Abdominal Vascular Imaging Including Mesenteric Ischemia

M. Prokop

Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands

Abdominal vascular imaging is moving away from catheter angiography towards computed tomographic angiography (CTA), and to a lesser degree, magnetic resonance angiography (MRA) or ultrasound. Ultrasound used to be performed mainly in young patients and in acute settings, but computed tomography (CT) is starting to take over most of the work in patients with acute abdomen. MRA remains a good technique for follow-up of stented aortic aneurysms and for the detection of renal artery stenoses. Its ease and speed has led to CT becoming the technique of choice for the vast majority of indications in abdominal vascular imaging.

Abdominal Aorta Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAA) become more common with severe atherosclerosis and old age. They are mainly located in the infrarenal aorta, which makes them amenable to endoluminal repair by stent graft placement. Extensive disease, however, may involve most of the tho-racoabdominal aorta. More frequently, AAAs extend distally into the iliac arteries. Most aneurysms are fusiform, a minority are saccular. Rupture is the main cause of death, although a substantial number of patients die from other causes related to their atherosclerosis.

The most important information that imaging should provide is listed in Table 1. In addition to spatial information for treatment planning, it is important to detect complications, such as (contained) rupture, perianeurys-matic fibrosis, fistulation or compression of abdominal structures. CTA and, to a lesser degree, gadolinium (Gd)-enhanced MRA are the imaging procedures of choice for the diagnosis of abdominal aortic aneurysms. If information is needed about the spinal blood flow, the coronary arteries, or cerebral or peripheral blood flow, catheter an-giography may remain necessary. 64-slice CT has the ability to provide this information in many cases, if necessary in combination with electrocardiogram (ECG) gating. Longitudinal curved planar reformats (CPR), maximum intensity projections (MIP) or volume-rendered im-

Table 1. Checklist for AAA and suspected aortic rupture

AAA workup

• Signs of rupture (confined perforation is not uncommon)

• Penetrating ulcer?

• Inflammatory aneurysm (perianeurysmal fibrosis)

• Distance from the aneurysm to the origin of the renal arteries (proximal neck?)

• Involvement or stenosis of splanchnic arteries

• Involvement of aortic bifurcation and iliac arteries

• Retroaortic left renal vein

Signs of perforation

• Stranding of para-aortic tissue

• Para-aortic hematoma

• Hyperattenuating ascites ages are necessary for optimum evaluation (Fig. 1). Volume rendering is able to simultaneously display calcifications, vessel lumen and thrombus, and is particularly useful for surgical planning. CPR are most important for measurements prior to stent graft placement. The involvement of vessel origins in the aneurysm complicates surgical treatment. It is therefore important to determine the precise location of the abdominal side branches in relation to an aneurysm of the abdominal aorta.

Mural thrombus is a frequent finding and causes underestimation of the size of an aneurysm on three dimensional (3D) representations unless there is calcification of the aneurysm wall. The thrombus itself may partially calcify. Irregularities and ulceration of the mural thrombus may indicate an increased risk of distal emboli, in particular during angiographic procedures.

Penetrating ulcers are a consequence of ulcerative aortic plaques [1, 2]. They develop after destruction of the intima and may form saccular aneurysms with a high propensity for acute hemorrhage or may progress to aortic dissection (Fig. 1). A penetrating ulcer can be suspected if the aneurysm has overhanging edges or a focal dissection.

b

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