Is the hernia to neck ratio important in abdominal aortic aneurysm (AAA) treatment?

The Importance of Hernia to Neck Ratio in Abdominal Aortic Aneurysm Treatment

Yes, the hernia to neck ratio is critically important in determining the suitability and success of endovascular aortic aneurysm repair (EVAR) procedures. 1 The ratio between aneurysm diameter and proximal neck diameter significantly influences clinical outcomes and complication rates in AAA treatment.

Why the Hernia-to-Neck Ratio Matters

Anatomical Considerations

• Proximal neck anatomy is paramount in evaluating AAA for EVAR, defined as the segment between the most caudal renal artery and the proximal boundary of the aneurysm 1
• Unfavorable neck anatomy (based on diameter, length, angulation, morphology, and calcification) is the most frequent cause of exclusion from standard EVAR 1
• More than 50% of patients have aneurysm morphology unsuitable for conventional EVAR due to neck issues 1

Specific Criteria for Neck Suitability

For conventional EVAR to be successful:

• Neck length must be >10-15 mm
• Neck diameter should be <30 mm
• Mural thrombus and calcification covering >90% of neck circumference increases risk of complications 1

Clinical Outcomes Based on Hernia-to-Neck Ratio

Research demonstrates that patients with larger aneurysm-to-neck ratios have significantly worse outcomes:

• Patients with AAA >60 mm and proximal neck >26 mm have:
  • Higher mortality rates
  • Increased rupture rates
  • Higher conversion rates to open repair 2

A meta-analysis found that patients with hostile neck anatomy (unfavorable hernia-to-neck ratios) experienced:

• 4-fold increased risk of type I endoleak
• 9-fold increased risk of aneurysm-related mortality within 1 year of treatment 3
• Required more adjunctive procedures to achieve proximal seal 3

Gender Differences in Neck Anatomy

Women with AAAs present with more challenging neck anatomy:

• Higher proportion of women have more pathologic neck anatomy (53% vs 22% in men) 4
• Women have more extensive aortic neck pathology, not just shorter necks 4
• This may explain why fewer women with AAA are treated with EVAR compared to open repair 4

Decision Algorithm for AAA Treatment Based on Neck Anatomy

1. Assess neck characteristics:

   • Length: <15 mm is considered hostile
   • Diameter: >32 mm is considered hostile
   • Angulation: >60° is unfavorable
   • Presence of circumferential thrombus or calcification
   • Conical shape of the neck

2. Determine treatment approach:

   • Favorable ratio: Standard EVAR is recommended for patients with suitable neck anatomy and reasonable life expectancy (>2 years) 1
   • Unfavorable ratio: Consider alternative approaches:
     • Fenestrated EVAR (FEVAR) for aortic necks of inadequate length 1
     • Open surgical repair for highly unfavorable anatomy 1

3. Post-procedure surveillance:

   • More rigorous follow-up for patients with unfavorable neck anatomy
   • Lifelong surveillance is mandatory after EVAR, especially in patients with challenging neck anatomy 1

Common Pitfalls to Avoid

• Underestimating neck pathology: Not just length but overall neck quality must be assessed
• Ignoring the ratio: Focusing only on absolute aneurysm size without considering the neck-to-aneurysm relationship
• Overlooking gender differences: Women require special attention to neck anatomy assessment
• Inadequate follow-up: Patients with unfavorable neck anatomy need more vigilant post-EVAR surveillance

The hernia-to-neck ratio should be a key factor in the decision-making process for AAA treatment, as it directly impacts procedural success, complication rates, and long-term outcomes.