| Abdominal Aortic AneurysmDefinition - A pathologic dilatation of a segment of the abdominal aorta
- Aortic wall diameter > 3 cm or 50% greater than the uninvolved proximal vessel
- Classification
- True aneurysm
- Involves all 3 layers of the vessel wall
- Pseudoaneurysm
- Intimal and medial layers of the vessel wall are disrupted.
- Dilatation is lined by adventitia only and sometimes by perivascular clot.
- Fusiform aneurysm
- Affects entire circumference of a segment of the vessel
- Makes a diffusely dilated lesion
- Saccular aneurysm
- Involves only a portion of the circumference
- Results in outpouching of the vessel wall
 Epidemiology - Incidence
- ~40,000 persons undergo aneurysmorrhaphy annually in the U.S.
- ~15,000 deaths in the U.S. are attributed to abdominal aortic aneurysm (AAA).
- Prevalence
- Rupture of AAA causes 1.3% of deaths in men 65–85 years of age.
- Sex
- Occurs more frequently in men than women
- Age
- Incidence increases with age.
- Race
- More common in white men than black men
- Prevalence in white and black women is similar.
Risk Factors - Existing atherosclerosis in other blood vessels
- Affected first-degree relatives
- Peripheral artery aneurysms
- Cigarette smoking
- Hypertension
Etiology - Exact etiology is unknown but is probably multifactorial.
- Genetics, biomechanics, and atherosclerosis are contributors.
- Results from conditions that cause degradation or abnormal production of the aortic wall’s structural components, elastin and collagen.
- Causes of aortic aneurysms may be broadly categorized as:
- Degenerative diseases
- Factors associated with degenerative aortic aneurysms include aging, cigarette smoking, hypercholesterolemia, male sex, and a family history of aortic aneurysms.
- The most common pathologic condition associated with degenerative aortic aneurysms is atherosclerosis.
- It is controversial whether atherosclerosis itself causes AAA or whether atherosclerosis develops as a secondary event in the dilated aorta.
- Inherited or developmental diseases
- Infections
- Mycotic aneurysms (Salmonella, staphylococcal, streptococcal, fungal)
- Vasculitis
- Behçet’s disease (causes thoracic and abdominal aortic aneurysms)
- Trauma
Associated Conditions Symptoms & Signs - AAA commonly produces no symptoms.
- Usually detected on routine examination as a palpable, pulsatile, and nontender mass, or as an incidental finding during abdominal radiography or ultrasonography.
- As AAAs expand, they may cause discomfort.
- Strong pulsations in the abdomen
- Pain in the chest, lower back, or scrotum
- Recent onset of aneurysmal pain is usually a harbinger of rupture and represents a surgical emergency.
- More often, acute rupture occurs without prior warning; this complication is always life threatening and requires emergency surgery.
- Acute pain and hypotension occur with rupture of the aneurysm.
- May present as syncope
- Rarely, there is leakage of the aneurysm, with severe pain and tenderness.
Differential Diagnosis - Asymptomatic AAA
- Solid-organ tumors
- Dermoid cysts
- Hepatobiliary, pancreatic, and renal disorders
- Symptomatic/ruptured AAA
Diagnostic Approach - AAA is commonly found as incidental finding on physical examination or imaging study.
- Once identified, work-up should focus on need for surgery.
- In a patient presenting with AAA and acute abdominal or back pain, rupture should be presumed and surgical evaluation undertaken immediately.
Laboratory Tests - Patients presenting with a ruptured AAA may have:
- Anemia due to retroperitoneal bleeding
- Acidosis
- In mycotic aneurysms, blood cultures are often positive and reveal the nature of the infecting agent.
Imaging - Abdominal ultrasonography
- Can delineate transverse and longitudinal dimensions of AAA and may detect mural thrombus
- Useful for serial documentation of aneurysm size
- Can be used to screen patients at risk for AAA
- Study of choice for rapid bedside diagnosis in patients presenting with suspected or actual rupture of AAA
- CT with contrast, MRI (See Figure 1.)
- Accurate, noninvasive tests to determine the location and size of AAA
- Not practical in patients who present with acute rupture of AAA
- Contrast aortography (See Figure 2.)
- Used for evaluation of aneurysms before elective surgery
- Carries a small risk of complications, such as bleeding, allergic reactions, atheroembolism and nephrotoxicity, especially in patients with baseline renal dysfunction
- Useful in documenting length of the aneurysm, especially upper and lower limits, and the extent of associated atherosclerotic vascular disease
- Presence of mural clots may reduce the luminal size; thus, aortography may underestimate the diameter of an aneurysm.
- Abdominal radiography
- May demonstrate calcified outline of the aneurysm.
- ~25% of aneurysms are not calcified and cannot be visualized by plain radiography.
- Usually an incidental finding, and not used for diagnosis
Diagnostic Procedures Treatment Approach - Operative repair of the aneurysm is indicated for AAAs of any size that are expanding rapidly or are associated with symptoms.
- Unstable patients who present with rupture should have standard resuscitative measures (e.g., intravenous access, cardiac monitoring, supplemental oxygen) while preparing for transfer to the operating room.
- For asymptomatic AAA, surgery is indicated if the diameter is > 5.5 cm.
- Operative repair for AAA 5–5.5 cm is controversial.
Specific Treatments Surgery- All patients with symptomatic AAA require urgent or emergent surgery.
- Asymptomatic patients with AAA > 5.5 cm in diameter should undergo repair.
- In surgical candidates, careful preoperative cardiac and general medical evaluations are essential.
- Follow with appropriate therapy for complicating conditions.
- Preexisting coronary artery disease
- Congestive heart failure
- Pulmonary disease
- Diabetes
- Advanced age
- β-adrenergic blockers decrease perioperative cardiovascular morbidity and mortality.
- Perioperative management should include placement of a Swan–Ganz catheter and arterial line to monitor and optimize:
- Left ventricular filling pressure
- Cardiac output
- Arterial pressure, especially during clamping and unclamping of the aorta and in the immediate postoperative period
- Percutaneous placement of endovascular stent grafts for treatment of infrarenal AAA is available for selected patients.
- Lower short-term morbidity compared with open surgical reconstruction
- Comparable long-term mortality compared with open surgical reconstruction
- Becoming an increasingly common technique for ruptured AAA
- Currently associated with a mortality rate of approximately 40%
- Lower mortality compared with open repair may reflect selected patient population.
Monitoring - Asymptomatic AAA < 5 cm should be followed by ultrasonography, CT, or MRI every 3 months if diameter is 4.5–5.5 cm and every 6 months if diameter is < 4.5 cm.
Complications - Rupture is the most important and life-threatening complication of AAA.
- Mortality rate approaches 50%.
- Risk of rupture increases with the size of the AAA.
- Formation of mural thrombi within the aneurysm may predispose to peripheral embolization.
Prognosis - Prognosis is related to both the size of the aneurysm and the severity of coexisting coronary artery and cerebrovascular disease.
- The risk of rupture increases with the size of the aneurysm.
- Annual risk of rupture
- < 4 cm: 0.3%
- 4–4.9 cm: 1.5%
- 5–5.9 cm: 6.5%
- >6 cm: Risk increases sharply.
- Operative mortality rate for elective surgery approximates 1–2%.
- After acute rupture, the operative mortality rate approximates 45–50%.
Prevention - Ultrasonographic screening in patients at risk may be helpful.
- In 1 larger study, ultrasonographic screening of men 65–74 years of age was associated with a risk reduction in aneurysm-related death by 42%.
- According to the Cochrane Database Review: [1]
- There is evidence of a significant reduction in mortality from AAA in men aged 65–79 years who undergo ultrasound screening.
- There is insufficient evidence to demonstrate benefit in women.
ICD-9-CM - 441.4 Abdominal (aortic) aneurysm without mention of rupture
- 441.3 Abdominal aneurysm, ruptured
See Also Internet Sites References - Cosford PA, Leng GC: Screening for abdominal aortic aneurysm. Cochrane Database Syst Rev , 2007 [PMID:17443519]
General Bibliography - Ashton HA et al: The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 360:1531, 2002 [PMID:12443589]
- Baril DT, Jacobs TS, Marin ML: Surgery insight: advances in endovascular repair of abdominal aortic aneurysms. Nat Clin Pract Cardiovasc Med 4:206, 2007 [PMID:17380166]
- Blanchard JF, Armenian HK, Friesen PP: Risk factors for abdominal aortic aneurysm: results of a case-control study. Am J Epidemiol 151:575, 2000 [PMID:10733039]
- Blankensteijn JD et al: Two-year outcomes after conventional or endovascular repair of abdominal aortic aneurysms. N Engl J Med 352:2398, 2005 [PMID:15944424]
- Fleming C et al: Screening for abdominal aortic aneurysm: a best-evidence systematic review for the U.S. Preventive Services Task Force. Ann Intern Med 142:203, 2005 [PMID:15684209]
- Greco G et al: Outcomes of endovascular treatment of ruptured abdominal aortic aneurysms. J Vasc Surg 43:453, 2006 [PMID:16520154]
- Isselbacher EM et al: Diseases of the aorta, in Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed, DP Zipes et al (eds). Philadelphia, Saunders, 2005
- Isselbacher EM: Thoracic and abdominal aortic aneurysms. Circulation 111:816, 2005 [PMID:15710776]
- Kim LG et al: A sustained mortality benefit from screening for abdominal aortic aneurysm. Ann Intern Med 146:699, 2007 [PMID:17502630]
- Lederle FA et al: Systematic review: repair of unruptured abdominal aortic aneurysm. Ann Intern Med 146:735, 2007 [PMID:17502634]
- Lederle FA et al: Immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med 346:1437, 2002 [PMID:12000813]
- Powell JT, Greenhalgh RM: Clinical practice. Small abdominal aortic aneurysms. N Engl J Med 348:1895, 2003 [PMID:12736283]
- Sakalihasan N, Limet R, Defawe OD: Abdominal aortic aneurysm. Lancet 365:1577, 2005 Apr 30-May 6 [PMID:15866312]
- Towne JB: Endovascular treatment of abdominal aortic aneurysms. Am J Surg 189:140, 2005 [PMID:15720980]
- United Kingdom Small Aneurysm Trial Participants: Long-term outcomes of immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med 346:1445, 2002 [PMID:12000814]
- This topic is based on Harrison’s Principles of Internal Medicine, 17th edition, chapter 242, Diseases of the Aorta by MA Creager and J Loscalzo.
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