Epidemiology

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Etiology

• Acquired
  • Hypertension (most common risk factor)
  • Trauma, e.g., deceleration injury in a motor vehicle collision, or iatrogenic injury during valve replacements or graft surgery (traumatic aortic dissection)
  • Vasculitis with aortic involvement (e.g., syphilis, Takayasu arteritis)
• Congenital
  • Connective tissue disease (Marfan syndrome, Ehlers-Danlos syndrome)
  • Bicuspid aortic valve (e.g., in Turner syndrome)

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Pathophysiology

Characteristic	Abdominal Aortic Aneurysm (AAA)	Aortic Dissection
Definition	Localized dilation of abdominal aorta >3cm	Tear in aortic wall creating false lumen
Risk Factors	Smoking (most important), male, hypertension, age >65, family history	Hypertension (most important), Marfan syndrome, bicuspid valve, pregnancy
Pathophysiology	Progressive weakening of arterial wall due to elastin degradation and inflammation; atherosclerosis leads to oxidative stress and matrix metalloproteinase activation	Intimal tear allows blood to enter media, creating false lumen; can be triggered by hypertensive crisis or inherited connective tissue disorders
Onset	Gradual	Sudden, acute
Pain	Usually asymptomatic; may have dull abdominal/back pain	Severe, tearing chest/back pain; migrating
Physical Exam	Pulsatile abdominal mass	Unequal pulses, BP differences between arms
Complications	Rupture with hemorrhagic shock	Organ ischemia, tamponade, aortic rupture
Imaging	Ultrasound, CT with contrast	CT angiogram, TEE
Treatment	Endovascular repair (EVAR) or open surgery if >5.5cm	Emergency surgery (Type A), medical management (Type B)
Mortality	80% if ruptured; 5% with elective repair	50% at 48h without treatment (Type A)

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Clinical features

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Diagnostics

Pathology

• Cystic medial degeneration: a degeneration (necrosis) of large blood vessels such as the aorta.
  • Seen in disorders that cause increased arterial wall stress (e.g., hypertension, coarctation of the aorta) as well as connective tissue disorders (especially Ehlers-Danlos syndrome and Marfan syndrome)
  • Can lead to aortic aneurysm and aortic dissection
  • Histopathology
    • Loss, thinning, disorganization, and fragmentation of elastic tissue in the media
    • Accumulation of mucoid extracellular matrix
    • Loss of smooth muscle nuclei

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Treatment

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Complications

• Aortic rupture and acute blood loss: acute back and flank pain (tearing pain), symptoms of shock → indication for emergency surgery
• Complications of Stanford type A dissections
  • Myocardial infarction (coronary artery occlusion)
  • Aortic regurgitation (extension of the dissection into the aortic valve)
  • Cardiac tamponade progressing to cardiogenic shock
  • Stroke (extension of the dissection into the carotids)
• Complications of both Stanford type A dissection and Stanford type B dissections
  • Arterial occlusion followed by ischemia of the:
    • Celiac trunk, superior/inferior mesenteric artery → acute abdomen, ischemic colitis
    • Renal arteries → acute renal failure (oliguria, anuria)
    • Spinal arteries → weakness of lower extremities or acute paraplegia