**10. Definitions of coronary artery involvement**

A number of definitions have been proposed to describe and quantitate coronary artery involvement. The Japanese Ministry of Health classification was first published in 1984. Aneurysms are considered to be small if their internal diameter is <5mm, medium if between 5-8mm, or giant if the internal diameter of the aneurysm is >8mm (Figure 5). These criteria are widely used and define absolute values for coronary artery dimensions and therefore do not account for differences in patient size or the usual caliber of different coronary artery branches. The American Heart Association AHA guidelines were published in 2004 and define coronary artery dimensions with respect to body surface area, which requires both weight and height measurements. These define a coronary artery as dilated if the intra-luminal diameter has a z-score of ≥ 2.5mm. Manlhiot et al. recently proposed a revision of this classification to account for differences in body size and caliber of coronary artery branches, and report that coronary artery abnormalities are small if the z-score is ≥ 2.5 to <5, large if the z-score is ≥ 5 to < 10, and giant if the z-score is ≥ 10 (Manlhiot et al., 2010). This method is however prone to significant variation in the calculated z-score with minor variation in measurement of coronary size. It is therefore too early to determine whether this classification will be widely employed.
