Neural Tube Defects

Objective :• Definition• Types• Causes• Detection• Prevention• Treatment

Embryology• The spinal cord begin developing in the third week of pregnancy from a flat piece of tissue called the

"neural plate". • The neural tube start as the neural plate ,which develops a groove in the middle called neural

groove.• It gradually deepens until it is completely separated from the surface ,that is the ectoderm.• Anterior neuropore closure – 25th day• Posterior neuropore closure – 27th day• This process is completed by the 28 th day of gestation

Definition• Neural tube defects (NTDs) are serious birth defects with symptoms that range from mild to severe

impairment. They are caused by incomplete development of the brain, spinal cord and/or their protective coverings.

• This neural tube fusing process usually is complete by 28 days of gestation.• Error in this fusing will result in a neural tube defect

Epidemiology• NTDs are among the most common birth defects.• They exhibit a marked geographical variation, with the incidence higher in Great Britain and lower

in Japan.• In white populations, the lowest birth incidence was noted in mainland Europe and the highest in

Great Britain (especially Ireland).• Currently, the highest reported incidence is in Northern China (3.7 cases per 1000 live births).• Indian and Eastern Mediterranean populations (with the exception of Israeli Jews) also have

relatively high incidences of NTDs. However, unlike the Western white populations, anencephaly is more common than spina bifida.

Risk factors• Pregnant women who are taking medication for epilepsy.• women with folic acid deficiencies • Race/geographical location:

certain Hispanic subpopulations, and among population groups in Ireland, China, and the United Kingdom.

• Maternal insulin-dependent diabetes mellitus • Maternal weight ,age• Maternal hyperthermia (i.e., exposure to high temperatures early in pregnancy, such as hot tub use or

high fever)

• Previous NTD-affected pregnancy

Types of NTD

• Anencephaly• Encephalocele• Hydranencephaly• Iniencephaly• Spina Bifida

– Spina Bifida Manifesta– Spina Bifida Occulta

1- Anencephaly• Means “without head”, foetus will be in an acranial state• Results from a neural tube defect that occurs when the cephalic (head) end of the neural tube fails to

close resulting in the absence of a major portion of the brain, skull, and scalp• Foetus will not gain consciousness due to the loss of the cerebrum that controls cognitive activities

and will be incompatible with life

2- Encephalocele

• It is a neural tube defect characterized by sac-like protrusions of the brain and the membranes that cover it through openings in the skull.

• Usually occipital, also called high spina bifida• Sometimes, associated with other conditions like multicystic kidneys or polydactyl

3- Hydranencephaly• This occurs when the cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal

fluid.• An infant with hydranencephaly may appear normal at birth or may have some distortion of the skull

and upper facial features due to fluid pressure inside the skull.• People will hydranencephaly will suffer from visual impairment, lack of growth, deafness, blindness,

paralysis, and intellectual deficits.

4- Iniencephaly

• Combines extreme retroflexion (backward bending) of the head with severe defects of the spine.• The neck is usually absent• Incompatible with life due to deformity of the body

5- Spina bifida• Failure of the laminae of the vertebrae to fuse together (the vertebral arches are absent)• Usually occurs in the lumbosacral region• Has two types:a) Spina bifida occultab) Spina bifida manifesta

a) Spina bifida occulta

b) Spina bifida manifesta• Manifesta means “open or shown”• Consists of two main appearances:

- Meningocele: cerebrospinal fluid only- Meningomyelocele: cerebrospinal fluid and nerve tissue

Element Meningocele MeningomyeloceleDefinition Fluid-filled sac with meninges involved but

neural tissue unaffected (cele means sac)Meninges and spinal tissue protruding through a dorsal defect in the vertebrae

Prognosis Least common form and least hazardous Most grave form

Types Dermal sinusLipoma of the cordDiastematomyeliomaThickened Filum TerminalThetered cord

MeningoceleMeningomyelocele

Investigation• Blood test• Ultrasound• Amniocentesis

Blood test :o Measures the level of maternal serum alpha fetoprotein (MSAFP) o Alpha-fetoprotein (AFP) is made naturally by the fetus and placenta.o But if abnormally high levels of this protein appear in the mother’s bloodstream it may indicate that the fetus has a NTD.o It is not a diagnostic tool, only serve as screening test.

Ultrasound : o Reliable tests for neural tube defecto Can be done in second trimester cause that’s when usually most of the symptoms of NTD exhibit

themselves

Amniocentesiso Indicates the level of amniotic fluid α-fetoprotein(AFAFP)o Normally, small amount of AFAFP is found.o When an open NTD is present, the amniotic fluid contains an elevated amount of AFP because the skin surrounding the baby's spine is gone and AFP leaks into the amniotic sac.

Prevention• There is no single cause of NTD nor any known way to prevent it entirely. • However, dietary supplementation with folic acid has been shown to be helpful in reducing the risk

of NTDs

Folic Acid • Sources: dark green vegetables, egg yolks, and some fruits. • Dosage: 0.4 mg/day (at least 3 months before conception &for the first 12 weeks of pregnancy)• Women who have already had a baby with a NTD, or are taking anticonvulsant medication should

take a higher dose of 4–5 mg/day

Treatment Medical care

The newborn with an open NTD should be kept warm and the defect covered with a sterile wet saline dressing. The patient should be positioned in the prone position to prevent pressure on the defect.

Surgical Careo The newborn with an open NTD should undergo prompt closure of the defect. The closure involves

classic neurosurgical techniques.o Children with hydrocephalus also should have a ventriculoperitoneal shunt placed at the time of

myelomeningocele closure.o Patients presenting with symptomatic Chiari malformations should undergo suboccipital craniotomy

and decompression of the posterior fossa and tonsils.o Children with syrinx need a laminectomy and placement of a syringosubarachnoid stent to divert the

CSF out of the central canal.

Done by Group 2