spina bifida /bif″ədə, bī″fədə/ , a congenital neural tube defect in which there is a developmental anomaly in the posterior vertebral arch. Spina bifida is relatively common, occurring approximately 10 to 20 times per 1000 births. It may occur with only a small deformed lamina separated by a midline gap, or it may be associated with the complete absence of laminae surrounding a large area. In cases where the separation is wide enough, contents of the spinal canal protrude posteriorly, and a myelomeningocele is evident. Neurological deficits do not usually accompany the anomalies involving only bony deformity. Direct signs and symptoms are rarely noted in spina bifida, which is frequently diagnosed accidentally during radiographic examinations required for other reasons. Spina bifida that does not involve herniation of the meninges or the contents of the spinal canal (spina bifida occulta) rarely requires treatment. Also called spinal dysrhaphism. See also spina bifida occulta.
