From the Guidelines
The normal aortic diameter is up to 2 cm in the anteroposterior (AP) diameter for the infrarenal abdominal aorta, as defined by the American College of Radiology 1.
Normal Aortic Diameter Variations
The normal aortic diameter varies by location, age, gender, and body size.
- In adults, the ascending aorta typically measures 2.0-3.7 cm,
- the descending thoracic aorta 1.7-2.6 cm,
- and the abdominal aorta 1.4-3.0 cm. Women generally have smaller aortic dimensions than men, and aortic diameter naturally increases with age (approximately 0.7-1.0 mm per decade) 1. Body surface area also influences aortic size, with larger individuals having proportionally larger aortas.
Defining Aneurysm and Ectasia
Clinicians use these normal ranges to identify aortic dilation or aneurysm, typically defining an aneurysm as a localized dilation exceeding 50% of the expected normal diameter 1.
- Aortic dilatation of <50% over normal qualifies as aortic ectasia,
- whereas aneurysms are diagnosed when there is at least 50% enlargement of the aortic lumen,
- or alternatively when the aortic diameter is more than two standard deviations above the mean for the patient’s sex and age.
Importance of Accurate Measurement
Accurate measurement is crucial for proper diagnosis and management decisions, as intervention is often recommended when the aorta reaches certain size thresholds (typically 5.0-5.5 cm for the ascending aorta, depending on other risk factors) 1. These measurements are usually obtained through imaging studies like CT, MRI, or echocardiography. The most recent and highest quality study, published in 2018, provides guidance on the diagnosis and management of patients with thoracic aortic disease, including the use of imaging studies to determine aortic diameter 1.
From the Research
Normal Aortic Diameter
The normal aortic diameter varies based on age, sex, and body size.
- Studies have shown that aortic diameters are larger in men than in women 2, 3, 4.
- Aortic root diameter increases with age, with a significant correlation between aortic diameters and age in both genders 2, 3, 5.
- Body surface area (BSA) and height are also major determinants of aortic diameter, with larger diameters observed in individuals with larger BSA or height 3, 5, 4.
Aortic Diameter Measurements
- Measurements of aortic diameter can be made using two-dimensional transthoracic color Doppler echocardiography (TTE) or magnetic resonance imaging (MRI) 2, 5.
- The aortic annulus, sinuses of Valsalva, and sinotubular junction are common measurement sites 2, 3.
- Indexed aortic diameters (adjusted for BSA or height) can provide a more accurate assessment of aortic size 3, 5, 4.
Normal Values
- The upper limits of normal for aortic diameters vary by age, sex, and measurement site 3, 5, 4.
- For example, the upper normal limit for body surface area-indexed ascending aortic diameter is around 21-28 mm/m2 for women and 20-23 mm/m2 for men, depending on age 5.
- Normal values for aortic root diameter have been reported to range from 2.1 to 4.3 cm in adults 4.