Quantitative evaluation of abdominal aortic aneurysm

Rupture of an abdominal aortic aneurysm (AAA) is usually predicted on the b asis of measuring the maximum diameter. However, since the size of a normal aorta varies depending on each individual, this indicator does not seem to be ideal. The authors propose a new indicator for the enlargement of aorta and have started clinical application of this technique. The abdominal aortic diameter was measured by using two-dimensional ultraso nography in 261 adults (aged 20 and over). The control group consisted of s ubjects with no evident aortic dilatation. Patients with AAA were divided i nto the nonruptured group and the ruptured group. Analysis of the data from the control group revealed that the abdominal aor tic diameter could be defined by the following equation: Diameter (mm) = 0. 147 x age (years) + 0.169 x height (cm) - 15.9. The baseline diameters of t he abdominal aorta were calculated by applying the age and height of indivi dual subjects in this equation. The measured diameter was divided by the ba seline diameter to obtain the aortic expansion index (AEI). If a cut-off va lue of the aneurysm diameter and the AEI (calculated by using age 20) for t he prediction of significant risk of rupture is set at 44.2 mm (= mean - 2S D of the aneurysm diameter in the ruptured group) and at 2.7 (= mean 2SD of the AEI in the ruptured group), the risk of rupture based on the diameter in the nonruptured group is underestimated in 11% of cases. However, when t he risk of rupture is based on the AEI, the risk is not underestimated in a ny case in the nonruptured group. The authors conclude that the AEI is a useful indicator for quantitatively evaluating the risk of rupture of an AAA.