Lumbar hemivertebra results due to the abnormal development of:

The embryonic mesoderm on either side of the notochord segments into paired somites, which differentiate into sclerotome. myotome .. and dermatome portions. The human vertebral column develops by endochondral bone formation from the paired sclerotome elements. The vertebral bodies are formed by fusion of a more compact caudal portion of each sclerotome with the less dense cranial portion of the sclerotome below, and dorsal migration of sclerotome tissue will give rise to the paired neural arches. At birth, ossification centers are present for the centrum of the vertebral body and for each half of the neural arches, which have a cartilaginous union to the centrum at the neurocentral synchondroses. Segmentation anomalies like with hemivertebrae, butterfly vertebrae, and block vertebrae occur due to abnormal development of Ventral sclerotome.