Aortoiliac Disease: Direct Reconstruction

Pathology

AIOD typically begins at the aortic terminus and common iliac artery origins and slowly progresses proximally and distally. Progression is variable but may ultimately result in total aortic occlusion ( Fig. 109.1 ). When collaterals are adequate, claudication symptoms are often tolerable and can be successfully managed nonoperatively for many years. Approximately one-third of patients operated on for symptomatic AIOD have significant orificial profunda femoris occlusive disease, and more than 40% have significant superficial femoral artery (SFA) disease. Disease can also extend superiorly to the level of the renal arteries (see Fig. 109.1 ). Although early reports indicated that up to one-third of patients with aortic occlusion went on to develop renal artery thrombosis during a period of 5 to 10 years, later prospective studies failed to confirm this observation. Renal or mesenteric arterial involvement sufficient to warrant concurrent repair is seen in only a minority of patients with AIOD.

Collateral Circulation

Although focal AI atherosclerotic disease commonly gives rise to claudication of varying degrees, it is rarely associated with chronic limb-threatening ischemia (CLTI). This is largely the result of abundant collateralization around the point of obstruction, which reconstitutes the infrainguinal system with sufficient flow to ensure adequate resting tissue perfusion ( Fig. 109.2 ). The primary compensatory networks develop from the lumbar and hypogastric feeding vessels and connect to circumflex iliac, hypogastric, femoral, and profunda recipients. Additional collaterals that arise in more severe cases include the internal mammary artery–to–inferior epigastric connection and the superior mesenteric artery-to-inferior mesenteric artery and hemorrhoidal artery pathway. The latter connection comprises the arc of Riolan and the meandering mesenteric artery ( Fig. 109.3 ); it is important to recognize the presence of such a large and significant collateral because it should be preserved during surgical reconstruction.

Epidemiology

The majority of patients presenting today with AIOD have diffuse disease at multiple levels of the vascular tree; in most cases, AIOD is found in combination with femoropopliteal or infrageniculate occlusive disease. Patients with isolated AIOD are generally younger, have a higher relative prevalence of smoking and hypercholesterolemia, are nearly as likely to be female as male, and typically have a normal life expectancy. In contrast, patients with more extensive multilevel disease are commonly older, more frequently have diabetes and hypertension, and are more likely to be male and to have concomitant cerebrovascular, coronary, and visceral atherosclerosis. Not surprisingly, patients with diffuse, multisegmental disease often present with ischemic rest pain or more severe perfusion impairment, leading to tissue loss or gangrene as opposed to isolated claudication. Such patients manifest a significant reduction in life expectancy compared with their age-matched counterparts.

A particularly virulent form of atherosclerotic disease is often found in young women who smoke. ^, Radiographic imaging in this subset of patients typically reveals atretic, narrowed vasculature with diffusely calcific atherosclerotic changes. Frequently, a focal stenosis is found posteriorly at or proximal to the aortic bifurcation ( Fig. 109.4 ). This disease distribution and characteristic patient profile have been termed small aortic syndrome or hypoplastic aortic syndrome . Such patients invariably have an extensive smoking history but may lack other typical risk factors for atherosclerosis. The diminutive size of the aorta and iliac vessels has important treatment implications in such patients; the durability of endovascular intervention or local endarterectomy is generally poor, particularly in the presence of continued cigarette use.

Presenting Symptoms

Chronic obliterative atherosclerosis of the distal aorta and iliac arteries commonly is manifested as symptomatic arterial insufficiency of the lower extremities, producing a range of symptoms from mild claudication to the spectrum of CLTI. Patients with hemodynamic impairment limited to the AI system may have intermittent claudication of the calf muscles alone or involvement of the thigh, hip, or buttock; patients with CLTI usually have multilevel disease of the AI and infrainguinal arteries. Those presenting with claudication secondary to AIOD are, on average, nearly a decade younger than those with claudication stemming from infrainguinal occlusive disease. Up to 30% of affected men may have difficulty achieving and maintaining an erection owing to inadequate perfusion of the internal pudendal arteries. In men, the well-characterized constellation of symptoms and signs known as Leriche syndrome, associated with terminal aortic occlusion, includes claudication (thigh, hip, or buttock), atrophy of the leg muscles, impotence, and reduced femoral pulses. The equivalent impact of impaired pelvic perfusion in women remains poorly understood but has attracted investigative attention.

History and Physical Examination

The diagnosis of AIOD can usually be made after a careful history and physical examination. In a patient with multiple vascular risk factors, claudication, and absent femoral pulses, the diagnosis of AIOD is straightforward. In other patients, symptoms of claudication can sometimes be difficult to distinguish from those of hip arthritis or nerve root irritation due to lumbar disk disease or spinal stenosis.

The variability of presenting signs and symptoms in patients with AIOD may cause diagnostic confusion. Although proximal claudication is most common, patients with AIOD in isolation or those with combined infrainguinal disease may present exclusively with calf claudication. Although the involved muscle groups may be atrophic from disuse in claudicants, the lower extremities frequently appear well perfused at rest. Femoral and even pedal pulses may be palpable at rest, reflecting the presence of robust collateral networks; pulses may diminish or become absent only after exercise. Similarly, a palpable thrill or audible bruit at the lower abdominal or groin level may only become detectable after exertion. Conversely, femoral bruits or diminished femoral pulses arising from CFA or profunda femoris stenoses can mistakenly be attributed to AI inflow disease.

Noninvasive Hemodynamic Assessment

Noninvasive arterial segmental systolic blood pressure measurements and pulse volume recordings can help confirm a clinical diagnosis of PAD and define the level and degree of obstruction (see Ch. 19 , Clinical Evaluation of the Arterial System). A resting difference of 20 mm Hg systolic or greater between the brachial and the proximal thigh pressures reflects a significant stenosis in the aorta or iliac arteries, but it may be confounded by proximal SFA occlusion. It is also important to recognize that upper thigh pressure is normally higher than brachial pressure, and that collaterals may offset a pressure gradient at rest but not during exertion. Thus, the absence of a resting pressure gradient meeting this threshold does not necessarily rule out the presence of symptomatic stenoses. A further reduction in pressure between the thigh and ankle level suggests concomitant femoropopliteal or tibial outflow disease. In patients with disabling symptoms with normal or near-normal resting ankle–brachial indices, repeating measurements after provocative graded exercise treadmill testing can be particularly useful if there is still clinical suspicion of AIOD. A careful history and physical examination combined with noninvasive hemodynamic studies usually provide sufficient data to establish the diagnosis. Further imaging is warranted only after risk/benefit assessment and the clinical decision to intervene has been reached.

Diagnostic imaging modalities that also facilitate revascularization planning include duplex ultrasound and axial imaging in the form of computerized tomographic angiography (CTA), magnetic resonance angiography (MRA), and arteriography; this topic is discussed in Chapter 108 (Lower Extremity Arterial Disease: Decision Making and Medical Treatment).

Impact of Endovascular Treatment

A significant paradigm shift has occurred in the treatment of PAD. ^, Angioplasty and stenting have become first-line therapy for most patients with AI, renal, subclavian, and coronary occlusive disease. Whereas percutaneous treatment of the aorta and iliac arteries was previously limited to short-segment, TransAtlantic Inter-Society Consensus (TASC) type A or B iliac lesions, it is now routinely applied to even long-segment (TASC type D) occlusions extending the length of the iliac arteries. In no other vascular territory has the shift from open surgery to interventional treatment been more apparent than in the AI segment. Using the Nationwide Inpatient Sample, one report documented an 850% increase in the use of percutaneous transluminal angioplasty and stenting for AIOD from 1996 to 2000, along with a simultaneous decrease of 16% in the rate of aortobifemoral grafting. Further reflecting this transformation in management strategy, in anatomically favorable circumstances, concomitant renal or mesenteric artery stenosis might be treated percutaneously as a staged initial procedure, even when subsequent open surgical AI reconstruction is planned. Decision making for surgical versus endovascular treatment is discussed in detail in Chapter 108 (Lower Extremity Arterial Disease: Decision Making and Medical Treatment).

In the current era, in which direct reconstruction for AIOD has been relegated to a second- or even third-line therapy, open bypass is increasingly undertaken in patients in whom endovascular treatment has failed or in those with such extensive disease that an endovascular approach is deemed inadvisable. This paradigm shift has been reflected in reports documenting the increasing complexity of aortobifemoral grafting, with a higher incidence of suprarenal clamping, adjunctive visceral revascularization, simultaneous operative inflow and outflow disease, and repeated grafting. ^{, ,} Patients with a combination of more proximal aneurysmal disease and common or external iliac occlusive disease continue to be good candidates for open reconstruction, although this group will continue to diminish with ongoing technologic advancements. Even patients with extensive calcification at the aortic bifurcation thought to be at risk for rupture with balloon angioplasty or those with disease extending to the CFA are no longer considered unsuitable for an endovascular approach. The incidence of rupture has proved low in the former group, and the introduction of low-profile covered stents and techniques of primary stenting is likely to further increase the safety of endovascular treatment in this setting. The latter patient subgroup can be managed with a hybrid approach, whereby the CFA plaque is treated with a traditional endarterectomy and patch repair and the iliac component is concurrently addressed with endovascular techniques. ^,

Patients with early recurrence of AIOD after angioplasty or stenting represent a growing group for whom open surgical repair may be indicated. Patients with significant renal failure in whom endovascular therapy entails a prohibitive risk of triggering dialysis dependence may also be considered better suited for operative repair. Complications of endovascular treatment, including dissection and vessel rupture, are infrequent indications for surgical reconstruction.

Claudication

The traditional indications for surgical reconstruction for symptomatic AIOD are disabling claudication, ischemic rest pain, and tissue loss. Claudication is a relative indication for intervention, given the natural history of the disease. Multiple reports, among them the Framingham Heart Study, indicate that patients with claudication have increased rates of cardiovascular mortality but an overall low risk of associated limb loss. ^, The majority of claudicants demonstrate a stable pattern of disease throughout their lifetimes or have an improvement in symptoms as a result of risk factor modification, whereas 20% to 30% require operation within 5 years as a result of disease progression. The annual rates of mortality and limb loss in patients with claudication have historically been reported as 5% and 1%, respectively. Some have suggested that claudicants with AIOD are more likely to progress to CLTI. In any case, the degree of disability that a particular level of claudication represents remains a subjective assessment by both the patient and the surgeon. As the associated risks of AI balloon angioplasty and stenting have fallen and the relative success rates have risen in recent years, the threshold for offering endovascular treatment to claudicants at all points along the clinical spectrum has significantly decreased. Indeed, patients once considered appropriate only for risk factor modification, exercise therapy, and medical treatment are now increasingly being offered percutaneous revascularization as a primary treatment option. Balloon technology is also increasingly being applied to hypogastric arterial disease, primarily for buttock or hip claudication, to a degree not previously seen and not paralleled by an increase in surgical revascularization.

The indications for surgical reconstruction for claudication have not shifted appreciably during this same period. Given its relatively benign natural history, maximal medical therapy continues to be appropriate for many patients with claudication. In contrast to patients with CLTI, it has been argued that an overly aggressive approach might place patients without limb-threatening conditions at unnecessary risk for adverse outcomes. The majority of claudicants remain stable for years, allowing time for collateral pathways to develop; this often results in sufficient improvement, making intervention unnecessary. On the other hand, in patients of low surgical risk with disabling symptoms from disease limited to the aortobifemoral segment, surgical bypass is an appropriate option. With current levels of perioperative morbidity and mortality, bypass can be undertaken safely and with the expectation of excellent long-term patency.

Chronic Limb-Threatening Ischemia

Although broad in spectrum, CLTI is associated with a more significant risk of amputation without revascularization. As such, the presence of ischemic rest pain, frank ulceration, or digital gangrene are well-accepted indications for surgical correction of AIOD. Patients with pregangrenous skin changes or frank gangrene typically have hemodynamically significant infrainguinal as well as AIOD. Thus, whereas patients treated for claudication or rest pain usually require only a single-stage inflow operation, simultaneous or staged inflow and outflow revascularization should be considered in patients with tissue loss where the goal remains the re-establishment of inline, pulsatile flow to the distal extremity to ensure healing (see Multilevel Occlusive Disease, below).

Patients with an aortic or iliac source of distal emboli, typically from an ulcerated atheromatous plaque or so-called “shaggy aorta,” represent another group in which operative reconstruction is usually indicated. Such patients may lack symptoms of claudication, and the culprit lesion(s) may not be hemodynamically significant. In these cases, the goal of intervention is to prevent recurrent distal embolization.

Studies have documented the generally excellent outcomes of aortobifemoral grafting in elderly patients, suggesting that in older patients who are otherwise good surgical risks, surgical therapy should not be withheld. Conversely, lower long-term patency rates with aortic bypass in younger patients (particularly those less than 50 years of age) or those with small aortic diameters suggest caution for considering early surgical intervention in such patients. ^,

Aortoiliac Endarterectomy

The first successful endarterectomy of an atherosclerotic CFA lesion by dos Santos was serendipitous, in that he had not originally intended to remove any intima or media. His success, after multiple failed attempts, was attributed to the novel use of heparin. Wylie et al. soon extended this technique to the AI level, and during the 1950s and 1960s, endarterectomy was the standard therapy for severe AIOD. Enthusiasm for the procedure dimmed, however, with the introduction of prosthetic graft material 10 years later, and AI endarterectomy was largely replaced by bypass grafting.

Patient Selection

Since endarterectomy eliminates the need for a prosthetic graft, it is an appealing alternative in the setting of infection and removes the possibility of myriad late graft-related complications. Advocates have likewise pointed to the advantages of endarterectomy in younger patients or those with small vessels who are less than ideal candidates for endovascular therapy or aortobifemoral grafting. Patients with erectile dysfunction attributable to proximal hypogastric occlusive disease are also well suited to this approach. Such patients can be expected to have a greater degree of improved pelvic perfusion after thorough endarterectomy of their AI and hypogastric segments compared with those undergoing ABFB grafting, and high rates of restored sexual function have been reported. ^,

Endarterectomy is most feasible and durable when it is applied to focal stenotic lesions in large-caliber, high-flow vessels. Indeed, the technique has proved particularly efficacious in patients with localized disease limited to the distal aorta or proximal common iliac arteries ( Figs. 109.4 and 109.5 ), and excellent long-term patency rates, on a par with aortic bypass grafting, have been reported. ^, In distinction, results in cases of long-segment disease involving the entire infrarenal aorta and extending into the external iliac arteries have been disappointing. The rise of endovascular therapy is further eroding the already small proportion of patients considered suitable for endarterectomy. As a result, the number of vascular surgeons who are comfortable and facile with this technique is limited.