (b) in a 46-year-old man with a prosthetic replacement of the ascending aorta show dilatation and partial thrombosis of the aortic false channel (x). A point of communication between the true lumen and the false channel also is depicted (arrow in b). (c, d) Axial (c) and coronal oblique (d) gadolinium-enhanced 3D MR angiograms in a 58-year-old man (same patient as Figure 9) with true lumen collapse show dilatation of the false channel along the abdominal aorta (*). (e) Photograph of an autopsy specimen from a patient who died several years after aortic replacement shows aneurysmatic dilatation and endothelialization of the false channel (arrowheads).

 

Figure 12
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  		Figure 12c.  Aneurysmatic dilatation of the false channel and collapse of the true lumen. (a, b) Axial T1-weighted SE MR image (a) and sagittal oblique gadolinium-enhanced 3D MR angiogram (b) in a 46-year-old man with a prosthetic replacement of the ascending aorta show dilatation and partial thrombosis of the aortic false channel (x). A point of communication between the true lumen and the false channel also is depicted (arrow in b). (c, d) Axial (c) and coronal oblique (d) gadolinium-enhanced 3D MR angiograms in a 58-year-old man (same patient as Figure 9) with true lumen collapse show dilatation of the false channel along the abdominal aorta (*). (e) Photograph of an autopsy specimen from a patient who died several years after aortic replacement shows aneurysmatic dilatation and endothelialization of the false channel (arrowheads).

 

Figure 12
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  		Figure 12d.  Aneurysmatic dilatation of the false channel and collapse of the true lumen. (a, b) Axial T1-weighted SE MR image (a) and sagittal oblique gadolinium-enhanced 3D MR angiogram (b) in a 46-year-old man with a prosthetic replacement of the ascending aorta show dilatation and partial thrombosis of the aortic false channel (x). A point of communication between the true lumen and the false channel also is depicted (arrow in b). (c, d) Axial (c) and coronal oblique (d) gadolinium-enhanced 3D MR angiograms in a 58-year-old man (same patient as Figure 9) with true lumen collapse show dilatation of the false channel along the abdominal aorta (*). (e) Photograph of an autopsy specimen from a patient who died several years after aortic replacement shows aneurysmatic dilatation and endothelialization of the false channel (arrowheads).

 

Figure 12
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  		Figure 12e.  Aneurysmatic dilatation of the false channel and collapse of the true lumen. (a, b) Axial T1-weighted SE MR image (a) and sagittal oblique gadolinium-enhanced 3D MR angiogram (b) in a 46-year-old man with a prosthetic replacement of the ascending aorta show dilatation and partial thrombosis of the aortic false channel (x). A point of communication between the true lumen and the false channel also is depicted (arrow in b). (c, d) Axial (c) and coronal oblique (d) gadolinium-enhanced 3D MR angiograms in a 58-year-old man (same patient as Figure 9) with true lumen collapse show dilatation of the false channel along the abdominal aorta (*). (e) Photograph of an autopsy specimen from a patient who died several years after aortic replacement shows aneurysmatic dilatation and endothelialization of the false channel (arrowheads).

 
Dissection Involving Aortic Branches.— The direct extension of a dissection flap into visceral aortic branches may result in luminal obstruction and subsequent ischemic complications. Approximately 30% of patients with aortic dissection have one or more ischemic complications of the peripheral vasculature, such as renal failure or mesenteric ischemia. Aortic branches may be compromised by a direct extension of the intimal flap and aortic hematoma into the branch wall, with resultant luminal stenosis or total obstruction. They also may be compromised by a dynamic obstruction of the lumen such as that caused by an intimal flap that covers the origin of the aortic branch like a curtain (19). As described earlier, dilatation of the patent false channel and subsequent collapse of the true lumen also may affect the branch vessels.

In addition, brachiocephalic arteries frequently are affected by residual dissection. Residual dissection in a brachiocephalic artery may be associated with an increased risk of a neurologic ischemic event, although that hypothesis is controversial (20,21).

Gadolinium-enhanced 3D MR angiography allows evaluation of visceral aortic branches (Fig 13) and supra-aortic vessels (Fig 14) in the same examination. Furthermore, the technique is useful for long-term follow-up to detect and monitor complications in these vessels.


Figure 13
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  		Figure 13a.  Distal residual dissection with involvement of visceral aortic branches. (a) Coronal gadolinium-enhanced 3D MR angiogram shows a supracoronary aortic prosthesis in a 56-year-old man. (b, c) Axial 3D MR angiograms from the same examination at the origin of the celiac trunk (b) and the superior mesenteric artery (c) show distal residual dissection that affects both vessels (arrow).

 

Figure 13
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  		Figure 13b.  Distal residual dissection with involvement of visceral aortic branches. (a) Coronal gadolinium-enhanced 3D MR angiogram shows a supracoronary aortic prosthesis in a 56-year-old man. (b, c) Axial 3D MR angiograms from the same examination at the origin of the celiac trunk (b) and the superior mesenteric artery (c) show distal residual dissection that affects both vessels (arrow).

 

Figure 13
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  		Figure 13c.  Distal residual dissection with involvement of visceral aortic branches. (a) Coronal gadolinium-enhanced 3D MR angiogram shows a supracoronary aortic prosthesis in a 56-year-old man. (b, c) Axial 3D MR angiograms from the same examination at the origin of the celiac trunk (b) and the superior mesenteric artery (c) show distal residual dissection that affects both vessels (arrow).

 

Figure 14
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  		Figure 14a.  Distal residual dissection with involvement of the supra-aortic vessels. Axial (a) and coronal (b) gadolinium-enhanced 3D MR angiograms in a 56-year-old man show residual dissection that extends into the brachiocephalic arterial trunk (arrow in b) and the left subclavian artery (arrow in a).

 

Figure 14
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  		Figure 14b.  Distal residual dissection with involvement of the supra-aortic vessels. Axial (a) and coronal (b) gadolinium-enhanced 3D MR angiograms in a 56-year-old man show residual dissection that extends into the brachiocephalic arterial trunk (arrow in b) and the left subclavian artery (arrow in a).

 
Proximal Aortic Dissection.— An aortic dissection flap proximal to the prosthesis also may be detected at follow-up imaging in patients in whom a supracoronary surgical procedure has been performed (Fig 15). A proximal dissection flap may affect the coronary artery origin and may result in myocardial ischemia. To correctly identify proximal aortic dissection, it is important to know what type of surgery was performed. For example, in a patient who has undergone surgical repair with the Cabrol technique, this anatomic feature on axial images may resemble a focal dissection at the aortic root (16).


Figure 15
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  		Figure 15a.  Proximal residual dissection in a 70-year-old man with a prosthetic tube replacement of the ascending aorta. (a) Sagittal oblique gadolinium-enhanced 3D MR angiogram shows a short flap in the lumen at the aortic root (arrow), just below the prosthesis. (b) Axial CT image shows the dissection (arrow) proximal to the prosthesis. The finding also was con-firmed at transesophageal echocardiography (not shown).

 

Figure 15
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  		Figure 15b.  Proximal residual dissection in a 70-year-old man with a prosthetic tube replacement of the ascending aorta. (a) Sagittal oblique gadolinium-enhanced 3D MR angiogram shows a short flap in the lumen at the aortic root (arrow), just below the prosthesis. (b) Axial CT image shows the dissection (arrow) proximal to the prosthesis. The finding also was con-firmed at transesophageal echocardiography (not shown).

 

   Conclusions
Top
 Abstract
 Introduction
 Surgical Procedures and...
 Postsurgical Complications
 Conclusions
References
 
MR imaging is considered the modality of choice for evaluation of the postoperative aorta in patients who have undergone surgery for type A aortic dissection. Gadolinium-enhanced 3D MR angiography, in particular, is very useful for evaluating blood flow through and around the prosthesis and identifying prosthetic and periprosthetic complications. The technique also can be used to monitor the diameters of the native aorta and the false and true channels. All the aortic branches, including the supra-aortic trunks and visceral vessels, can be evaluated in one examination.


   Footnotes
 

Abbreviations: SE = spin echo, 3D = three-dimensional


   References
Top
 Abstract
 Introduction
 Surgical Procedures and...
 Postsurgical Complications
 Conclusions
 References
 

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