Occlusive Disease of the Aorta and Branches

The vast majority of stenotic (Fig. 19) and occlusive diseases of the aorta in the western world result from atherosclerosis. Occlusion of the abdominal aorta can be acute or chronic. Abrupt occlusion of the aortic bifurcation is rare. It is characterized by the sudden onset of pain, pallor, paralysis, and coldness in the legs. Usually a filling defect-meniscus on MIP projections indicates embo-lus. Urgent embolectomy is indicated and can usually be performed transfemorally. Chronic occlusion of the aortic bifurcation (Leriche's syndrome) is usually due to arteriosclerosis, is most frequently seen in the elderly, especially males with a history of smoking and manifests as intermittent claudication in the legs and buttocks and erectile impotence (Fig. 20). Leriche syndrome typically re-

Leriche Syndrome

Fig. 19a, b. Stenosis of the abdominal aorta just above the level of the bifurcation in a young male with a history of smoking. The coronal (a) and parasagittal (b) MIP reformations of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) show high grade stenosis of the aorta (arrows) in otherwise normal looking vessels of the abdomen [Image courtesy of Dr. G. Schneider]

Fig. 19a, b. Stenosis of the abdominal aorta just above the level of the bifurcation in a young male with a history of smoking. The coronal (a) and parasagittal (b) MIP reformations of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) show high grade stenosis of the aorta (arrows) in otherwise normal looking vessels of the abdomen [Image courtesy of Dr. G. Schneider]

Leriche Syndroom

Fig. 20a, b. MIP reformation (a) and volume rendered image (b) of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) show occlusion of the abdominal aorta (Leriche syndrome) just below the renal arteries (arrowin a). Note the extensive collaterals that developed due to the slow progression of the disease [Image courtesy of Dr. G. Schneider]

Fig. 20a, b. MIP reformation (a) and volume rendered image (b) of a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) show occlusion of the abdominal aorta (Leriche syndrome) just below the renal arteries (arrowin a). Note the extensive collaterals that developed due to the slow progression of the disease [Image courtesy of Dr. G. Schneider]

Aorta Collaterals
Fig. 21. Leriche syndrome of the infrarenal aorta with iliolumbar collaterals (arrow) and reconstitution of perfusion at the level of the femoral arteries (arrowheads). Volume rendered image from a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) [Image courtesy of Dr. G. Schneider]
Sindrome Iliolumbar
Fig. 22. Occlusion of the right iliac artery at the level of the bifurcation with collateral pathways via the iliolumbar vessels (arrows). MIP reformation from a 3D CE MRA dataset (Gd-BOPTA, 0.1 mmol/kg) [Image courtesy of Dr. G. Schneider]
Mra Leriche

Fig. 23. Four station moving table MRA in a patient with Leriche syndrome. The assembly of the different MIP images of the four CE MRA stations (Gd-BOPTA, 0.15 mmol/kg) shows occlusion of the aorta (arrow) with extensive collateralization (arrowheads) from lumbar and gluteal as well as inferior epigastric arteries. Note that the complete run-off vessels are displayed revealing no further high-grade stenosis [Image courtesy of Dr. G. Schneider]

Fig. 23. Four station moving table MRA in a patient with Leriche syndrome. The assembly of the different MIP images of the four CE MRA stations (Gd-BOPTA, 0.15 mmol/kg) shows occlusion of the aorta (arrow) with extensive collateralization (arrowheads) from lumbar and gluteal as well as inferior epigastric arteries. Note that the complete run-off vessels are displayed revealing no further high-grade stenosis [Image courtesy of Dr. G. Schneider]

sults in extensive collateral development and filling of the distal vessels with reconstitution at the iliac or common femoral arteries (Fig. 21). Collateral pathways include the Arc of Riolan, the marginal artery of Drummond, iliolumbar collaterals (Fig. 22), superior and inferior epigastric arteries, and gluteal collaterals. CE MRA represents an ideal imaging technique for evaluation of patients with suspected abdominal aortic occlusion [26, 27]. Conventional angiography is difficult in these patients, since access from the femoral arteries is limited. It is therefore necessary to perform arterial puncture of the brachial artery, a technique that is associated with a higher incidence of complications than catheterization procedures from the femoral artery. CE MRA is also preferable for these patients because the gadolinium chelates utilized are not associated with a significant risk of nephrotoxicity, as opposed to the iodinated contrast agents used in conventional angiography and CTA. Furthermore, MRA provides an excellent imaging technique for imaging the vessels distal to the aortic occlusion [28]. In this case, moving table MRA is also performed to evaluate the superficial femoral arteries and the infrapopliteal vessels (Fig. 23). This information is important, since the surgeon needs to know of the status of the distal runoff vessels. Understanding this anatomy is especially important for the femoral vessels, which serve as the distal terminus of the aortal-to-femoral bypass grafts.

The differential diagnosis for aortic occlusion

Occluded Renal Artery
Fig. 24. A coronal oblique MIP image from an arterial-phase gadolinium-enhanced MR angiographic examination reveals occlusion of the abdominal aorta below the origin of the renal arteries in a patient with Takayasu arteritis

includes aortic dissection with occlusion of true lumen by enlarging false lumen, and various coarctation syndromes (e.g., neurofibromatosis, Williams' syndrome, Takayasu's arteritis) (Fig. 24). Radiation-induced and giant cell arteritis are other relatively frequent causes of aortic diseases. In Takayasu's disease, also called pulseless syndrome, the aortic arch vessels are primarily affected, al-thoughthe thoracic and abdominal aorta and pulmonary arteries may also be involved. The aorta may become inflamed by various processes. Inflammatory aortic diseases usually involve all three layers of the aorta (i.e., intima, media, adventitial and the inflammatory infiltrate may vary from predominantly round cells in Takayasu's ar-teritis to giant cells in giant cell arteritis. Inflammation may occlude affected arteries or weaken vessel walls with subsequent aneurysm formation. Postcontrast Tl-weightedimages are important for the evaluation of arteritis, which may exhibit enhancing wall thickening in its early stages. The soft-tissue differentiation possible with MR imaging is valuable for the differentiation of active versus quiescent forms of Takayasu disease.

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