A congenital (present at birth) malformation; there are two main forms – spina bifida occulta being more common. There is a deficit in the posterior part of the SPINAL COLUMN, usually in the LUMBAR region. Generally this causes no problems and the person may be unaware of its presence until it is disclosed by an X-ray taken for some other reason. Occasionally it is associated with a hairy patch or birthmark on the back, and a few children develop a mild spastic gait or bladder problems.

Much more serious is spina bifida cystica, in which the spinal-wall defect is accompanied by a protrusion of the spinal cord, which appears as a bulge in the midline of the back, covered by a thin membrane. Where this herniation contains elements of the spinal cord, it is termed a meningomyelocele. Usually affecting the lumbo-sacral region, the range of severity may vary considerably and, while early surgery with careful attention in a minor case may achieve good mobility, normal bladder function and intellect, a more extensive protrusion may cause complete ANAESTHESIA of the skin, with increased risk of trauma; extensive paralysis of the trunk and limbs, with severe deformities; and paralysis and insensitivity of the bladder and bowel. Involuntary movements may be present; HYDROCEPHALUS occurs in 80 per cent of cases and may worsen after surgery to close the defect in the back. The decision on whether or when to operate is decided on the basis of the individual person's clinical condition. The incidence of the condition can be reduced if pregnant women take the vitamin folic acid during their pregnancy.