Introduction:
The second most prevalent congenital abnormalities influencing the growth of the central nervous system in humans are neural tube defects (NTDs). While the exact cause of NTD remains unknown, several hereditary and environmental risk factors have been well documented. NTDs, traditionally classified into two primary subgroups (open and closed defects), have wildly varying prognoses, primarily based on the location of the lesion.
What Are Neural Tube Defects?
Major birth anomalies of the central nervous system, known as neural tube defects (NTDs), result from a malfunction in the neurulation phase (the generation of the neural tube, and it occurs by the completion of the fourth week of gestation) of embryogenesis. The location of the defect determines the type and severity of malformation since the migration and merging of the neural plate eventually forms the neural tube. It includes deformities of the brain and spinal cord.
Both sides of the fetus's spine, or backbone, typically come together during the first month of gestation to encircle and safeguard the spinal cord, spinal nerves, and meninges, or the tissues that cover the spinal cord. The neural tube is used at this stage to describe the developing brain and spine. The neural tube develops into the brain at the top and the spinal cord at the bottom as the development continues. An NTD occurs when the neural tube does not entirely seal anywhere throughout its whole length.
Open NTDs typically encompass various elements of the CNS. They are caused by an impairment of primary neurulation, resulting in the neural tube failing to close properly across the dorsal midline. The primary characteristic of open defects is the exterior projection or exposure of neural tissue. Approximately 80 % of NTDs are open NTDs, with meningocele (also known as spina bifida), myelomeningocele, encephalocele, and anencephaly being the most prevalent types.
Closed NTDs are caused by a deficiency in secondary neurulation and are restricted to the spine (occasionally affecting the brain). The defect is completely encased by epithelium, protecting the neural tissue. However, the skin around it may be abnormal.
What Is the Epidemiology of Neural Tube Defects?
Epidemiological research has shown that NTDs are caused by multiple factors. Regional variation, ethnic backgrounds, economic status, and genetic susceptibility have all been linked to variations in incidence. Anencephaly and spina bifida are the two most prevalent NTDs. About 1,500 babies in the United States are affected by spina bifida annually, with myelomeningocele constituting the most prevalent type. In the United States, anencephaly strikes roughly 1,000 babies annually.
What Are the Clinical Presentations of Neural Tube Defects?
Some examples of cranial manifestations are as follows:
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Anencephaly - A significant section of the brain, skull, and scalp is absent during the development of an embryo.
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Encephalocele(Meningocele or Meningomyelocele) - A neural tube defect called encephalocele is characterized by the brain's sac-like projections and the membranes covering them emerging through holes in the skull.
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Craniorachischisis Totalis - It is characterized by meninges and neural tissue herniation along with anencephaly and spina bifida throughout the spinal column.
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Congenital Dermal Sinus - A passageway that extends from the skin's outer layer into the deeper tissues and eventually enters the brain or spinal cavity.
Some examples of spinal presentations are as follows:
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Spina Bifida - A birth condition where the membranes surrounding the spinal cord and the spine do not fully close during the early stages of pregnancy.
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Diastematomyelia - A congenital condition characterized by a split in the spinal cord.
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Diplomyelia - The spinal cord's duplication distinguishes it.
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Caudal Agenesis - The absence of the sacrococcygeal bone characterizes it.
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Lipomyelomeningocele - A disorder known as lipomyelomeningocele occurs when the spinal cord and its membranes are attached to an abnormally large fat buildup.
What Signs of Neural Tube Defects Are Present?
Depending on the particular kind of abnormality, there are differences in the symptoms linked to NTDs.
Physical issues (such as paralysis and issues controlling one's bowels and urine), deafness, vision loss, cognitive impairment, unconsciousness, and, in rare instances, death are among the symptoms. Not all NTD sufferers exhibit any symptoms. With some NTDs, the majority of children either pass away or become severely disabled.
How to Diagnose Neural Tube Defects?
Medical professionals use the following tests for identifying neural tube defects (NTDs) before birth and after birth:
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Laboratory Test: Amniotic fluid, fetal plasma, and maternal serum can all be used to test maternal serum alpha-fetoprotein (MSAFP). Usually, it is evaluated at 16 to 18 weeks of pregnancy. The liver, gastrointestinal system, and fetal yolk sac produce a fetus-specific protein called MSAFP. Institutions interpret data differently, but generally speaking, anything two to three times higher than average (for a given gestational age) is deemed inappropriate. Nonetheless, various fetal and maternal factors may influence how the data are interpreted. An ultrasound exam is usually performed after abnormal MSAFP test results to check for potential NTD, the fetus's survival, and other information.
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Prenatal Ultrasound: Prenatal ultrasound screens for Neural Tube Defects (NTDs). All pregnant women should have access to ultrasound-based NTD screening. Its application in postnatal imaging has been restricted due to advancements in alternative imaging modalities.
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Magnetic Resonance Imaging in Neonates: When examining neural tissue and determining the nature of a newborn's defect, Magnetic Resonance Imaging (MRI) is the preferred method. Unless the infant has exceptional deficiencies unrelated to the open defect, this procedure is not generally carried out. This makes related malformations, both intraspinal and intracranial, visible.
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Computed Tomography: Direct inspection of the bone defect and structure is possible with a Computed Tomography (CT) scan. This examination can also identify the existence or non-existence of hydrocephalus or other cranial abnormalities, however, it is important to take into account the radiation exposure of young children from CT scans.
How Are Neural Tube Defects Managed Prenatally?
Parental considerations about fetal karyotyping and choosing to proceed with or end the pregnancy are necessary for the prenatal care of neural tube defects. When a mother's pregnancy continues and NTDs are discovered, she needs extensive counseling. This includes getting correct information about the likelihood of a recurrence and preparing the parents in case their kid dies at delivery or has a disability.
Early intervention has been made possible by advancements and a rise in the frequency of maternal screening (ultrasound and serum tests). Prior to 26 weeks of gestation, fetal surgery has been carried out to minimize the development of Arnold-Chiari malformations and, ultimately, hydrocephalus; fetal surgery for myelomeningocele can avert excessive CSF loss from the posterior region, thereby averting Chiari II malformation, hydrocephalus, and syringomyelia.
How Are Neural Tube Defects Managed in Newborns Postnatally?
The cornerstone of medical care for open Neural Tube Defects (NTDs) is neurosurgical intervention; closed NTDs usually do not require immediate surgery.
When a newborn has an open NTD, the abnormality should be treated with a sterile dressing of moist saline, and antibiotics for prophylactic reasons should be considered. The newborn should be kept warm. To avoid applying pressure on the deformity, the patient needs to be positioned prone (lying face down). For myelomeningocele, timely defect correction is recommended, ideally during the initial 72 hours of life. To create a neural tube that covers the open caudal end of the spinal cord with a layer of pia mater, the lateral margins of the open neural plate are approximated using traditional neurosurgery procedures.
During myelomeningocele closure, a ventriculoperitoneal shunt (a medical gadget that releases pressure that fluid buildup has placed on the brain) implantation should be taken into consideration for infants born with severe hydrocephalus (the accumulation of cerebrospinal fluid in ventricles in the brain).
Spinal cord tethering may result in gradual neurologic decline and is occasionally linked to myelomeningoceles or lipomeningocele. For patients with severe and increasing disabilities, which is indicated by growth and bending of the spinal column and stretching of the tethering cord, untethering treatments are necessary.
Conclusion:
NTDs are thought to be related to folic acid deficits, anti-seizure medications, and weight gain during pregnancy. Folate supplementation can reduce NTDs by 70 percent when taken before and continued during pregnancy. Preconception maintenance of a healthy BMI ought to be advised as well.
