hemivertebra /-vur″təbrə/ , an abnormal condition characterized by the congenital failure of a vertebra to develop completely. It is possibly caused by the complete failure of the growth center of one vertebral body. Usually half of the vertebra involved is completely or partially developed, and the other half is absent. One or more vertebrae may be involved. The different conditions produce varying degrees of balanced or unbalanced scoliosis. As a result of the developmental abnormality of the spine, a wedge-shaped vertebra develops, and adjacent vertebral bodies expand to fit the deformity or tilt to accommodate wedge-shaped articulation. Hemivertebra may be classified according to the degree of developmental failure of involved vertebral growth centers. When two vertebral bodies are involved and growth centers on the same side fail to develop, moderate to severe unbalanced congenital scoliosis results. When growth centers fail to develop on opposite sides, balanced congenital scoliosis results. Singular hemivertebra may cause few if any signs and symptoms. Depending on the degree of congenital scoliosis involved, any associated deformity may become more apparent with growth. Other types of hemivertebra, especially those involving unbalanced congenital scoliosis, usually progress markedly with growth and have a relatively poor prognosis unless early spinal fusion prevents further spinal curvature. No treatment may be required for the form of the condition associated with balanced congenital scoliosis.
