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Aortic Aneurysm for USMLE Step 2 & COMLEX-USA Level 2

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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 form when structural changes occur in the aortic wall, including degradation of elastin and collagen.
  • Types:
    • Abdominal Aortic Aneurysm (AAA): Typically below the renal arteries; more common than TAA.
    • Thoracic Aortic Aneurysm (TAA): Involves the thoracic aorta, often associated with genetic disorders.
  • Causes:
    • AAA: Primarily caused by atherosclerosis.
    • TAA: Related to connective tissue diseases (e.g., Marfan syndrome, Ehlers-Danlos syndrome) or chronic hypertension.
Risk Factors
  • Smoking: Strongest modifiable risk factor for AAA.
  • Hypertension: Increases wall stress, contributing to aneurysm formation.
  • Genetic predispositions: Marfan syndrome, bicuspid aortic valve, and other connective tissue disorders elevate the risk for TAA.
  • Age and gender: Aneurysms are more common in men over 60 years of age.
Symptoms and Signs
  • Asymptomatic: Aneurysms often grow silently and are discovered incidentally on imaging.
  • Symptoms:
    • AAA: Abdominal or back pain, pulsatile mass in the abdomen.
    • TAA: Chest pain, hoarseness, dysphagia (compression of surrounding structures).
  • Complications:
    • Rupture: Sudden, severe pain with hypotension and shock.
    • Aortic dissection: Tearing chest or back pain, commonly in TAA.
    • Thrombosis and embolism: Distal ischemia due to thrombus formation in the aneurysm.
Diagnostic Workup
  • Ultrasound: First-line screening for AAA in at-risk populations (e.g., men aged 65-75 who have smoked).
  • CT angiography: Gold standard for detailed visualization of both AAA and TAA for preoperative planning.
  • MRI: Alternative for patients with contrast allergies or for follow-up in genetically predisposed individuals (e.g., Marfan syndrome).
Management
  • Conservative:
    • Regular imaging surveillance for small, asymptomatic aneurysms (e.g., <5.5 cm).
    • Smoking cessation, hypertension control, statin therapy.
  • Surgical indications:
    • AAA >5.5 cm or TAA >5.5-6.0 cm (depending on location).
    • Rapid growth (>0.5 cm over 6 months).
    • Symptomatic aneurysms or those showing signs of impending rupture.
  • Surgical options:
    • Endovascular Aneurysm Repair (EVAR): Minimally invasive; preferred for anatomically suitable AAAs.
    • Open surgical repair: Necessary for large or complex aneurysms, particularly for TAA.
Postoperative Care
  • Imaging surveillance: Lifelong follow-up after EVAR to monitor for endoleaks or graft complications.
  • Medications:
    • Antihypertensives, especially for TAA, to reduce wall stress and prevent further aneurysm expansion.
    • Statins for underlying atherosclerosis.
Essential Points
  • AAA screening is crucial for men aged 65-75 with a history of smoking, using abdominal ultrasound.
  • Rupture risk increases with aneurysm size, and AAA rupture is a medical emergency with high mortality.
  • Surgical repair is recommended for aneurysms larger than 5.5 cm or those growing rapidly.
  • Genetic syndromes like Marfan syndrome require careful monitoring, as they predispose to TAA.