neural tube defect


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defect

 [de´fekt]
an imperfection, failure, or absence.
congenital heart defect see congenital heart defect.
aortic septal defect see aortic septal defect.
atrial septal defect see atrial septal defect.
filling defect an interruption in the contour of the inner surface of stomach or intestine revealed by radiography, indicating excess tissue or substance on or in the wall of the organ.
neural tube defect see neural tube defect.
septal defect a defect in the cardiac septum resulting in an abnormal communication between opposite chambers of the heart. Common types are aortic septal defect, atrial septal defect, and ventricular septal defect. See also congenital heart defect.

neural

 [noor´al]
pertaining to a nerve or to the nerves; called also nervous.
neural tube defect a congenital defect in closure of the bony encasement of the spinal cord or of the skull. The most severe defects are a fissure along the entire length of the spinal column that leaves the meninges and spinal cord exposed (rachischisis), or herniation through the skull of a saclike structure containing brain tissue and meninges (encephalocele). anencephaly is a major defect in which the brain is absent and there is only an exposed vascular mass with no bony covering.

Classification and nomenclature of spinal column defects are based on the extent to which the meninges and spinal cord are involved. spina bifida refers to abnormal closure with or without visible protrusion of the meninges and spinal cord through the cleft in the spinal column. If there is no visible protrusion, the condition is called spina bifida occulta. An external protrusion consisting of a saclike structure is called spina bifida cystica. Two subtypes of spina bifida cystica are meningocele, which involves the meninges surrounded by spinal fluid, and myelomeningocele (or meningomyelocele), in which the sac contains meninges, spinal fluid, and a portion of the spinal cord with its nerves.

Developmental defects of the neural tube tend to run in families and are believed by most authorities to occur during early development of the embryo. Prenatal detection of some major open neural tube defects is possible through ultrasonic scanning of the uterus and laboratory evaluation of the amniotic fluid. In the presence of anencephaly and meningomyelocele there are elevated concentrations of alpha-fetoprotein in the amniotic fluid.

Genetic predisposition to neural tube defects is inheritable; thus family history is significant in predicting the risk of recurrence. For example, a couple who has had one child with such a defect has a one in twenty (5 per cent) probability of having a second child with the disorder. The risk is doubled to one in ten (10 per cent) if two of their children are so affected. Siblings of an affected child who are themselves normal are at greater than average risk of producing a child with a similar problem.
Treatment. Immediate care of the neonate with a neural tube defect includes prevention of infection and assessment of neurological involvement. Later, an orthopedic assessment is done to identify problems related to locomotion. Corrective procedures such as casting, bracing, and traction are indicated if there is hope for some functioning of the lower extremities. Associated anomalies of the hip, knee, and foot may require correction by orthopedic surgery.

Meningoceles usually are repaired to prevent infection, especially if there is danger of rupture of the sac. Most authorities recommend closure within the first 24 to 48 hours after birth. However, authorities do not agree on whether an attempt should be made to perform skin closure over a myelomeningocele. If hydrocephalus develops, the treatment of choice is a ventriculoperitoneal shunt or some other procedure to drain spinal fluid and decompress the fluid-filled ventricles.

Bowel and bladder dysfunction usually occur as a result of myelomeningocele. Management of neurogenic bladder and incontinence includes preventing urinary stasis and infection and providing some means for collecting urine. Fecal incontinence may be amenable to bowel training and modification of the diet. In some children a colostomy is the most desirable way to handle the problem.
Patient Care. Immediate concerns in the care of the newborn with a neural tube defect center on protection of the fragile sac from trauma and infection, observation for complications, and support and guidance for parents and family members. Positioning before and after surgery is critical. Preoperatively, the goal is to minimize tension on and trauma to the sac. The baby may be placed in a prone position with head slightly lower than body to reduce spinal fluid pressure in the sac. The hips are slightly flexed to relieve tension on the spine. After surgery, it may be desirable to elevate the head because of increased intracranial pressure and impending hydrocephalus. Many surgeons allow a side-lying position postoperatively because of diapering and feeding problems associated with the prone position. The variety of allowable positions permits frequent position changes to avoid pressure sores. As soon as the operative site is sufficiently healed, the baby can be held for feeding and receiving the body contact every neonate needs. If a baby with inoperable myelomeningocele cannot be held and cuddled, stroking, fondling, and other comfort measures can be used to meet the need for tactile stimulation.

Long-term care will depend on the specific orthopedic, urologic, and neurologic problems each child has. Patients will require continued guidance and support. Comprehensive care for the patient and family can only be provided by a coordinated team of health care providers, including physicians, nurses, physical therapists, rehabilitation specialists, and social workers. The familial tendency toward neural tube defects demands that genetic counseling be available to the family.

neural tube defect

n.
Any of various congenital defects of the brain and spinal cord, such as spina bifida, resulting from incomplete closing of the neural tube in an embryo.

neural tube defect (NTD)

any of a group of congenital malformations involving defects in the skull and spinal column that are caused primarily by the failure of the neural tube to close during embryonic development. In some instances the cleft results from an abnormal increase in cerebrospinal fluid pressure on the closed neural tube during the first trimester of development. The defect may occur at any point along the neural axis or extend the entire length of the spinal column, as in holorachischisis. The amount of deformity and disability depends on the degree of neural involvement, the most severe defect being complete cranioschisis, or the total absence of the skull and defective brain development. Other cerebral dysplasias resulting from the failure of the cranial end of the neural tube to fuse are meningoencephalocele and cranial meningocele. These defects, usually accompanied by severe mental and physical disorders, occur most often in the occipital region of the skull but may also occur in the frontal or basal regions. Most neural tube malformations are caused by incomplete fusion of one or more laminae of the vertebral column, with varying degrees of tissue protrusion and neural involvement. The two most common NTDs are spina bifida and anencephaly. Other NTDs include rachischisis, myelocele, myelomeningocele, and meningocele. In all of these conditions there is constant risk of rupture of the saclike protrusion and danger of meningeal infection. Often immediate surgical repair is necessary. Adequate folate levels during the first month after conception are important in preventing neural tube defects; the U.S. Public Health Service recommends that all women of childbearing age increase their folate intake to 400 mg per day. Many of the major neural tube defects can be determined prenatally by ultrasonic scanning of the uterus and by tests for the presence of elevated concentrations of alpha-fetoprotein levels in the amniotic fluid. Such diagnostic tests are preferably performed during the 14th to 16th week of gestation so that termination of the pregnancy is possible. See also anencephaly, Arnold-Chiari malformation, spina bifida cystica.

neural tube defect

Neurology Any of the congenital developmental defects of the CNS characterized by defective closure of the neural tube at one or more segments; NTDs range from asymptomatic to extreme–anencephaly with absent cranial vault and most or all of the cerebral hemispheres and spina bifida cystica attributable to multifactorial events and noxious environmental agents; NTDs occur in 1:1000-5000 live births, ♂:♀ ratio 2-3:1, with regional differences–eg, higher in Ireland–2-7% recurrence rate Clinical Cinercephaly, cephalocele, spina bifida, and myelodysplasia; failure to close neural tube at 4th-5th fetal wk Lab ↑ α-fetoprotein, detected in antenatal screening of maternal serum or amniotic fluid Prevention Multivitamins in early pregnancy ↓ risk of NTDs

neu·ral tube de·fect

(nūr'ăl tūb dē'fekt)
A birth defect that may be caused by a deficiency of folate early in pregnancy, characterized by incomplete midline fusion of the developing central nervous system.
References in periodicals archive ?
Apparent prevention of neural tube defects by periconceptional vitamin supplementation.
Relatives of people with a neural tube defect face higher risks of having a child with a neural tube defect than the general population.
Buccimazza SS, Molteno CD, Dunne TT, et al Prevalence of neural tube defects in Cape Town, South Africa.
The use of folic acid for the prevention of neural tube defects and other congenital anomalies.
The incidence rates (per 1000 conceptions resulting in live births) of each condition (open neural tube defects, cleft lip and palate, cardiac anomalies, and gastroschisis) was calculated for each season (spring, summer, autumn, and winter).
Even though taking folic acid every day is not a guarantee, it has been shown to reduce the risk of spina bifida and other neural tube defects (NTDs) by up to 75 percent.
The FSA and the chief medical officer can be confident in recommending that the UK Government introduce the mandatory fortification of flour, which could prevent about 400 pregnancies affected by neural tube defects each year.
Supplementing a woman's diet with folic acid reduces her chances of having a child with a neural tube defect.
I read with interest the recent report on Epidural Analgesia for Labour in a Patient with Neural Tube Defect (1).
1) An analysis of data from a population-based surveillance system indicates that in 1999 and 2000, the annual number of pregnancies in which a neural tube defect (a serious malformation of the spine or brain) was diagnosed prenatally was 27% lower than it had been in 1995-1996; similarly, the annual number of infants born with such defects was 26% lower than it had been in the earlier period.