What is the normal diameter of the ascending aorta?

Normal Ascending Aorta Diameter

In adults, the normal ascending aorta diameter averages 34.1 ± 3.9 mm in men and 31.9 ± 3.5 mm in women, with values varying by age, sex, and body surface area. 1

Sex-Specific Normal Values

• Men have ascending aortic diameters averaging 34.1 mm (range approximately 26-42 mm, representing mean ± 2 SD) 1
• Women have ascending aortic diameters averaging 31.9 mm (range approximately 25-39 mm) 1
• Men consistently have larger aortic diameters than women by 1 to 3 mm across all measurement locations 1

Key Measurement Considerations

The ascending aorta consists of two distinct segments with different normal dimensions 1:

• The aortic root (including sinuses of Valsalva) is normally 0.5 cm larger in diameter than the tubular ascending aorta 1
• The sinotubular junction marks the transition between these segments 1
• Measurements must be taken perpendicular to blood flow axis to avoid overestimation from oblique imaging planes 1, 2

Clinical Thresholds for Abnormality

The European Society of Cardiology defines an enlarged ascending aorta as ≥42 mm, with normal being <38 mm 3:

• Diameters >2 SD above the mean (adjusted for age, sex, and body surface area) are considered ectatic or dilated 1
• Aneurysm is defined as 150% of normal diameter, which approximates 5.0 cm for the ascending aorta 1

Body Size Indexing

For patients with extreme height variations, indexing to body size provides more accurate assessment 1:

• Expected aortic root size = 2.423 + (age in years × 0.009) + (BSA in m² × 0.461) - (sex [1=male, 2=female] × 0.267) 1
• A z-score can be calculated by dividing the difference between observed and expected diameter by 0.261 cm 1
• For patients >1 SD above or below mean height, a maximal cross-sectional area/height ratio ≥10 cm²/m warrants consideration for intervention 1

Age-Related Changes

• Aortic diameter increases with age, though the relationship is modest 1
• The formula above accounts for approximately 0.009 cm increase per year of age 1

Important Clinical Pitfalls

The majority of the population (79.2%) has ascending aortic diameters <3.5 cm, making the normal aorta "deceptively small" 4:

• Only 2.6% of the general population has diameters of 4.0-4.4 cm 4
• Only 0.22% have diameters ≥4.5 cm 4
• 62% of acute type A aortic dissections occur at diameters <5.5 cm, and 42% occur at <5.0 cm 5
• In women, 12% of dissections occur with maximal dimensions <4.0 cm 5

Imaging Modality Differences

• CT and MRI measurements from sinus-to-commissure are generally smaller than echocardiographic sinus-to-sinus measurements 1
• Echocardiography uses leading-edge technique at end-diastole for aortic root, while some protocols use inner-edge measurements at end-systole 1
• CT imaging is considered the gold standard for measuring thoracic aortic diameter 2
• Contrast use and whether internal versus external diameters are measured affects reported values 1