In spina bifida, the bones of the spine (vertebrae) do not form normally. Spina bifida can vary in severity.

In occult spinal dysraphism, one or more vertebrae do not form normally, and the spinal cord and the layers of tissues (meninges) surrounding it may also be affected. There are several types with differing neurologic severities. The diagnosis is sometimes suggested by symptoms in the lower back, such as a tuft of hair, a dimpling, or a pigmented area on the skin over the defect.

In a meningocele, the meninges protrude through the incompletely formed vertebrae, resulting in a fluid-filled bulge under the skin. The spinal cord is in its normal location.

The most severe type is a meningomyelocele, in which the meninges and spinal cord protrude. The affected area appears raw and red, and the infant is likely to be severely impaired.