Abdominal Aortic Dissection

Aortic dissection occurs when blood dissects into the media of the aortic wall through an intimal tear. It is generally secondary to hypertension. In young patients with aortic dissection, an underlying process such as Marfan syndrome should be investigated. Dissection originating in the in-frarenal abdominal aorta is very rare and, given the vagueness of presenting symptoms of uncomplicated dissection, diagnosis is very difficult in the early stages. In the absence of a pulsatile abdominal mass, acute uncomplicated aortic dissection should be considered in the differential diagnosis of a sudden onset of abdominal and back pain [22].

Stanford type A dissections are treated in emergency by surgery while dissections arising distal to the left subclavian artery (Stanford type B) are usually treated medically [23]. However, delayed mortality caused by organ malperfusion is a major determinant of prognosis for both types of dissection. When an ischemic complication is clinically diagnosed, the mortality rate is of 50% in patients with type A dissection and 28 to 67% in patients with type B dissection. To manage such complications, minimum invasive endovascular approaches have been developed with promising results in selected patients. However, the success of such procedures is still dependent on early diagnosis.

Abdominal Aortic Dissection

Fig. 14. The MIP image of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) of a patient with chronic Stanford Type B dissection shows retrograde filling of the false lumen (arrow) from a re-entry in the iliac artery as well as branching of the right renal artery (arrowhead) from the false lumen [Image courtesy of Dr. G. Schneider]

Fig. 14. The MIP image of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) of a patient with chronic Stanford Type B dissection shows retrograde filling of the false lumen (arrow) from a re-entry in the iliac artery as well as branching of the right renal artery (arrowhead) from the false lumen [Image courtesy of Dr. G. Schneider]

An MR angiography study must evaluate the extent of the dissection, the sizes of the true and false lumina, the patency of the false lumen, and abdominal branch vessel involvement [24] (Fig. 14). The presence of a compressed true lumen, defined as dissection flap oriented concave to the false lumen, should be assessed. Branch lumen, including right and left renal arteries, celiac artery, mesenteric artery, and right and left common iliac arteries, is considered to be dissected when the branch arose from the false aortic lumen or when an intimal flap is shown to extend into the branch lumen (Fig. 15). The number of dissected aortic branches (i.e. renal, celiac, mesenteric and common iliac arteries) per patient should be noted. Association of significant visual lower enhancement of a segment or the entire parenchyma of a viscera in comparison with the contralateral paired viscera (for the kidney) is a sign of poorer prognosis (Fig. 16). Imaging should extend from the arch to the aortic bifurcation (Fig. 17). MIP images may not show the intimal flap; however, axial reformatted images from CE MRA are helpful for visualization of the intimal tear and re-entrysites. CEMRA is also helpful in postoperative follow-up [25]. It can accurately depict associated complications, including thrombosis, hemorrhage, aortoenteric fistula, and pseudoaneurysms. Potential drawbacks of MRI include false positives. On CE MRA these may include a central line artifact. This occurs when the acquisition is performed too early as the

Chronic Dissection
Fig. 15. MIP reformation of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) of a patient with chronic Stanford Type B dissection with multiple re-entries (arrows) and extension of the dissection membrane into the right renal artery (arrowhead [Image courtesy of Dr. G. Schneider]

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Fig. 16. Chronic Stanford Type B dissection. The sagittal MIP projection (a) shows the flattened true lumen anteriorly (arrow in a) from which the celiac artery and the superior mesenteric artery branch. In a slightly tilted projection (b) the origin of the left renal artery from the false lumen can be identified (arrow in b) [Image courtesy of Dr. G. Schneider]

Fig. 17. Parasagittal arterial-phase MIP image from a 3D gadolinium-enhanced MR angiographic examination demonstrates near occlusion of both the true and false lumens of a Stanford Type B dissection
Mra Celiac Artery

Fig. 18a-d. Penetrating atherosclerotic ulcer of the aorta at the level of the diaphragm. The coronal MIP projection (a) of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) already demonstrates the outpouching (arrow) of the perfused lumen extending beyond the contour of the aorta. This is even better appreciated on a sagittal MIP reformation (arrowin b). Additional volume rendered images (c, d) are helpful to further evaluate the relationship between the penetrating atherosclerotic ulcer and the celiac artery, in this case demonstrating a short distance between the ulcer and the origin of the celiac artery (arrowin d) as well as a stenosis of the celiac artery approximately 1.5 cm from its origin [Image courtesy of Dr. G. Schneider]

Fig. 18a-d. Penetrating atherosclerotic ulcer of the aorta at the level of the diaphragm. The coronal MIP projection (a) of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) already demonstrates the outpouching (arrow) of the perfused lumen extending beyond the contour of the aorta. This is even better appreciated on a sagittal MIP reformation (arrowin b). Additional volume rendered images (c, d) are helpful to further evaluate the relationship between the penetrating atherosclerotic ulcer and the celiac artery, in this case demonstrating a short distance between the ulcer and the origin of the celiac artery (arrowin d) as well as a stenosis of the celiac artery approximately 1.5 cm from its origin [Image courtesy of Dr. G. Schneider]

concentration of intraortic gadolinium is rising. This artifact can be readily differentiated from an aortic dissection as it does not take a spiral course as with a true intimal flap.

Penetrating atherosclerotic ulcer is characterized by ulceration of an atherosclerotic plaque that penetrates through the intima into the media of the aortic wall. It typically affects elderly individuals with hypertension and extensive aortic atherosclerosis. It is seen as an outpouching extending beyond the contour ofthe aortic lumen and can become quite large (Fig. 18). A penetratingathero-sclerotic ulcer is typically located in the descend-ingaorta but can be seen in the abdominal aorta. It can be associated with a variable degree of hematoma within the aortic wall. Placement of an endovascular stent-graft is becoming a popular method of treating this entity, given that the disease tendsto occur in elderly patients with comor-bid conditions that putthem at high surgical risk.

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