Background Although many theories have been established to explain the mechanism of aneurysm development following steno-occlusive or hypertensive disease, the effect of the geometrical shape of the inner elastic membrane on the maximum dilatation capacity of arteries has not been adequately investigated so far. This subject was investigated. Methods This study was conducted in 24 rabbits. The rabbits were divided into 3 groups: as the control, (n = 5), the SHAM (n = 5), and the study group (n = 14). In the study group, BCCAL was performed. After decapitation, the basilar artery vasodilatation index (VDI) and the actual length of the inner elastic membrane (IEM) were estimated. The relationship between the true length of IEM and VDI values was compared statistically using the Mann-Witney -U test. Results Mean blood pressures were 113 +/- 7 mmHg in animals at the beginning of the experiment (n = 24), and 119 +/- 9 mmHg in GII and 122 +/- 11mmHg in GIII after BCCAL (n = 12). Before decapitation, the mean blood pressures were 115 +/- 10 mmHg in GI, 116 +/- 10 mmHg in GII, and 127 +/- 11mmHg GIII. The DADA values of animals were 20 +/- 4mm in GI; 28 +/- 6mm in GII and 37 +/- 9mm in GIII. The VDI value of BA was 1.390 +/- 0.220 in GI; 1.013 +/- 0.108 in GI; 0.019 +/- 0.011in GII group. Conclusion An inverse relationship was discovered between the DADA/VDI values. BCCAL may lead to severe dangerous histopathological changes at the BA. Lower DADA or higher VDI values may lead to severe basilar enlargement, endothelial losing, inner elastic membrane rupture, and aneurysm formation after BCCAL.