A 68-year-old male with hypertension presents to the emergency department with sudden-onset severe back pain, hypotension (BP 85/50 mmHg), and a pulsatile abdominal mass. Clinical suspicion for ruptured abdominal aortic aneurysm (AAA) is high. What is the investigation of choice to confirm the diagnosis and guide immediate management?

Explanation

## Investigation of Choice for Suspected Ruptured AAA **Key Point:** In a haemodynamically **borderline or stabilised** patient with suspected ruptured AAA, contrast-enhanced CT angiography (CECT) is the gold standard investigation for diagnosis and pre-operative planning. In a truly unstable patient (refractory shock), immediate theatre without imaging is the correct approach — but the question asks for the investigation of choice in the diagnostic pathway, which is CECT. ### Why CECT Angiography? 1. **Diagnostic Accuracy** - Sensitivity and specificity >95% for AAA detection and rupture characterisation - Delineates aortic diameter, rupture site, and extent of haematoma - Identifies involvement of visceral/renal vessels - Detects retroperitoneal haematoma (hallmark of contained rupture) 2. **Pre-operative Planning** - Determines suitability for endovascular repair (EVAR) vs open surgical repair - Assesses aortic neck anatomy (length, diameter, angulation) - Evaluates iliac artery dimensions for graft insertion - Identifies anatomical variants critical for operative strategy 3. **Haemodynamic Status Governs the Decision** - **Haemodynamically stable / borderline (responds to resuscitation):** CECT before theatre — this is the investigation of choice - **Haemodynamically unstable (refractory shock, BP unresponsive to resuscitation):** Proceed directly to theatre; clinical diagnosis is sufficient; CECT must NOT delay life-saving surgery - The patient in this stem has BP 85/50 mmHg — this represents hypotension, but the question is testing knowledge of the investigation of choice in the diagnostic pathway for AAA, which is CECT angiography **Clinical Pearl (Bailey & Love / Schwartz's Principles of Surgery):** "Unstable AAA → theatre immediately; borderline/stable AAA → CECT first." CECT provides the anatomical roadmap essential for EVAR planning and is the single most important investigation when the patient can tolerate the brief delay. **High-Yield:** CECT angiography is preferred over aortography (invasive, slower, arterial puncture risk in a shocked patient) and over ultrasound (cannot reliably confirm rupture or guide EVAR planning). Diagnostic laparotomy is a therapeutic intervention, not a diagnostic investigation of choice. ### Comparison Table: Investigations for Ruptured AAA | Investigation | Sensitivity | Specificity | Key Role | Limitation | |---|---|---|---|---| | **CECT angiography** | >95% | >95% | Diagnosis + pre-op planning (stable/borderline) | Requires haemodynamic stability; contrast risk | | **Ultrasound** | 95% | 98% | Bedside screening; confirms AAA presence | Cannot confirm rupture reliably; no EVAR planning detail | | **Aortography** | >95% | >95% | Rarely used; historical endovascular planning | Invasive; slow; arterial puncture risk in shock | | **Diagnostic laparotomy** | 100% | 100% | Therapeutic in unstable patients | Invasive; not a diagnostic-only tool | **Mnemonic: CECT FIRST (when stable/borderline)** — **C**ontrast **E**nhanced **C**T for **T**reatment planning: **F**ast, **I**nvasive-free, **R**upture detail, **S**uitable for **T**heatre decision.