Significance of resegmentation in the pathogenesis of vertebral body malformation

Human embryos and fetuses were investigated histologically to elucidate the possible pathogenesis of congenital malformations of the vertebral body. Special attention was paid to early development of the vertebral column, particularly the often-questioned stage of resegmentation, important as the stage during which the malformations might develop. Evidence of resegmentation was found in 7 embryos ranging from 7 mm C-R length (5 weeks after fertilization) to 13 mm (6 weeks). Moreover, the formation of the definitive vertebral body was considered to be intimately related to the intersegmental artery. As for Junghanns' concept that the cartilaginous body consists of two lateral halves, it was not observed in our specimens, nor was it found in the latest literature on normal vertebral development. Congenital malformations of the vertebral body were classified into two categories: failure of formation and failure of segmentation. They were demonstrated in an embryo of 13 mm and a fetus of 70 mm which were in the developmental stages of chondrification and early ossification, respectively. According to these observations, we conclude that most malformations of the vertebral body occur in the early stage of definitive vertebral body anlage formation.