Vascular Surgery JC003: Pulsating Abdominal Mass: Aortic Aneurysm Flashcards
Definition of Aneurysm
- Permanent
- Localised
- Dilatation of an artery
- ***50% ↑ in normal diameter (i.e. 1.5 times)
Classification of Aneurysm
By ***form:
1. Fusiform
- dilatation uniformly affecting the wall
- Saccular (Berry)
- dilatation on one side of wall - Dissecting (i.e. aortic dissection)
- tear in wall of artery —> pressure of blood —> create a dilatation within wall of aneurysm
By ***structure:
1. True
- wall of aneurysm contain all 3 layers of artery
- False (Pseudoaneurysm)
- small hole in artery –> chronic pressure –> **laminated thrombus formation on wall with outer layer of **compressed fibrous tissue
- still have dilatation of artery but not see all 3 layers of artery
***Clinical features + Complications of Aneurysm
- Mostly ***Asymptomatic –> Incidental, Pulsatile abdominal mass
- Pain (indicate impending rupture)
Complications:
1. **Rupture (∵ dilated, weakened, under pressure)
2. **Thrombosis (∵ lack of laminar flow)
3. **Embolism
4. **Infection (∵ thrombus rich in nutrients for bacterial growth)
5. ***Pressure effects (e.g. aortic aneurysm press on SVC stopping venous return, pressing on RLN causing hoarseness and cough)
Abdominal Aortic Aneurysm (AAA)
- Most common aneurysm
- Most life-threatening aneurysm
(- Most are TRUE aneurysm)
Location:
- Middle-upper abdomen
- **Around umbilicus (bifurcation of abdominal aorta)
- Below renal artery: **Infrarenal AAA
Anatomy:
- **Left renal vein crosses anteriorly to Abdominal aorta
- **IMA only major artery coming off Infrarenal aorta
—> involved / sacrificed in AAA
Etiology of AAA
Unknown, probably Multi-factorial
- Mechanical
- **Degeneration (atherosclerosis)
- **High BP - Enhancement of proteolytic activity
- ↑ MMP (matrix metalloproteinases) –> digest CT of wall - Genetic
- **Marfan’s
- **Ehlers-Danlos IV
–> developmental defects in crosslinks of CT in aortic wall - Autoimmune
- ***Vasculitis - Infection
Pathology of AAA
Non-specific pathological results of burnout, destroyed artery
1. **Loss of elastin + smooth muscles cells
2. **Disruption of ECM
3. ***Inflammatory infiltrates
Natural history:
Expansion: LaPlace’s law: ~5mm / year
Risk of rupture at 5 years:
- <5 cm: 20%
- **>5 cm: 50% (i.e. **10% per year)
Physical examination of AAA
- Confirm AAA
- mass above umbilicus
- ***expansile (push hands apart, abnormal) + pulsation (may also feel transmitted pulsation in younger, thinner normal people) - Extent of AAA
- size (estimate max diameter)
- **upper border (go above renal artery? can get above?)
–> can get above: Infrarenal
–> cannot get above (expanding continuously to rib cage): **Suprarenal aneurysm
- lower border (involve iliac arteries?)
–> if pulsation / masses at iliac fossa: Common iliac artery extension (Iliac aneurysms) - CVS examination
- peripheral pulses (esp. ***popliteal (concomitant aneurysm))
- heart
- BP
Investigations of AAA
- AXR / CXR
- detected incidentally
- mass / shadow
- rim of ***calcification on aortic wall -
USG (diagnosis)
- large mass filled with blood (with Doppler) / thrombus (∵ slow blood flow in lumen due to laminar flow –> promote thrombus formation at the side)
- measure **AP + **Transverse diameter (no need measure length: irrelevant) - CT
- not necessary unless want to intervene
- know ***level of aneurysm (e.g. Suprarenal aneurysm, Iliac aneurysms)
- multiplanar reconstruction to give good visualisation
AAA screening programmes in men >65:
- good evidence of early screening –> ↓ cumulative mortality
- USPSTF recommend 1-time screening with USG in men 65-75 with smoking history
- not in HK (∵ AAA not regarded as common)
Operative considerations in AAA
***Pre-op assessments
1. Symptoms
- any symptoms = urgent
- Size / Max diameter (most important)
- ***5cm - Medical risk
- associated diseases - Life expectancy
- e.g. end stage cancer - Age
- generally not a CI (unless very sick)
Operative mortality (need to balance Risk of operation vs Risk of rupture)
Risk of operation:
- intact aneurysm: 3-5%
Risk of mortality upon rupture:
- ruptured aneurysm: >50%
- unoperated rupture: 100%
Conclusion:
- ALL AAA ***>5cm should be operated on unless patient medically unfit (operative mortality > risk of rupture) / limited life expectancy
Small AAA (<5cm)
Evidence:
- **Not much benefit in terms of survival (vs Surveillance group)
- Note that these patients will eventually need surgery years down the line anyway
–> **No evidence support early surgery
Pre-operative preparation
General:
1. Blood tests (**RFT)
2. **ECG
3. ***CXR
Cardiac:
1. ***Cardiac assessment / intervention
Preparations:
1. Monitors
2. Blood tests
Major operative mortality: **MI (∵ older patients, circulation disturbed during operation due to clamps on aorta, wounds in abdomen, patients do not breathe well, smokers –> develop **hypoxia –> heart overload –> MI)
***Surgical treatment
- Open repair (traditional)
- **Aneurysmectomy + **Inlay graft (to maintain aortic continuity)
- require laparotomy
–> flip bowels to one side + open posterior peritoneum (∵ aorta is retroperitoneal)
–> clamp above aneurysm to stop bloodflow of aorta (proximal control) + clamps at iliac artery (distal control)
–> cut open aneurysm + suture ***lumbar arteries to prevent backward bleeding
–> suture prosthetic graft (Dacron / Nylon) onto 2 ends
–> close aneurysm sac to protect graft
(Graft: Tube graft for standard AAA, Aorto-iliac bifurcated graft for extension to iliac arteries)
- must under GA - Endovascular aneurysm repair (EVAR) (minimally invasive)
- ***Aortic stent graft: a graft supported by stent –> NOT a stent!
- major bifurcated piece (main body / long limb) + contralateral extension limb (short limb)
- stay in place by hooks + friction (through expanding stent)
- can be performed on patients previously deemed unfit for open surgery
- advantage: minimal invasive, can be done as day case, LA, no ICU care, minimal blood loss, faster recovery
Open repair vs EVAR:
- EVAR has **lower 30 day mortality (1.7% vs Open repair 4.7%)
- **similar aneurysm-related mortality
- **similar all-cause mortality
- long-term (>7 years): EVAR lost advantage (∵ **secondary intervention required + sicker patients in general)
- ***higher secondary intervention long-term
***Complications of Open surgery
General complications:
1. **Cardiac (e.g. post-op MI ∵ clamp + declamp)
2. **Respiratory (e.g. pneumonia ∵ cannot breathe well, sputum retention, hypoxia)
Specific complications:
1. Haemorrhage
-
Bowel ischaemia
- **IMA tied off –> blood supply of left colon relied on SMA collaterals now (*Marginal artery of Drummond) –> if SMA also have disease / incomplete marginal arcade –> Necrosis of left colon -
**Paraplegia
- **Segmental arteries sacrificed –> impair blood supply of spinal cord (although mostly from **artery of Adamkiewicz) –> **spinal cord ischaemia –> Paraplegia
- usually in extensive involvement of aorta in AAA -
**Impotence / Retrograde ejaculation
- damage to **sympathetic chains / ***parasympathetic nerves in front of bifurcation - ***“Trash foot”
- Distal embolisation –> ischaemia of toes - Renal failure
- damage to renal blood flow during surgery
Disadvantages of EVAR
Not suitable for everyone:
1. A neck should be present (no suprarenal extension) for landing zone
- **length: >1.5 cm
- **diameter: <32 mm
- ***angle: <45o
-
**CIA cannot be too big (∵ graft need bottom anchor for landing zone)
- **internal iliac artery need to be preserved as well (at least one, otherwise **bowel (rectum) ischaemia, **buttock claudication, **impotence)
- **length
- ***diameter -
**Good access required
- femoral artery **>7 mm
- ***no tortuosity - ***Calcifications undesirable
- can prevent access - Not durable vs Open
- Sac management issues
- Inefficient surveillance (need a lot of imaging)
***Complications of EVAR: Endoleaks
- ***Endoleaks
- ∵ durability of stent grafts
- presence of contrast within aneurysm sac after EVAR
- type 1-5
- need for surveillance + secondary intervention
Type 1:
- large pressure leaks: attachment leak from side of graft at the top
- unacceptable
- high risk situation
(- detected during intra-op)
Type 2:
- back bleeding from lumbar arteries / IMA
- most common (>20%)
(- treated by embolisation by IR)
Type 3:
- large pressure leaks: leak between components of graft (e.g. separation of junctions)
- unacceptable
(- detected during intra-op)
Type 4:
- leak from little holes within fabric of graft
Type 5:
- leakage site cannot be identified
(From SpC bedside:
2. Stent migration
3. Stent thrombosis
4. Same as open surgery (Haemorrhage, Bowel ischaemia, Paraplegia, Impotence / retrograde ejaculation, “Trash foot”, Renal failure))
