Myelomeningocele is a birth defect in which the backbone and spinal canal do not close before birth. The condition is a type of spina bifida.

Myelomeningocele is one of the most common birth defects of the central nervous system. It is a neural tube defect in which the bones of the spine do not completely form, resulting in an incomplete spinal canal. This causes the spinal cord and meninges (the tissues covering the spinal cord) to stick out of the child's back.

Myelomeningocele accounts for about 75% of all cases of spina bifida and may affect as many as 1 out of every 800 infants. Spina bifida includes any birth defect involving insufficient closure of the spine.

The rest of myelomeningocele cases are most commonly:

• Spina bifida occulta, a condition in which the bones of the spine do not close but the spinal cord and meninges remain in place and skin usually covers the defect
• Meningoceles, a condition where the tissue covering the spinal cord sticks out of the spinal defect but the spinal cord remains in place.

Other congenital disorders may also be present in the child. Hydrocephalus may affect as many as 90% of children with myelomeningocele. Other disorders of the spinal cord or musculoskeletal system may be seen, including syringomyelia and hip dislocation.

The cause of myelomeningocele is unknown. However, folic acid deficiency is thought to play a part in neural tube defects. Also, if a child is born with myelomeningocele, subsequent children in that family have a higher risk than the general population.

Some theorize that a virus make play a role, since there is a higher rate of this condition in children born in the early winter months. Research also indicates possible environmental factors such as radiation.

A newborn may have a sac sticking out of the mid to lower back. The doctor cannot see through the sac when shining a light behind it. Symptoms include:

• Loss of bladder or bowel control
• Partial or complete lack of sensation
• Partial or complete paralysis of the legs
• Weakness of the hips, legs, or feet of a newborn

The exposed spinal cord is susceptible to infection. Other symptoms may include:

• Hair at the back part of the pelvis called the sacral area
• Dimpling of the sacral area

Prenatal screening can help diagnose this condition. During the first trimester, pregnant women can have a blood test called a triple screen. This test screens for myelomeningocele, Down syndrome, and other congenital diseases in the baby. Most women carrying a baby with spina bifida will have a higher-than-normal levels of a protein called maternal alpha fetoprotein (AFP).

If the triple screen test is position, further testing is needed to confirm the diagnosis. Such tests may include:

• Pregnancy ultrasound
• Amniocentesis

Myelomeningocele can be seen after the child is born. A neurologic examination may show that the child has loss of nerve-related functions below the defect. For example, watching how the infant responds to pinpricks at various locations may reveal where he or she can feel the sensations.

Tests done on the baby after birth may include x-rays, ultrasound, CT, or MRI of the spinal area.