Abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a focal dilatation of the abdominal aorta to more than 1.5 times its normal diameter. AAAs are classified by location as either suprarenal or infrarenal aneurysms. Men of advanced age are at increased risk for their formation; smoking and hypertension are also major risk factors. AAAs are frequently asymptomatic and therefore detected incidentally. Symptomatic AAAs can manifest with lower back pain, a pulsatile abdominal mass, and a bruit on auscultation. Abdominal ultrasound is the best initial and confirmatory test to diagnose AAAs and determine their extent. Observation, close follow-up, and reduction of cardiovascular risk factors are indicated for small aneurysms, whereas pronounced (> 5.5 cm) or rapidly expanding aneurysms require surgery. Surgical treatment involves open resection of the aneurysm with graft placement or, increasingly, endovascular stent placement. The prognosis is markedly worse if dissection or aneurysm rupture occurs. AAA rupture typically presents with sudden onset of severe tearing back or abdominal pain, a painful pulsatile mass, and hypovolemic shock, and should be managed with emergent surgery. All men between 65 and 75 years of age with a history of smoking should be screened once with an ultrasound to exclude an AAA. See also thoracic aortic aneurysm for more information.

• Localized dilation of all three layers of the abdominal aortic wall (intima, media, and adventitia) to ≥ 3 cm ^[1]

• Peak incidence: 60–70 years (rare in patients < 50 years)
• Sex: ♂ > ♀: ∼ 2:1

Epidemiological data refers to the US, unless otherwise specified.

• Risk factors
  • Advanced age
  • Smoking (most important risk factor)
  • Atherosclerosis
  • Hypercholesterolemia and arterial hypertension
  • Positive family history
  • Trauma

• Localization
  • Infrarenal: below the renal arteries
    • Most common location ^[2]
    • One-third of aneurysms extend into the iliac arteries. ^[1]
  • Suprarenal: above the renal arteries
• Shape
  • Saccular (spherical) ^[3]
  • Fusiform (spindle-shaped)

• Inflammation and proteolytic degeneration of connective tissue proteins; (e.g., collagen and elastin and/or smooth muscle cells) in high-risk patients → loss of structural integrity of the aortic wall →; widening of the vessel → mechanical stress (e.g., high blood pressure) acts on weakened wall tissue → dilation and rupture may occur.
• The aneurysmatic dilatation of the vessel wall may cause disruption of the laminar blood flow and turbulence.
• Possible formation of thrombi in the aneurysm → peripheral thromboembolism

References:^[4][5]

Aortic aneurysms are usually asymptomatic or have nonspecific symptoms. They are often discovered incidentally on ultrasound or CT scan. Rupture or dissection of the aneurysm is a life-threatening condition (see “Ruptured AAA”).

• Lower back pain
• Pulsatile abdominal mass at or above the level of the umbilicus
• Bruit on auscultation
• Peripheral thrombosis and distal atheroembolic phenomena (e.g., blue toe syndrome and livedo reticularis)
• Decreased ankle brachial index

The diagnosis of AAA is confirmed by imaging showing aortic diameter > 3 cm. Unstable patients should be taken directly to the OR for emergency surgery if ruptured AAA is suspected (see ruptured AAA). There are no laboratory findings specific to AAA. ^[1]

Imaging should not delay treatment if AAA is suspected in hemodynamically unstable patients.

Imaging ^[6][7]

• Abdominal ultrasound (formal ultrasound or POCUS)
  • Indications
    • Best initial and confirmatory test in:
      • Asymptomatic patients
      • Patients with abdominal pain and no known AAA or risk factors for AAA
    • To determine the presence, size, and extent of an aneurysm
    • Screening and surveillance
  • Formal ultrasound ^[8]
    • Obtain longitudinal and transverse views for:
      • Proximal, mid, and distal abdominal aorta
      • Both proximal common iliac arteries
    • Obtain AP dimension measurements of the greatest diameters of each vessel.
  • See “POCUS for suspected AAA” for the point-of-care imaging technique and findings.
  • Supportive findings
    • Dilatation of the aorta ≥ 3 cm ^[1]
    • Thrombus may be present (hyperechoic)
  • Disadvantages: Abdominal ultrasound has low sensitivity for aneurysmal leaks, branch artery involvement, and suprarenal involvement, and its findings are insufficient for procedural planning. ^[1][9]

If a large (> 5.5 cm) aneurysm is seen on ultrasound in a patient presenting with abdominal pain, refer the patient for treatment immediately.

• CT angiography abdomen and pelvis
  • Indications
    • Imaging modality of choice in symptomatic patients and for preintervention planning
    • To help confirm the diagnosis when ultrasound is not possible in asymptomatic patients
    • More detailed evaluation of the location, size, and extent of the aneurysm, involvement of branch vessels, and presence of thrombus or rupture
  • Supportive findings
    • Dilatation of the aorta ≥ 3 cm and possibly branch vessels ^[1]
    • Thrombus may also be present (hypodense, nonenhancing)

• See differential diagnoses of acute abdomen in acute abdomen.
• Other types of aortic aneurysm (e.g., thoracic aortic aneurysm): See table below.

The differential diagnoses listed here are not exhaustive.

Approach ^[1][11]

• Patients with any symptoms: immediate vascular surgery consult
  • Suspected or known rupture (regardless of patient stability) : emergency repair within 90 minutes (see “Ruptured AAA”)
  • Patients with signs or symptoms of impending rupture; : urgent aneurysm repair, ideally within normal working hours, as this is associated with better outcomes Consider stabilizing comorbidities for a successful outcome unless this delays surgery by more than a few hours; the patient should be monitored in the ICU in the meantime.
    • Ensure blood product availability.
    • Maintain BP strictly within normal parameters.
    • Consult anesthesia.
    • Optimize the treatment of and stabilize any comorbidities that could increase perioperative risk (e.g., ADHF, AKI).
• Asymptomatic patients: elective aneurysm repair or aneurysm surveillance
• All patients: reduction of cardiovascular risk factors ^[1]
  • Appropriate medical management; of other atherosclerotic risk factors (e.g., hypertension, diabetes, hyperlipidemia)
  • Smoking cessation

Consult vascular surgery and the ICU about any patients with a symptomatic AAA.

Invasive treatment: AAA repair

• Indications ^[1]
  • Emergency repair: unstable patients
  • Urgent repair: impending rupture or leaking AAA
  • Elective repair
    • Fusiform aneurysm with maximum diameter ≥ 5.5 cm and low or acceptable surgical risk
    • Small fusiform aneurysm expanding ≥ 1 cm per year
    • Saccular aneurysm ^[1]
    • Aneurysm with maximum diameter 5.0–5.4 cm in women
    • Small aneurysm (4.0–5.4 cm) in patients requiring chemotherapy, radiotherapy, solid organ transplantation: individual approach

Procedures ^[1]

• Endovascular aneurysm repair (EVAR)
  • Indications: minimally invasive procedure that is preferred over open surgical repair for most aneurysms, especially in patients with a high operative risk
  • Procedure: Under fluoroscopic guidance, an expandable stent graft is placed via the femoral or iliac arteries intraluminally at the site of the aneurysm.
  • Disadvantage: Reintervention rates are higher for EVAR than for OSR.
• Open surgical repair (OSR)
  • Indications
    • Mycotic aneurysm or infected graft
    • Persistent endoleak and aneurysm sac growth following EVAR
    • Anatomical contraindications for EVAR
  • Procedure: A laparotomy is performed and the dilated segment of the aorta is replaced with a tube graft or Y-prosthesis (bifurcated synthetic stent graft).

Conservative treatment: AAA surveillance without repair

• Small (< 5.5 cm), asymptomatic AAA can typically be observed with interval surveillance ultrasound. ^[14]
  • To identify the expansion rate and thus decrease the risk of rupture
  • Frequency depends on the size of the aneurysm.

Regular monitoring is essential because aneurysm size and expansion rate are strong predictors for the risk of rupture.

Risk factors

• Rapidly expanding aneurysm
• Large diameter aneurysm
• Smoking, tobacco use

Clinical features

• Hypovolemic shock (especially in free ruptures)
• Sudden onset of severe, tearing back or abdominal pain with radiation to the flank, buttocks, legs, or groin
• Painful pulsatile mass
• Grey Turner sign and/or Cullen sign (if there is an extensive retroperitoneal hematoma)
• Nausea, vomiting
• Syncope
• Hematuria

Diagnostics ^[1][11][15]

The optimal diagnostic approach depends on patient stability, available resources, and clinical suspicion. Follow local protocols if available.

• Unstable patients: The diagnosis is clinical; refer directly for operative treatment. ^[1][11]
  • Consider POCUS to rapidly confirm the presence of an AAA.
  • Do not use POCUS to exclude a ruptured AAA if there is high clinical suspicion.
• Stable patients (controversial) ^{[1][11][15][16]}
  • Consider imaging (in consultation with a vascular surgeon) provided it does not delay definitive management, for the following reasons:
    • To evaluate for alternate etiologies if the diagnosis is uncertain ^[1]
    • Anatomic assessment (e.g., with a thoracoabdominal CTA) to determine candidacy for EVAR and guide operative planning. ^[11]
  • Closely monitor patients clinically during transfer outside of critical care areas for imaging.

Imaging modalities

• CTA thorax, abdomen, and pelvis
  • Study of choice if imaging can be performed without delaying operative repair ^[11][16]
    • Higher detection rates for contained rupture and retroperitoneal bleeds than ultrasound
    • Allows surgeons to determine if a patient is suitable for EVAR
  • Characteristic findings
    • Sign of impending rupture: high-attenuation crescent within mural thrombus ^[17]
    • Signs of rupture: retroperitoneal hematoma, retroperitoneal stranding, indistinct aortic wall, extravasation of contrast
• POCUS: In an unstable patient, assume that a visible AAA on POCUS is a ruptured AAA until proven otherwise.
  • Key finding: dilatation of the aorta ≥ 3 cm
  • Other possible findings
    • Periaortic fluid
    • Free intraperitoneal or retroperitoneal fluid, depending on the location of the rupture
  • For more detailed findings see “POCUS for suspected AAA.”

Additional studies

• Laboratory findings that may be seen:
  • CBC: ↓ hemoglobin, ↓ hematocrit, ↓ red blood cell count
  • Metabolic acidosis in cases of shock
• ECG: may show ischemic changes secondary to acute blood loss ^[15]

Treatment ^[1][11]

The main goal of treatment is operative repair by a vascular surgeon without delay.

• Initial management (ideally within 30 minutes)
  • Large-bore IV access
  • Start continuous monitoring and reassess regularly as patients may deteriorate rapidly.
  • Immediate hemodynamic support
    • Fluid resuscitation, or if available, blood transfusion, ideally using blood products in a 1:1:1 ratio ^[11][15]
    • Use vasopressors and inotropes with caution. ^[15]
    • Target: permissive hypotension (e.g., SBP 70–90 mm Hg) ^[1]
  • Urgent vascular surgery and anesthesia consult ^[1]
  • Pain management with IV opioids
• Definitive treatment (ideally within 90 minutes): emergency EVAR or OSR ^[1][11]
• Palliation: Consider in frail patients with multiple comorbidities. ^[11]

Refer all patients with a suspected ruptured AAA for immediate operative evaluation.

Prognosis

• High mortality rate (∼ 81%) ^[18]
• Older age, loss of consciousness, and cardiac arrest prior to surgery are associated with high mortality.

• Abdominal aortic aneurysm rupture
• Embolism: caused by thrombotic material from the aneurysm
• Aortic dissection
• Postoperative complications ^[19]
  • Ischemia of the bowel, kidneys, and spinal cord
  • Anterior spinal artery occlusion
  • Prosthetic graft infection
  • Aortoenteric fistula
  • Complications following EVAR ^[1]
    • Endoleak
    • Access site complications, e.g., bleeding, hematoma, false aneurysm
    • Graft limb thrombosis

We list the most important complications. The selection is not exhaustive.

Ruptured abdominal aortic aneurysm

• Immediate vascular surgery consult for emergency surgical repair if ruptured aneurysm is suspected
• Unstable patients: Transfer to the OR immediately.
• Stable patients: Consider CTA if it can be performed rapidly and close monitoring is possible.
• NPO
• IV access with two large-bore peripheral IV lines
• Check CBC, type and screen, obtain patient consent for blood transfusion, and order pRBCs (prepare for massive transfusion protocol).
• IV fluid resuscitation with goal SBP of 70–90 mm Hg (permissive hypotension) ^[1][20]
• IV opioid analgesics

Symptomatic abdominal aortic aneurysm

• Urgent vascular surgery consult for surgical repair
• CT angiography abdomen and pelvis with IV contrast for preintervention planning if patient is hemodynamically stable
• Transfer to OR.
• NPO
• IV access with two large-bore peripheral IV lines
• Check CBC, type and screen, obtain patient consent for blood transfusion, and order pRBCs (prepare for massive transfusion protocol).
• Consider IV fluid resuscitation.
• IV opioid analgesics

Primary prevention ^[1]

See “ASCVD prevention” for detailed information on primary prevention.

• The following measures are thought to reduce the risk of developing an AAA:
  • Eating nuts, fruits, and vegetables more than three times a week
  • Exercising more than once a week
  • Smoking cessation

Secondary prevention ^[1][18]

• Screening for abdominal aneurysm with abdominal ultrasound
  • One-time screening in men aged 65–75 years with a history of smoking ^[1][18]
  • Also consider one-time screening for the following groups: ^[1][18]
    • Individuals aged 65–75 years with a positive family history
    • Individuals aged > 75 years in good health with a positive family history
    • Women aged 65–75 years with a history of smoking
    • Individuals aged > 75 years in good health with a history of smoking
  • Consider rescreening after 10 years if the aortic diameter was > 2.5 cm but < 3 cm in the initial assessment. ^[1]

Tertiary prevention ^[1]

• Elective repair to prevent rupture (see “Treatment”)
• Aneurysm surveillance
• Smoking cessation

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