What are the normal diameters of the aorta and iliac (internal iliac and external iliac) arteries?

Normal Diameters of the Aorta and Iliac Arteries

Abdominal Aorta

The normal infrarenal abdominal aorta measures up to 2 cm (20 mm) in anteroposterior diameter, with diameters between 2-3 cm considered ectatic and ≥3 cm meeting criteria for aneurysm. 1

• The proximal abdominal aorta averages 21.49 ± 2.49 mm 2
• The middle abdominal aorta measures approximately 16.94 mm (median) 2
• The distal abdominal aorta measures approximately 15.65 mm (median) 2
• Men have significantly larger abdominal aortic diameters than women across all segments 2
• The absolute threshold for aneurysm is approximately 10% smaller in women than in men 1

Thoracic Aorta

Ascending Aorta

Men average 34.1 ± 3.9 mm and women average 31.9 ± 3.5 mm for the ascending thoracic aorta. 1, 3

• The normal range extends from approximately 26-42 mm in men and 25-39 mm in women (mean ± 2 SD) 3
• The aortic root (including sinuses of Valsalva) is normally 0.5 cm larger than the tubular ascending aorta 3
• Aneurysm is defined as ≥5.0 cm (150% of normal diameter) for the ascending aorta 1
• Diameters >2 SD above the mean (adjusted for age, sex, and body surface area) are considered ectatic or dilated 1, 3

Descending Thoracic Aorta

Men average 25.8 ± 3.0 mm and women average 23.1 ± 2.6 mm for the descending thoracic aorta. 1, 4

• At the mid-descending level, normal ranges are 23.9-29.8 mm in males and 24.5-26.4 mm in females 4
• At the diaphragmatic level, measurements are 24.3-26.9 mm in males and 24.0-24.4 mm in females 4
• The aorta gradually tapers from 3.5-4.0 cm at the aortic root to 2.4-2.7 cm at the diaphragm 1, 4
• Aneurysm is defined as ≥4.0 cm for the descending aorta 1

Common Iliac Arteries

The common iliac arteries measure approximately 10-11 mm in diameter, with an average of 10.52 mm across multiple measurement sites. 5, 2

• Right proximal common iliac artery: 10.76 mm (median) 2
• Left proximal common iliac artery: 10.41 mm (median) 2
• Right distal common iliac artery: 10.74 mm (median) 2
• Left distal common iliac artery: 10.67 mm (median) 2
• Men have significantly larger common iliac artery diameters than women 2
• The common iliac arteries average 5.59 mm in length 5

Key Factors Affecting Diameter

Body Size and Demographics

• Aortic diameter increases by 0.27 mm per unit of BMI 4
• Body surface area, height, weight, and BMI are significantly positively correlated with both aortic and iliac artery diameters 2
• Men consistently have larger diameters than women by 1-3 mm across all measurement locations 3, 4

Age-Related Changes

• Aortic diameter increases with age at approximately 0.12-0.29 mm per year at each measured level 4
• The diameter of the abdominal aorta and distal common iliac arteries significantly increase with age 2
• Age-adjusted normal values are necessary to differentiate pathologic changes 6

Critical Measurement Considerations

Measurements must be taken perpendicular to the blood flow axis to avoid overestimation from oblique imaging planes. 3, 4

• CT imaging is the gold standard for measuring aortic diameter 3, 4
• CT and MRI measurements from sinus-to-commissure are generally smaller than echocardiographic sinus-to-sinus measurements 3
• Oblique slices can significantly overestimate true aortic diameter, leading to unnecessary intervention 4
• Intraluminal measurements (excluding vessel wall) are approximately 2-2.5 mm smaller than total diameter measurements 6

Clinical Thresholds

• The European Society of Cardiology defines an enlarged ascending aorta as ≥42 mm, with normal being <38 mm 3
• For indexed measurements, aortic root dilatation is suspected when diameter/BSA is >22 mm/m² in male adults 7
• Z-scores (standard deviations from the mean) are particularly useful for evaluating aortic dimensions at extreme ages 7