Butterfly vertebrae UMLS:C1844752 Anterior rachischisis HP:0003316 Butterfly vertebrae A butterfly vertebra (sagittal cleft vertebra or anterior rachischisis) is a sagittal defect in the vertebral body caused by failure of fusion of the two lateral chondrification centers during embryogenesis. The name is based on the appearance of the two hemivertebrae emerging as butterfly wings from the central cleft on x-ray. Sagittal clefting of vertebrae Vertebral clefting