Aneurysm is considered a severe (pathological) form of dilatation of a segment of a blood vessel. In clinical practice, dilatation and aneurysm are occasionally used interchangably. In this subhierarchy, we therefore use aneurysm as the primary label and list dilatation as a broad synonym.

Aortic dilatation refers to a dimension that is greater than the 95th percentile for the normal person age, sex and body size. In contrast, an aneurysm is defined as a localized dilation of the aorta that is more than 150 percent of predicted (ratio of observed to expected diameter 1.5 or more). Aneurysm should be distinguished from ectasia, which represents a diffuse dilation of the aorta less than 50 percent of normal aorta diameter.

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Aortic dilatation, Bulge in wall of large artery that carries blood away from heart

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