A 58-year-old man with a 10-year history of type 2 diabetes and hypertension presents with acute-onset severe epigastric pain radiating to the back, associated with hypotension (BP 90/60 mmHg) and tachycardia (HR 110/min). CT angiography of the abdomen reveals a 5 cm infrarenal abdominal aortic aneurysm (AAA) with a crescent-shaped area of high attenuation within the thrombus, adjacent to the aortic wall, and extravasation of contrast into the periaortic space. Which of the following angiographic findings best explains the acute clinical presentation?

Explanation

## Clinical Interpretation of Acute AAA Rupture ### Key Radiological Findings **Key Point:** The crescent sign (crescentic area of high attenuation within thrombus) represents acute intramural hematoma or sentinel bleed — a precursor to frank rupture. Combined with periaortic contrast extravasation, this indicates **contained rupture** with active bleeding. **High-Yield:** Acute aortic syndrome encompasses three entities: 1. Aortic dissection (intimal flap, true/false lumens) 2. Intramural hematoma (no intimal tear; crescent of blood in media) 3. Penetrating aortic ulcer (focal disruption of intima) In this case, the **crescent sign** + **periaortic extravasation** = acute aortic syndrome (specifically intramural hematoma/sentinel bleed progressing to contained rupture). ### Pathophysiology of Contained Rupture 1. **Intramural hematoma** develops when rupture of vasa vasorum (nutrient vessels in the aortic media) occurs, dissecting blood into the medial layer 2. **Sentinel bleed** = small initial hemorrhage that may self-tamponade 3. **Contained rupture** = bleeding breaks through the aortic wall but is contained by the surrounding fascia (retroperitoneum) 4. **Frank rupture** = uncontained extravasation into the peritoneal cavity (rapidly fatal) The **crescent sign** is the imaging hallmark of acute intramural hematoma and indicates imminent or ongoing rupture. ### Why This Is Acute Aortic Syndrome, Not Chronic AAA | Feature | Acute Rupture/Syndrome | Chronic AAA | |---------|------------------------|-----------| | **Symptom onset** | Sudden, severe | Asymptomatic or chronic pain | | **Hemodynamics** | Hypotensive, tachycardic | Variable | | **Crescent sign** | Present (acute hematoma) | Absent | | **Periaortic extravasation** | Active contrast leak | No extravasation | | **Imaging evolution** | Changes over hours | Stable | **Clinical Pearl:** The combination of **hemodynamic instability + crescent sign + contrast extravasation** is a surgical emergency requiring immediate operative intervention (open repair or EVAR if anatomy permits). ### Management Implications - **Contained rupture** = urgent but potentially salvageable with rapid intervention - **Frank rupture** = mortality >50% even with immediate surgery - **Imaging role** = rapid diagnosis via CT angiography to guide triage to OR/IR **Mnemonic: AAA RUPTURE SIGNS** — Acute pain, Aortic crescent, Abdominal/back radiation; Rupture (extravasation), Unstable vitals, Pulsatile mass, Tachycardia, Underperfusion, Renal/limb ischemia, Emergent surgery. ### Why Sentinel Bleed Is the Correct Framing The **sentinel bleed** (small initial hemorrhage) is the clinical-radiological bridge between intact AAA and frank rupture. It represents the **acute aortic syndrome** phase where the aortic wall has begun to fail but hemorrhage is still contained by surrounding tissues. This is the window for emergency surgical/endovascular repair.