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Aortic aneurysm and dissection for USMLE 3

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Aortic aneurysm and aortic dissection for the USMLE Step 3 Exam
Aortic Aneurysm
  • Definition:
    • An aortic aneurysm is a dilation of the aorta that exceeds 1.5 times its normal diameter, often classified as thoracic aortic aneurysm (TAA) or abdominal aortic aneurysm (AAA).
    • AAA is more common, often occurring below the renal arteries.
  • Risk Factors:
    • Non-modifiable: Advanced age, male sex, and family history.
    • Modifiable: Smoking (most significant modifiable risk factor), hypertension, and atherosclerosis.
    • Genetic Disorders: Marfan syndrome, Ehlers-Danlos syndrome, and bicuspid aortic valve are associated with TAA.
  • Pathophysiology:
    • The weakening of the aortic wall is due to structural degradation of elastin and collagen, influenced by chronic inflammation and extracellular matrix breakdown.
    • Risk factors contribute to vascular wall stress, leading to aneurysm expansion and possible rupture.
  • Clinical Presentation:
    • Asymptomatic: AAAs are often discovered incidentally.
    • Symptomatic: Expanding or ruptured aneurysms may present with back or abdominal pain; a pulsatile abdominal mass is possible with AAA.
  • Diagnosis:
    • Imaging:
    • Ultrasound: First-line screening for AAA.
    • CT Angiography (CTA): Preferred for detailed preoperative assessment, especially in symptomatic cases or suspected rupture.
    • Screening Guidelines: One-time ultrasound for men aged 65-75 who have a history of smoking.
  • Management:
    • Medical Management: Smoking cessation, blood pressure control (often with beta-blockers or ACE inhibitors).
    • Surveillance: Regular imaging for AAAs under 5.5 cm.
    • Surgical Indications:
    • AAA: Indicated if >5.5 cm in men, >5.0 cm in women, or expanding >0.5 cm/year.
    • TAA: Surgery recommended for aneurysms >5.5-6.0 cm or with rapid expansion.
    • Procedures: Open repair or endovascular aneurysm repair (EVAR) for AAA; thoracic endovascular aortic repair (TEVAR) for TAA.
Aortic Dissection
  • Definition:
    • Aortic dissection occurs when an intimal tear allows blood to enter the aortic media, creating a false lumen that dissects the wall layers.
  • Classification:
    • Stanford Classification:
    • Type A: Involves the ascending aorta and requires emergent surgical intervention.
    • Type B: Involves only the descending aorta and is managed medically unless complications develop.
Types of aortic dissection
  • Pathophysiology:
    • Dissection typically occurs in areas of high shear stress, such as the proximal ascending aorta, especially in patients with weakened vessel walls.
    • Risk Factors: Hypertension, connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome), bicuspid aortic valve, and stimulant use (e.g., cocaine).
  • Clinical Presentation:
    • Classic Symptom: Sudden onset of severe, “tearing” chest or back pain.
    • Type A: May lead to aortic regurgitation, myocardial ischemia, or tamponade.
    • Type B: Can cause malperfusion syndromes affecting abdominal organs, spinal cord, or lower extremities.
  • Diagnosis:
    • Imaging:
    • CT Angiography (CTA): First-line imaging, particularly in hemodynamically stable patients, for defining the true and false lumens.
    • Transesophageal Echocardiography (TEE): Often used in unstable patients or intraoperatively, especially for Type A dissections.
  • Management:
    • Type A Dissection: Immediate surgery to prevent fatal complications such as rupture or tamponade.
    • Type B Dissection:
    • Medical Management: Blood pressure control with a target systolic BP of 100-120 mmHg using beta-blockers and vasodilators.
    • Endovascular Repair: Considered if complications arise, such as persistent pain, malperfusion, or aneurysmal expansion.
Key Points
  • Aortic Aneurysm:
    • Defined as an aortic dilation, more common in the abdominal aorta (AAA) than thoracic (TAA).
    • Key risk factors: Age, male sex, smoking, hypertension, and genetic disorders.
    • Managed with surveillance for smaller aneurysms, with surgical repair for larger or symptomatic ones.
  • Aortic Dissection:
    • Involves a tear in the aortic wall creating a false lumen, classified as Type A (ascending aorta) or Type B (descending aorta).
    • Presents with acute “tearing” chest or back pain; CTA is the preferred diagnostic tool.
    • Type A dissections require immediate surgery; Type B dissections are often managed medically unless complications occur.

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