Abdominal aortic aneurysm

Question 1

What is the difference between true and false aortic aneurysms?

Answer 1

True - all 3 layers of the arterial wall are involved False - only a single layer of fibrous tissue forms the aneurysm wall.

Question 2

How common are true aortic abdominal aneurysms?

Answer 2

• incidence of 0.06 per 1000 people
• commonest in elderly men
• UK now introducing the aneurysm screening program
  
  • abdominal aortic ultrasound measurement in all men aged 65 years

Question 3

What are the causes of abdominal aortic aneurysm?

Answer 3

1. Standard arterial disease (commonest):

• hypertensive
• diabetes
• smokers.

2. Connective tissue diseases:

• Marfan’s
• Extracellular matrix disrupted with a change in the balance of collagen and elastic fibres.

Question 4

Where do aortic abdominal aneurysms rupture?

Answer 4

• 20% rupture anteriorly into the peritoneal cavity (very poor prognosis)
• 80% rupture posteriorly into the retroperitoneal space

Question 5

How do you assess the risk of abdominal aortic aneurysm?

Answer 5

• Risk of rupture related to aneurysm size
• 2% of aneurysms < 4cm in diamete rupture over 5 years
• 75% of aneurysms measuring > 7cm rupture

Explained by Laplaces’ law which relates size to transmural pressure.

Patients with an aneurysm size of > 5cm get CT scanning of the chest, abdomen and pelvis to delineate anatomy and planning treatment.

Depending upon co-morbidities, surgery is generally offered once the aneurysm is between 5.5cm - 6cm.