Congenital defect in the posterior bony wall of the spinal canal involving the laminae, is known as spina bifida. This is most commonly seen in the lumbo-sacral region. Sometimes the contents of the canal may protrude through the defect.

Development of the spinal cord:

1. During the 2nd week of intrauterine life a dorsal groove appears on the surface of the embryo, which is known as the neural groove.
2. The margins of the neural groove unite so that it becomes converted into a tube, from which the nervous system is developed. This tube is known as neural tube and the lumen, within it, is called the neural canal. This neural canal persists as the central canal. The neural tube becomes separated from the surface by an ingrowth of the mesoderm.

Development of the vertebral column

1. In front of the neural tube there is a solid rod of cells, known as the notochord. Around the notochord the vertebral bodies develop. The fusiform cells of the sclerotome multiply rapidly and migrate to enclose the notochord in a mesenchymal sheath to form mesenchymjal vertebral column. In each segment bars of cartilage appear on either side of the notochord, which develop into vertebral bodies.
2. From each of the bodies there extend two projections which grow round the neural tube to form the vertebral arch or neural arch. Each half of the neural arch is chondrified from a centre which extends forwards into the pedicles to meet and fuse with the centrum (which forms the vertebral body) and backwards into the laminae, but the cartilaginous liminae do not meet one another dorsally until the 4th month of intra-uterine life. The transverse and articular processes are chondrified in continuity with the neural arch.
3. Such fusion first occurs in the thoracic region. From there fusion extends upwards and downwards.
4. Failure of fusion of these arches gives rise to spina bifida.

Incidence

The incidence of spina bifida (excluding spina bifida occulta) is 0.1%.

Types of spina bifida

1. Spina bifida occulta
2. Meningocele
3. Meningomyelocele
4. Syringomyelocele
5. Myelocele

Myelocele is the commonest type of spina bifida, if the spina bifida occulta is excluded. But unfortunately many cases with myelocele are still born. Even if they born alive, death occurs within a few days from infection of the cord and meninges.

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Related posts:

1. Spina Bifida Occulta
2. Syringomyelocele and Myelocele
3. Thoraco Lumbar Spine Injuries Overview
4. Tuberculosis of Spine-An Overview
5. Meningomyelocele