Abdominal Aortic Aneurysm - Quick Consult
Last Updated / Reviewed: June 2022

Definition
Pathophysiology
Key History
Key Physical Exam
Risk Factors for AAA
Differential Diagnosis
Diagnostic Testing
Clinical Risk and Safety Pearls
Treatment

Definition

Abdominal aortic aneurysm, also written as AAA and often pronounced 'triple-A', is a localized dilatation of the abdominal aorta that exceeds the normal aortic diameter by more than 50%. The normal diameter of the infrarenal aorta is 2 cm. AAA is caused by a degenerative process of the aortic wall, however the exact etiology remains unknown. It is most commonly located below the kidneys (infrarenally; 90%); other possible locations are above or at the level of the kidneys (suprarenal and pararenal). The aneurysm can extend to include one or both of the iliac arteries. An aortic aneurysm may also occur in the thorax.

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Pathophysiology

The signs and symptoms of an AAA reflect the anatomy of the normal aorta. A review of these anatomical factors can sometimes assist in making the diagnosis.
  1. The aorta enters the abdomen at the level of the twelfth acute vertebra and bifurcates into the common iliac arteries at the level of the umbilicus.
  2. The aorta is retroperitoneal throughout its course in the abdomen and normally does not extend to the right of the midline of the abdomen. If the examiner detects aorta to the right of the midline, this may represent an aortic aneurysm.
  3. Various portions of the gastrointestinal tract, venous channels, osseous structures, ureters, nerves, and nerve roots are close to the aorta and may be involved in the pathophysiology and symptoms of an AAA.
  4. The aorta also gives off many branches while in the abdomen: the renal, superior mesenteric, inferior mesenteric, celiac, and spinal radicular arteries. Involvement of these arteries is responsible for the development of certain unusual or atypical neurologic and ischemic signs and symptoms associated with AAA.
  5. In over 95% of cases, abdominal aneurysms arise below the origins of the renal arteries.
  6. The normal infrarenal aorta averages approximately 2.0 cm in diameter.
  7. The most widely used definition of an AAA is an aorta that is dilated at least 1.5 times that of the adjacent intact aorta, or any abdominal aorta with a diameter of 3.0 cm or greater.
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Key History

  • Abdominal pain with shock
  • Abdominal pain with syncope
  • Pain in the:
    • Abdomen
    • Back
    • Flank
  • Pain is acute or sudden in onset
  • Pain may be severe and constant
  • Pain may radiate to chest, thigh, inguinal area or scrotum
  • Shock (may be absent if rupture is contained)
  • Flank pain or radiation to the flank is common, often mistaken for renal colic
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Key Physical Exam

  • Pulsatile mass
  • Abdominal tenderness
  • Classic triad of: mass, pain, hypotension occurs in 30-40% of cases
  • Abdominal bruit
  • Decreased femoral pulses
  • Decreased urine output
  • Back pain
  • Hematuria
  • A pulsation to the right of the midline of the abdomen. A tortuous or prominent
    aorta generally does not present to the right of the midline
  • A left lower quadrant abdominal mass with abdominal tenderness and distention (AAA can rupture into LLQ)
  • Livedo reticularis: one or more cool painful cyanotic toes and palpable pedal pulses (i.e., emboli to the toes)
  • Aortoenteric fistula (AEF): Rupture of an AAA into the gastrointestinal tract
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Risk Factors for AAA

  • Age > 65
  • Male (4:1 male:female)
  • 1st degree relative w/ AAA
  • Prior AAA or femoral or popliteal aneurysm
  • Occlusive peripheral vascular disease
  • HTN
  • COPD
  • Smoking
  • Connective tissue disorder
  • Ehlers Danlos Syndrome
  • Marfan's Syndrome
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Differential Diagnosis

Gastrointestinal Genitourinary Cardiovascular
  • Appendiceal neoplasm
  • Appendicitis
  • Cecal diverticulitis
  • Cholecystitis
  • Cholelithiasis
  • Constipation
  • Crohn's disease
  • Diverticulitis
  • Gastroenteritis
  • GERD
  • GI Bleed
  • Hepatitis
  • Intestinal obstruction
  • Irritable bowel syndrome
  • Meckel’s diverticulitis
  • Mesenteric adenitis
  • Mesenteric ischemia
  • Omental torsion
  • Pancreatitis
  • Peptic ulcer disease
  • Perforated ulcer
  • Peritonitis
  • Small bowel obstruction
  • Typhlitis
Gynecological Other
  • Dysmenorrhea
  • Ectopic pregnancy [QC]
  • Endometriosis
  • Menorrhagia
  • Ovarian torsion
  • PID
  • Ruptured cyst (Mittelschmerz)
  • Tubal ovarian abscess
  • Diabetes ketoacidosis
  • Hemolytic Uremic Syndromes
  • Herpes zoster
  • Henoch Schoenlein purpura
  • Pneumonia
  • Sickle cell crisis
  • Streptococcal pharyngitis

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Diagnostic Testing

Text / literature information and recommendations include:
  1. Ultrasonography – 100% sensitive in detecting AAAs provided a good study can be obtained. Primary role is to screen patients at risk quickly in the emergency department. Accomplished at bedside, operator dependent, but the aorta is sometimes not well visualized. Note: cannot be used to determine if the AAA has ruptured. Rupture can be confirmed only if free intraperitoneal or retroperitoneal blood is seen (identifies leakage only 4% of the time).
  2. CT – 100% accurate determining presence of AAA. Study takes more time, and is appropriate only in hemodynamically stable patients. CT scan is more sensitive in detecting retroperitoneal hemorrhage associated with aneurysm rupture – reported sensitivity ranges from 77-100%. Does not accurately identify aortoenteric or venous fistula, inflammatory aneurysms or infections.
  3. Helical CT & CTA - Dual-slice helical CT correlates well with surgical findings in measuring the proximal and distal extent of the aneurysm. CT and CT angiography are not only less invasive than conventional aortography but also allow for more rapid scanning times and evaluation of the rest of the abdomen. Again, appropriate only in hemodynamically stable patients.
  4. MRI - MRI with MRA has 100 percent sensitivity in detecting aneurysms, and successfully identifies the proximal and distal extent of the aneurysms, the number and origins of renal arteries, and the presence of inflammation. Again, appropriate only in hemodynamically stable patients.
  5. KUB – reveals aortic calcification 60% of the time
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Clinical Risk and Safety Pearls

  • Only 30% of patients present with the classic triad of abdominal pain, a palpable mass, and hypotension.
  • Rupture of an AAA usually occurs into the retroperitoneum, where hemorrhage may be temporarily limited by clotting and tamponade at the rupture site.
  • Of patients with ruptures, 10% to 30% have free intraperitoneal rupture, which is often rapidly fatal. Occasionally, rupture occurs into the gastrointestinal tract or the inferior vena cava.
  • A pulsatile mass may not be palpable in up to 50% of patients with a ruptured AAA.
  • Studies have shown that among patients older than age 65 referred to a urologist for renal colic, 10% actually have an AAA.
  • AAAs typically rupture into the retroperitoneal space. The second most common site of rupture is the left lower quadrant. Studies demonstrate that 12% of AAAs are diagnosed initially as diverticulitis.
  • Consider the diagnosis in every older patient with abdominal, back, or flank pain.
  • A long duration of symptoms does NOT preclude the diagnosis of ruptured AAA.
  • Hypotension is present in only one-half to two-thirds of patients with rupture and is often a late finding.
  • Any size aneurysm can rupture, but it is more likely in aneurysms > 5 cm in diameter.
  • There is virtually no risk of causing aneurysm rupture by abdominal palpation.
  • Blue Toe syndrome is highly suggestive of a proximal source of emboli and an AAA may be the source.
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Treatment

Common text / literature recommendations include:

The appropriate degree of preoperative volume resuscitation is controversial. In the prehospital setting and in the emergency department before the availability of a surgeon and the operating room, the blood pressure should be raised with crystalloid or blood products to a level that maintains adequate cerebral and myocardial perfusion.
  1. Two large bore IVs should be placed
  2. Type and cross-matched for packed red cell transfusion
  3. Immediate surgical repair; endovascular repair may be possible for patients at poor surgical risk
  4. If hypertensive: Esmolol, labetalol, or nitroprusside are used to reduce pressure on the aortic wall
  5. A patient with a ruptured AAA should be moved as expeditiously as possible to the operating room. Precious time should not be spent with prolonged resuscitation or diagnostic imaging.
  6. Incidental diagnosis of AAA in the Emergency Department - If the AAA is small and felt to be asymptomatic, the patient will need mandatory, time-specific instructions for follow up. Document these instructions/expectations in the medical record and stress compliance with follow up on discharge. Current literature supports close monitoring of aneurysms < 5.5 cm and elective surgical repair for aneurysms ≥ 5.5 cm or for an aneurysm that has increased in size by 0.5 cm in the past 6 months dependent on surgical risk factors.
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  1. American College of Emergency Physicians Policy Statement. Ultrasound Guidelines: Emergency, Point-of-Care, and Clinical Ultrasound Guidelines in Medicine. Approved June 2016.
  2. Expert Panel on Vascular Imaging; Reis SP, Majdalany BS, AbuRahma AF, et al. ACR Appropriateness Criteria®: Pulsatile Abdominal Mass-Suspected Abdominal Aortic Aneurysm. J Am Coll Radiol. 2017;14(5S):S258-S265.
  3. Fink, HA, Lederle, FA, Roth, CS, et al. The accuracy of physical examination to detect abdominal aortic aneurysm. Arch Intern Med 2000; 160:833.
  4. Isselbacher, EM. Thoracic and abdominal aortic aneurysms. Circulation 2005; 111:816.
  5. Lederle FA. The rise and fall of abdominal aortic aneurysm. Circulation. 124: 1097, 2011. [PMID: 21900095]
  6. Lederle FA, Johnson GR, Wilson SE, et al. The Aneurysm Detection and Management Study Screening Program: validation cohort and final results. Arch Intern Med. 160: 1425, 2000. [PMID: 10826454]
  7. Rooke TW, Hirsch AT, Misra S, et al. 2011 ACCF/AHA Focused Update of the Guideline for the Management of Patients with Peripheral Artery Disease. J Am Coll Cardiol. 2011;58(19):2020-2045.
  8. Singh, K, Bonaa, KH, Jacobsen, BK, et al. Prevalence of and risk factors for abdominal aortic aneurysms in a population-based study: The Tromso Study. Am J Epidemiol 2001; 154:236.
  9. Shibamura, H, Olson, JM, van Vlijmen-Van, Keulen C, et al. Genome scan for familial abdominal aortic aneurysm using sex and family history as covariates suggests genetic heterogeneity and identifies linkage to chromosome 19q13. Circulation 2004; 109:2103.
  10. Swerdlow NJ, Wu WW, Schermerhorn ML. Open and endovascular management of aortic aneurysms. Circ Res . 2019;124(4):647-661.
  11. Tintinalli, JE, Stapczynski JS. Tintinalli’s Emergency Medicine. Chapter 60. 8th ed. McGraw Hill, 2016.

This is intended solely as reference material and is not a recommendation for any specific patient. The practitioner must rely upon his or her own professional judgment and medical decision-making to determine whether it is relevant in a particular case. Materials are derived from medical and nursing texts, medical literature and national guidelines and should not be considered complete or authoritative. Users must rely on specific patient presentation, experience and judgment when utilizing any of the information contained herein relative to an actual patient.
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