Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAA) occur in 57% of the population older than 60 years of age. Although most patients with AAA are asymptomatic, they can present with symptoms of mass effect, compression of abdominal organs, or visceral or peripheral emboli originating from the wall of the aneurysm. Rarely, patients present with back pain, which can represent rupture of the aneurysm, a surgical emergency. Patients older than 60 years of age who smoke and who are known to have atherosclerosis, hypertension, and/or chronic obstructive pulmonary disease are at increased risk for AAA. Routine screening of these patients by ultrasound is warranted. In the United States 15,000 deaths per year are attributed to abdominal aortic aneurysms. Classically, AAAs have been attributed to a weakening of the arterial wall as a result of atherosclerotic vascular disease caused by the atheromatous lesions seen on pathologic examination. Atherosclerotic aneurysms are typically fusiform (Fig. 4), although focal eccentric aneurysmsdue to atherosclerosis are occasionally encountered (Fig. 5). Recent evidence supports a multifactorial process in which atherosclerosis is involved. Other etiologic co-factors under investigation include changes in the matrix of the aortic wall with age, proteolysis, metalloproteinase changes, inflammation, infectious agents (Fig. 6) (e.g., syphilis, mycotic infections), and a genetic predisposition (e.g., Marfan syndrome, Ehlers-Danlos syndrome). Inflammatory aneurysms, once believed to be distinct entities, are currently

Ehlers Danlos Syndrome Angiography

Fig. 5. Focal eccentric aneurysm (arrow) of the infrarenal abdominal aorta due to atherosclerosis, revealed on a MIP reformation of a 3D CE MRA dataset (Gd-BOPTA 0.1 mmol/kg). Note in addition the high grade stenosis of the right renal artery (arrowhead) [Image courtesy of Dr. G. Schneider]

Fig. 4. Fusiform infrarenal aneurysm of the abdominal aorta (arrows) as displayed on a MIP reformation of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) [Image courtesy of Dr. G. Schneider]

Fig. 5. Focal eccentric aneurysm (arrow) of the infrarenal abdominal aorta due to atherosclerosis, revealed on a MIP reformation of a 3D CE MRA dataset (Gd-BOPTA 0.1 mmol/kg). Note in addition the high grade stenosis of the right renal artery (arrowhead) [Image courtesy of Dr. G. Schneider]

considered one extreme in the spectrum of atherosclerotic aneurysms; these account for 3-10% of all AAAs. Clinical and imaging characteristics differentiate inflammatory from noninflammatory aneurysms. Mycotic aneurysms result from weakening of the vessel wall by a bacterial infection, causing saccular outpouching, most commonly in-volvingthe suprarenal portion of the aorta (Fig. 6). Contrast-enhanced MR angiography can demonstrate the aneurysm itself, whereas postcontrast T1-weighted imaging may demonstrate enhancement in and around the vesselwall [13].

Once an aneurysm is identified, it should be repaired or followed up with imaging, depending on the clinical scenario and the size of the aneurysm at the time of diagnosis. Most aneurysms (80%) demonstrate progressive enlargement. The natural history of AAAs is closely related to size. Rupture is uncommon if aneurysms are < 5 cm wide but dramatically more common if > 6 cm. Thus, elective surgical repair is usually recommended for all aneurysms > 6 cm in size unless surgery is con-traindicated [ 14]. In patients who are good surgical risks, elective repair is generally recommended for

Mycotic Aortic Aneurysm

Fig. 6a, b. Mycotic aneurysm of the suprarenal portion of the aorta with involvement of the renal arteries, the superior mesenteric artery and the celiac artery. The whole volume MIP image (a) of a 3D CE MRA dataset (Gd-BOPTA 0.1 mmol/kg) shows an eccentric aneurysm with occlusion of the left renal artery. A subvolume MIP reformation in sagittal projection (b) additionally reveals occlusion of the celiac artery [Images courtesy of Dr. G. Schneider]

Fusiform Aneurysm Abdominal

Fig. 7. Patient post surgery of an infrarenal AAA and graft anastomosis to both femoral arteries. The MIP reformation shows normal postsurgical proximal and distal anastomosis as well as a retrograde filling of the iliac arteries (arrows) which were bypassed during surgery. The graft was connected to the femoral arteries since an anastomosis at the level of the iliac arteries was not possible due to advanced atherosclerotic disease. Note the non-contrasted inferior pole of the right kidney (arrowhead) which is caused by occlusion of a lower pole artery of the right kidney during surgery and the additional development of a suprarenal aneurysm [Images courtesy of Dr. G. Schneider]

Fig. 7. Patient post surgery of an infrarenal AAA and graft anastomosis to both femoral arteries. The MIP reformation shows normal postsurgical proximal and distal anastomosis as well as a retrograde filling of the iliac arteries (arrows) which were bypassed during surgery. The graft was connected to the femoral arteries since an anastomosis at the level of the iliac arteries was not possible due to advanced atherosclerotic disease. Note the non-contrasted inferior pole of the right kidney (arrowhead) which is caused by occlusion of a lower pole artery of the right kidney during surgery and the additional development of a suprarenal aneurysm [Images courtesy of Dr. G. Schneider]

aneurysms between 5 and 6 cm in size for whom mortality is about 2 to 5%. Surgical repair consists of excision of the aneurysm and replacement with a synthetic conduit (Fig. 7); the graft may have to be carried into either or both iliac arteries if the aneurysm also involves these vessels (Fig. 8). Extension of the aneurysm above the renal arteries necessitates their reimplantation onto the synthetic graft or the creation of bypass grafts to them. Treatment of a mycotic aneurysm consists of vigorous antibiotic therapy directed at the specific organism, followed by excision of the aneurysm. Early diagnosis and treatment favourably influence outcome.

The Society for Vascular Surgery (SVS) and the International Society for Cardiovascular Surgery (ISCS) have suggested the classification of aneurysms by their site, origin, histologic features, and clinicopathologic manifestations. The morphologic features, including the maximum diameter in both the anteroposterior and lateral dimensions and the length of the aneurysm, and any involvement of major branch vessels should be reported (Fig. 9). All of these features can be identified and characterized with MR imaging [15, 16]. The shape of the aneurysm (fusiform or saccular)

Arotic Dissection Post Surgery
Fig. 8. Normal post surgical findings in a patient post AAA surgery without stenosis or aneurysm formation at the proximal or distal anastomosis (arrows) [Image courtesy of Dr. G. Schneider]

and its relationship to branch vessels should be described (Fig. 10). Arterial wall complications such as expansion over time, compression or erosion into adjacent structures, rupture, dissection, and thrombotic occlusion should also be documented [17].

Many refinements in treatment technique have occurred, but none as significant as the stent-graft [ 18]. With the advent of the endoluminal repair of aneurysms [19], several additional morphologic characteristics should be recorded. These determine if endovascular repair is possible, and if so, what type of device can be used. These features include the following: greatest mural diameter, extent of aneurysm (e.g., length of proximal and distal neck, extension into iliac arteries), tortuosity of the aorta, anatomy of the iliac arteries (e.g., iliac artery occlusive disease, tortuosity, caliber, patency of internal iliac arteries and relation of aneurysm to the iliac arteries, presence of concomitant iliac artery aneurysms), presence and degree of intralu-minal thrombus, presence and degree of calcification in the neck and iliac arteries, and anatomy of the femoral arteries (e.g., caliber, degree of calcification or occlusive disease) [20] (Fig. 11).Accurate

Mra Abdomen Mesenteric Arteries

Fig. 9a, b. The MIP image (a) of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) shows an infrarenal AAA (arrow) and possibly a reduced enhancement of the lower pole of the left kidney. On a subvolume MIP reformation (b) a lower pole artery of the left kidney (arrow) branching at the level of the AAA can be demonstrated, which is the reason for the delayed enhancement of the lower pole of the left renal artery (arrowheads) [Images courtesy of Dr. G. Schneider]

Fig. 9a, b. The MIP image (a) of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) shows an infrarenal AAA (arrow) and possibly a reduced enhancement of the lower pole of the left kidney. On a subvolume MIP reformation (b) a lower pole artery of the left kidney (arrow) branching at the level of the AAA can be demonstrated, which is the reason for the delayed enhancement of the lower pole of the left renal artery (arrowheads) [Images courtesy of Dr. G. Schneider]

Suprarenal Aaa Images

Fig. 10. A coronal arterial-phase MIP image from a 3D gadolinium-enhanced MR angiographic examination reveals a suprarenal extension of an abdominal aortic aneurysm

Suprarenal Aneurysm PhotosGadolinium Aneurysm

Fig. 11a, b. Pretreatment assessment of abdominal aortic aneurysm: Coronal (a) and sagittal (b) arterial-phase MIP images from a 3D gadolinium-enhanced MR angiographic examination reveal an infrarenal aneurysm. Evaluation of the extent of the aneurysm, the length and diameter of the proximal and distal neck, the extension into the iliac arteries as well as the tortuosity of the aorta in both planes is demonstrated

Fig. 11a, b. Pretreatment assessment of abdominal aortic aneurysm: Coronal (a) and sagittal (b) arterial-phase MIP images from a 3D gadolinium-enhanced MR angiographic examination reveal an infrarenal aneurysm. Evaluation of the extent of the aneurysm, the length and diameter of the proximal and distal neck, the extension into the iliac arteries as well as the tortuosity of the aorta in both planes is demonstrated

Tortuosity The Aorta

Fig. 12. Post operative control of abdominal aortic aneurysm. Coronal arterial-phase MIP image from a 3D gadolinium-enhanced MR angiographic examination demonstrates the patency of the bypass with no anastomotic stenoses or aneurysm visualization of the visceral vessels is important in determining stenosis of these vessels. Evaluation of calcification may be difficult with MR and a CT without iodine injection is usually necessary for a complete preoperative evaluation of AAA.

It is preferable to perform follow-up imaging with a noninvasive test such as MRA. Standard follow-up is recommended at one month and 6 months after stent placement or after surgery (Fig. 12).The majority of endoleaks are of Type 2, which may be caused by backfilling of the aneurysm sac by either the lumbar arteries or the inferior mesenteric artery (Fig. 13). Aortic stent-grafts (AneuRx, Talent) produce minimal artifact from the nitinol within the stent-graft [21]. While this causes local distortion of the post-contrast images, vessel patency and endoleak can be visualized. Embolization coils cause major distortion artifacts, obscuring all adjacent organs, as well as vessel lumen patency.

Fig. 12. Post operative control of abdominal aortic aneurysm. Coronal arterial-phase MIP image from a 3D gadolinium-enhanced MR angiographic examination demonstrates the patency of the bypass with no anastomotic stenoses or aneurysm try J*1 T

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