Foot complications associated with diabetes are the most common cause of nontraumatic lower extremity amputations in the industrialized world. Research indicates that the risk of lower limb amputation is 15 to 46 times higher in diabetic patients than in those without the disease.1 Common risk factors include peripheral neuropathy, structural foot deformity, infection, ulceration, and peripheral arterial occlusive disease.
Diabetic patients are four times more likely than the general population to develop peripheral arterial occlusive disease. This condition typically spares the proximal vessels in diabetic patients and mainly affects the more distal arteries in the calf with long-segment obstructions. These lead to rest pain, ischemic ulcers, toe gangrene, and osteomyelitis (Figure 1). Diabetic patients are consequently five times more likely to develop critical limb ischemia than the nondiabetic population.1-3
Surgical revascularization in patients with lower limb ischemia requires precise preoperative imaging of the peripheral vessels. The ultimate aim is to reduce the rate of foot amputations in these patients. The outcome of distal bypass or intervention is greatly affected by the presence or absence of adequate pedal outflow.
Identification of distal vessels in the foot, including the pedal arch, is crucial when planning advanced distal revascularization.2-4 Failure to identify vessels that could be recanalized or used for a distal graft anastomosis may result in unnecessary amputations. Preoperative imaging must provide a sufficiently detailed depiction of the pedal arteries.
The main options for noninvasive imaging are contrast-enhanced MR angiography and contrast-enhanced multislice CTA. MRA offers certain advantages over CTA. Patients are not exposed to ionizing radiation or to potentially nephrotoxic iodinated contrast media. The use of iodinated
contrast may be a concern for certain elderly patients with critical limb ischemia and associated renal insufficiency.
Just a few studies have compared the accuracy of contrast-enhanced pedal MRA with digital subtraction angiography.4-8 Our own study involving 24 diabetic patients demonstrated that pedal arch vessels were identified significantly more often on MR angiograms (22 feet) than on DSA images (nine feet) (Figure 2).5 The dedicated contrast-enhanced pedal MRA protocol showed patent pedal vessels not revealed by DSA in nine out of 24 patients (38%). Changes were made to seven patients' treatment plans: Two patients received a pedal bypass graft instead of amputation, and five patients underwent femoropedal bypass grafting instead of femorocrural or femoropopliteal bypass grafting.
Dorweiler et al considered the effect of grafting to DSA-occult pedal vessels, rather than grafting to vessels visible on DSA. They concluded that the long-term performance of grafts to vessels not visible on DSA was not impaired.4 Contrast-enhanced pedal MRA was found to be a meaningful adjunct in patients for whom detection of a distal target vessel suitable for bypass grafting would lead to limb salvage rather than major amputation. This applied particularly to diabetic subjects.
