Aortic aneurysm

Overview

•Aneurysm - permanent dilatation >1.5x normal diameter; AAA defined as infrarenal aorta ≥3 cm (normal ~2 cm)
•Fusiform - circumferential dilatation (most common); saccular - asymmetric outpouching (higher rupture risk per unit size)
•90-95% of AAAs are infrarenal

Risk factors

Risk factors for AAA
Male sex - 4-6x more common than women
Smoking - most impactful modifiable factor
Hypertension
Hypercholesterolaemia / atherosclerosis
Age >65
Family history
Marfan syndrome - TAA (FBN1 mutation)
Bicuspid aortic valve - TAA
🎯
Diabetes mellitus is protective against AAA - a classic exam distractor. It stiffens rather than weakens the aortic wall.

Presentation

•Intact AAA - usually asymptomatic; may have pulsatile expansile epigastric/periumbilical mass, vague back pain
•Ruptured AAA classic triad:
•Sudden severe abdominal/back pain - tearing/ripping, may radiate to flank, groin, or perineum
•Pulsatile abdominal mass - present in ~50%
•Haemodynamic instability - hypotension, tachycardia, shock
🚨
Contained retroperitoneal rupture can give deceptively stable initial BP - retroperitoneal tamponade temporarily limits haemorrhage. These patients can deteriorate precipitously. In any man >60 with sudden severe back/flank pain, rupture must be excluded.
⚠️
Ruptured AAA is frequently misdiagnosed as renal colic (flank pain + haematuria from ureteric compression) or musculoskeletal back pain.

Investigations

•First-line (intact/screening): abdominal ultrasound - cheap, no radiation, used for screening and surveillance
•Emergency (unstable): bedside FAST ultrasound - rapid confirmation of large AAA and free fluid
•Bloods: FBC, U&Es, coagulation, group and crossmatch (6-8 units in suspected rupture), ABG

🏆 Gold standard

•CT angiography (CTA) - precise diameter, extent, relation to renal arteries; used for operative planning; only in haemodynamically stable patients

Management

•Risk factor modification (all AAAs): smoking cessation (most impactful), BP control, statin therapy, antiplatelet agents
•Elective repair (≥5.5 cm or rapid expansion): EVAR or open surgical repair
•EVAR - lower 30-day mortality/morbidity; requires lifelong surveillance for endoleaks; 30-day mortality ~1-2%
•Open repair - 30-day mortality ~4-5%; less intensive post-op surveillance required
Step 1 · Immediate
  1. 1Call vascular surgery immediately
  2. 22x large-bore IV cannulae, urgent bloods including crossmatch 6-8 units
  3. 3Permissive hypotension - target systolic BP 50-100 mmHg to preserve retroperitoneal tamponade
  4. 4Avoid aggressive fluid resuscitation
Haemodynamically unstable
Bedside FAST USS only - transfer direct to theatre. Do NOT delay for CT.
Haemodynamically stable
CT angiography to confirm and plan repair (EVAR vs open).
Step 3 · Operative
  1. 1Emergency open repair or EVAR depending on anatomy and centre expertise
  2. 2Post-op ITU admission; monitor for AKI, ischaemic colitis, DIC

Complications

•Rupture: haemorrhagic shock, AKI, ischaemic colitis (IMA ligation), DIC
•Open repair: MI (most common cause of post-op death), stroke, renal failure, aortoenteric fistula (late - presents with GI haemorrhage), graft infection
•EVAR: endoleak (most important), graft migration, limb thrombosis, contrast nephropathy
•Endoleaks: Type I (seal failure at fixation points) and Type III (graft material failure) require reintervention; lifelong annual CT surveillance post-EVAR

Prognosis

Mortality by scenario
ScenarioMortality
Ruptured AAA - untreated~100%
Ruptured AAA - overall (including pre-hospital deaths)~40-50%
Ruptured AAA - reaches theatre alive~20-30% in high-volume centres
Elective EVAR 30-day mortality~1-2%
Elective open repair 30-day mortality~4-5%

Surveillance thresholds (NICE)

AAA diameter
Management
3.0-4.4 cm (small)
USS surveillance every 12 months
4.5-5.4 cm (medium)
USS surveillance every 3 months
≥5.5 cm or rapid expansion
Refer for elective repair
Women with known AAA
Consider intervention at 4.5 cm (higher rupture risk)

NHS AAA Screening Programme

•Single abdominal USS offered to all men aged 65
•Women not included - prevalence too low to be cost-effective at age 65
•Rationale: elective repair mortality ~1-5% vs ruptured AAA mortality ~40-50%