In the ICD (International Classification of Diseases) 10 two branches are designed for AAA. Branch I71.3 “Abdominal aortic aneurysm, ruptured” defines a ruptured aneurysm, and branch I71.4 “Abdominal aortic aneurysm, without mention of rupture” defines the condition of AAA without rupture {8}.

The National Library of Medicine (where the medical literature catalogue PubMed is also located) defines the MeSH (medical subject headings) term used for AAA as “An abnormal balloon- or sac-like dilatation in the wall of the abdominal aorta which gives rise to the visceral, the parietal, and the terminal (iliac) branches below the aortic hiatus at the diaphragm” The definition was introduced in the year 1993 {9}.

There are several other definitions of AAA in the literature including "An aneurysm is a focal dilation of a blood vessel with respect to the original or adjacent artery. An abdominal aortic aneurysm is defined as an aortic diameter at least one and one-half times the diameter measured at the level of the renal arteries. The normal diameter of the abdominal aorta is approximately 2.0 cm (range 1.4 to 3.0 cm) in most individuals; a diameter greater than 3.0 cm is considered aneurysmal". {1}

A more pathophysiological definition of AAA is given by {3}: “the progressive loss in the capacity to resist high intraluminal pressure, related to the degradation of the arterial wall”.