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Aortic Aneurysm for USMLE Step 3 & COMLEX-USA Level 3

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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 due to structural changes in the aortic wall, including degradation of elastin and collagen.
  • Types:
    • Abdominal Aortic Aneurysm (AAA): Typically below the renal arteries; most common.
    • Thoracic Aortic Aneurysm (TAA): Involves the thoracic aorta and is often linked to genetic disorders.
  • Causes:
    • AAA: Primarily caused by atherosclerosis.
    • TAA: Related to cystic medial necrosis, connective tissue disorders (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: Conditions like Marfan syndrome, bicuspid aortic valve, and other connective tissue disorders increase the risk for TAA.
  • Age and gender: More common in men over 65 years.
Symptoms and Signs
  • Asymptomatic: Most aortic aneurysms remain silent until complications arise and are often detected incidentally during imaging.
  • Symptoms:
    • AAA: Abdominal, flank, or back pain, and pulsatile mass.
    • TAA: Chest pain, dyspnea, hoarseness (due to compression of the recurrent laryngeal nerve), dysphagia, or superior vena cava syndrome (if large enough).
  • Complications:
    • Rupture: A life-threatening emergency that presents with hypotension, severe pain, and potential syncope.
    • Aortic dissection: Sudden, tearing chest or back pain; more common with TAA.
    • Thrombosis or embolism: Distal ischemia from thrombus formation in the aneurysm.
Diagnostic Workup
  • Ultrasound: First-line imaging for AAA, especially for screening in men aged 65-75 with a history of smoking.
  • CT angiography: Gold standard for diagnosing and assessing both AAA and TAA, providing detailed sizing and location, critical for preoperative planning.
  • MRI: An alternative for patients unable to undergo CT, especially in genetic syndromes like Marfan syndrome.
Management
  • Conservative:
    • Routine surveillance imaging for small, asymptomatic aneurysms (e.g., <5.5 cm).
    • Lifestyle changes: Smoking cessation, blood pressure control, and statin therapy.
  • Surgical indications:
    • AAA >5.5 cm or TAA >5.5-6.0 cm, depending on location.
    • Rapid growth (>0.5 cm in 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
  • Surveillance: Lifelong imaging follow-up after EVAR to monitor for complications like endoleaks or graft issues. Periodic imaging is also needed after open repair to ensure graft integrity.
  • Medications:
    • Antihypertensives are critical, particularly in TAA patients, to reduce the risk of further aneurysm growth or dissection.
    • Statins are often prescribed for patients with atherosclerosis-related aneurysms.
Essential Points
  • AAA screening: Recommended in men aged 65-75 who have ever smoked, using abdominal ultrasound.
  • Rupture risk: Increases with aneurysm size; AAA rupture is a medical emergency with a high mortality rate.
  • Surgical intervention: Recommended for aneurysms larger than 5.5 cm, symptomatic aneurysms, or those growing rapidly.
  • Genetic conditions: Syndromes like Marfan and Ehlers-Danlos require vigilant monitoring as they predispose to TAA and dissection.