Anemia of Prematurity - Portal Neonatal

Neural Tube Defects in the Neonatal Period
Last Updated: November 6, 2004
Synonyms and related keywords: NTD, spina bifida, myelomeningocele, meningocele, spina
bifida aperta, spina bifida cystica, spina bifida occulta, rachischisis, craniorachischisis, cranium
bifida, encephalocele, anencephaly, lipomeningocele, lipomyelomeningocele, occult spinal disorder,
dysraphism, embryologic induction disorder, Chiari malformation, CM
AUTHOR INFORMATION Section 1 of 11
Author: Richard G Ellenbogen, MD, Professor and Chairman, Theodore S Roberts Endowed
Chair, Chief of Neurological Surgery, Seattle Children's Hospital and Regional, Department of
Neurological Surgery, University of Washington School of Medicine
Richard G Ellenbogen, MD, is a member of the following medical societies: American Academy of
Neurological Surgery, and American College of Surgeons
Editor(s): Shelley C Springer, MD, MBA, MSc, Neonatologist, Assistant Professor of Pediatrics,
Department of Pediatrics, University of Wisconsin, Madison; Robert Konop, PharmD, Director,
Clinical Account Management, Ancillary Care Management; Brian S Carter, MD, Associate
Director, Associate Professor, Department of Pediatrics, Division of Neonatology, Vanderbilt
University Medical Center and Gateway Medical Center; Carol L Wagner, MD, Associate
Professor, Department of Pediatrics, Division of Neonatology, Medical University of South
Carolina; and Neil N Finer, MD, Director, Division of Neonatology, Professor, Department of
Pediatrics, University of California at San Diego
INTRODUCTION Section 2 of 11
Congenital deformities involving the coverings of the nervous system are called neural tube defects
(NTDs). NTDs vary in severity. The mildest form is spina bifida aperta, in which osseous fusion of
one or more vertebral arches is lacking without involvement of the underlying meninges or neural
tissue. A slightly more severe form of spina bifida, which is discussed in detail in this article, is
spina bifida cystica or myelomeningocele, in which a saclike casing is filled with cerebrospinal fluid
(CSF), spinal cord, and nerve roots that have herniated through a defect in the vertebral arches and
dura (see Image 1).
Anencephaly and rachischisis are extremely severe forms of NTD in which an extensive opening in
the cranial and vertebral bone exists with an absence of variable amounts of the brain, spinal cord,
nerve roots, and meninges. Anencephaly has been studied since antiquity, and an almost dizzying
array of synonyms and classifications exists. For a more complete description of anencephaly, see
the Bibliography for the seminal work written by Lemire, Beckwith, and Warkany in 1978.
Malformations of the brain and spinal cord may result from genetic mutation or may be acquired
deformities. Most malformations, especially those such as NTDs, occur early in embryogenesis and
are likely the result of aberrant expression of a yet undefined developmental gene or family of
genes. The nervous system develops in a precise temporal embryologic sequence; therefore, an
interruption of one part of the developmental sequence often affects remaining development.
The NTD discussed in this article is classified as an embryologic induction disorder. It results in
failure to properly form both the mesoderm and neuroectoderm. The primary embryologic defect in
all NTDs is failure of the neural tube to close, affecting neural and cutaneous ectodermal structures.
The inciting event can be traced to days 17-30 of gestation.
The precise etiology and the specific genes that may be involved during this abnormal neural
ontogenesis have not yet been elucidated. These deformities are not only disorders of embryologic
induction but also disorders of cellular migration and include the secondary mechanical
complications that occur with an unprotected nervous system. Specifically, the amniotic fluid can
have a caustic and destructive effect on the open neural structures.