Abdominal aortic aneurysm

I. What every physician needs to know.

Abdominal aortic aneurysm (AAA) is defined as a permanent dilatation of all three layers of the abdominal aortic wall with a diameter measuring 3 cm or larger. By comparison, a pseudoaneursym is defined as communication of blood between the layers of the arterial wall, without dilation. AAA is most commonly seen in persons greater than 50 years of age and in men more than women. Broadly, degeneration of the vessel wall, inflammation, and infection are the main underlying causes of AAA. Degenerative aneurysms are most commonly related to atherosclerotic disease. Trauma, infections such as tuberculosis and syphilis, and connective tissue diseases such as Marfan’s syndrome, are associated with AAA, however, few diagnosed AAAs are attributable to these causes.

AAA is characterized by chronic transmural inflammation with destructive remodeling of the elastic media and depletion of smooth muscle cells in the media. Proteinases degrade elastin and collagen, leading to a decrease in the tensile strength of the aortic wall, and consequently to the formation of aneurysms. AAA types are classified according to location: infrarenal, suprarenal, and pararenal. The most common type of AAA is infrarenal, where the aneurysm begins below the level of the renal arteries and an associated mural thrombus is present in most instances.

There is a variant of AAA known as the inflammatory type which is characterised by inflammatory thickening of the aneurysm wall, perianeurysmal fibrosis and adherence to surrounding structures. It accounts for 5-10% of all AAAs. Patients with this form of AAA are more likely to be symptomatic even without any rupture.

II. Diagnostic Confirmation: Are you sure your patient has abdominal aortic aneurysm?

AAA is often asymptomatic and the physical examination has a low sensitivity for diagnosing AAA. The ability to detect AAA on physical examination depends on the diameter of the AAA and the abdominal girth. The physical examination should be performed by a bimanual palpation of the supraumbilical area.

Ultrasound is the diagnostic imaging method of choice. It is relatively inexpensive, painless, has minimum risk and can be used to measure longitudinal, anterorposterior and transverse dimensions of the aorta with great accuracy. Ultrasound imaging is used for the initial assessment, surveillance, and screening of AAA.

If the diameter of AAA is such that surgery may be warranted, a computed tomography (CT) scan is required to determine the transition between the normal and aneurysmal aorta, the extension of the AAA and iliac arteries, and the patency of the visceral arteries. The CT scan will also permit measurement of the thickness of any mural thrombus, if present. If extravasation of contrast material is visible, this would be diagnostic for a rupture.

Magnetic resonance imaging (MRI) may be used in patients who cannot tolerate the traditional nephrotoxic contrast.

A calcified aortic wall may be seen on a plain X-ray, but this form of imaging is of limited use for this condition. X-ray is therefore not routinely used for diagnosis in patients with symptoms or risk factors concerning for AAA.

A. History Part I: Pattern Recognition

A thorough medical, social and family history is necessary in order to determine the risk factors for developing AAA. Most patients with AAA are usually asymptomatic and the diagnosis is usually an incidental finding on exam, or, more often, on imaging being done for other purposes. Groin, back or abdominal pain in the presence of an abdominal pulsatile mass should raise suspicion for AAA. If correlating symptoms are present, there should be heightened concern for rupture. Symptoms and signs can include non-specific abdominal pain, lower back pain, GI bleeding or hematuria. In symptomatic patients, urgent evaluation of the aorta by CT scan is indicated, in order to exclude a rupture and to determine the size of the aorta.

B. History Part 2: Prevalence

Risk factors for developing AAA and for progression of disease include: male gender, age of 65 and greater, a smoking history, hypertension, and dyslipidemia. Men are five times more likely to develop AAA than women and women tend to develop AAA roughly 10 years later than men. There is a greater incidence of AAA rupture in women than in men with AAAs of the same size. In assessing smoking history, the number of years of smoking is more important than the number of cigarettes per year.

The incidence of AAA has increased within the last decade due to an increase in the aging population and because of tobacco use. AAA is now the 13th leading cause of death in the United States, and accounted for about 9000-15000 deaths per year for ruptured aortic aneurysm. The prevalence is between 1.3% to 7.6% in men and 1-2.2% in women and rates as high as 8.3% have been reported in women with a strong family history of AAA.

The mortality rate is 5% in asymptomatic patients, 26% in symptomatic patients and up to 35% in patients with a ruptured AAA.

C. History Part 3: Competing diagnoses that can mimic abdominal aortic aneurysm.

The differential diagnosis for AAA will include the differentials for a pulsatile abdominal mass. Ruptured viscus, mesenteric ischemia, strangulated hernia, ruptured visceral artery aneurysms, acute cholecystitis, acute pancreatitis, ruptured hepatobiliary cancer, lymphoma, and diverticular abscess should be considered in the differential diagnosis of symptomatic AAA.

D. Physical Examination Findings.

The physical exam findings will depend on the size and if the AAA is already ruptured or not.

In asymptomatic AAA, physical examination is not very sensitive. The findings depend on the size of the aneurysm and the abdominal girth. AAAs which are 3-3.9 cm in diameter can be palpated 29% of the time and AAAs greater than 5 cm are palpated 76% of the time.

Most non-ruptured AAA are non-symptomatic, but a few patients do present with chronic vague abdominal pain, groin pain or back pain and pain with deep manipulation. In these patients an urgent CT scan of the abdomen with contrast should be obtained.

The popliteal and femoral pulses should also be evaluated in these patients. Sixty two percent of patients with popliteal aneurysm also have AAA, 85% of patients with femoral artery aneurysm also have AAA and 14% of patients with AAA have femoral or popliteal aneurysms.

Ruptured AAA presents with a triad of sudden onset of mid abdominal or flank pain that may radiate to the scrotum, shock, and a pulsatile abdominal mass.

Anterolateral wall rupture into the peritoneal space is highly fatal. Most of the ruptures, where patients survive to undergo initial hospital evaluation are posterolateral wall ruptures into the retroperitoneal space.

E. What diagnostic tests should be performed?

Once a patient has known risk factors for AAA, a thorough physical examination of the abdomen should be performed. If a palpable pulsatile mass is found, ultrasound should be used for screening or to confirm the presence of AAA. Also, men who have ever smoked and are between the ages of 65-75 years should have a one-time screening for AAA with ultrasonography.

If there is high suspicion for AAA, even if there are no findings on the physical examination, an ultrasound of the abdomen should be performed. Once an abdominal aortic aneurysm is found, a CT scan is needed to delimit the area of the AAA, determine whether thrombus is present, and exclude a rupture.

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

No laboratory results are required to establish the diagnosis of AAA.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

In patients with the risk factors, a thorough physical examination should be performed and an abdominal ultrasound should be performed.

In symptomatic patients a CT scan of the abdomen is required.

In symptomatic patients who cannot tolerate the traditional contrast (renal failure or contrast allergy), MRI should be used.

F. Over-utilized or “wasted” diagnostic tests associated with this diagnosis.

III. Default Management.

There is a high mortality rate in patients with a ruptured AAA. Risk of rupture depends on the size, rate of expansion and gender.

The factors below are used as indicators for elective repair.

Based on the AAA diameter the risk of rupture is:

0% risk if less than 4 cm
0.5-5% if 4.0-4.9 cm
3-15% if 5.0-5.9 cm
10-20% if 6-6.9 cm
20-40% if 7.0-7.9 cm
30-50% if greater than 8 cm

Aneurysms that expand to greater than 5 cm in diameter in 6 months are at a greater risk of rupture, and there is a greater risk of rupture in women as compared to men. In some studies, the rate of rupture of AAA with a diameter of 4.0-5.5 cm was four times more in women than in men.

Other factors like continuation of tobacco use, poorly controlled hypertension and increased wall stress are also risk factors for rupture.

A. Immediate management.

The immediate management of AAA depends on the size, the presence of symptoms, the presence of a rupture, and the expansion rate of the aneurysm.

In asymptomatic patients, if the AAA diameter is 3-3.9 cm an ultrasound surveillance is required every 12 months. If the AAA diameter is 4-4.5 cm, ultrasound surveillance is necessary every 6 months. If the AAA diameter is greater than 4.5 cm, the patient should be referred to a vascular surgeon for elective repair.

All symptomatic patients need an immediate CT scan of the abdomen or MRI for patients who cannot get a CT scan with contrast. If there is no rupture, then patients should be treated based on the size as above and the rate of expansion.

For ruptured AAA, an emergency surgical consult and surgical intervention is required. Patients should be placed on intravenous fluids immediately.

B. Physical Examination Tips to Guide Management.

Other than a thorough bimanual palpation of the abdomen, the femoral and popliteal pulses should also be checked for aneurysms, since patients with femoral or popliteal aneurysms have a high incidence of AAA.

C. Laboratory Tests to Monitor Response To, and Adjustments in, Management.

There are no specific laboratory tests that are required for patients with AAA. Preoperative work-up with appropriate labs should be obtained for patients who have to undergo surgical intervention.

D. Long-term management.

In patients with small to medium sized AAA, medical therapy may be beneficial. This includes treatment with beta- blockers and possibly aspirin and statins. The most important major risk factor for AAA formation and growth is smoking. Therefore, smoking cessation is the most important intervention in patients requiring long-term management of AAA.

E. Common Pitfalls and Side-Effects of Management.

N/A

IV. Management with Co-Morbidities.

Comorbidities should be appropriately managed in all patients with AAA.

Blood pressure should be appropriately managed, and smoking cessation is imperative in these patients.

In patients with infections causing AAA, for example, syphilis, appropriate antibiotics should be administered.

Once the patient is a surgical candidate and the surgery is an elective surgery, comorbidities should be optimally managed prior to surgery.

In patients with kidney failure, in whom you are unable to administer traditional dye, an MRI would be an alternative diagnostic method.

A. Renal Insufficiency.

Use MRI for diagnosis rather than a CT scan with contrast.

B. Liver Insufficiency.

No special considerations.

C. Systolic and Diastolic Heart Failure.

Optimal medical management of heart failure.

D. Coronary Artery Disease or Peripheral Vascular Disease.

Optimal medical management.

E. Diabetes or other Endocrine issues.

Optimal blood glucose control.

F. Malignancy.

No specific recommendation.

G. Immunosuppression (HIV, chronic steroids, etc).

No specific recommendation.

H. Primary Lung Disease (COPD, Asthma, ILD).

Retroperitoneal surgical approach is recommended for repair.

I. Gastrointestinal or Nutrition Issues.

No specific recommendation.

J. Hematologic or Coagulation Issues.

No specific recommendation.

K. Dementia or Psychiatric Illness/Treatment.

No specific recommendation.

V. Transitions of Care.

A. Sign-out considerations While Hospitalized.

No special considerations for sign out.

B. Anticipated Length of Stay.

C. When is the Patient Ready for Discharge.

D. Arranging for Clinic Follow-up/Screening

The USPSTF recommends one-time screening for abdominal aortic aneurysm (AAA) with ultrasonography in men ages 65-75 years who have ever smoked, but recommends clinicians selectively offer screening for AAA in men ages 65-75 years who have never smoked rather than routinely screening all men in this group.

The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for AAA in women ages 65-75 years who have ever smoked, but recommends against routine screening for AAA in women who have never smoked.

AAA with a diameter of 5.5 cm or greater in men should be strongly considered for surgery (evidence A).

AAA expanding at more than 0.6 cm a year should be considered for surgery (evidence A).

1. When should clinic follow up be arranged and with whom.

In asymptomatic patients, if the infrarenal aorta is less than 3cm no further testing is required. If the diameter of the aneurysm is 3-3.9 cm, an ultrasound should be performed every 2-3 years, for AAA with a diameter of 4-5.4 cm, ultrasound or computed tomography scan should be performed every 6-12 months and for AAA with a diameter greater than 5.5 cm, a vascular consult is warranted. The 2011 ACC/AHA guidelines recommended surgical repair of abdominal aortic aneurysms greater than or equal to 5.5 cm in diameter in asymptomatic patients.

The primary care physician should arrange follow-up to the primary care clinic based on the above criteria. The screening results should be discussed with the patient and further management arrangements planned on each visit. Once a patient becomes a surgical candidate based on the above recommendations, the patient should be referred to the vascular surgeon.

2. What tests should be conducted prior to discharge to enable best clinic first visit.

No specific tests are required prior to discharge for patients with recent AAA repair.

3. What tests should be ordered as an outpatient prior to, or on the day of, the clinic visit.

None

E. Placement Considerations.

F. Prognosis and Patient Counseling.

VI. Patient Safety and Quality Measures.

A. Core Indicator Standards and Documentation.

B. Appropriate Prophylaxis and Other Measures to Prevent Readmission.

Appropriate management of comorbidities as noted above.

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Erbel, R, Aboyans, V, Boileau, C. “2014 ESC Guidelines on the diagnosis and treatment of aortic diseases: Document covering acute and chronic aortic diseases of the thoracic and abdominal aorta of the adult. The Task Force for the Diagnosis and Treatment of Aortic Diseases of the European Society of Cardiology (ESC)”. Eur Heart J.. vol. 35. 2014 Nov 1. pp. 2873-926.

Guirguis-Blake, JM, Beil, TL, Sun, X. “Primary Care Screening for Abdominal Aortic Aneurysm: A Systematic Evidence Review for the U.S. Preventive Services Task Force [Internet]”. 2014 Jan..

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