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Aortic Aneurysm for the American Board of Internal Medicine (ABIM) Exam

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Overview of Aortic Aneurysm
  • Definition: Aortic aneurysm refers to a segmental, full-thickness dilation of the aorta, exceeding 50% of its normal diameter due to weakening of the vessel wall.
Pathophysiology
  • Wall weakening: Aneurysms develop due to structural changes in the aortic wall, such as the degradation of elastin and collagen.
  • Types:
    • Abdominal Aortic Aneurysm (AAA): The most common type, typically located below the renal arteries.
    • Thoracic Aortic Aneurysm (TAA): Involves the thoracic aorta and is often associated with genetic conditions, such as Marfan syndrome and Ehlers-Danlos syndrome.
  • Causes:
    • AAA: Primarily due to atherosclerosis.
    • TAA: Related to connective tissue disorders, hypertension, and cystic medial necrosis.
Risk Factors
  • Smoking: The most significant modifiable risk factor for AAA.
  • Hypertension: Increases wall stress, contributing to aneurysm formation.
  • Genetic predispositions: Conditions such as Marfan syndrome, bicuspid aortic valve, and other connective tissue disorders increase the risk for TAA.
  • Age and gender: Aneurysms are more common in men over the age of 65.
Symptoms and Signs
  • Asymptomatic: Aneurysms are often silent and discovered incidentally on imaging.
  • Symptoms:
    • AAA: Abdominal or back pain and a pulsatile mass in the abdomen.
    • TAA: Chest pain, hoarseness, or dysphagia due to compression of nearby structures.
  • Complications:
    • Rupture: Sudden severe pain with hypotension and shock.
    • Aortic dissection: Tearing chest or back pain, especially in TAA.
    • Thromboembolism: Thrombus formation within the aneurysm may lead to distal ischemia.
Diagnostic Workup
  • Ultrasound: The first-line screening test for AAA, especially in men aged 65-75 who have smoked.
  • CT angiography: The gold standard for diagnosing and evaluating both AAA and TAA, particularly for preoperative planning.
  • MRI: An alternative to CT, especially useful for patients with contrast allergies or for follow-up in genetic conditions like Marfan syndrome.
Management
  • Conservative:
    • Routine surveillance imaging for small, asymptomatic aneurysms.
    • Smoking cessation, blood pressure control, and statin therapy for managing atherosclerosis.
  • Surgical indications:
    • AAA >5.5 cm or TAA >5.5-6.0 cm depending on location.
    • Rapid expansion (>0.5 cm in 6 months).
    • Symptomatic aneurysms or those at risk of rupture.
  • Surgical options:
    • Endovascular Aneurysm Repair (EVAR): A minimally invasive option preferred for AAA when anatomy allows.
    • Open surgical repair: Required for large or complex aneurysms, particularly in TAA.
Postoperative Care
  • Surveillance: Lifelong imaging follow-up after EVAR to monitor for endoleaks or other complications, and periodic imaging after open repair.
  • Medications:
    • Antihypertensives: Crucial for controlling blood pressure and reducing the risk of dissection, particularly in TAA patients.
    • Statins: Used to manage underlying atherosclerosis.
    • Beta-blockers: Recommended for patients with genetic conditions like Marfan syndrome to reduce wall stress.
Essential Points
  • AAA screening: Recommended in men aged 65-75 with a history of smoking.
  • Rupture risk: AAA rupture presents with hypotension, back pain, and a pulsatile abdominal mass, requiring emergency intervention.
  • TAA: More common in patients with connective tissue disorders such as Marfan syndrome, and may present with compression-related symptoms like hoarseness.
  • Surgical repair: Indicated for aneurysms larger than 5.5 cm or those rapidly expanding.
  • Early detection and risk factor management: Essential for reducing mortality and improving outcomes associated with rupture.
  • Fluoroquinolone caution: The FDA recommends avoiding fluoroquinolones in patients with aortic aneurysm, as they may increase the risk of dissection and rupture, unless no alternatives are available.