What is the normal diameter of the ascending thoracic aorta?

Normal Diameter of the Ascending Thoracic Aorta

The normal diameter of the ascending thoracic aorta varies by gender, with average measurements of 34.1 ± 3.9 mm for men and 31.9 ± 3.5 mm for women, according to the Framingham Heart Study. 1

Normal Dimensions by Gender and Age

• For men, the normal aortic root diameter ranges from 3.63 to 3.91 cm when measured by CT 1
• For women, the normal aortic root diameter ranges from 3.50 to 3.72 cm when measured by CT 1
• The ascending aorta (tubular portion) has a normal diameter of approximately 2.86 cm for both females and males when measured by chest X-ray 1
• The ascending aorta diameter increases with age at a rate of approximately 0.12 to 0.29 mm per year 1, 2
• Men generally have aortic diameters 1-3 mm larger than women, though this difference decreases with age 2

Factors Affecting Aortic Diameter

• Body size significantly impacts aortic dimensions - body mass index affects aortic diameter by approximately 0.27 mm per unit of BMI 1, 2
• Age is a major determinant, with aortic diameter increasing approximately 1 mm per decade 3, 4
• Gender affects measurements, with men having approximately 1.9 mm larger diameters than women 4
• Hypertension can result in aortic diameters approximately 0.9 mm larger than in normotensive individuals 4

Measurement Considerations

• Different imaging modalities may yield different measurements 2
• Measurements should be taken perpendicular to the axis of blood flow to avoid overestimation 2
• The aortic diameter gradually tapers downstream from the sinuses of Valsalva 1
• An ascending aorta that exceeds the diameter of the aorta at the level of the sinuses of Valsalva is considered enlarged, even if both are within normal range 1, 2

Upper Normal Limits by Age

• For women, the upper normal limits (mean + 2 standard deviations) of intraluminal ascending aortic diameter are:

  • 35.6 mm for ages 20-40 years 3
  • 38.3 mm for ages 41-60 years 3
  • 40.0 mm for ages over 60 years 3

• For men, the upper normal limits are:

  • 37.8 mm for ages 20-40 years 3
  • 40.5 mm for ages 41-60 years 3
  • 42.6 mm for ages over 60 years 3

Clinical Implications

• Aortic diameters greater than the upper limits of normal (2 SD above the mean diameter as adjusted for age, sex, and body surface area) but not meeting criteria for aneurysm may be considered ectatic or dilated 1
• The term aneurysm is reserved for diameters that are 150% of normal, which is approximately 5.0 cm for the ascending aorta 1
• For better risk assessment, aortic diameter can be indexed to height (aortic height index) or body surface area (aortic size index) 2
• In clinical practice, aortic root dilatation can be suspected in male adults when aortic diameter is >40 mm or when the indexed diameter/BSA is >22 mm/m² 2

Measurement Methods

• Transthoracic echocardiography (TTE) measurements show mean diameters in men and women of 3.2 and 3.0 cm respectively for the ascending aorta 5
• CT and MRI measurements from sinus to commissure are generally smaller than echocardiographic measurements from sinus to sinus 2
• The aortic wall thickness is normally less than 4 mm when measured by CT or TEE 1

Understanding normal aortic dimensions is crucial for identifying pathological dilation and making appropriate clinical decisions regarding follow-up and intervention.