Summary

An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta to >1.5 times its normal diameter (Normal ~2.0cm, so AAA is defined as ≥3.0cm). It is primarily a degenerative condition associated with aging, male sex, and SMOKING. The natural history is progressive expansion leading to Rupture, which carries an overall mortality of >80%. Most AAAs are asymptomatic until rupture. Screening programmes (NAAASP in the UK) target men aged 65+. Elective repair is indicated when the risk of rupture exceeds the risk of surgery, typically at a diameter of 5.5cm. Repair options are Endovascular Aneurysm Repair (EVAR) or Open Surgical Repair (OSR). The management of ruptured AAA is a supreme emergency requiring Permissive Hypotension and immediate clamping. [1,2]

Key Facts

• Definition: Aorta diameter ≥3.0cm.
• Threshold for Surgery: ≥5.5cm (Men) or Rapid growth (>1cm/year).
• Screening: Men aged 65 (Ultrasound).
• Primary Risk Factor: Smoking (Strongest association).
• Normal Aorta: ~2.0cm.
• Rupture Mortality: ~80% (50% die before hospital, 50% die in hospital).
• Type: 95% are Infra-renal (below the kidney arteries).

Clinical Pearls

"The Classic Triad": Ruptured AAA presents with HoTN (Hypotension), Back Pain, and a Pulsatile Mass. However, only 50% have all three. Do not rely on valid triad to act.

"Renal Colic Mimic": A leaking AAA causes retroperitoneal haematoma, infiltrating the psoas muscle and irritating the ureter. This mimics renal colic (loin to groin pain) perfectly. In any man >60 with "renal colic", EXCLUDE AAA FIRST (Urgent CT).

"Expansile vs Transmitted": To distinguish an aneurysm from a mass overlying the aorta: A finger on each side of the mass moves APART (Expansile). If they just move UP, it is a transmitted pulse.

"Trash Foot": Multiple small black toes/patches on the foot with palpable pedal pulses. Caused by micro-emboli showering from the AAA thrombus.

"Permissive Hypotension": If ruptured, do NOT fluid resuscitate to normal BP. Keep SBP 70-90mmHg. Raising the pressure will blow out the tenuous clot and kill the patient. "Fill them and you kill them."

Anatomy

• Infrarenal (95%): Below the renal arteries.
• Juxtarenal: Extends up to renals but does not involve them (Needs supra-renal clamp).
• Suprarenal: Involves visceral arteries (SMA/Celiac).
• False Aneurysm (Pseudoaneurysm): A collection of blood outside the vessel wall contained by tissue. (Not a true AAA).

Mechanism: Degradation vs Repair

• Degeneration: The primary problem is the loss of Elastin and Collagen in the tunica media.
• Inflammation: Infiltration of inflammatory cells (Macrophages/Lymphocytes) releasing Matrix Metalloproteinases (MMPs) - specifically MMP-2 and MMP-9 - which digest the aortic wall.
• Atherosclerosis: Almost always present, but chicken-egg debate. Thrombus lines the sac.
• Laplace's Law: Tension = Pressure x Radius. As the aneurysm grows (Radius increases), the wall tension increases linearly. This creates a positive feedback loop: Expansion -> More Tension -> More Expansion -> Rupture.

Target: Men aged 65. Single Ultrasound Scan. Rationale: Rupture is preventable if caught early.

          AAA DETECTED (Ultrasound)
                     ↓
      ┌──────────────┼───────────────┐
    <3.0cm       3.0-5.4cm        ≥5.5cm
      ↓              ↓               ↓
   DISCHARGE     SURVEILLANCE     REFER VASCULAR
                                     ↓
                              CT ANGIOGRAM + CPET
                                     ↓
                        ┌────────────┴─────────────┐
                     FIT FOR OPEN              FIT FOR EVAR ONLY
                     (Younger, Healthy)        (Frail, "Hostile Chest")
                        ↓                          ↓
                     Anatomy Suitable?         Anatomy Suitable?
                    (Neck >10mm, <60°)       (Neck >10mm, Access ok)
                        ↓                          ↓
                   **OPEN REPAIR**              **EVAR**
                (Gold Standard Long term)    (Low peri-op risks)

Risk Factor Modification (ALL Patients)

• Smoking Cessation: Crucial. Slows growth rate by 50%.
• BP Control: Target <130/80.
• Statin: Atorvastatin 20-80mg (Pleiotropic effects stabilize plaque).
• Antiplatelet: Aspirin 75mg.

1. Open Surgical Repair (OSR)

• Concept: Laparotomy. Cross-clamp aorta (Strain on heart!). Open aneurysm sac. Sew in Dacron graft (Tube or Y-graft).
• Pros: Durable. Proven long-term (20+ years). No surveillance needed. No endoleaks.
• Cons: Major physiological hit. High peri-op mortality (3-5%). Long recovery (3-6 months). Hernia risk.

2. Endovascular Aneurysm Repair (EVAR)

• Concept: Stent-graft inserted via Femoral Arteries. Deployed inside aorta to exclude the aneurysm.
• Pros: Minimally invasive. Local anaesthetic possible. Low peri-op mortality (1%). Quick recovery (Home in 2 days).
• Cons: Endoleaks (Failure of seal). Sac can still rupture. Needs LIFELONG SURVEILLANCE (CT/US). Re-intervention rate high (20%).
• Criteria:
  • Neck Length >10-15mm (Seal zone).
  • Neck Angulation <60 degrees.
  • Access vessels >7mm diameter.

Failure of the EVAR stent to exclude blood from the aneurysm sac.

Step 1: Access

• Ultrasound-guided puncture of Common Femoral Arteries.
• Pre-close technique (Perclose Proglide) to allow percutaneous closure.

Step 2: Wiring

• Stiff wires (Lunderquist) passed up to thoracic aorta.
• Pigtail catheter marked at renal arteries.

Step 3: Deployment

• Main Body deployed. Critical Step: Ensure top of fabric is immediately below lowest renal artery for maximal seal, but DO NOT COVER RENALS.
• Contralateral gate cannulation.
• Iliac limbs deployed to the Internal Iliac origin.

Step 4: Completion

• Balloon moulding of seal zones.
• Angiogram: Check for Endoleaks. Check Renals/Internals patent.

Landmark Trials

1. EVAR-1 Trial: EVAR vs Open. EVAR has better 30-day survival (1.7% vs 4.7%). But by 8 years, Open Repair catches up (due to endoleaks/ruptures in EVAR group) and becomes superior in terms of re-interventions and long-term cost.
2. EVAR-2 Trial: Unfit patients randomized to EVAR vs No Intervention. Result: EVAR did not improve survival (patients died of cancer/heart failure anyway). Conclusion: Do not operate on unfit patients just because you can.
3. IMPROVE Trial (Ruptured AAA): EVAR strategy vs Open for ruptures. No difference in mortality, but EVAR patients go home faster/better QoL.

Guidelines (NICE / ESVS)

• Screening for Men 65+.
• Consider repair at 5.5cm.
• Open Repair is standard for young/fit. EVAR for older/frail with suitable anatomy.

1. Recognition

• Hypotension + Back Pain = Rupture until proven otherwise.

2. Resuscitation (Permissive Hypotension)

• Target SBP: 70-90 mmHg. Just enough to perfuse brain (Conscious).
• Do NOT bolus fluids: Dilutes clotting factors, pops the clot.
• Analgesia: IV Morphine.

3. Immediate Transfer

• Straight to Theatre (or CT if stable-ish and diagnosis unsure).
• Code Red: Activate Massive Transfusion Protocol (MTP).

4. Control

• Endovascular: REBOA (Balloon in aorta) via groin.
• Open: Supraceliac clamp (high in abdomen) to stop inflow.

5. Repair

• Usually Open Repair for unstable rupture (unless hybrid theatre and EVAR fit).

What is an AAA?

The aorta is the main hosepipe carrying blood from the heart to the body. An aneurysm is a "ballooning" or swelling of this artery in the tummy. It happens due to weakness in the wall, often caused by smoking or aging.

Is it dangerous?

Small aneurysms (<5.5cm) are safe and just need regular scans to check they aren't growing fast. Large aneurysms (≥5.5cm) are dangerous because they can burst (rupture). A ruptured AAA is like a burst dam—it causes massive internal bleeding and is often fatal before you reach the hospital.

How do we treat it?

If it is large, we offer repair to prevent it bursting.

1. Keyhole (EVAR): Putting a strengthening pipe (stent) inside the aneurysm through the groins. It acts like a liner for a chimney. Safer surgery, but needs yearly scans forever to check the seal hasn't leaked.
2. Open Surgery: A big operation to cut out the weak bit and sew a new tube in. Harder to recover from, but once it's done, it's fixed for life.

What can I do?

STOP SMOKING. This is the single most important thing. It slows the growth of the aneurysm.