Abdominal Aortic Aneurysm Flashcards
Define aneurysm.
A weakening of the vessel wall causing bulging/increased diameter of an artery.
What is an abdominal aortic aneurysm?
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.
How common is the prevalence of AAA in UK NHS screening programme?
Screening at 65yrs shows 1.34% prevalence
Where do leaking abdominal aneurysms usually occur? What are the two types?
90% below the renal arteries (abover the bifurcation of the common iliac)
Can be saccular (outpocketing) or fusiform (diffuse swelling)
List the risk factors associated with AAA.
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
What is the pathophysiology of AAA development?
Histologically there is obliteration of collagen and elastin in the media and adventitia, smooth muscle loss and infiltration of immune cells.
Four main mechanisms:
- Proteolytic degradation of connective tissue by MMP
- Inflammation and immune responses
- Biochemical wall stress
- Molecular genetics - heritability is high
Where do AAA rupture into?
Peritoneal space OR
Retroperitoneal tissue - almost always fatal
* prone to rupture when they reach 6-7cm
Name 3 specific types of AAA (classification).
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.
What is a mycotic aneurysm?
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.
How does Marfan’s increase the risk of AAA?
Abnormality in fibrillin type 1 found in elastin → mature aorta has abnormal elastic properties, progressive stiffening and dilation
What is the biggest molecular cause of AAA? What protects?
METALLOPROTEINASES diminish the integrity of the arterial wall - SMOKING remains the most important risk factor.
Describe the epidemiology of AAA.
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%.
Describe the clinical presentation of a leaking abdominal aneurysm.
- 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
What are the presenting symptoms of an AAA?
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
What should you ask about in a history of suspected AAA?
- Smoking
- Family history
- Tissue disorders
What are the signs of an AAA on physical examination?
- 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.
What investigations would you do for an AAA?
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
How are aortic aneurysms surgically fixed?
Most aneurysms are conveniently located below the renal arteries so that surgical resection with placement of a dacron graft can be done
What would imaging show in an AAA?
- 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.
What would CT angio show in a ruptured AAA?
Signs of rupture:
- Retroperitoneal haematoma
- Discontinuity of aortic wall
- Extravasation of contrast into peritoneal cavity
How do you manage a ruptured and an unruptured AAA?
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.
What is EVAR?
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.
What is the difference between a true and false aneurysm?
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.
What is an endoleak?
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
Who gets screened for AAA?
Males over 65
Discuss how you would manage small, medium and large asymptomatic aneurysms.
Describe what defines a low rupture risk aneurysm.
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)
Describe what defines a high rupture risk aneurysm.
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
What is the most common type of congenital aneurysm?
Berry aneurysm - in the brain
How do you optimise a patient for elective AAA repair?
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
What are the complications of AAA and its management?
- 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
What is the prognosis with AAA?
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%
