Children's Hospital Colorado

Myelomeningocele (Spina Bifida)

What is myelomeningocele (spina bifida)?

Myelomeningocele (MMC) is a congenital birth defect of the spine and spinal cord. A serious form of spina bifida, myelomeningocele occurs when a baby's spine (the backbone), spinal cord and spinal canal don't close as they normally would.

This condition develops before birth, usually within the third or fourth week of pregnancy.

How does myelomeningocele occur?

Spina bifida occurs in the first three to four weeks of a woman's pregnancy when the spinal cord is forming. At this point, a baby's developing brain and spine are referred to as the "neural tube."

Normally, during these first few weeks of development, the two sides of a baby's back (known as the neural plate and surrounding tissues) fold to form a tube called the spinal cord. The spinal cord separates from the covering tissues, including the meninges, bone and muscles.

MMC is a neural tube defect in which the bones of the spine don't completely form, resulting in an incomplete spinal canal. Because the spinal canal remains open, the spinal cord and meninges protrude from the baby's back.

Babies with MMC-type spina bifida can have a sac protruding from the opening in the spine. This sac may contain:

  • Cerebrospinal fluid
  • Nerves
  • Parts of the spinal cord

What causes myelomeningocele?

Spina bifida is caused by incomplete closure and development of the fetal spine very early in pregnancy. The exact cause of MMC is not completely understood, but evidence suggests that genes and environmental factors may be involved.

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Nicholas Behrendt, MD

Nicholas Behrendt, MD

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Traci Nivens, MD

Traci Nivens, MD

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