Description and Special Anatomic Considerations

Vascular bypass surgery involves placement of a conduit to serve as an alternative vascular pathway to a diseased or obstructed arterial bed. Vascular surgical conduits are anatomically classified on the basis of the locations of the proximal and distal anastomoses. The most common infrainguinal bypass is the femoropopliteal bypass, between the common femoral and the popliteal arteries (Fig. 114-1A,B). The distal anastomosis may be to either the above-knee or the below-knee segment of the popliteal artery (Fig. 114-1C). Conduits are further defined according to the material from which they are constructed. They may be native, such as an autogenous vein or artery, or they may be prosthetic, such as expanded polytetrafluoroethylene (ePTFE) or Dacron. The native greater saphenous vein is preferred for bypass surgery in the lower extremity because it performs better than any other conduit choice. However, it may not always be an available option because donor veins may be diseased or may have been previously harvested for other vascular procedures, such as coronary artery bypass surgery. Other autogenous veins used as vascular conduits include the short saphenous vein, the femoral vein (also known as the superficial femoral vein) within the thigh, and the basilic and cephalic veins of the upper extremity.

FIGURE 114-1 Femoropopliteal bypass graft. Images (A to C, cranial to caudal) from a right leg arteriogram show the proximal anastomoses (A, arrow) of a femoropopliteal bypass graft and the course of the graft (B, arrow) in the medial right thigh. The distal anastomosis of this femoropopliteal bypass graft is to the below-knee segment of the popliteal artery (C, arrow). Note the focal bulges (C, arrowhead) in the graft where venous valves were present in this in situ saphenous vein graft. These valves would have been excised with a valvulotome at the time of bypass surgery.

The autogenous greater saphenous vein conduits can be further subdivided into in situ and reversed vein grafts. Use of an in situ vein graft involves mobilization of only the proximal and distal ends of the vessel while allowing most of the vein to remain within its vascular bed. The venous valves must be incised, and venous tributaries arising from the in situ graft must be ligated. Proximal and distal anastomoses to the artery are then created at the mobilized ends of the in situ graft. A reversed saphenous vein graft must first be carefully harvested from the thigh, with ligation of all tributary vein branches. The vein is reversed during the bypass procedure, which allows unobstructed flow through the venous valves. Because of the reversal of the vein, the smaller distal end of the harvested vein is anastomosed to the larger caliber proximal artery, a situation that has generated a variety of surgical strategies to deal with the mismatch. Some surgeons use a harvested saphenous vein in a nonreversed fashion after incising the valves.

Prosthetic grafts typically are used for aortobifemoral and extra-anatomic bypass surgery, such as axillofemoral or cross-femoral bypass graft surgery; when they are used for femoropopliteal bypass surgery, long-term patency is significantly improved when the distal anastomosis is to the above-knee rather than the below-knee segment of the popliteal artery. There are relatively poor results for distal revascularization with prosthetic grafts. If bypass to the below-knee popliteal arterial segment is necessary, an autogenous vein graft is indicated; if the greater saphenous vein is not an option as a conduit, other autogenous veins may be used. Composite grafts that use a prosthetic above the knee coupled with an autogenous graft to cross the joint and to anastomose to the below-knee segment are also used.

Prosthetic grafts have certain advantages, including ease of use, shortened surgical times, and less extensive operative dissection. The disadvantages relative to autogenous grafts include higher frequencies of intimal hyperplasia, thrombosis, and anastomotic stenoses. There are also higher rates of graft infections, material deterioration, and anastomotic pseudoaneurysms than in their native counterparts.

The lack of a completely satisfactory prosthetic substitute for the greater saphenous vein has led to the use of other biologic conduits, such as human umbilical vein, arterial or venous homografts, and xenografts. There are certain inherent problems, such as aneurysmal degeneration (Fig. 114-2), and long-term patency issues that are unique to these biografts, and results remain mixed compared with prosthetic grafts.⁷

FIGURE 114-2 A and B, This bovine xenograft used for distal bypass to the dorsalis pedis artery (arrow) underwent severe degeneration, as seen in this arteriogram. There are multiple stenoses and aneurysms present in the graft as a result of the degeneration. This is an inherent problem in both xenografts and homografts. C, Gray-scale ultrasound image of the bovine xenograft at knee level demonstrates that there is marked aneurysmal degeneration with considerable laminar thrombus (T) and an eccentric patent lumen (asterisk).

Extra-anatomic bypass refers to grafts that are constructed in anatomic locations that are significantly different from the normal location of the diseased arteries that are being bypassed. Typical examples are the cross-femoral (femorofemoral) and axillofemoral bypass grafts (Figs. 114-3 to 114-5). These were originally designed for patients too ill to undergo direct aortofemoral bypass or to replace grafts that were infected; these are still the primary indications. In addition, they now often serve as adjuncts to endovascular repair of abdominal aortic aneurysms (EVAR), particularly in the category of aorto–uni-iliac EVAR. These grafts are usually constructed of prosthetic material and generally have somewhat lower long-term patency than more traditional vascular bypass grafts, such as the aortobifemoral bypass graft. The obturator bypass (Fig. 114-6) was developed to replace femoropopliteal bypass surgery in patients with groin infections involving the native arteries or previously placed grafts and in patients with other complicating circumstances in the groin, such as trauma or previous radiation treatment. This bypass can be constructed with prosthetics or with autogenous vein.⁸

FIGURE 114-3 Axillofemoral bypass graft. Digital subtraction angiography (DSA) images (A to C, cranial to caudal) show the proximal limb (A, arrow) of an axillofemoral bypass graft, the thoracic course (B, arrow) of the axillofemoral bypass graft, and the distal anastomoses to the profunda femoral artery (C, arrow). A femorofemoral bypass graft (not shown) was also constructed in this patient.

FIGURE 114-4 Conventional x-ray arteriogram shows a right-to-left femorofemoral bypass graft (white arrow). The study also reveals an inflow stenosis (black arrow) in the right external iliac artery stent graft and occlusion of the heavily calcified native superficial femoral artery (arrowheads) in this patient who had also previously undergone a femoropopliteal bypass graft. This patient will require correction of the inflow abnormality and either thrombolysis of the bypass graft or surgical revision.

FIGURE 114-5 CTA shows a right-to-left femorofemoral bypass graft constructed in a patient who had previously undergone endovascular repair of an abdominal aortic aneurysm and subsequently had occlusion of the left limb of the graft.

FIGURE 114-6 CTA shows that there has been placement of an obturator bypass (arrow) in this patient who has previously had placement of an axillofemoral and right-to-left femorofemoral bypass, followed by a left axillofemoral bypass graft. Both procedures eventually failed because of chronic infection in the left inguinal region, necessitating the obturator bypass.

Indications

Patients with lower extremity peripheral arterial disease that is manifested as claudication are typically managed medically, with an emphasis on lifestyle and risk factor modification coupled with an exercise regimen. Although many patients will show symptomatic improvement, a large number will have progression of disease. In addition, compliance of patients with such a management strategy is generally poor. Disabling, lifestyle-limiting claudication or progression to critical limb ischemia, characterized by rest pain or tissue loss, may eventually occur and thus require either infrainguinal bypass surgery or endovascular revascularization.

Patients with peripheral arterial disease may be classified by both a clinical description of the symptoms and objective testing criteria by the Rutherford categories of chronic limb ischemia (Table 114-1). These aid in prognosis and treatment planning.

The anatomic location of the peripheral arterial disease affects the choice of a surgical or endovascular procedure. Arterial bypass remains the standard for revascularization and is indicated in patients with long-segment chronic total occlusion of the superficial femoral artery, chronic total occlusion of the popliteal artery and proximal trifurcation vessels, diffuse, severe multiple stenoses or occlusions that involve the entirety of the superficial femoral artery, and recurrent stenoses or occlusions after two or more prior endovascular treatments.

Contraindications

Arterial bypass surgery is contraindicated if there is insufficient inflow or outflow to maintain patency of the vascular conduit. Before bypass, therefore, some type of imaging (CT angiography [CTA], MR angiography [MRA], or catheter angiography) is generally performed for delineation of arterial anatomy and to identify an appropriate target artery for distal anastomoses. If there is no target vessel or there is uncorrected inflow disease, arterial bypass surgery will have a poor outcome.

A conduit should not be constructed in an actively infected tissue bed. An infection should be aggressively treated to resolution; if vascularity is insufficient to allow healing, extra-anatomic bypass or amputation should be considered.

Outcomes and Complications

Long-term graft patency, limb salvage, and mortality are the primary reported endpoints for revascularization procedures. Relief of symptoms is subjective and thus more difficult to accurately quantify and assess.

Graft patency is described as primary, assisted primary, and secondary. Primary patency indicates that no additional procedures have been performed that involve the vascular conduit, including any graft extensions that may be required for progression of disease distally. Assisted primary patency includes any minor revisions or endovascular treatments of lesions that threaten graft patency. If the graft has thrombosed and patency is restored by thrombolysis, thrombectomy and revision, or other means, this is considered secondary patency.

Complications and lesions that threaten vascular conduit longevity include infection, development of anastomotic stenoses (Fig. 114-7) or pseudoaneurysms, progression of disease distal to the graft resulting in inadequate outflow, failure to incise all valves or to ligate all venous side branches within an in situ bypass graft, intimal hyperplasia, poor conduit quality, and degeneration of the graft. Such complications will require open surgical or endovascular correction.

FIGURE 114-7 A, DSA reveals a stenosis (arrow) of an in situ femoropopliteal bypass graft at the distal anastomoses to the below-knee popliteal artery. B, Magnified DSA arteriogram delineates the high-grade distal anastomotic stenosis more clearly. C, The anastomotic stenosis was treated with balloon angioplasty, successfully eliminating the stenosis and maintaining graft patency. This is an example of assisted primary patency.

Local complications, including hemorrhage, infection, and graft thrombosis, may occur at the time of the initial surgery. Hemorrhage is usually related to an anastomotic problem, such as a suture line disruption, or to a poorly ligated side branch (arterial or venous). Graft infections commonly result from hospital-acquired organisms in the early period and are increased in the presence of hematoma, lymphocele, or wound infection. Graft infections occurring more than 3 months after the bypass are usually due to microorganisms such as normal skin flora. Infections are manifested on imaging studies as perigraft fluid collections and may be confirmed with CT- or ultrasound-guided aspiration followed by culture and sensitivity testing. Special culture techniques may be required.

The outcomes of various infrainguinal bypass procedures with use of currently available vascular conduits are summarized in Tables 114-2 to 114-4. With regard to extra-anatomic bypass grafts, the long-term patency rates are typically lower than for the anatomically positioned grafts. The obturator bypass graft for infrainguinal occlusive disease has reported patency rates of 73% and 57% at 1 and 5 years, respectively, which are somewhat lower than with conventional femoropopliteal bypass.⁸

Imaging Findings

Description and Special Anatomic Considerations

Both percutaneous transluminal angioplasty and intravascular stent placement have become widely accepted as primary treatment of infrainguinal peripheral arterial disease so that endovascular treatments now have an extremely important role in its management. Application of endovascular therapies remains a dynamic process as currently available technology evolves and new treatment devices and options are introduced (e.g., atherectomy, covered stents, cryoplasty, drug-eluting stents, lasers, biodegradable stents).

The most frequently employed endovascular treatment options are angioplasty and intravascular stent placement. Angioplasty may be used as a stand-alone primary therapy (Figs. 114-8 and 114-9) or may be combined with stent placement. Stents provide an intravascular scaffold for the vessel lumen and are available in a variety of materials, configurations, and delivery systems. Stents may be constructed from stainless steel, platinum, Elgiloy, and nitinol and may be combined with ePTFE or Dacron to produce a covered stent endoprosthesis or “stent graft.” Noncovered stents may be constructed with “open” or “closed cell” designs, which influence stent flexibility, conformability, radial strength, fracture resistance, and restenosis rates. In addition, there are balloon-mounted and self-expanding stents available in both the noncovered and covered groups (Figs. 114-10 and 114-11). Balloon-mounted stents are typically sized to correspond to the desired diameter of the vessel lumen, whereas self-expanding stents are usually oversized and may require secondary angioplasty to achieve a satisfactory diameter.

FIGURE 114-8 Angioplasty balloons are available in various lengths and diameters and have varying burst pressures, depending on the material from which they are constructed. This is a noncompliant balloon, meaning that the balloon will retain a tubular shape and will not conform to the vessel luminal characteristics by expanding beyond the manufacturer’s predetermined maximum diameter.

FIGURE 114-9 A, DSA image shows two stenoses (arrows) in the mid and distal superficial femoral artery. B, After angioplasty, there is restoration of a normal luminal caliber in the treatment areas (arrows). C, Magnification view of the distal treatment zone in B after angioplasty shows small linear contrast collections (arrows) paralleling the vessel lumen. These represent “cracks” or fissures within the plaque that have resulted from the angioplasty. The mechanism is that of a controlled fracture of the plaque, often accompanied by stretching of the muscular media. Over time, this usually remodels and assumes a more normal appearance.

FIGURE 114-10 Noncovered stents are available as either self-expanding (A) or balloon mounted (B). The self-expanding stent is typically oversized relative to the native artery to be treated, whereas the balloon-mounted stent is more precisely sized to the native vessel diameter.

FIGURE 114-11 Covered stents (stent grafts or vascular endoprostheses) are available as either self-expanding (A) or balloon mounted (B).

Given the decreased restenosis rates in the coronary arteries that have resulted from use of drug-eluting stents, there has been considerable enthusiasm for extending the application to treatment of the lower extremity arteries. Initial results have been mixed, but clinical trials remain ongoing.

Atherectomy involves a catheter-based atherosclerotic plaque excision system consisting of two components: a low-profile monorail excision catheter and a palm-sized power drive unit. A tiny rotating blade housed near the catheter tip is exposed when activated, removing and capturing thin shavings of plaque from the arterial wall into a collection chamber. Atherectomy thus permits “debulking” of atheroma from the lesion and may be used as a primary therapy or in combination with other endovascular treatment options. Catheters vary in diameter and tip length to accommodate various lesions (Figs. 114-12 and 114-13).

FIGURE 114-12 Graphic of the FoxHollow SilverHawk atherectomy catheter shows the cutting blade (arrowhead) within the cutting window engaging the atheroma (black arrow). As thin shavings of atheroma are excised, they are collected in the nose cone (white arrow) at the catheter tip.

FIGURE 114-13 A, Image from an atherectomy procedure shows a focal stenosis in the superficial femoral artery (arrow) before intervention. B, A guide wire has been advanced across the stenosis, and the atherectomy catheter (arrow) has been introduced. C, After the atherectomy, there is an almost completely normal appearance to the artery at the site of the previous stenosis (arrow).

Cryoplasty is an angioplasty-based technology that uses liquid nitrous oxide as the balloon inflation medium, which lowers the balloon surface temperature to −10° C. Theoretically, cryoplasty causes an altered plaque response in which, as a result of freezing, microfractures form and weaken the plaque, contributing to a more uniform vessel dilation and less injury to the media. There may also be less elastic recoil and an induction of cellular apoptosis through freezing (Fig. 114-14).^9,10

FIGURE 114-14 A, Image from a cryoplasty procedure shows a high-grade superficial femoral artery stenosis (arrowhead) on the diagnostic DSA arteriogram. B, Fluoroscopic spot film shows that the cryoplasty balloon (arrows) is inflated within the stenotic area; note the atherosclerotic calcification adjacent to the cryoplasty balloon. C, After cryoplasty, there is a normal caliber to the arterial lumen in the treatment zone (arrows).

Another angioplasty-based technology is cutting balloon angioplasty, in which multiple small atherotomes (microsurgical blades) are fixed longitudinally on the outer surface of a noncompliant balloon. These expand radially during balloon inflation, delivering longitudinal incisions into the plaque and the vessel. Theoretically, there should be advantages to cutting balloon angioplasty through reduction of vascular injury by scoring of the vessel and the plaque longitudinally rather than by causing an uncontrolled disruption of the atherosclerotic plaque. However, in a randomized trial of 1385 coronary lesions, there was no significant difference between cutting and standard angioplasty at 6-month follow-up in angiographic and clinical results. The primary endpoint of angiographic restenosis at 6 months was 31.4% in the cutting balloon angioplasty group versus 30.4% in the standard group. This trial showed that cutting balloon angioplasty is equivalent in safety and efficacy endpoints to standard angioplasty, but it did not prove superiority for the general pool of percutaneous coronary intervention patients.¹¹

There are varying opinions as to the optimal endovascular treatment strategy for infrainguinal lesions with regard to angioplasty alone, angioplasty accompanied by primary stenting, and the use of noncovered versus covered stents. Treatment options depend on the route of arterial access; the type, length, and location of the lesions; the presence or absence of inflow disease; the quality of the runoff vessels distal to the lesions; the overall clinical status of the patient; and the skills and long-term success rates of the operator. The cost associated with endovascular procedures is also a consideration; generally, these technologies are substantially more expensive than open surgical revascularization procedures.

Infrainguinal lesions may be treated either with an ipsilateral antegrade femoral artery puncture or from the contralateral approach, with the catheter and wire advanced across the aortic bifurcation to gain access to the arteries of the affected limb. The successful use of the latter approach depends on the distal aortic and pelvic arterial anatomy; tortuous or stenotic iliac arteries or an acutely angled aortic bifurcation may significantly complicate the negotiation of the catheter into the treatment area. This approach may be necessary for treatment of lesions that involve the common femoral or the proximal superficial or profunda femoral arteries.

Indications

Determination of which lesions are appropriate for endovascular treatment versus traditional surgical revascularization continues to be an evolving and sometimes controversial process. Addressing these concerns has resulted in multidisciplinary attempts to categorize lesions, to stratify the risks and benefits of endovascular treatment, and to propose treatment guidelines. In 1994, the American Heart Association proposed percutaneous transluminal angioplasty guidelines for endovascular versus surgical treatment. These have since been revised as longer follow-up data have become available and as intravascular stents have been incorporated into endovascular treatment regimens.

The TransAtlantic Inter-Society Consensus Working Group (TASC) developed another classification system in 2000¹² and addressed both aortoiliac and infrainguinal occlusive disease, with the latter guidelines limited to femoropopliteal disease. These guidelines were updated in 2007¹³ and reflect the expanded role of endovascular therapy as a primary option in the treatment of vascular occlusive disease (Table 114-5).

TABLE 114-5 TransAtlantic Inter-Society Consensus (TASC II) Recommendations (Femoropopliteal Arterial Disease)

Description and Special Anatomic Considerations

Lower extremity arterial occlusions resulting from distal embolization or acute thrombosis may manifest as a profoundly ischemic limb and constitute a surgical emergency. Initially, the underlying cause of the occlusion should be determined (e.g., cardiac embolus from atrial fibrillation or myocardial infarction versus in situ thrombosis associated with atherosclerosis). The patient’s clinical history and the nature of the symptoms frequently suggest the etiology of the occlusion. Embolic occlusions usually cause more severe ischemia because of the lack of collaterals, whereas thrombosis in the presence of preexisting disease may be better tolerated because there are established collaterals. The decision about appropriate imaging, such as angiography, is based on the clinical status of the limb, the presumed etiology of the occlusion, and the need to visualize distal runoff. Imaging is important in management as it localizes the level of obstruction, determines if there are multiple levels of occlusion, assesses for inflow and outflow disease, and guides the appropriate site for the arteriotomy. Surgical intervention is usually the primary consideration in treating acute limb ischemia, although endovascular treatment options are available. Surgical thrombectomy with Fogarty balloon catheters is often an effective treatment, but if it is unsuccessful, vascular bypass surgery may be necessary. Some patients may also require surgical fasciotomy if a compartment syndrome has developed. Endovascular options are appropriate when the limb is sufficiently perfused to allow pharmacologic or mechanical thrombolysis.

Treatment of an acutely thrombosed surgical bypass graft may be influenced by additional factors, such as progression of disease involving the native inflow or outflow arteries and the nature of the vascular conduit itself.

Indications

The clinical presentation of the patient and the severity of the limb ischemia usually dictate the appropriate therapy. A classification system for categorization of the acutely ischemic limb serves to direct the intervention. This classification is detailed in Table 114-6.

Contraindications

Thrombolytic therapy may have advantages over surgical thrombectomy, particularly in the treatment of thrombosed surgical vein conduits. Fogarty balloon embolectomy may damage the endothelium of a vein graft and thus increase potential thrombogenicity. Synthetic conduits, however, usually respond well to surgical thromboembolectomy. Patients who have profound limb ischemia are at a high risk for limb loss and thus require rapid revascularization. One must be vigilant for life-threatening reperfusion syndrome; profound acidosis, hyperkalemia, myoglobinuria, renal failure, and even death may occur. Primary amputation may be more appropriate in some patients with irreversible limb ischemia.

Outcomes and Complications

Surgical thromboembolectomy of an acutely ischemic limb with an inflatable balloon catheter is considered a relatively minor and technically simple operation. However, there may be high perioperative mortality that can be attributed to serious underlying cardiac disease or to the consequences of reperfusion of the ischemic limb and subsequent release of toxic metabolites. On occasion, pulmonary emboli may result from secondary venous thrombi, or there may be reactive hyperemia after successful revascularization that may increase cardiac workload of the heart and cause acute cardiac failure. There are studies that report a 30-day mortality exceeding 20% and amputation rates above 10% after arterial embolectomy. Several studies have also shown that older patients have a higher mortality rate,¹⁴ and mortality is greater with proximal occlusions than with distal occlusions.^15–18 A short duration of symptoms before embolectomy has been reported to increase mortality, whereas other authors have found no effect on mortality. According to Levy and Butcher,¹⁴ severe ischemia did not increase the mortality rate, whereas Balas and colleagues¹⁹ concluded the opposite. Many studies report higher amputation rates when embolectomy was delayed^14,15,19; other authors have found no adverse effect of delayed treatment.^20–22 High amputation rates have also been associated with age, advanced arteriosclerotic disease,¹⁹ severe ischemic symptoms, and thrombotic compared with embolic occlusion.²³ In addition, there is a worse prognosis the more distally the occlusion is located, and the prognosis is also worse with common femoral emboli than at other sites.

Imaging Findings

Patients with clinical evidence of acute embolic or thrombotic occlusion may require emergent CTA or catheter angiography, followed by thromboembolectomy and subsequent endovascular or surgical interventions and vascular reconstruction if there is profound limb ischemia. For patients with moderate ischemia (TASC acute limb ischemia category IIa), initial diagnostic angiography should be performed, followed by primary thrombectomy and subsequent intraoperative angiography with immediate endovascular or operative treatment of remaining vascular problems. As an alternative therapeutic option, if the limb remains well perfused, catheter-directed thrombolytic infusion therapy may be appropriate in selected patients, with the intention of subsequent limb revascularization or unmasking of relevant disease that may allow endovascular or surgical vascular reconstruction.

In either situation, it is important to have preoperative or intraoperative images of the arterial inflow, the compromised vascular segments, and the outflow anatomy. In cases of embolic occlusion, there may be multiple areas of involvement, and emboli may be bilateral. In addition, if the emboli are from a cardiac source, compromise of the renal or mesenteric vasculature must be excluded. Thus, the clinical presentation of the patient will dictate the scope and proper choice of imaging.

Description and Special Anatomic Considerations

In contrast to the surgical management of thromboembolic disease, endovascular therapy employs both mechanical and pharmacologic methods for thrombolysis. With regard to the pharmacologic approach, a catheter is introduced into the occluded segment and a drug is infused that activates plasminogen and thus initiates thrombolysis. A variety of thrombolytic agents have been used, including streptokinase, urokinase, and recombinant tissue plasminogen activator (alteplase, tPA) and its derivative (reteplase, r-PA). The first two agents are now infrequently used for intra-arterial thrombolysis, mainly because of improvements in available agents. The newer plasminogen activating agents are now the agents of choice, with the activity of these agents enhanced in the presence of fibrin. All of these agents eventually fragment and dissolve thrombus and generally are most effective in the presence of acute or subacute thrombosis. When thrombosis is chronic and well organized, thrombolysis is much less successful.

For intra-arterial pharmacologic thrombolysis to be most effective, a catheter must first be advanced across the occluded segment; inability to cross the thrombosed segment generally indicates a more chronic process that will probably respond poorly to thrombolysis. A variety of infusion catheters are available; the majority are constructed with multiple side holes that allow maximal exposure of the surface area of the thrombus to the pharmacologic agent. Thrombolysis may be accelerated by the forceful pulsed injection of the fibrinolytic agent directly into the clot. Newer catheter systems combine pharmacologic with mechanical thrombolysis by use of ultrasound or rheolytic technologies to enhance drug activity (Fig. 114-16C,D).

There are also percutaneous mechanical thrombectomy devices available that are designed to achieve thrombolysis without use of pharmacologic agents. These devices use a variety of techniques that include forceful fluid jets, suction, lasers, ultrasound, rotating baskets or coils, and impellers. Whereas many of these were originally designed for declotting of dialysis grafts, they are often used intra-arterially.

Indications

Catheter-directed thrombolysis is indicated in the lower extremities when there is symptomatic acute or subacute thrombotic arterial occlusion. It is also used in the treatment of occluded surgical bypass grafts or endovascular stents, for restoration of patency; often, thrombolysis will demonstrate a high-grade stenosis that has progressed to thrombotic occlusion and may be treated with angioplasty or stenting.

Mechanical thrombectomy devices are most effective in fresh thrombus and are often used in patients with a contraindication to pharmacologic thrombolysis. They may also be used in combination with a pharmacologic agent to rapidly reduce the volume of thrombus and thus shorten the duration of treatment.

Contraindications

Thrombolysis is contraindicated in patients in whom there is irreversible limb ischemia because the reperfusion will result in severe metabolic consequences. Patients who are currently experiencing active bleeding, have recently undergone major surgery, have had recent stroke or craniotomy, or have primary or metastatic brain tumors generally are poor candidates for pharmacologic thrombolysis because of the potential for significant bleeding complications. A profoundly ischemic limb may be inappropriate for thrombolysis because the time requirements for successful treatment may be prohibitive; these patients require rapid restoration of arterial circulation to avoid limb loss. Surgical intervention with thromboembolectomy and bypass may therefore be more appropriate in such patients.

Outcomes and Complications

The success of pharmacomechanical thrombolysis is highest in short-segment occlusions that are acute or subacute (<6 months). Technical success, which is defined as recanalization of the artery and restoration of antegrade blood flow, with less than 5% residual thrombus, can be achieved in a high percentage of patients. Clinical success rates, in which there is a return to pre-thrombosis baseline status, vary, depending on whether the treatment involves the native arterial circulation, an autogenous or synthetic surgical bypass graft, or a thrombosed intravascular stent. Although graft patency can initially be restored in most patients, the 5-year primary patency rate is low, even with close surveillance. Even with surgical graft revision after successful thrombolysis, there is a 5-year primary patency rate of only around 50%, probably due to a combination of progression of disease and permanent vessel wall damage. In addition, if there is no distal runoff beyond the occluded segment, patency usually will not be maintained after thrombolysis, either alone or in combination with surgery.

The major complications of thrombolytic therapy include hemorrhage (access site and elsewhere), reperfusion syndrome, distal embolization, pericatheter thrombosis, and allergic or idiosyncratic drug reactions.

Imaging Findings

Thrombolytic therapy is performed only after a diagnostic study such as CTA, MRA, or catheter angiography has documented the extent of disease and the quality of the arterial runoff. The diagnostic study can also aid in determining the optimal approach (e.g., antegrade puncture vs. contralateral access) for introduction of the thrombolytic infusion catheter or mechanical device. Once thrombolysis is initiated, intermittent repeated imaging of the treatment zone is necessary for evaluation of the response to therapy. The duration of thrombolytic therapy may be prolonged because long infusion times are sometimes required for restoration of patency. It is also important that the cause of the thrombosis (e.g., anastomotic stenosis, distal progression of disease, graft degeneration) be demonstrated on the imaging study and corrected by the appropriate surgical or endovascular means.

One should always re-evaluate the runoff anatomy after catheter-directed or mechanical thrombolysis; distal embolization of embolic or thrombotic debris may occur during treatment.

Description and Special Anatomic Considerations

Aneurysms of the lower extremity arteries, although less common than in the thoracoabdominal aorta, are nonetheless an important disease process that may require surgical revascularization. Such aneurysms include degenerative or true aneurysms, in which all layers of the arterial wall are involved, and pseudoaneurysms, which do not include all layers. Pseudoaneurysms are often iatrogenic or post-traumatic. The choice of bypass surgery or endovascular repair depends on the aneurysm location and the clinical presentation. Iatrogenic post-catheterization pseudoaneurysms commonly involve the common femoral artery and are generally treated percutaneously, with certain exceptions as discussed later.

Vascular trauma involves the lower extremities in up to one third of patients. It may be either blunt or penetrating; treatment varies according to the type and extent of injury. Small intimal injuries or arteriovenous fistulas may spontaneously resolve, whereas major injuries may require open repair that involves vascular reconstruction or bypass. Injuries to small branch vessels may be amenable to coil embolization. Several other entities may require arterial surgical excision and vascular bypass.

Arteriovenous Fistula and Malformation

Arteriovenous fistulas (AVFs) and vascular anomalies such as venous or arteriovenous malformations are also managed by exclusion procedures. AVFs may be managed surgically through ligation of the involved vessels, but endovascular treatment with embolization or covered stent placement has become the treatment of choice in many of these lesions (Fig. 114-17). Vascular anomalies are also generally treated by transcatheter delivery of embolic agents, although there are cases in which combined endovascular and surgical techniques have been effectively used.

FIGURE 114-17 Arteriovenous fistula. DSA image obtained during popliteal angiography shows simultaneous filling of the popliteal artery (arrow) and vein (arrowhead), indicating an arteriovenous communication. This was an iatrogenic arteriovenous fistula as a result of a retrograde popliteal artery puncture performed during an endovascular procedure.

Indications

Popliteal artery aneurysms are degenerative in more than 90% of cases and are bilateral in 60% to 70%. Thrombosis of the aneurysm or distal embolization of mural thrombus occurs far more frequently than rupture, which is the least frequent complication (Fig. 114-18). Popliteal artery aneurysms should be treated before the patient becomes symptomatic because nearly 50% of patients with asymptomatic aneurysms will develop distal ischemia within 5 years. Treatment is indicated in all symptomatic aneurysms and in asymptomatic aneurysms more than 2 cm in diameter. Surgical excision and bypass is the traditional treatment; the vascular conduit options include autogenous and prosthetic.

FIGURE 114-18 DSA images from runoff arteriogram of both legs show abrupt occlusion of the right popliteal artery (A, arrowhead) at the adductor hiatus with distal reconstitution (B, arrow) at patellar level. The poorly developed collaterals are consistent with the history of acute right leg ischemia. There is also some slight irregularity to the contour of the left popliteal artery. After catheter-directed thrombolysis, patency is restored to the popliteal artery (C), but there is an irregular contour. The clinical presentation and the bilateral popliteal artery irregularity prompted further evaluation with ultrasound to assess for popliteal artery aneurysm. Duplex color flow Doppler ultrasound image (D) obtained after the successful thrombolysis procedure shows a patent central channel within a thrombus-containing right popliteal artery aneurysm (white arrows).

Pseudoaneurysms of the common femoral artery occur more frequently than true aneurysms and are frequently related to catheterization procedures or vascular anastomoses. Post-catheterization pseudoaneurysms may often be treated nonoperatively, whereas surgical revision is required if the anastomotic aneurysm is of sufficient size. Small femoral pseudoaneurysms that are a result of catheterization procedures may be treated with percutaneous thrombin injection. This has largely replaced ultrasound compression of the pseudoaneurysm as the preferred treatment. Pseudoaneurysms involving the brachial or axillary arteries are generally treated with surgical evacuation and primary arterial repair as necessary; even a small pseudoaneurysm may potentially compress adjacent nerves, with resultant sensory and motor deficits. Furthermore, thrombin injection can potentially result in upper extremity arterial thrombosis or distal embolization to the hand or digits.

True degenerative common femoral artery aneurysms larger than 2.5 cm are typically treated with surgical excision and bypass. Other true degenerative aneurysms that occur in the lower extremities are much less common; when they are identified in the superficial femoral artery, profunda femoral artery, or tibial artery, an evaluation should be initiated for an unusual etiology, such as the Ehlers-Danlos syndrome (Fig. 114-19).

FIGURE 114-19 DSA image shows an eccentric saccular aneurysm (arrowhead) arising from the popliteal artery in a patient with Ehlers-Danlos syndrome.

Popliteal artery entrapment is manifested as exercise-induced calf and foot claudication; when these symptoms are present in a young person with no risk factors for atherosclerotic disease, this diagnosis should be considered. With the functional form, the ankle-brachial index is normal at rest, whereas it is abnormal in up to 30% of individuals with the anatomic form. As previously noted, when this entity is left untreated, there may be progression to aneurysm formation, arterial occlusion, or distal embolization. All patients with entrapment of types I to V are typically offered surgery when they are diagnosed. At exploration, if the popliteal artery is patent and undamaged, treatment is confined to resection of the entrapment mechanism. In the presence of arterial disease, the popliteal artery is resected and replaced with a saphenous vein graft after resection of the entrapment. Treatment of the functional form is much less well defined; surgical intervention is individualized.

Patients who are diagnosed with adventitial cystic disease and who fail to respond to surgical cyst evacuation or in whom there has been progression to arterial occlusion require arterial bypass. The adjacent greater or small saphenous veins are the conduits of choice.

Whereas conservative management may be appropriate for small iatrogenic AVFs, early surgical or endovascular repair is indicated in most AVFs of a traumatic nature. Several studies show that less morbidity and mortality is associated with early repair than with delayed treatment; delayed treatment may allow the development of significant venous hypertension. Treatment of vascular malformations is dictated by the patient’s symptoms.

Contraindications

As previously noted, anastomotic pseudoaneurysms require surgical revision if they are sufficiently large. Currently, there are no satisfactory endovascular treatment options as pseudoaneurysms associated with vascular anastomoses result from disruption at the suture site. Pseudoaneurysms that occur spontaneously may be mycotic, and these would therefore also require surgical repair. Similarly, extremely large iatrogenic post-catheterization pseudoaneurysms that cause significant mass effect (e.g., claudication, neuropathy, limb ischemia, skin necrosis) should be treated surgically. Very small iatrogenic pseudoaneurysms (1.5 cm or less) associated with catheterization procedures may be observed for continued expansion. If they remain stable, without continued expansion, treatment may be unnecessary. Continued enlargement, however, generally mandates intervention. Larger pseudoaneurysms, with a sufficiently narrow “neck” between the true arterial lumen and the pseudoaneurysm, may be treated with thrombin injection when they involve the femoral arteries. If there is a very large or nonexistent neck to the pseudoaneurysm, this should be considered an arterial laceration and should be surgically repaired because it is unlikely that it can be effectively managed by more conservative means. Similarly, even relatively small pseudoaneurysms of the upper extremity arteries should be surgically treated, given the significant potential for adverse outcomes if they are observed or percutaneously treated.²⁴

Adventitial cystic disease does not respond well to ultrasound- or CT-guided cyst aspiration. The cyst lining continues to secrete the mucinous fluid, with resultant recurrence of the arterial compression.

Outcomes and Complications

Symptomatic aneurysms of the lower extremities that present with either acute thrombosis or significant distal embolization have much worse surgical outcomes than those aneurysms that are electively treated. With regard to popliteal artery aneurysms, a recent review of consecutive patients who underwent surgical repair in two vascular surgery units between 1988 and 2006 in the United Kingdom reported 5-year primary graft patency, secondary graft patency, limb salvage, and patient survival rates of 75%, 95%, 98%, and 81%, respectively. The 10-year primary graft patency rates were significantly lower for emergency cases (59%) compared with elective cases (66%).⁹ There are increased amputation rates and substantially higher morbidity and mortality associated with emergency treatment of peripheral aneurysms. In addition, adjunctive procedures, such as preoperative or intraoperative thrombolysis, may be necessary. Thrombolysis may be problematic in a severely ischemic limb, however, as there may be insufficient perfusion to allow the time required for successful thrombolysis. Also, during the thrombolysis procedure because there is fragmentation of the clot and resultant passage of small fragments distally into the smaller runoff arteries, there may be further worsening of the ischemia. This may then necessitate emergent surgical intervention. Such complications of thrombolysis are typically seen more frequently in patients undergoing thrombolysis for acute thrombosis of a peripheral arterial aneurysm than in patients in whom thrombolysis is performed for thrombotic or embolic occlusion of atherosclerotic occlusive lesions or thrombosed bypass grafts. When complications occur in association with thrombolytic therapy for acutely thrombosed aneurysms, amputation rates are high. This is particularly true if there is significant runoff disease or the thrombolysis procedure is excessively lengthy.

Treatment of patients with popliteal artery entrapment syndrome in whom significant arterial degenerative changes have occurred requires arterial bypass, as previously noted. There are reports of long-term patency exceeding 10 years in patients treated with saphenous vein bypass grafts. Because there is no definite correlation between the duration of the popliteal artery entrapment and the development of degenerative changes in the artery, surgical release of the entrapment is indicated at the time of diagnosis.

Cases of adventitial cystic disease that have progressed to arterial occlusion and have been treated with either operative cystotomy or complete cystectomy followed by arterial bypass with a vein graft are reported to have better long-term outcomes than those treated with cyst aspiration, thrombolysis, and angioplasty. The angioplasty approach has resulted in early recurrence because there is continued secretion by the cyst.

Surgical treatment of anastomotic pseudoaneurysms has patency rates similar to those of the initial primary surgery, provided there has been no disease progression in the runoff anatomy at or distal to the anastomoses. Similarly, there are excellent surgical results for primary repair of a post-catheterization pseudoaneurysm.²⁴

Successful surgical or endovascular repair of a post-traumatic AVF is largely dependent on the complexity of the fistula, the anatomic location, and whether the abnormality is acute or chronic. Results are generally less satisfactory in chronic, complex, and centrally located AVFs.

Imaging Findings

Preoperative imaging of lower extremity aneurysms or pseudoaneurysms allows both diagnosis and treatment planning. The length and extent of the aneurysm, the amount of intraluminal thrombus, the inflow and runoff anatomy, and the relationship to adjacent structures should be delineated. In cases of popliteal artery aneurysms presenting with acute thrombosis or distal embolization, clear definition of the runoff circulation is essential for treatment planning. Thrombolysis or intraoperative embolectomy may be necessary if no runoff vessels can be identified. In addition, imaging confirmation of a thrombosed popliteal artery aneurysm is necessary. Because angiography will demonstrate only the arterial lumen, a thrombosed aneurysm may not be suspected if there is insufficient mural calcium. Other imaging modalities, such as ultrasonography, MR, or CT, may be necessary for confirmation. Similarly, a popliteal artery aneurysm that contains significant intraluminal thrombus may not be clearly appreciated as aneurysmal without supplemental imaging (see Fig. 114-18D).

For post-catheterization pseudoaneurysms, imaging is necessary to identify the size and depth of the pseudoaneurysm and the depth, width, and length of the track that connects to the “feeding” artery from which the pseudoaneurysm arose. Adjacent venous structures should be evaluated for any evidence of deep venous thrombosis from expansion of the hematoma that may be associated with the pseudoaneurysm. A post-catheterization pseudoaneurysm has a typical color Doppler ultrasound appearance in which there is a turbulent swirling flow pattern within a sac that expands and contracts with the cardiac cycle. Pulsed wave Doppler demonstrates a to-and-fro waveform (Fig. 114-20). If management involves thrombin injection, imaging is generally performed both during and after treatment to ensure precise needle placement within the pseudoaneurysm, complete thrombosis of the sac, and preserved patency of the feeding artery.²⁴

FIGURE 114-20 A, Color Doppler ultrasound image of an iatrogenic post-catheterization femoral artery pseudoaneurysm shows turbulent swirling flow within a sac that expands and contracts with the cardiac cycle, referred to as a yin-yang pattern. B, Doppler arterial waveform analysis also reveals the to-and-fro waveform that is characteristic of a pseudoaneurysm.

In patients with popliteal artery entrapment syndrome, clinical examination with “stress maneuvers,” such as forced plantar flexion or sometimes dorsiflexion, may produce significant reduction in the distal pulses. Imaging with continuous wave Doppler study, MRI, and angiography may be employed for diagnosis, but these also require an intraprocedural provocative stress maneuver for confirmation.

Adventitial cystic disease has a characteristic appearance on imaging studies as a result of cystic compression of the popliteal artery. Both ultrasound and MR images clearly demonstrate the cystic structures within the arterial wall and the mass effect on the adjacent artery. The angiographic appearance is that of a “spiral-shaped” stenosis and is unique to this entity (Fig. 114-21).

FIGURE 114-21 DSA images in oblique (A) and frontal (B) projections show a long “spiral-shaped” stenosis (arrowheads) of the popliteal artery, which is characteristic of cystic adventitial disease. Axial T2-weighted MRI (C) of the knee in the same patient shows multiple cysts (arrowheads) compressing the popliteal arterial lumen and thus causing the characteristic angiographic appearance.

Description and Special Anatomic Considerations

Lower extremity aneurysms have been traditionally treated with surgical excision and bypass. However, with the continuing refinements in covered stent graft endoprostheses and the expanding role of this technology, endoluminal bypass has been offered as an alternative treatment for peripheral arterial aneurysmal disease. This is a treatment modality that is considered investigational by many operators at present because no long-term data are currently available. Present data suggest that endovascular repair of popliteal artery aneurysms offers medium-term benefits similar to those of the traditional surgical repair. There are valid concerns about short-term graft thrombosis and increased reintervention rates compared with open surgery.

In contrast, endovascular treatment of iatrogenic post-catheterization pseudoaneurysms is a well-established therapy, with excellent long-term data available.²⁴ With certain exceptions noted in the section on surgical treatment of these pseudoaneurysms, percutaneous thrombin injection is the preferred management.

Endovascular exclusion procedures are also well established in the treatment of post-traumatic or iatrogenic AVFs and vascular anomalies such as tumors and vascular malformations. Traumatic AVFs may result from stab or gunshot wounds or may be caused by blunt trauma. These injuries are less common in the lower extremities than in the neck, thoracic outlet, and upper extremities. Iatrogenic AVFs are generally related to catheterization procedures but may also be associated with surgical operations. AVFs may be treated by endovascular means with use of agents such as coils, covered stents, or mechanical occluders (e.g., Amplatzer plug). Vascular anomalies are categorized by both the type of vascular channel (arterial, venous, or lymphatic) and the flow dynamics (high-flow or low-flow). The high-flow anomalies include arteriovenous malformations, hemangiomas, and AVFs; low-flow anomalies include venous, capillary, and lymphatic malformations. Like AVFs, vascular anomalies are treated with embolization, sclerotherapy, or a combination of both modalities. Embolization is typically used in high-flow malformations; sclerotherapy is used primarily in low-flow anomalies and for the primary treatment of the nidus of a high-flow malformation after vascularity has been reduced by embolization.

Indications

The indications for endovascular exclusion of lower extremity arterial aneurysms are the same as those for traditional surgical excision and bypass. Many clinicians currently view the endovascular exclusion option as an inferior therapy compared with open surgery because of relatively frequent associated thrombosis. At present, it is typically reserved for older patients or those with significant medical comorbidities. Thrombolysis may be required for peripheral aneurysms that become symptomatic because of thromboembolic complications to reestablish patency and distal perfusion before any surgical or additional endovascular intervention.

Endovascular treatment of iatrogenic post-catheterization arterial pseudoaneurysms is indicated when there is continued expansion of a small (<1.5 cm) pseudoaneurysm or there are symptoms related to mass effect.

Contraindications

If there are insufficient proximal and distal disease-free arterial segments adjacent to a peripheral arterial aneurysm, there will not be adequate fixation zones for secure attachment of the endoprosthesis. This may result in either migration of the endoprosthesis or failure to exclude the aneurysm, with a resultant endoleak. Many investigators think that aneurysms occurring in areas where there is complex motion, such as the hip or knee, may have better long-term results when they are treated surgically.

Pseudoaneurysms that are extremely large or are mycotic in etiology should be surgically treated, as previously noted. This applies to both anastomotic and post-catheterization pseudoaneurysms.

Outcomes and Complications

For endovascular repair of peripheral aneurysms to be accepted as a valid alternative to open repair, it must be equivalent or superior to the accepted standard.^25–28 Mohan and coworkers²⁹ reported a cumulative primary patency rate of 74.5% and a cumulative secondary patency rate of 83.2% at 24 and 36 months, respectively. Tielliu and colleagues³⁰ reported overall 3- and 5-year patency rates of 77% and 70% for primary patency and 86% and 76% for secondary patency, respectively, in 73 popliteal artery aneurysms treated by endovascular means. This group found that the use of clopidogrel (75 mg daily) was a significant predictor of the success of a popliteal artery stent graft. In these two series, the use of versatile and flexible new stent grafts for endovascular popliteal artery aneurysm repair yielded patency results that are comparable to those of conventional open surgical repair, which has an average 5-year graft patency of 70% to 80%.^29–31

There have been more than 45 series reporting the safety and efficacy of thrombin injection for post-catheterization pseudoaneurysms, with a 97% overall cumulative success rate. Potential complications include thrombosis of the underlying native artery, distal embolization of thrombotic material, deep venous thrombosis, allergic reaction to the thrombin, local erythema, and infected abscess. The complication rate is extremely low, however, with a reported overall incidence of 1.3% and an embolic rate of 0.5%.²⁴

Endovascular treatment results for vascular anomalies are largely dependent on the type of malformation. Arteriovenous malformations have a high recurrence rate if they are treated with proximal embolization. Use of a technique in which outflow of the dominant draining vein is occluded, followed by central sclerosis of the nidus of the malformation, is the most effective treatment method. Unfortunately, some patients experience significant tissue ischemia as a result of treatment; complications such as skin or soft tissue necrosis, nerve damage, non-target embolization, pulmonary embolism, and coagulopathies may occur. Somewhat better results are generally achieved with venous and lymphatic malformations.

Imaging Findings

As with surgical exclusion procedures, successful endovascular treatment requires appropriate preoperative imaging. The morphology of the aneurysm and of the adjacent arterial segments and the distal runoff should be clearly defined. This will allow both appropriate sizing and optimal placement of the endoprosthesis. This can be accomplished with CTA, MRA, or conventional catheter angiography. If CTA is performed preoperatively, one may obtain volume rendered three-dimensional images of the aneurysm through the use of postprocessing and reformatting software (Fig. 114-22A). Images such as these allow one to view the aneurysm in multiple projections and to obtain “centerline” measurements that allow more accurate determination of the appropriate length of the endoprosthesis. Accurate intraoperative imaging is also essential for accurate endovascular aneurysm repair. Iodinated contrast medium is injected either through an intravascular sheath or through a catheter that has been positioned proximal to the aneurysm so that angiographic images are obtained. Anteroposterior and lateral angiographic views are generally obtained to delineate the aneurysm morphology intraprocedurally and to assess for any branch vessels that arise within the treatment zone. Angiography of the runoff arterial anatomy is also obtained to verify the quality and patency of the vasculature. After endovascular treatment, the proximal and distal attachments and the course of the prosthesis should be clearly demonstrated. Delayed images should be obtained to assess for an endoleak. The distal runoff anatomy should once more be evaluated; any compromise may significantly affect the long-term outcome (Fig. 114-22B,C and Fig. 114-23).

FIGURE 114-22 A, Three-dimensional volume rendered reformatted image of a popliteal artery aneurysm as seen on CTA is useful for depicting the morphology of the aneurysm. In this case, the aneurysm measurements and those of the segments above and below the aneurysm are less accurate than if they were measured directly on axial images; the opacity settings on this three-dimensional volume rendered image depict only the contrast-filled portion of the arterial lumen and do not account for any intraluminal thrombus. However, length measurements would be accurate because they can be obtained as centerline measurements. B, Intraoperative arteriogram depicts the morphology of the popliteal artery aneurysm before endovascular repair. It clearly demonstrates that there are no critical arterial branches arising from the aneurysm or from the treatment zone where the endoprosthesis will be placed. C, Angiographic image obtained after the deployment of the endoprosthesis reveals its correct placement that extends between the disease-free segments of the popliteal artery cephalad and caudad to the aneurysm. The stent graft was gently distended at each attachment site with an angioplasty balloon after deployment.

FIGURE 114-23 A, This angiographic image shows a catheter with the tip (arrow) in the distal end of a previously placed femoropopliteal artery bypass graft, above a distal anastomotic popliteal artery pseudoaneurysm (arrowhead). B, In the postdeployment angiographic image, placement of the covered stent graft is confirmed. After gentle angioplasty at the proximal and distal attachment sites, the graft is fully distended and there is no filling of the pseudoaneurysm, indicating successful exclusion, with no endoleak. The runoff arterial anatomy distal to the endoprosthesis remained intact (not shown). C, The deployed endoprosthesis (arrows) can be seen as very flexible and conforming to the course of the distal bypass graft and the popliteal artery as they cross the knee joint. Note the relatively poor radiopacity of this stent graft and the lack of radiopaque markers at either end of the graft. These factors must be considered during deployment to ensure precise placement of the endoprosthesis.

Iatrogenic or post-traumatic pseudoaneurysms must also be clearly defined, particularly the relationship of neck and the parent feeding artery. After treatment, one should document complete thrombosis of the pseudoaneurysm and patency of the adjacent native vascular structures (Fig. 114-24).

FIGURE 114-24 Left femoral arteriogram (A) shows a large iatrogenic pseudoaneurysm (arrowheads) arising from the profunda femoral artery as a result of an arterial injury during an orthopedic procedure. The location of this pseudoaneurysm would make open surgical repair very difficult. Angiographic image (B) after transcatheter treatment with a combination of embolization coils and thrombin shows that the pseudoaneurysm has been successfully thrombosed and the surrounding vasculature preserved.

It is essential to clearly define the complex arterial and venous anatomy of an arteriovenous malformation before and after treatment. The images that are obtained before treatment should demonstrate the feeding arteries, the nidus, and the major draining veins as clearly as possible; this will allow optimal treatment planning. As with any vascular intervention, the post-treatment images should document both the results of the procedure and the status of the adjacent vascular structures.

KEY POINTS

Arterial bypass remains the standard for revascularization.

Arterial bypass is indicated in patients with long-segment chronic total superficial femoral artery occlusion, chronic total popliteal artery or proximal trifurcation vessel occlusion, diffuse multiple stenoses or occlusions involving the entire superficial femoral artery, and recurrent stenoses or occlusions after two or more prior endovascular treatments.

Surveillance of bypass grafts is critical to ensure long-term patency, given that a relatively high percentage of vascular conduits develop problems that threaten longevity. The simplest and most effective surveillance tool is duplex ultrasonography coupled with ankle-brachial index measurement.

Determination of which lesions are appropriate for endovascular treatment versus traditional surgical revascularization continues to be an evolving and sometimes controversial process.

The characteristics of the lesion greatly affect outcomes of endovascular revascularization procedures as the aim of these procedures is essentially to repair a diseased arterial segment in situ as opposed to bypass or replacement of the diseased segment.

In general, short segmental stenoses respond well to angioplasty and may not require stent placement, whereas long-segment, diffusely diseased, or heavily calcified lesions may require stent placement to achieve and to maintain patency.

The indiscriminate application of endovascular technique based solely on whether it is technically possible to treat a given lesion, as opposed to a patient-oriented approach, generally leads to poor outcomes.

Symptomatic aneurysms of the lower extremities that present with either acute thrombosis or significant distal embolization have much worse surgical outcomes than do those aneurysms that are electively treated.