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Abdominal Aortic Aneurysm (AAA)

Epidemiology

• 4-6 : 1 Male : Female ratio
• 4-8% if age > 65
• Most infrarenal

Etiology

• Usually due to atherosclerotic disease
• Risk factors:
  • smoking
  • male sex
  • age
  • pre-existing atherosclerosis
  • obesity
  • Hyperlipidemia
  • HTN (Hypertension)
  • Family History

Screening / Surveillance

• ACC/AHA: One-time abdoimnal ultrasound in all men older 60 years with or without Family History of AAA (IIC) and all men > 65 that have ever smoked (IA)

• USPSTF: One-time abdominal ultrasound for men age 65-75 who have ever smoked (Grade B) and selective screening for male who never smoked 65-75 (Grade C). Screening for women not recommended.

• Surveillance:
  • 3-3.4 cm: U/S q3y
  • 3.5-4.4 cm: U/S or CT q12mo
  • 4.5-5.4 cm: U/S or CT q6mo

Imaging Modalities

• Abdominal Ultrasound: screening and surveillance of infrarenal AAAs. High Se/Sp (>90%), operator-dependent
• CT w/ contrast: high Se/Sp, better than U/S for suprarenal AAAs
• MRI/MRA: good Se/Sp, preferred for aortic root imaging and for imaging tortuous aortas
• CXR: “enlarged aorta” nonspecific (tortuous aorta vs. aneurysm)
• TTE (transthoracic echocardiogram): useful for root and proximal thoracic aorta; TEE: will visualize entire thoracic aorta but rarely used.

Treatment

Medical:

• Smoking cessation (slows AAA growth by up to 25%)
• Reduce Blood Pressure in accordance with ACC/AHA standards
• Meds:
  • Statins (reduce all-cause mortality in patients post surgery)
  • Beta Blockers (may slow expansion; IA for perioperative use)
  • ACEi (controversial; may prevent rupture but may speed growth)
  • Low dose ASA (may slow growth)
  • Antibiotics (e.g., roxithromycin may reduce expansion rate ,not mortality)

Surgical:

• Men: > 5.5 cm OR growing at >0.5 cm/year OR symptomatic Women: > 4.5-5cm (controversial)
• Open repair (~4-6% 30 day mortality) vs. EVAR (only~50% suitable, c/b endoleaks [continued blood flow intoaneurysmal cavity, ~1% 30 day mortality]).

Complications

• Rupture: Devastating mortality. AAA annual rupture rates are 4%, 7%, 20% at 5, 6, and 7cm, respectively.
  • Risk factors for Rupture:
    • size,
    • rate of expansion,
    • female gender
  • Symptoms of AAA Rupture: Triad of:
    • abdominal / back pain
    • pulsatile abdominal mass
    • hypotension
  • Immediate surgery (don’t image)

• Dissection: pain (chest/abdomen/back), occlusion of aortic vessels, thromboembolism

• Post-repair:
  • EVAR: endoleak, graft failure, thrombosis.
  • Open: MI, embolization, AKI, ischemic colitis

Thoracic Aortic Aneurysm (TAA)

Epidemiology

• 1.7 : 1 Male : Female ratio
• Mostly age of 50-70
• 50% Ascending Aorta, 40% Descending Aorta, 10% Aortic Arch

Etiology

• Atherosclerotic: Majority of cases. Mostly in Descending Aorta.
  • Risk factors:
    • Smoking,
    • Hyperlipidemia,
    • HTN (Hypertension)

• Structural/genetic: Mostly in root and ascending aorta.
  • Causes:
    • Connective tissue disease (Marfan, Ehlers-Danlos, Loeys-Dietz)
    • Turner syndrome
    • Bicuspid Aortic Valve
    • Trauma

• Infectious:
  • tertiary syphilis
  • mycotic aneurysm (mostcommon organisms: Staphylococcus spp., Salmonella spp.)

• Inflammatory:
  • GCA (Giant cell arteritis): ~10% have TAA
  • Takayasu arteritis
  • Rheumatoid arthritis
  • Psoriasis
  • Behcet’s
  • Wegener’s Granulomatosis

Screening / Surveillance

• General population: Not recommended

• Indications:
  • At time of diagnosing Marfan (IC), Turner (IC) ,Loeys-Dietz, Takayasu arteritis or (Giant cell arteritis).
  • 1st degree relatives of patients with TAA, dissection, bicuspid valve (IB/IC).

• Surveillance:
  • If aneurysm only, then same as AAA.
  • If also with dissection, image at 1, 3, 6, & 12 months then annually.
  • Image entire aorta (CT/MRI) if multiple aneurysms (~25% TAA will have AAA; ~25% AAA will have TAA).

Imaging Modalities

• Abdominal Ultrasound: screening and surveillance of infrarenal AAAs. High Se/Sp (>90%), operator-dependent
• CT w/ contrast: high Se/Sp, better than U/S for suprarenal AAAs
• MRI/MRA: good Se/Sp, preferred for aortic root imaging and for imaging tortuous aortas
• CXR: “enlarged aorta” nonspecific (tortuous aorta vs. aneurysm)
• TTE (transthoracic echocardiogram): useful for root and proximal thoracic aorta; TEE: will visualize entire thoracic aorta but rarely used.

Treatment

Medical:

• Reduce BP (<140/90 or <130/80 if DM or CKD; littl eactual evidence, IB)
• Smoking cessation; avoid straining
• Stress test used to guide BP management (follow SBP response to stress)
• Meds:
  • Beta Blockers proven to decrease TAA growth in Marfan
  • ARBs slow aortic root aneurysm expansion in Marfan patients, likely via TGF-B inhibition (NEJM 2008;358:2787)
  • Statins if LDL<70, some evidence

Surgical:

• Root / ascending TAAs: usually concomitant aortic valve replacement
• Arch / descending TAAs: mostly open graft, (EVAR). Ischemic brain/spine injury most worrisomecomplication.

Complications

• Rupture: Devastating mortality. AAA annual rupture rates are 4%, 7%, 20% at 5, 6, and 7cm, respectively.
  • Risk factors for Rupture:
    • size,
    • rate of expansion,
    • female gender
  • Symptoms of TAA Rupture: Triad of:
    • abdominal / back pain
    • pulsatile abdominal mass
    • hypotension
  • immediate surgery (don’t image)

• Dissection: pain (chest/abdomen/back), occlusion of aortic vessels, thromboembolism

• Post-repair:
  • EVAR: endoleak, graft failure, thrombosis.
  • Open: MI, embolization, AKI, ischemic colitis

References:

1. https://pubmed.ncbi.nlm.nih.gov/27585511/