1. Normal Aortic Diameters by Segment
(Measured inner-edge to inner-edge on CT/MRI)
| Aortic Segment | Men (cm) | Women (cm) | Indexed to BSA (cm/m²) |
|---|---|---|---|
| Aortic root | 3.0–3.7 | 2.8–3.3 | ≤1.9–2.1 |
| Ascending aorta | 3.0–3.5 | 2.8–3.3 | ≤1.7–2.0 |
| Aortic arch | 2.5–3.0 | 2.3–2.8 | ≤1.5–1.7 |
| Descending aorta | 2.2–2.8 | 2.0–2.5 | ≤1.3–1.5 |
| Abdominal aorta | 1.8–2.5 | 1.6–2.2 | ≤1.1–1.3 |
2. Age-Adjusted Aortic Diameters
Aortic diameter increases with age (~0.1 cm/decade after age 40).
| Age Group | Ascending Aorta (Men, cm) | Ascending Aorta (Women, cm) |
|---|---|---|
| 20–40 yrs | 2.8–3.2 | 2.6–3.0 |
| 40–60 yrs | 3.0–3.5 | 2.8–3.3 |
| >60 yrs | 3.2–3.7 | 3.0–3.5 |
3. Height-Adjusted Aortic Diameters
Aortic Size Index (ASI) = Aortic diameter (cm) / Height (m)
- Normal ASI: <1.8–2.0 cm/m (varies by segment).
- High risk: ASI ≥2.5 cm/m (e.g., Marfan syndrome intervention threshold).
Example:
A 1.6m-tall woman with a 3.8 cm ascending aorta:
ASI = 3.8 / 1.6 = 2.38 cm/m → High risk despite absolute diameter <4.0 cm.
4. BSA-Adjusted Aortic Diameters
BSA (m²) = √[Height (cm) × Weight (kg) / 3600]
Indexed diameter = Aortic diameter (cm) / BSA (m²)
| Population | Normal Indexed Ascending Aorta (cm/m²) | Intervention Threshold |
|---|---|---|
| General | ≤1.7–2.0 | ≥2.75 |
| Marfan syndrome | ≤1.5–1.7 | ≥2.5 |
| Bicuspid aortic valve | ≤1.8–2.0 | ≥2.5 |
Example:
A man with BSA 2.0 m² and ascending aorta 4.5 cm:
Indexed = 4.5 / 2.0 = 2.25 cm/m² → Monitor closely (near threshold).
5. Gender-Specific Differences
Women have smaller aortas but higher rupture risk at smaller diameters (due to smaller BSA/height).
2022 ACC/AHA Guidelines:
- Women with AAA: Repair at ≥5.0 cm (vs. 5.5 cm in men).
- Women with TAA: Consider repair at 4.5–5.0 cm if high-risk (e.g., Loeys-Dietz).
6. Pediatric Aortic Z-Scores
For children, diameters are expressed as Z-scores (standard deviations from mean for age/BSA):
- Normal: Z-score <2.
- Abnormal: Z-score ≥2 (e.g., in Marfan, Ehlers-Danlos).
Formula:
Z = (Observed diameter - Mean diameter for BSA/age) / Standard deviation
7. Practical Implications
- Small-stature patients: Use ASI or BSA-indexing to avoid underestimating risk.
- Women: Lower absolute thresholds for intervention.
- Pediatrics: Rely on Z-scores, not absolute values.
Key References
- 2022 ACC/AHA Guidelines (JACC, DOI: 10.1016/j.jacc.2022.08.004).
- Roman et al. (1989): BSA-indexing for aortic root.
- Campens et al. (2014): Height-adjusted aortic diameters.