Lower Extremity Aneurysms
Amy B. Reed
Introduction
Lower extremity arterial aneurysms are often readily diagnosed owing to their superficial nature and ease of palpation. True aneurysms involving all vessel wall layers are commonly encountered in the popliteal artery and less so in the femoral and tibial arteries. Given the explosion of minimally invasive arterial techniques being performed percutaneously, femoral pseudoaneurysms are unfortunately not rare. Anastomotic and mycotic pseudoaneurysms can be seen due to infection and trauma. This chapter will review the management of both true and false aneurysms of the lower extremity.
Incidence
True lower extremity aneurysms involving all three layers of the vessel wall are rare. While the exact incidence of femoral and popliteal aneurysms is difficult to determine, the number being recognized is increasing. Aging populations, increased arterial trauma, more common use of invasive techniques, and imaging all contribute to the rise in number of peripheral aneurysms being diagnosed. Screening studies involving men between the ages of 65 and 80 years identified popliteal artery aneurysms in 1%.
An increasing number of false aneurysms or pseudoaneurysms appears to be occurring as the incidence of catheter-based diagnostic and therapeutic arterial interventions increases along with lower extremity bypass surgery. Pseudoaneurysms—iatrogenic, infectious, or traumatic—are identified by their lack of involvement of all three vessel wall layers as is typically seen in true aneurysms. The incidence of pseudoaneurysm after diagnostic procedures is, 0.3%—slightly higher at 1.5% after therapeutic procedures—in general due to use of larger sheaths. False aneurysms can also arise from trauma during surgery such as orthopedic procedures. Femoral pseudoaneurysms develop after 0.08% of total hip arthroplasties, and popliteal aneurysms arise following 0.17% total knee arthroplasties.
Femoral Artery Aneurysms
Femoral artery aneurysms are the most common peripheral aneurysm if both true and false aneurysms are considered together. Their clinical importance rests in the fact that they are limb-threatening lesions and can jeopardize the viability of the leg if thrombosis, embolization, or rupture occurs. The vast majority of true aneurysms are degenerative lesions, commonly known as atherosclerotic aneurysms, whereas false aneurysms include anastomotic, traumatic, and mycotic lesions. Rarely, femoral aneurysms develop secondary to connective tissue disorders. The femoral region is the most common site for anastomotic aneurysms, pseudoaneurysms, and mycotic aneurysms associated with trauma; so the presentation and surgical repair of these lesions are discussed.
Degenerative (Atherosclerotic) Femoral Aneurysms
Incidence and Natural History
The exact incidence of degenerative (atherosclerotic) common femoral artery aneurysms in the general population remains undefined. They are found in 6.8% of all patients with abdominal aortic aneurysms, and 85% of patients with femoral artery aneurysms have abdominal aortic aneurysms.
Femoral aneurysms most frequently affect the common femoral artery. They may be classified as type I, those limited to the common femoral artery, or type II, those involving the orifice of the profunda femoris artery.5 Type I and type II aneurysms occur with nearly equal frequency. This classification becomes important in reference to vascular reconstructive procedures, with type II aneurysms requiring more complex reconstructions to ensure continued patency of both the superficial and profunda femoris arteries. Isolated lesions of the profunda femoris artery are rare (2% of femoral artery aneurysms), and are prone to rupture because they are difficult to diagnose at the asymptomatic stage. Isolated superficial femoral artery aneurysms are also uncommon, but one-third of patients present with rupture and one quarter with thrombosis.
Femoral artery aneurysms can be limb-threatening lesions and are frequently associated with limb-threatening popliteal aneurysms and life-threatening abdominal aortic aneurysms. Multiple aneurysms are common in patients with femoral artery aneurysms. In a series of 100 patients with degenerative femoral artery aneurysms seen at a single institution, 72% of patients had bilateral femoral artery aneurysms.5 In addition, aortoiliac aneurysms were detected in 85% of patients, thoracic aortic aneurysms in 6%, and popliteal aneurysms in 44%, of which 55% were bilateral.
Clinical Manifestations
The clinical manifestations of femoral artery aneurysms cover the spectrum from asymptomatic to severe ischemia of the lower extremity. Although 40% of patients are asymptomatic at the time of diagnosis, the majority present with local symptoms or complaints of lower extremity ischemia. Local pain or observation of a groin mass is the only complaint in 18% of patients. Lower extremity venous disease is present in 8%, being attributable to venous obstruction by the femoral artery aneurysm in 4%, but venous obstruction is rarely the sole sign of an aneurysm. Lower extremity ischemic symptoms of claudication, rest pain, or gangrene are present in 42% of patients and often lead to the diagnosis of the femoral artery aneurysm.
As with aneurysms in other locations, femoral artery aneurysms may be complicated by embolization, thrombosis, or rarely rupture. Peripheral embolization may be identified on physical examination as it produces signs as mild as spotty discoloration of the toes to as severe as peripheral gangrene. Although embolization is reported in about 10% of aneurysms, the femoral artery aneurysm is not necessarily the source of these emboli because many patients have a concomitant popliteal aneurysm. In larger clinical series, 1% to 16% of patients with degenerative femoral artery aneurysms present with an acute thrombosis, whereas 1% to 16% have a chronically thrombosed lesion. Rupture is reported in 1% to 14% of aneurysms.
Diagnosis
In most cases the diagnosis of femoral artery aneurysm is suspected by the finding of a pulsatile groin mass on routine physical examination or during evaluation for vascular disease. If the femoral artery aneurysm is small or thrombosed, detection on physical examination may be difficult.
Although a radiograph of the region may occasionally demonstrate the calcified rim of the aneurysm, only ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) can reliably establish the diagnosis of the femoral aneurysm. In addition, these modalities are useful in accurately defining the size of the lesion and evaluating associated aneurysmal disease in the distal aorta and popliteal regions. These findings are particularly important because life-threatening abdominal aortic aneurysms are missed on physical examination in 50% of patients with multiple aneurysms. The diagnostic accuracy of arteriography is limited because it demonstrates only the residual lumen and an aneurysm filled with smooth mural thrombus may be missed, but the definition of the vascular anatomy of the lower extremity provided by angiography is helpful in planning the appropriate operative procedure.
Although a radiograph of the region may occasionally demonstrate the calcified rim of the aneurysm, only ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) can reliably establish the diagnosis of the femoral aneurysm. In addition, these modalities are useful in accurately defining the size of the lesion and evaluating associated aneurysmal disease in the distal aorta and popliteal regions. These findings are particularly important because life-threatening abdominal aortic aneurysms are missed on physical examination in 50% of patients with multiple aneurysms. The diagnostic accuracy of arteriography is limited because it demonstrates only the residual lumen and an aneurysm filled with smooth mural thrombus may be missed, but the definition of the vascular anatomy of the lower extremity provided by angiography is helpful in planning the appropriate operative procedure.
Treatment
Operative treatment is indicated for aneurysms causing local symptoms and presenting with limb-threatening complications. Asymptomatic aneurysms >2.5 cm in diameter should also be repaired unless the patient is at a prohibitive risk for operative intervention. In patients with small, asymptomatic aneurysms, observation may be appropriate, particularly in the patient with multiple medical problems who would be at high risk for surgery. When nonoperative management is selected, the size of the aneurysm should be documented by ultrasonography. The patient should be followed at regular intervals with ultrasound scans and careful examination for occult complications. Operative treatment should be undertaken without undue delay if the femoral aneurysm enlarges, produces symptoms, or is complicated by embolization, thrombosis, or rupture.
Surgical Strategy
The operative approach is individualized based on associated aneurysmal disease. In patients with multiple asymptomatic aneurysms, treatment is staged. The life-threatening aortic lesions are treated before limb-threatening femoropopliteal lesions. Femoral artery aneurysms are addressed after popliteal lesions unless the femoral aneurysm is repaired in combination with treatment of the aortic or popliteal aneurysm. If an aortofemoral bypass is necessary, the femoral aneurysm should be treated at the same time to avoid later anastomotic aneurysm formation. The graft limb can be anastomosed into an interposition graft that has replaced the femoral aneurysm. Similarly, if a stent graft is placed for treatment of an abdominal aortic aneurysm in a patient with femoral artery aneurysms, the aneurysm should be repaired with an interposition graft. In patients with severe lower extremity ischemia, the femoral aneurysm is treated with an interposition graft, from which the proximal anastomosis of the required femoropopliteal or femorotibial bypass is based.
Technique
The operative procedure for treatment of an isolated femoral artery aneurysm is determined by aneurysmal involvement of the superficial and deep femoral arteries as well as by the existence of lower extremity occlusive disease. The femoral artery aneurysm is usually approached through a longitudinal groin incision. When addressing an unusually large aneurysm or a ruptured aneurysm, however, initial proximal control of the external iliac artery through a retroperitoneal approach is advisable. After proximal and distal arterial control is obtained, the aneurysm sac is opened and the atheromatous debris removed. Small aneurysms may be excised, but routine excision of large aneurysms is not recommended as these lesions can often be adherent to the adjacent vein and nerve. For type I aneurysms, the preferred treatment is reconstruction with an interposition graft of Dacron or expanded polytetrafluoroethylene (ePTFE) with the proximal anastomosis at the distal external iliac artery or proximal common femoral artery and the distal anastomosis at the femoral bifurcation.
For type II aneurysms with patent superficial and profunda femoris arteries, an interposition graft to the profunda femoris artery with reimplantation of the superficial femoral artery is one standard configuration. If the superficial femoral artery is chronically occluded and the patient has minimal symptoms, an interposition graft to the profunda femoris artery alone is sufficient. If the patient has severe lower extremity ischemia, this is typically followed by a standard distal reconstruction. If recent emboli or in situ thrombosis have occluded the outflow tract, percutaneous mechanical thromboembolectomy or catheter-directed thrombolytic therapy is useful before open arterial reconstruction is undertaken.
Results
Results of surgical therapy depend upon the patency of the distal vasculature. More than 80% of asymptomatic patients have excellent long-term results, whereas 68% of those presenting with lower extremity ischemia achieve satisfactory long-term outcomes.
Mycotic Femoral Aneurysms
The term mycotic aneurysm is currently used to refer to any infected aneurysm. Mycotic aneurysms today are often a complication of parental drug abuse, but can follow arterial trauma of any form, including invasive diagnostic and therapeutic procedures. In the past, septic emboli from bacterial endocarditis were a major cause of mycotic aneurysmal degeneration, but this is less common today. With the advent of antibiotics, aneurysms secondary to syphilis or tuberculosis are rare. With the change in cause, the location of mycotic aneurysms has shifted from central to peripheral arteries with the femoral artery being the most common site. The importance of mycotic aneurysms comes from their propensity to rupture.
Pathogenesis
The pathogenesis of mycotic aneurysms can be divided into four major categories, although other less common causes also exist. Firstly, septic emboli from bacterial endocarditis may lodge in normal arteries, causing infection that weakens the arterial wall, resulting in aneurysm formation. These lesions are often multiple. Secondly, during an episode of bacteremia, microorganisms may lodge in a preexisting atherosclerotic plaque or aneurysm and begin to multiply with the same result. Thirdly, mycotic aneurysms are caused by contiguous spread of bacteria from a local abscess. The inflammatory process destroys the arterial wall, causing pseudoaneurysm formation. Finally, trauma to the artery with concomitant contamination may result in formation of an infected pseudoaneurysm. This mechanism of mycotic aneurysm formation is being seen more frequently, coincident with the increased use of catheter-based procedures. Bacteria may be introduced concomitantly with needle puncture or by migration during prolonged arterial catheterization. Mycotic aneurysms accompanying drug abuse may be secondary to direct contamination of the arterial wall, or they may result from destruction of the vessel wall by a local abscess.
The bacteriology of arterial infections depends upon the cause of the lesion. Aneurysms
secondary to bacterial endocarditis grew Pneumococcus, Streptococcus, and Enterococcus species most frequently in the past, but recently, organisms such as staphylococci, Salmonella, Escherichia coli, and Proteus have also been cultured. Staphylococcus aureus is the most common pathogen in mycotic femoral artery aneurysms secondary to trauma and drug abuse, occurring in >65% of cases. In this population, at least 50% of the S. aureus organisms are resistant to methicillin.
secondary to bacterial endocarditis grew Pneumococcus, Streptococcus, and Enterococcus species most frequently in the past, but recently, organisms such as staphylococci, Salmonella, Escherichia coli, and Proteus have also been cultured. Staphylococcus aureus is the most common pathogen in mycotic femoral artery aneurysms secondary to trauma and drug abuse, occurring in >65% of cases. In this population, at least 50% of the S. aureus organisms are resistant to methicillin.
Clinical Manifestation
The typical patient with a mycotic femoral aneurysm presents with a history of chills and fever, and a tender, enlarging, pulsatile groin mass. The patient may have a history of intravenous drug use, recent arterial catheterization, penetrating trauma, or bacterial endocarditis. Local signs of infection, including tenderness, erythema, and warmth are noted on physical examination. Lower extremity edema may occur secondary to venous or lymphatic obstruction. Petechial skin lesions, splinter hemorrhages, cutaneous abscesses, and septic arthritis may occur as a result of emboli originating from a mycotic aneurysm. A “sentinel bleed” may occur and signals impending rupture and life-threatening hemorrhage. Emergency surgery is indicated.
