Congenital malformations of the nervous system: neural tube defects

Neural tube defects affect the brain and spinal cord, and are among the most common of the congenital anomalies (see Fig. 4.1). Panel A shows a cross section of the rostral end of the embryo at approximately three weeks after conception, showing the neural groove in the process of closing, overlying the notochord. The neural folds are the rising margins of the neural tube, topped by the neural crest, and demarcate the neural groove centrally. Panel B shows a cross section of the middle portion of the embryo after the neural tube has closed. The neural tube, which will ultimately develop into the spinal cord, is now covered by surface ectoderm (later, the skin). The intervening mesoderm will form the bony spine. The notochord is regressing. Panel C shows the developmental and clinical features of the main types of neural tube defects. The diagram in the centre is a dorsal view of a developing embryo, showing a neural tube that is closed in the centre but still open at the cranial and caudal ends. The dotted lines marked A and B refer to the cross sections shown in Panels A and B. Shaded bars point to the region of the neural tube relevant to each defect.

In anencephaly, the absence of the brain and calvaria can be total or partial. Craniorachischisis is characterized by anencephaly accompanied by a contiguous bony defect of the spine and exposure of neural tissue. In open spina bifida, a bony defect of the posterior vertebral arches (in this case, the lower thoracic vertebrae) is accompanied by herniation of neural tissue and meninges and is not covered by skin. In iniencephaly, dysraphia in the occipital region is accompanied by severe retroflexion of the neck and trunk. In encephalocele, the brain and meninges herniate through a defect in the calvaria. In closed spina bifida, unlike open spina bifida, the bony defect of the posterior vertebral arches (in this case, the lumbar vertebrae), the herniated meninges, and neural tissue are covered by skin.

The most prevalent types of neural tube defects are anencephaly, encephalocele and spina bifida.

Fig. 4.1. Neural tube defects [1]
Neural tube defects Neural tube defects detailed illustration

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Anencephaly

  Anencephaly (Q00.0)

A total or partial absence of the brain, together with total or partial absence of the cranial vault and the covering skin. [2]

Anencephaly Anencephaly

Craniorachischisis

  Craniorachischisis (Q00.1)

The presence of anencephaly with a contiguous spine defect without meninges covering the neural tissue (rachischisis). [2]

Craniorachischisis Craniorachischisis Craniorachischisis Craniorachischisis Craniorachischisis Craniorachischisis

Iniencephaly

  Iniencephaly (Q00.2)

A rare and complex neural tube defect characterized by extreme retroflexion of the head, variably combined with rachischisis of the cervical and thoracic spine and, more rarely, with occipital encephalocele. In iniencephaly, the cranium is always closed. [2]

Iniencephaly Iniencephaly

Encephalocele

  Frontal encephalocele (Q01.0)

Herniation of brain tissue, usually covered by meninges, through a defect in the frontal bone. [2]

Frontal Encephalocele Frontal Encephalocele Frontal Encephalocele
  Nasofrontal encephalocele (Q01.1)

Herniation of brain tissue, usually covered by meninges, through an opening between the frontal bone and the nasal and ethmoid bones. [3]

Nasofrontal encephalocele Nasofrontal encephalocele
  Occipital encephalocele (Q01.2)

Herniation of brain tissue, usually covered by meninges, through an opening in the occipital bone. [2]

Occipital Encephalocele Occipital Encephalocele
  Parietal encephalocele (Q01.80)

Herniation of brain tissue, usually covered by meninges, through an opening in one of the parietal bones. [4]

Parietal Encephalocele Parietal Encephalocele
  Orbital encephalocele (Q01.81)

Herniation of brain tissue, usually covered by meninges, through one of the orbits. [3]

Orbital Encephalocele Orbital Encephalocele
  Nasal encephalocele (Q01.82)

Herniation of brain tissue, usually covered by meninges, through an opening in the nasal region. [5]

Nasal Encephalocele Nasal Encephalocele

Spina Bifida

  Cervical spina bifida

Most cases of cervical spina bifida will eventually develop hydrocephalus, although this may not be immediately obvious at birth; therefore, coding for cervical spina bifida with or without hydrocephalus could be difficult at birth. Close follow-up of these neonates is important for consideration of shunt surgery. [2]

Cervical Spina Bifida Cervical Spina Bifida Cervical Spina Bifida Cervical Spina Bifida
  Cervical spina bifida with hydrocephalus (Q05.0)

Protrusion of meninges and/or spinal cord through an opening in the cervical region of the spine, associated with hydrocephalus. It may be open, with or without membrane covering; or closed, covered by normalappearing skin. Hydrocephalus is present as a result of obstruction to the flow of cerebrospinal fluid, secondary to the hindbrain herniation associated with Chiari II malformation.

Cervical spina bifida with hydrocephalus
  Cervical spina bifida without hydrocephalus (Q05.5)

Protrusion of meninges and/or spinal cord through an opening in the cervical region of the vertebral column. It may be open, with or without membrane covering; or closed, covered by normal-appearing skin.

Cervical spina bifida without hydrocephalus
  Thoracic spina bifida

Most cases of thoracic spina bifida will eventually develop hydrocephalus, although this may not be immediately obvious at birth; therefore, coding for thoracic spina bifida with or without hydrocephalus could be difficult at birth. Close follow-up of these neonates is important for consideration of shunt surgery. [2]

Thoracic Spina Bifida Thoracic Spina Bifida
  Thoracic spina bifida with hydrocephalus (Q05.1)

Protrusion of meninges and/or spinal cord through an opening in the thoracic region of the vertebral column, associated with hydrocephalus. It may be open, with or without membrane covering; or closed, covered by normal-appearing skin. Hydrocephalus is present as a result of obstruction to the flow of cerebrospinal fluid, secondary to the hindbrain herniation associated with Chiari II malformation.

Thoracic spina bifida with hydrocephalus
  Thoracic spina bifida without hydrocephalus (Q05.6)

Protrusion of meninges and/or spinal cord through an opening in the thoracic region of the vertebral column. It may be open, with or without membrane covering; or closed, covered by normal-appearing skin.

Thoracic spina bifida without hydrocephalus
  Lumbar spina bifida

Some cases of lumbar spina bifida will eventually develop hydrocephalus, and this may not be immediately obvious at birth; therefore, coding for lumbar spina bifida with or without hydrocephalus could be difficult at birth. Close follow-up of these neonates is important for consideration of shunt surgery. [2, 6]

Lumbar Spina Bifida Lumbar Spina Bifida Lumbar Spina Bifida
  Lumbar spina bifida with hydrocephalus (Q05.2)

Protrusion of meninges and/or spinal cord through an opening in the lumbar region of the vertebral column, associated with hydrocephalus. It may be open, with or without membrane covering; or closed, covered by normalappearing skin. Hydrocephalus is present as a result of obstruction to the flow of cerebrospinal fluid, secondary to the hindbrain herniation associated with Chiari II malformation.

Lumbar spina bifida with hydrocephalus
  Lumbar spina bifida without hydrocephalus (Q05.7)

Protrusion of meninges and/or spinal cord through an opening in the lumbar region of the vertebral column. It may be open, with or without membrane covering; or closed, covered by normalappearing skin.

Lumbar spina bifida without hydrocephalus
  Sacral spina bifida

Few cases of sacral spina bifida will develop hydrocephalus, compared with the other types of spina bifida. The presence of hydrocephalus in infants with sacral spina bifida may not be immediately obvious at birth; therefore, coding for sacral spina bifida with or without hydrocephalus could be difficult at birth. Close follow-up of these neonates is important for consideration of shunt surgery. [2]

Sacral Spina Bifida Sacral Spina Bifida
  Sacral spina bifida with hydrocephalus (Q05.3)

Protrusion of meninges and/or spinal cord through an opening in the sacral region of the vertebral column, associated with hydrocephalus. It may be open, with or without membrane covering; or closed, covered by normalappearing skin. Hydrocephalus is present as a result of obstruction to the flow of cerebrospinal fluid, secondary to the hindbrain herniation associated with Chiari II malformation.

Sacral spina bifida with hydrocephalus
  Sacral spina bifida without hydrocephalus (Q05.8)

Protrusion of meninges and/or spinal cord through an opening in the sacral region of the vertebral column. It may be open, with or without membrane covering; or closed, covered by normal-appearing skin.

Sacral spina bifida without hydrocephalus

 

  1. Source: adapted, with permsiion from the publisher, from Botto et al. N. Engl. J. Med. 1999;341:1509–19.
  2. Photograph source: courtesy of CDC-Beijing Medical University collaborative project.
  3. Photograph source: courtesy of Jaime Frías, MD, USA.
  4. Photograph source: courtesy of Registro Nacional de Anomalías Congénitas Argentina (RENAC), Centro Nacional de Genética Médica, ANLIS, Ministerio de Salud de la Nación.
  5. Photograph source: courtesy of Estudio Colaborativo Latino Americano de Malformaciones Congénitas (ECLAMC).
  6. Photograph source: courtesy of Idalina Montes, MD and Rafael Longo, MD, FACS, Puerto Rico.

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