Background No clinical study has systematically analyzed and compared circumferential neointimal and plaque distribution of stent neointimal proliferation and in native atherosclerotic plaques.This study aimed to investigate and compare the patt of instent neointimal formation and native atherosclerosis in the coronary bifurcation lesions by volumetric analysis using systematic intravascular ultrasound (IVUS).Methods We examined bifurcation lesions in native coronary artery (plaque group,n=102) and stented bifurcations at 9-month follow-up (neointima group,n=51) using volumetric IVUS analysis of both the main vessel (MV) and side branch (SB).Three 5-mm segments were analyzed; the proximal MV (MVp),distal MV (MVd) and SB ostium (SBo).For each segment,volumetric analysis was performed in each of four quadrants (divided according to the branch takeoff and the geometric center of the lumen); carinal,epicardial,abcarinal,and myocardial.The eccentricity index was defined as the ratio of the abcarinal plaque (or neointimal) volume to the carinal plaque (or neointimal) volume.Results The plaque distribution differed significantly between the four quadrants,with the largest in the abcarinal quadrant,followed by the myocardial,epicardial,and carinal quadrants.The distribution of neointima was similar in the MV,but the four quadrants in the SB did not differ significantly.The eccentricity indices of both the MVd (P ＜0.001) and SBo (P=0.001) were significantly higher for the plaque group than the neointima group.Conclusions The distribution of neointimal proliferation seems to have a similar patt to that of atherosclerotic plaque in native coronary arteries,particularly in the main vessel,but the trend is less prominent.