Abdominal Aortic Aneurysm

Question 1

Define aneurysm.

Answer 1

A weakening of the vessel wall causing bulging/increased diameter of an artery.

Question 2

What is an abdominal aortic aneurysm?

Answer 2

A permanent pathological dilation of the aorta with a diameter >1.5 times the expected anteroposterior (AP) diameter of that segment (or >3cm), given the patient’s sex and body size.

Question 3

How common is the prevalence of AAA in UK NHS screening programme?

Answer 3

Screening at 65yrs shows 1.34% prevalence

Question 4

Where do leaking abdominal aneurysms usually occur? What are the two types?

Answer 4

90% below the renal arteries (abover the bifurcation of the common iliac)

Can be saccular (outpocketing) or fusiform (diffuse swelling)

Question 5

List the risk factors associated with AAA.

Answer 5

Risk factors:

• Smoking - each year smoking increases risk by 4%
• FH - doubled risk if present in first degree relative
• Age
• Male - x4-6 but risk of rupture is greater in women
• Congenital/connective tissue disorders - Marfan’s, bicuspid aortic valves, pregnancy.
• Others:
  
  • hyperlipidaemia,
  • hypertension
  • atherosclerosis,
  • increased weight, central obesity,
  • non-diabetic (diabetes actually protects against growth and enlargement of AAA)
  • European
  • COPD

Question 6

What is the pathophysiology of AAA development?

Answer 6

Histologically there is obliteration of collagen and elastin in the media and adventitia, smooth muscle loss and infiltration of immune cells.

Four main mechanisms:

1. Proteolytic degradation of connective tissue by MMP
2. Inflammation and immune responses
3. Biochemical wall stress
4. Molecular genetics - heritability is high

Question 7

Where do AAA rupture into?

Answer 7

Peritoneal space OR

Retroperitoneal tissue - almost always fatal

* prone to rupture when they reach 6-7cm

Question 8

Name 3 specific types of AAA (classification).

Answer 8

Congenital = e.g. bicuspid aortic valves and Marfan syndrome.

Infectious = mycotic aneurysm.e.g. Staphylococcus and Salmonella are most common. Chlamydia pneumoniae or tertiary syphilis may also cause it.

Inflammatory = an abnormal accumulation of macrophages and cytokines in diseased tissue. Pathologically there is perianeurysmal fibrosis, thickened walls, and dense adhesions.

Question 9

What is a mycotic aneurysm?

Answer 9

An aneurysm caused by BACTERIAL infection of the arterial wall (even though mycotic usually refers to fungal infection)

Infections cause false aneurysm to form, which are unstable and highly prone to rupture.

Question 10

How does Marfan’s increase the risk of AAA?

Answer 10

Abnormality in fibrillin type 1 found in elastin → mature aorta has abnormal elastic properties, progressive stiffening and dilation

Question 11

What is the biggest molecular cause of AAA? What protects?

Answer 11

METALLOPROTEINASES diminish the integrity of the arterial wall - SMOKING remains the most important risk factor.

Question 12

Describe the epidemiology of AAA.

Answer 12

Deaths from AAA since 1997 have been declining due to fall in smoking rates and rise in elective AAA repairs.

x4-6 more prevalent in males

In the US, prevalence in white male smokers is about 6%.

Question 13

Describe the clinical presentation of a leaking abdominal aneurysm.

Answer 13

• Severe central abdominal pain, commonly radiating to the back and may be to the groin along the course of the genito-femoral nerve.
• The patient may collapse from the accompanying hypotensive shock or suddenly die

Question 14

What are the presenting symptoms of an AAA?

Answer 14

Patients are usually asymptomatic and their abdominal aortic aneurysm is detected incidentally.

In the minority of patients who experience symptoms, abdominal, back, and groin pain are typical + hypotension

Question 15

What should you ask about in a history of suspected AAA?

Answer 15

• Smoking
• Family history
• Tissue disorders

Question 16

What are the signs of an AAA on physical examination?

Answer 16

• Palpable EXPANSILE abdominal mass - but this is only sensitive in thin patients and those with AAA>5cm.
• Hypotension - people with a ruptured AAA present with triad of (1) abdominal +/- back pain, (2) pulsatile abdominal mass, (3) hypotension.

Question 17

What investigations would you do for an AAA?

Answer 17

1st - Abdominal ULTRASOUND

Other

• Cross match/group and save - if suspected ruptured
• Clotting screen
• ESR/CRP - elevated suggests inflammatory AAA
• FBC - check for leukocytosis and anaemia (indicate infectious AAA)
• Culture - same as above
• Contrast CT angio or MRA - may show discontinuity of aortic wall close to the renal arteries

Question 18

How are aortic aneurysms surgically fixed?

Answer 18

Most aneurysms are conveniently located below the renal arteries so that surgical resection with placement of a dacron graft can be done

Question 19

What would imaging show in an AAA?

Answer 19

• US can be used to show aneurysm but not to exclude it
• Contrast CT is used to assess extent and anatomy of the AAA

Abdominal aortic dilation x >1.5 the expected AP diameter of that segment, usually a threshold diameter of ≥3 cm is used

NB: US is of little utility is the aneurysm is close to the renal arteries. CT is useful in this case.

Question 20

What would CT angio show in a ruptured AAA?

Answer 20

Signs of rupture:

• Retroperitoneal haematoma
• Discontinuity of aortic wall
• Extravasation of contrast into peritoneal cavity

Question 21

How do you manage a ruptured and an unruptured AAA?

Answer 21

Ruptured -

• ABCDE
• Senior help or referral within 30mins
• Bedside USS or contrast-CTA
• Resuscitation - aim for SBP 70-90 with blood:FFP 1:1
• Endovascular aneurysm repair (EVAR),
• +/- perioperative antibiotics

Symptomatic but not ruptured -

• Urgently refer for surgical repair - pain heralds aneurysm expansion and impending rupture; EVAR or open repair
• +/- low dose aspirin - to reduce pre-op cardiovascular risk),
• +/- perioperative antibiotic therapy

Incidental asymptomatic -

• Refer for surveillance - within 2 weeks if _>_5.5cm, or within 12 weeks if 3.0-5.4cm.
• Secondary prevention- stop smoking, exercise pre-op, low-dose aspirin, reduce hypertension, statin, BB if MI risk is high
• +/- surgical repair - consider for _>_5.5cm or >4.0cm but growing >1cm/yr.

Question 22

What is EVAR?

Answer 22

EndoVascular Aneurysm Repair

Keyhole surgery used to repair an aneurysm. Performed through a small hole in groin rather than an incision in the abdomen as done in traditional surgery.

Question 23

What is the difference between a true and false aneurysm?

Answer 23

A true aneurysm is one that involves all three layers of the wall of an artery (intima, media and adventitia). Often caused by atherosclerosis.

A false aneurysm, or pseudoaneurysm, is a collection of blood leaking completely out of an artery or vein, but confined next to the vessel by the surrounding tissue. Can be caused by trauma (like a haematoma with a lumen). Does not involve any vessel layers.

Question 24

What is an endoleak?

Answer 24

Endoleak is defined as a persistent blood flow outside the lumen of an endoluminal graft but within the aneurysm sac or adjacent vascular segment being treated by the device used for endovascular aneurysm repair (EVAR).

Endoleaks are caused by incomplete sealing or exclusion of the aneurysm sac

Question 25

Who gets screened for AAA?

Answer 25

Males over 65

Question 26

Discuss how you would manage small, medium and large asymptomatic aneurysms.

Answer 26

Question 27

Describe what defines a low rupture risk aneurysm.

Answer 27

Low rupture risk

• asymptomatic, aortic diameter < 5.5cm (i.e. small and medium aneurysms)
• abdominal US surveillance (on time-scales outlines above) and optimise cardiovascular risk factors (e.g. stop smoking)

Question 28

Describe what defines a high rupture risk aneurysm.

Answer 28

Symptomatic, aortic diameter >=5.5cm or rapidly enlarging (>1cm/year)

• refer within 2 weeks to vascular surgery for probable intervention
• treat with EVAR or open repair

Question 29

What is the most common type of congenital aneurysm?

Answer 29

Berry aneurysm - in the brain

Question 30

How do you optimise a patient for elective AAA repair?

Answer 30

Pre-operatively:

• Stop smoking
• Healthy lifestyle
• All patients get antiplatelet therapy perioperatively - aspirin or clopidogrel
• Do not start BB - does not slow down AAA expansion
• Statin 4 weeks before
• Antibiotic prophylaxis
• Analgesia
• VTE prophylaxis - 7 days LMWH prior or stockings/IPC

Intraoperatively:

• Cell salvage or ultrafiltration
• Blood transfusion if Hb <100g/L with 1:1:1 FFP, blood and platelets
• Avoid hypothermia

Question 31

What are the complications of AAA and its management?

Answer 31

• Abdominal compartment syndrome
• Ileus, obstruction, ischaemic colitis
• AKI
• Post-implantation syndrome - malaise up to 10days after surgery
• Impaired sexual function
• Anastomotic pseudoaneurysm
• Aortic neck dilation
• Graft infection
• Endoleak - occurs in 1 in 4 over time

Low likelihood:

• Amputation due to limb ischaemia
• Spinal cord ischaemia
• Ureteric obstruction
• Functional gastric outlet obstruction
• Graft limb occlusion
• Distal embolisation

Question 32

What is the prognosis with AAA?

Answer 32

If untreated then will grow and eventually rupture - most patients do not survive to reach the operating theatre

5yr survival after surgical repair is 60-75%