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Myelomeningocele (Spina Bifida)

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What is myelomeningocele (spina bifida)?

Spina bifida myelomeningocele, also called myelomeningocele (MMC) or MMC spina bifida, is a congenital (present at birth) condition of the spine and spinal cord. Spina bifida is known as a neural tube defect, which is a group of conditions that occur when the neural tube doesn’t close fully. Myelomeningocele, a serious form of spina bifida, occurs when a baby's spine, 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.

What causes spina bifida myelomeningocele?

Myelomeningocele happens when a baby’s spine doesn’t fully close and occurs very early in pregnancy. The exact cause of MMC is not fully known, but evidence suggests that genes (passed down from parents) and environmental factors may be partially involved.

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

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 (protective layers of membrane), bone and muscles.

MMC is a neural tube issue in which the bones of the spine don't completely form, resulting in an incomplete spinal canal. Because the spinal canal is open, the spinal cord and meninges (membranes that line the spinal canal) stick out from the baby's back.

Babies with spina bifida MMC can have a sac coming out of the opening in the spine. This sac may contain:

  • Cerebrospinal fluid (fluid that surrounds the brain and spinal cord to protect them from injuries and provide nutrients)
  • Nerves
  • Parts of the spinal cord

How common is MMC?

Researchers estimate that worldwide, MMC occurs in about 0.8 to 1 out of every 1,000 live births. In the United States, the rate is slightly lower at 0.2 to 0.4 out of every 1,000 live births.

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