Group 12: Neural Tube Defect


       Neural tube defects (NTDs) are a group of disorders that arise early in ...

       There are three types of NTDs :
           i.   Anencephaly
          ii.   Spina bifida
         iii.   En...
iii.   Ultrasonography
                    A diagnostic test.
                    98% accurate.
     After birth:
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Ntd Group 12


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Ntd Group 12

  1. 1. Group 12: Neural Tube Defect Definition  Neural tube defects (NTDs) are a group of disorders that arise early in fetal development and can cause life- long complications of varying severity  During the first 3-4 weeks of development, specific cells in an embryo curl up and their edges fuse together to form a narrow tube that becomes the foundation of the spinal cord, brain, and the bone and tissues that surround it  This neural tube fusing process usually is complete by 28 days of gestation – before many women even know that they are pregnant  If the tube does not close properly along its entire length, then a NTD will form at the open location Incidence  The true incidence of Neural Tube Defects appears to be decreasing in most parts of the world.  Estimates of rate approximate 0.2-0.4 per 1000 live births  Low socio-economic background  Race/Geographical location - eg: India, China, certain Hispanic subpopulation  Most common presentation of NTD: - Spina Bifida 55% - Anencephaly 45% - Encephalocele 5% Etiology of NTD • Anti-epilepsy medications • Folic acid deficiency • Folate antimetabolites (such as methotrexate) • Hyperthermia in early development • Insulin dependent diabetes melitus • Teratogens-arsenic, mycotoxins • Inherited with multifactorial pattern • Maternal weight and age Risk assessment a. Precise aetiology for the majority of these defects is unknown b. Multifactorial causation (partgenetic)  Family history(2-5% risk if one affected child)  Folate deficiency  Anti-epileptic drugs : Valproic acid, Tegretal  IDDM
  2. 2. Types  There are three types of NTDs : i. Anencephaly ii. Spina bifida iii. Encephalocele  Anencephaly : - Characterized by absence of large part of the brain and the skull. - Causes: failure of closure of the cephalic end of the neural tube - Features: - infants are born without a forebrain - The remaining brain tissue is often exposed; it is not covered by bone or skin  Spina bifida : - (a congenital malformation) in which there is a bony defect in the vertebral column - so that part of the spinal cord, which is normally protected within the vertebral column, is exposed - caused by : the failure of the neural tube to close during embryonic development - Types of SB : i. Spina bifida occulta (closed): 20% ii. Spina bifida manifesta (open): 80% o Meningocele: CSF only o Meningomyelocele( CSF+ Nerve fibers)  Encephalocele : - Is a severe birth defect - Caused by incomplete development of the skull that subsequently allows part of the brain to protrude through the hole in the skull - Babies with encephalocele ordinarily don't survive very long after birth, and if they do survive, they usually are severely mentally retarded Diagnosis  Can be done prenatal or after birth  Prenatal screening: i. Measuring maternal serum alpha fetoprotein(AFP)  This is the first prenatal screening done at 15-20 weeks of gestation.  AFP is the major serum protein in early embryonic life. It is believed to be involved in preventing fetal immune rejection and is first made in the yolk sac and then later in the GI system and liver of the fetus.  AFP goes from the fetal blood stream to the fetal urinary tract, where it is excreted into the maternal amniotic fluid. It can also leak into the amniotic fluid from open neural tube defects in which the fetal blood stream is in direct contact with the amniotic fluid.  Concentration of more than 1000 ng/mL is indicative for NTD (normal:500 ng/mL)  More than 75% accurate.  Determining precise gestational age is essential because fetal AFP levels are age specific and can peak in a normal fetus at 12-15 weeks' gestation. ii. Measuring AFP in amniotic fluid (amniocentesis)  A diagnostic test.  More accurate especially at 15-20 weeks of gestation.  Detects approximately 98% of all neural tube defects.
  3. 3. iii. Ultrasonography  A diagnostic test.  98% accurate.  After birth: i. Physical exam ii. Spine X-ray iii. CT or MRI Treatment  In utero: Surgery  Covering the neural placode with skin to decrease the damage inflicted to the exposed neural structures by amniotic fluid.  Closure of neural placode to decrease loss of CSF.  After birth:  Depends on the type of spina bifida.  Spina bifida occulta usually requires no treatment as it causes no symptoms  Spina bifida manifests require surgery often within the first 24 to 48 hours: - To protect the exposed spinal cord. - Help preserve whatever nerve function the baby has. - Help prevent infection of the exposed nerves and other tissues. Prognosis  Depends on the nature of the defect and associated malformation  Infections  Associated motor and sensory problems, particularly lower limb  Associated learning disability, developmental delay and hearing impairment  Bladder and bowel dysfunction Prevention  Periconceptional folic acid supplementation can prevent most neural tube defects if widely used. Supplementation must begin before conception for it to be effective.  To prevent first occurrence, women who are planning to become pregnant should take 400mcg folic acid daily before conception and during first 12 weeks of pregnancy. To prevent recurrence, 5mg/day folic acid should be taken.  Food fortification with the addition of folate to grain products is considered the most effective method of ensuring adequate intake of folic acid in pregnant women.