Summary

Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta to greater than 1.5 times its normal diameter, typically defined as greater than 3.0cm. The vast majority are infrarenal, degenerative, and associated with atherosclerosis. AAA is usually asymptomatic until rupture, which carries mortality exceeding 80%. The UK NHS AAA Screening Programme targets men aged 65 to detect and monitor aneurysms before catastrophic rupture.

Key Facts

• Definition: Aortic diameter greater than 3.0cm (normal approximately 2.0cm)
• Prevalence: 5-10% of men over 65; 1% of women
• Mortality: Ruptured AAA carries greater than 80% overall mortality
• Screening threshold: Intervention considered at 5.5cm diameter
• Location: 95% are infrarenal
• Key management: Surveillance for small; surgical repair (EVAR or open) for large or symptomatic

Clinical Pearls

The Triad: Suspect ruptured AAA in any patient with sudden abdominal or back pain, hypotension, and pulsatile abdominal mass. Do not delay for imaging if clinically obvious.

Permissive Hypotension: In suspected rupture, maintain systolic BP 80-100mmHg. Aggressive fluid resuscitation may dislodge the tamponading clot and cause exsanguination.

Renal Colic Mimic: Elderly men presenting with "renal colic" and haemodynamic instability must have AAA excluded. This is a common fatal misdiagnosis.

Why This Matters Clinically

AAA rupture is one of the most fatal surgical emergencies. Early detection through screening and elective repair before rupture transforms a condition with greater than 80% mortality into one with less than 5% operative mortality. Recognition of the atypical presentation mimicking renal colic saves lives.

Structured Approach

General:

• Haemodynamic status (BP, HR, capillary refill)
• Signs of shock (pallor, sweating, confusion)
• Peripheral pulses (may be reduced in rupture or embolisation)

Abdominal Examination:

• Inspect for visible pulsation
• Palpate gently for pulsatile expansile mass above umbilicus
• Differentiate from transmitted pulsation (transmitted = pulsatile but not expansile)
• Assess tenderness (suggests impending rupture)
• Measure width of pulsation with two hands if possible

Peripheral Vascular:

• Femoral, popliteal, posterior tibial, dorsalis pedis pulses
• Look for concurrent peripheral aneurysms (popliteal present in 15% of AAA patients)

Special Tests

Natural History

• AAA growth rate approximately 2-3mm per year
• Risk of rupture increases exponentially with size:
  • Less than 4cm: Less than 0.5% per year
  • 4-5cm: 1% per year
  • 5-6cm: 5-10% per year
  • Greater than 6cm: 10-25% per year
• Rupture carries greater than 80% overall mortality (50% die before reaching hospital)

Outcomes with Treatment

Prognostic Factors

Good Prognosis:

• Early detection through screening
• Elective repair before rupture
• Smoking cessation
• Good cardiac function (low anaesthetic risk)
• EVAR-suitable anatomy

Poor Prognosis:

• Rupture before surgery
• Advanced age (greater than 80)
• Significant comorbidities (cardiac, renal, respiratory)
• Suprarenal extension
• Post-operative complications (renal failure, bowel ischaemia)

Key Guidelines

1. NICE NG156 (2020) — Abdominal aortic aneurysm: diagnosis and management. Recommends EVAR or open based on individual assessment; surveillance thresholds. NICE NG156
2. NAAASP (UK NHS Screening Programme) — Men invited for screening in year they turn 65. Surveillance thresholds: less than 3cm discharge, 3-4.4cm annual, 4.5-5.4cm 3-monthly. NHS AAA Screening
3. ESVS Guidelines (2019) — European Society for Vascular Surgery clinical practice guidelines on management of AAA. Threshold 5.5cm; consideration of 5.0cm in women.

Landmark Trials

UK Small Aneurysm Trial (1998) — Early surgery versus surveillance for 4.0-5.5cm AAAs

• 1090 patients randomised
• Key finding: No benefit to early surgery for small aneurysms
• Clinical Impact: Established 5.5cm as the threshold for intervention

EVAR-1 Trial (2004, updated 2010) — EVAR versus open repair for elective AAA

• 1082 patients randomised
• Key finding: Lower 30-day mortality with EVAR (1.8% vs 4.3%), but benefit lost by 2 years; higher reintervention with EVAR
• Clinical Impact: EVAR is preferred for high-risk patients; open repair remains valid for fit patients

IMPROVE Trial (2014) — EVAR versus open for ruptured AAA

• 613 patients
• Key finding: No difference in 30-day mortality (35% both groups); EVAR associated with shorter hospital stay
• Clinical Impact: EVAR is a viable option for ruptured AAA in suitable anatomy

RESCAN Study (2013) — Meta-analysis of AAA screening

• 127,891 men screened
• Key finding: Screening reduces AAA-related mortality by 45% at 13 years
• Clinical Impact: Justifies national screening programmes

Evidence Strength

What is an Abdominal Aortic Aneurysm?

Your aorta is the main blood vessel that carries blood from your heart down through your belly to your legs. Think of it like the main water pipe in your house. An aneurysm is a bulge in the wall of this pipe, like a weak spot in a balloon. If it gets too big, it could burst, which is very dangerous.

Why does it matter?

Most aneurysms cause no symptoms and are found by screening or by chance. However, if an aneurysm bursts, it causes massive internal bleeding. Unfortunately, many people do not survive a burst aneurysm. The good news is that if we find an aneurysm before it bursts, we can monitor it and fix it before it becomes dangerous.

How is it treated?

1. Watching and waiting: For small aneurysms (less than 5.5cm), we do regular scans to check if it is growing. Most grow slowly.
2. Lifestyle changes: Stopping smoking is the single most important thing you can do. We also control blood pressure and cholesterol.
3. Keyhole surgery (EVAR): If the aneurysm is big enough to need fixing, we often use a stent inserted through a small cut in the groin. This is less invasive.
4. Open surgery: Sometimes we need to do a larger operation through the belly to replace the weak part with a new tube. This is more major but very effective.

What to expect

• If you are having regular scans, you will come to the hospital every few months to a year for an ultrasound.
• If you have keyhole surgery, you may go home in 1-3 days and need rest for a few weeks. You will need CT scans for life to check the stent.
• If you have open surgery, expect to stay in hospital for about a week and take 2-3 months to fully recover.

When to seek help

Call 999 or go to A&E immediately if you experience:

• Sudden severe pain in your belly or back
• Feeling faint or collapsing
• Any new symptoms if you have a known aneurysm
• Your tummy feels tender over the aneurysm

The "Vascular Status" Station

1. Inspection (End of Bed)

• Patient: Cachectic? Painful? (Rupture). Connective tissue features (Marfanoid)?
• Abdomen: Visible pulsation (thin patients). Scars (Previous laparotomy/EVAR).
• Legs: Mottling, dusky toes (Trash foot - embolisation).

2. Palpation of the Aorta

• Technique: Patient flat, hips flexed (relax abs). Use two hands.
• Start: Xiphisternum. Move inferiorly.
• Differentiate:
  • Pulsatile: Movement occurs.
  • Expansile: Hands move apart (The key sign of aneurysm).
• Limits: Bifurcation is at the Umbilicus (L4). So palpate above the umbilicus.

3. The Trap: "Mass Assessment"

• A pulsatile mass is NOT always an aneurysm.
• Differentials:
  • Thin patient (normal aorta).
  • Mass transmitted pulsation (Pancreatic tumor, pseudocyst, lymph nodes) - Hand moves up/down, not apart.
  • Tortuous aorta.

4. Check Distal Perfusion

• Blue Toe Syndrome: Micro-emboli from the aneurysm sac showering the toes. Palpable pulses but necrotic toes.
• Popliteal Aneurysms: "Widened" popliteal pulse. 50% of popliteal aneurysms have an AAA. 15% of AAAs have a popliteal aneurysm.

Viva Questions:

• Q: Who gets screened for AAA in the UK?
  • A: Men in their 65th year are invited for a one-off ultrasound. Women are not (low prevalence).
• Q: Define an Aneurysm.
  • A: Permanent focal dilatation of an artery >50% of its normal diameter (>3cm for Abdominal Aorta).
• Q: What is the risk of rupture at 6cm?
  • A: Approximately 10-20% per year.
• Q: Why do we not operate on 4cm aneurysms?
  • A: The risk of surgery (approx 3-5%) exceeds the risk of rupture (less than 1%).
• Q: What is the primary cause of death after elective AAA repair?
  • A: Myocardial Infarction. (AAA is a marker of systemic vascular disease).

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists for emergency situations.