Peripheral arterial occlusive disease (PAOD) is an umbrella term for all forms of impaired arterial circulation caused by stenotic or obstructive vascular processes including lesions of the aorta and arteries supplying the extremities (Spengel et al. 2001). Chronic arterial occlusive disease, unlike acute disease, is characterized by slow development of single or multiple stenotic lesions, which in over 90 % of cases affect the arteries of the pelvic region and legs. Steno-occlusive disease of the leg arteries leads to intermittent claudication due to muscle ischemia and increasingly limits the pain-free walking distance. About 20 % of patients with poor circulation of the legs have PAOD (Alexander 1992).

Three types of occlusive disease of the lower extremities can be distinguished by level of involvement: (1) aortoiliac disease with steno-occlusive lesions in the aorta and/or iliac arteries, (2) femoropopliteal PAOD, and (3) PAOD of more distal arteries (calf and foot). Only about one third of PAOD patients have ischemic symptoms (McDermott et al. 2002). Many patients limit their activities to reduce PAOD-related symptoms. Initially, they report feeling well but when questioned admit that they can only walk a short distance (Table 9.2).

The prevalence of stenotic and occlusive lesions of the distal leg varies with age and sex and also depends on the presence of risk factors (Kannel et al. 1970). The leading risk factors are smoking, diabetes mellitus, arterial hypertension, hyperlipoproteinemia, hypercholesterolemia, and hyperfibrinogenemia. The prevalence is 2.5 % before age 60 and as high as 18.8 % in those over 70 (Kannel 1996). Half of patients with lower leg occlusion have diabetes mellitus (Albers et al. 2005; Hirsch et al. 2005; Schneider et al. 1993).

PAOD patients have an increased risk of cerebrovascular and cardiovascular events (Criqui et al. 1997; Ness and Aronow 1999); the risk is the same regardless of whether they are symptomatic or asymptomatic (Hooi et al. 1998, 2001). Hence, the traditional concept of asymptomatic PAOD seems to downplay the risk. Patients with chronic PAOD have a mortality rate of over 20 % in the first year after diagnosis (Hirsch et al. 2005). Atherosclerotic occlusion most commonly affects the anterior tibial artery, followed by the posterior tibial artery and the fibular artery. Occlusion of a single calf artery with patency of the other branches is clinically silent. MR angiography with administration of gadolinium-based contrast medium is comparable to digital subtraction angiography (DSA) in terms of specificity and sensitivity for anatomic localization and grading of stenosis severity (Fig. 9.1).

Evaluation of vascular disease of the upper extremities was not part of the whole-body MRI protocol used.

A prevalence of renal artery stenosis (RAS) of 6.8 % has been reported by Hansen et al. (2002), but in high-risk groups, it may be as high as 50–70 % (Schwartz and White 1964; Harding et al. 1992; Weber-Mzell et al. 2002; Jean et al. 1994). Roughly two thirds of renal artery stenoses are due to atherosclerotic plaques, and one third of these are bilateral. Fibromuscular dysplasia accounts for the other third. Uni- or bilateral RAS underlies the development of arterial hypertension in 1–5 % of cases. Fibromuscular dysplasia is the predominant cause of RAS in young patients, usually women aged 20–40, and tends to affect the distal renal arteries. New-onset hypertension or progression of known hypertension in older individuals is mostly attributable to atherosclerotic stenosis, which typically involves the proximal renal arteries (Fig. 9.2).

Clinically, RAS may be asymptomatic or may present with renovascular hypertension or renal dysfunction. Mixed forms are also possible (Balk et al. 2006; Safian and Textor 2001). RAS greater than 70 % is considered hemodynamically relevant.

An acute ischemic event is not likely to be encountered in the classic screening situation. It is more likely to incidentally detect chronic mesenteric stenosis promoting or maintaining ischemia of upper abdominal organs and of the small and large intestines (abdominal angina).

The incidence of chronic occlusive disease of a mesenteric artery is approx. 5 % in patients presenting with abdominal pain of unknown cause. Because chronic occlusion progresses slowly and collaterals provide compensatory blood supply, the imaging appearance or autopsy findings do not tend to correlate with the clinical picture. Mesenteric stenosis is present in 80 % of individuals over 60 but rarely becomes clinically apparent. Symptoms do not develop unless there is appreciable ischemia in a target organ, which in turn requires a high-grade stenosis of at least 70 % (Luther 2001).