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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Pediatric Neurosurgery

Types and Anatomy: Understanding Your Baby's Unique Diagnosis

At a Glance

Neural tube defects (NTDs) are birth defects of the brain and spine. The specific type, such as myelomeningocele or anencephaly, and the exact location on the spine (lesion level) determine the severity. The lesion level is the most important factor in predicting a child's future mobility.

Understanding the specific type of neural tube defect (NTD) your baby has is a vital step in preparing for the future. These conditions are classified by their anatomy—specifically, what parts of the nervous system are affected and whether the defect is “open” (exposed to the environment) or “closed” (covered by skin) [1][2].

The Spina Bifida Spectrum

Spina bifida occurs when the protective bony arch of the spine does not close completely [1]. There are several distinct forms:

  • Spina Bifida Occulta: This is a “closed” defect and the mildest form [1]. The skin covers a small gap in the vertebrae, but the spinal cord and nerves are usually unaffected [3]. Many people never even know they have it [4].
  • Meningocele: In this form, a sac of fluid (the meninges, or protective covering of the spinal cord) pushes through the opening in the spine [1][3]. Crucially, the spinal cord itself is not in this sac, so nerve damage is often minimal or absent [5].
  • Myelomeningocele (MMC): This is the most common and severe “open” form of spina bifida [6]. A sac containing both the meninges and the spinal cord nerves pushes through the opening [1]. Because these nerves are exposed to amniotic fluid during pregnancy, they are often damaged, leading to varying degrees of paralysis and other health challenges [7][8].
  • Myeloschisis: This is similar to MMC, but there is no sac at all [1]. The neural tissue is a flattened mass directly exposed to the outside, which is associated with the most significant neurological impairments [1][3].

Cranial Neural Tube Defects

While spina bifida affects the spine, other NTDs affect the head and brain:

  • Anencephaly: This is a fatal condition where the upper part of the neural tube fails to close [9]. As a result, the major portions of the brain, skull, and scalp do not develop [10]. Babies with this condition are either stillborn or live for only a very short time after birth [9].
  • Encephalocele: This is a rare defect where a portion of the brain and its coverings (meninges) poke through an opening in the skull [11]. The outcome for a child with an encephalocele depends heavily on where the opening is and how much brain tissue is involved [11][12].

The Importance of the “Lesion Level”

The single most important factor in predicting a child’s physical function—especially their ability to walk and manage their bladder—is the lesion level [4]. This refers to the exact spot on the spine where the defect is located.

Spinal nerves act like power lines, sending signals from the brain to specific parts of the body. In general, nerves above the lesion level work normally, while nerves below the lesion level may not [4].

Lesion Level Typical Functional Impact
Thoracic (Chest) Usually requires a wheelchair for mobility; full support needed for bladder/bowel [13].
High Lumbar (Mid-back) May walk short distances with significant bracing and crutches; often uses a wheelchair for longer distances [13].
Low Lumbar (Lower-back) Often able to walk with some bracing (like ankle braces) and may use crutches [13][14].
Sacral (Tailbone) Most likely to walk independently, though they may still have challenges with foot strength or bladder control [13][15].

Doctors use prenatal ultrasound and MRI to determine this level as accurately as possible, which helps families and medical teams plan for the specific care the baby will need after birth [5][16].

Common questions in this guide

What is the difference between open and closed spina bifida?
Open spina bifida means the spinal cord or nerves are exposed to the amniotic fluid, which can cause nerve damage during pregnancy. Closed spina bifida is covered by skin, so the nerves are usually protected and unaffected.
What is the most common type of spina bifida?
Myelomeningocele is the most common and severe form of open spina bifida. In this condition, a sac containing both the protective coverings and the spinal cord nerves pushes through an opening in the baby's spine.
What does the 'lesion level' mean for my baby?
The lesion level is the specific spot on the spine where the defect is located. It is the most important factor in predicting your child's future physical function, as nerves below this level may not work normally.
Will my baby be able to walk with spina bifida?
A child's ability to walk depends heavily on their lesion level. Babies with lower spinal lesions, like sacral or low lumbar, are more likely to walk independently or with minor bracing, while those with higher lesions typically require wheelchairs.
What is a meningocele?
A meningocele is a type of spina bifida where a fluid-filled sac pushes through the opening in the spine, but the spinal cord is not inside it. Because the spinal cord is unaffected, nerve damage is often minimal or absent.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.At what specific vertebral level is my baby's lesion located?
  2. 2.Based on the lesion level, what is the current prediction for their future mobility and bowel/bladder control?
  3. 3.Is this considered an 'open' or 'closed' defect, and how does that change the risks for infection or nerve damage?
  4. 4.Is there a sac covering the nerves (meningocele/myelomeningocele), or is the neural tissue completely exposed (myeloschisis)?
  5. 5.Are there any other associated brain findings, such as the Chiari II malformation or hydrocephalus?

Questions For You

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References

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This page explains neural tube defect anatomy and terminology for educational purposes. Your pediatric neurosurgeon or maternal-fetal medicine team is the best source for interpreting your baby's specific diagnosis and prognosis.

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