Abdominal Masses: Vascular

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15,000 deaths in the United States each year, making AAA the 14th leading cause of death in this country, similar in magnitude to emphysema, renal disease, and homicide.

Note that Chapter 22 covers abdominal masses that are not vascular.

Presentation

The most common presentation of an AAA is that of a painless pulsatile abdominal mass. The primary clinical concern regarding an AAA is that of rupture. Rupture of an AAA is associated with a mortality rate of between 50% and 90%. It therefore is incumbent upon the clinician to recognize an asymptomatic AAA and to refer the patient with the aneurysm for appropriate management.

Pathophysiology and Etiology

The pathophysiology and the etiology of AAA remain somewhat controversial. Abdominal aortic aneurysms long have been considered to be atherosclerotic in nature, and several of the major risk factors for atherosclerotic occlusive disease, such as smoking, hypertension, and elevated cholesterol, may be additive to the patient’s inherent risk of AAA development. The question then is: Why do some patients with the above-mentioned risk factors develop occlusive disease, while other patients have dilated vessels with or without associated occlusive disease? Patients who have AAA may be congenitally predisposed to the development of AAA. This may explain the approximately 5 : 1 predominance of males to females with this condition.

Relationship to Other Vascular Aneurysms

Patients with AAA also may be predisposed to peripheral aneurysms. It therefore is incumbent upon the examining physician to examine the patient closely for the presence of other aneurysms.

Fortunately, most peripheral aneurysms can be diagnosed by physical exam. The popliteal artery is the most common site for peripheral aneurismal disease. The danger of popliteal artery aneurysms is their propensity to thrombosis, embolization, and, rarely, rupture, making them similar to femoral artery aneurysms and all peripheral aneurysms. A patient with unilateral popliteal artery aneurysms has an approximately 50% chance of a contralateral aneurysm and a greater than 30% chance of having an AAA. The complications of acute thrombosis or distal embolization of a peripheral aneurysm can be severe and can be associated with amputation rates as high as 20% to 50%. It is best to treat these and all aneurysms electively and prior to the development of symptoms. Surgical exclusion and bypass usually are the preferred therapy, with very acceptable long-term results. Thrombolytic therapy can be very helpful in opening distal outflow in acutely thrombosed peripheral aneurysms.

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patient must never be sent to the CT scanner. Stable patients in whom a possible leaking or symptomatic AAA is suspected but whose diagnosis is uncertain should have a CT scan only if escorted by a physician, only with continuous blood pressure (BP) monitoring, and only with a large-bore (16-gauge or larger catheters) IV access in place. The patient should have had a vial of blood sent to the blood bank for type and crossmatch as well. It is highly recommended that the hospital’s operating room (OR) staff be notified that a possible leaking or ruptured AAA is being evaluated so that the OR can be ready for an expeditious transfer for operative repair. In short, a CT scan for the evaluation of a possible ruptured AAA is a useful and proactive study.

The role of angiography in preoperative assessment has evolved from an absolute necessity to one selectively employed for those patients for whom a specific indication exists (e.g., renal vascular disease or severe peripheral vascular disease). A high-quality CT scan with IV contrast generally is felt to be the preoperative test of choice for most vascular surgeons. With the advent of endovascular stent graft repair of AAA, many surgeons now again are using angiography routinely for precise measurement and planning of stent graphs.

How to Determine Which Patients Need Surgical

Repair of an Aneurysm

The primary concern with AAA is that there is increased tension on the arterial wall as the AAA expands. Remember Laplace’s law: the larger the aneurysm, the greater the likelihood of rupture and the resultant catastrophic consequences (Tables 23.1 and 23.2). It there-

Table 23.1. Estimates of annual growth rates based on initial aneurysm size (cm/yr).

Source: Modified from Wilson K, et al. Expansion rates of abdominal aortic aneurysms. Eur J Endovasc Surg 1997;13:521–526, with permission. Copyright 1997 Elsevier LTD. With permission from Elsevier. Reprinted from Winterstein BA, Baxter BT. Diseases of the Abdominal Aorta and Its Branches. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer-Verlag, 2001, with permission.

a Bernstein EF, et al. Surgery 1976;80(6):765–773.

b Bernstein EF, et al. Ann Surg 1984;200(3):255–263.

c Nevitt MP, et al. N Engl J Med 1989;321(15):1009–1014. d Limet R, et al. J Vasc Surg 1991;14(4):540–548.

e Kremer H, et al. Klin Wochenschr 1984;62(23):1120–1125. f Delin A. Br J Surg 1985;72(7):530–532.

g Brown P, et al. J Vasc Surg 1996;23(2):213–220.

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Table 23.2. Risk factors associated with aneurysm expansion and rupture.

Initial size of aneurysm

Hypertension

Cigarette smoking

Chronic obstructive pulmonary disease

Severe cardiac disease

Advanced age

Previous stroke

Family history of abdominal aortic aneurysm

Source: Reprinted from Winterstein BA, Baxter BT. Diseases of the abdominal aorta and its branches. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer-Verlag, 2001, with permission.

fore is necessary to define the risk/benefit ratio of AAA rupture versus operative risk.

Such analysis has been done, and, while there is evidence to support operative intervention of “small” aneurysms (those between 4 and 5 cm in size) in selected cases, most surgeons feel that 5 cm is the size for which the risk of rupture is high enough to accept the operative risk of intervention. This surgical threshold may change with the evolution of endovascular stent grafting.

Preoperative Risk Assessment and Surgical Approach

Preoperative evaluation of patients with AAA includes a thorough history and physical exam, with particular attention to the patient’s medical comorbidities. A great deal has been written about preoperative risk assessment (see Chapter 1), and, intuitively, it would make sense to evaluate the patient for significant coronary artery disease (CAD) and intervene if significant CAD was unmasked. There is very little evidence, however, that aggressive preoperative cardiac risk assessment significantly has lowered operative mortality. The primary improvements in surgical outcome more likely can be attributed to improved surgical and anesthetic techniques.

Operative repair of AAA is performed best electively on asymptomatic patients with AAAs greater than 5 cm in transverse diameter. The patients should be medically stable. Standard open surgical repair remains a significant operative intervention, with an operative mortality rate of between 3% and 5% at the best surgical centers.

Operative intervention carries significant morbidity, including myocardial infarction (MI), stroke, renal insufficiency, blood loss, colonic ischemia, distal ischemia, and, very infrequently, spinal ischemia. The majority of these complications can be avoided with proper preoperative planning, proper intraoperative technique, and superb postoperative care.

Standard open operative repair remains the gold standard of care for patients with AAA. Endovascular stent grafts increasingly are being employed successfully on selected patients with AAA and have

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resulted in promising shortand medium-term results. The obvious appeal of an endovascular approach is that it is minimally invasive and obviates the significant incisional discomfort and recovery of the standard operation. The overall cost-effectiveness and utility of this procedure await further testing and development.

Case Discussion

With regard to the case presented at the beginning of this chapter, several important points can be made. The diagnosis of an AAA is made ideally and most cost-effectively by a thorough physical exam, and such an exam ideally is done prior to an intervention and not after the fact. Frequently, very large aneurysms cannot be palpated readily on physical exam due to the significant girth of many patients, and the “incidental” finding of an AAA is becoming more and more the norm rather than the exception. The ordering of the CT scan in this case is appropriate, although it probably does not need to be done on an emergent basis. Obviously, if the patient were having severe abdominal pain after the procedure, then a more urgent radiologic exam, if not emergent surgery, would be indicated. The concern about an emergent CT scan is that it frequently is performed hastily and frequently does not employ IV contrast, which greatly helps the surgeon understand the vascular anatomy. Such hastily performed CT scans are adequate for revealing the presence or absence of an aneurysm, something that the physician already knows based on his physical exam; however, frequently these scans lack the anatomic detail that is clinically helpful. In this case, it would be better to evaluate the patient electively with a high-quality CT scan of the abdomen and pelvis with 3-mm cuts. This allows the vascular surgeon to evaluate optimally the extent of an aneurysm and to make an accurate assessment as to the best and safest way to repair the aneurysm. If the aneurysm is greater than 5 cm in transverse diameter, it should be repaired electively, assuming that the patient is a reasonable operative risk.

Summary

The diagnosis, workup, and treatment of vascular abdominal masses have been presented in this chapter. A basic understanding of abdominal anatomy and physiology greatly assists in the evaluation of a patient with a vascular abdominal mass. Classifying the mass anatomically, based on etiology and clinical course, greatly helps in the understanding of the problem and type of intervention necessary to facilitate proper therapy. The diagnosis and treatment of vascular abdominal masses frequently requires input from several medical and surgical specialists. In addition to primary care specialists, gastroenterologists, oncologists, general surgeons, surgical oncologists, gynecologists, radiologists, infectious disease specialists, urologists, and vascular surgeons often contribute in the management of a patient with a vascular abdominal mass. The overall prognosis of a patient with a vascular

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abdominal mass depends on the nature of the mass, the timing of the diagnosis, and the overall condition of the patient. Elective intervention, whether medical or surgical, generally is better than delayed or emergent intervention.

Selected Readings

Busuttil R, Abou-Zamzam AM, Machleder HI. Collagenase activity of the human aorta: a comparison of patients with and without abdominal aneurysms. Arch Surg 1980;115:1373–1378.

Carpenter JP, Barker CF, Roberts B, Berkowitz HD, Lusk EJ, Perloff LJ. Popliteal artery aneurysms: current management and outcome (see comments). J Vasc Surg 1994;19:65–72; discussion 72–73.

Golden MH, Whittemore AD, Donaldson MC, et al. Selective evaluation and management of coronary artery disease in patients undergoing repair of abdominal aortic aneurysms: a 16-year experience. Ann Surg 1990;212: 415–423.

Johnston K, Rutherford RB, Tilson MD, et al. Suggested standards for reporting on arterial aneurysms. J Vasc Surg 1991;3:452–458.

March RJ. Abdominal aortic aneurysm. In: Millikan KW, Saclarides TJ, eds. Common Surgical Diseases. New York: Springer-Verlag, 1998.

Moore W, Rutherford R. Transfemoral endovascular repair of abdominal aortic aneurysm: results of the North American EVT phase 1 trial. J Vasc Surg 1996;23:543–553.

Shortell C, DeWeese JA, Ouriel K, Green RM. Popliteal artery aneurysms: a 25year surgical experience. J Vasc Surg 1991;14:771–776; discussion 776–779.

Winterstein BA, Baxter BT. Diseases of the abdominal aorta and its branches. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer-Verlag, 2001.

Zarins C, Harris EJ. Operative repair for aortic aneurysms: the gold standard. J Endovasc Surg 1997;4:232–241.