Cardiovascular · Year 1 · from Cardiovascular
Case 3: Abdominal Aortic Aneurysm - Symptomatic
Patient Presentation
Demographics: 72-year-old male
Chief Complaint: Abdominal and back pain
History of Present Illness: A 72-year-old male with history of hypertension, hyperlipidemia, and 60 pack-year smoking history presents with 2 days of constant dull abdominal and lower back pain. The pain is not related to eating or position. He denies nausea, vomiting, or changes in bowel habits. He has felt increasingly fatigued. He mentions that his doctor noted a "wide aorta" on ultrasound 3 years ago but he was lost to follow-up.
Physical Examination:
- Vital Signs: BP 155/95 mmHg, HR 88 bpm, RR 18/min, SpO2 98% on room air
- General: Uncomfortable, shifting position frequently
- Abdomen:
- Pulsatile mass palpable in periumbilical region
- Mild tenderness to deep palpation over mass
- No peritoneal signs
- Peripheral pulses: 2+ femoral, popliteal, dorsalis pedis bilaterally
Workup
- Labs:
- Hemoglobin: 11.2 g/dL (mildly low)
- Creatinine: 1.4 mg/dL
- Type and screen: Obtained
- CT Angiography (Abdomen/Pelvis):
- Infrarenal abdominal aortic aneurysm measuring 7.2 cm in maximal diameter
- Mural thrombus present
- No active extravasation of contrast
- Crescent sign (high attenuation within mural thrombus) - concerning for impending rupture
- Comparison to prior US (3 years ago): Was 4.8 cm (significant growth)
Diagnosis
Large symptomatic abdominal aortic aneurysm with signs of impending rupture
Vascular Physiology Correlation:
Laplace's Law for cylindrical structures: Wall Tension = (Pressure × Radius) / Wall Thickness
As aneurysm enlarges:
- ↑ Radius → ↑ Wall tension
- ↓ Wall thickness (aneurysmal dilation thins wall) → ↑ Wall tension
- Creates positive feedback loop → progressive enlargement → rupture
AAA Risk factors:
- Smoking (strongest association)
- Male sex, age >65
- Hypertension
- Family history
- Atherosclerosis
Aneurysm wall composition:
- Loss of elastic fibers in tunica media
- Chronic inflammation
- Matrix metalloproteinase (MMP) degradation of connective tissue
- Smooth muscle cell apoptosis
Why infrarenal location?
- Fewer vasa vasorum (wall blood supply) in infrarenal aorta
- Reflected pulse waves increase wall stress
- Higher content of type III collagen (weaker than type I)
Rupture risk by size:
| Diameter | Annual rupture risk |
|---|---|
| <4 cm | ~0% |
| 4-5 cm | 0.5-5% |
| 5-6 cm | 3-15% |
| 6-7 cm | 10-20% |
| >7 cm | 20-40% |
Warning signs of rupture:
- New/worsening pain
- Tender aneurysm
- Crescent sign on CT
Treatment
- Urgent surgical repair (symptomatic = surgical emergency regardless of size)
- Blood products: Type and crossmatch, alert blood bank
- Options:
- Open surgical repair: Laparotomy with graft placement
- Endovascular aneurysm repair (EVAR): If anatomy suitable (adequate landing zones)
- Preoperative optimization:
- Hemodynamic monitoring
- IV access, arterial line
- Beta-blockers to reduce shear stress
- If rupture occurs:
- Permissive hypotension (SBP 80-90) until aortic cross-clamp
- Massive transfusion protocol
- Emergent surgery
Clinical Image
Image Description: CT angiogram demonstrating a large infrarenal abdominal aortic aneurysm with mural thrombus. The contrast-enhanced lumen is visible within the dilated aortic sac, which measures significantly greater than the normal aortic diameter.
Source: Radiopaedia - Abdominal aortic aneurysm License: CC BY-NC-SA 3.0 URL: https://radiopaedia.org/cases/abdominal-aortic-aneurysm-aaa-3