Objective To explore the belongingness,name and clinical significance of a sort of osteal structure variation (OSV) posterior,outboard and superior to the ditch of vertebral artery of atlas.Methods 23 cases of OSV were collected among 426 patients underwent MSCT intracranial and cervical angiography with volume rendering technique (VRT)to notice the pier point,shape and direction of protuberance,and the relation and influence to the vertebral artery.Results The incidence of OSV was 5.40%(23/426) in which 31 sides were detected,and 1 5 cases in unilateral and 8 cases in bilateral.Simple type was showed at 1 9 sides,compound type at 12 sides with other ponticulus.According to the shape of the ponticulus,simple root was seen at 1 7 sides(13 inferior root and 4 lat-erial root),opposite beaked at 5 sides,complete type at 9 sides.OSV was located at posterior,outbord and superior to the ditch of vertebral artery of atlas and closed to the vertebral artery.The vertebral artery was influenced by OSV as following:in simple OSV vertebral artery stenosis was seen at 4 sides in which unite convulsion was showed at one side;in compound OSV vertebral artery ste-nosis was seen at 5 sides,in which unite convulsion was showed at 2 sides.Conclusion OSV is similar to ponticulus posticus(PP)and ponticulus lateralis(PL),and has similarly importance clinical significance,and should belong to the ponticulus of atlas,and to be named as ponticulus borderland(PB).