Neural Tube Defects

Neelam Maurya

8 years ago

INTRODUCTION

Deformities involving CNS covering
Vary in severity – from the simples Spina Bifida Aperta (incomplete fusion of vertebral arches)
Extreme Forms; Anencephaly and Raquischisis where wide openings in cranial and vertebrae bones also absence of brain, nerves and meninges
Most malformation especially NTD’S occur early embryogenesis – are likely aberrant expression of yet undefined developmental gene.
CNS develops in a precise embriologic sequence; therefore interruption of one area affects remaining development.
NTD’S – mainly embryologic induction disorder failure to properly form mesoderm-neuroectoderm.
Primary defect = failure of Neural tube to close affecting neural-cutaneus ectodermal structures.
Inciting events traced to 17-30 days gestation.
Primary defect – failure of neural folds to fuse in midline and form neural tube (Neuroectoderm)
Also maldevelopment of mesoderm (forms skeletal and muscular structures that cover neural structures)
Defects can be open (communicateatmosphere) or closed (skin covered).
They can be ventral or dorsal

EMBRYOLOGY:

2 processes form the C.N.S.

Neurulation – formation o neural structures into a tube thereby forming brain – spinal cord
Neurulation – formation lower spinal cord lumbar and sacral elements.
First Neural plate at 17 days, then neuronal fold at 21 days and fusion of n. folds at 23 days.
Any disruption in this 3 stages = Craniorachischisi (most severe form NTD)

ETIOLOGY:

Teratogens-(hyperthermia, sulfas,antihistaminics, nutrition deficiencies and anticonvulsivants use)
Most strongly tied = carbamazepine, valproic acid (folate antagon)
Folate deficiency

ANENCEPHALY:

One of the most common – no survival possible.
Absence of calvarium, posterior bone elements and deficiency in procencephalus.
The pituitary gland is often absent or hypoplastic
Facial presentation,Shoulder dystocia,Prematurity, Increased alpha-fetoprotein & Polyhydramnios
Marked diminution of the size of the adrenal glands probably secondary to the absence of the pituitary gland.
About 70% of anencephalic fetuses are females

SPINA BIFIDA OCCULTA:

Mildest form, one or more vertebrae (usually L5 and S1) are not closed but no protrusion of spinal cord.
Could be associated with Syrinomelia or tethered cord.
Most common birth defect in north India is Neural tube defects (Spina bifida)
Banana sign seen in the fetal brain
17% of population – most asymptomatic – just skin dimple with hair or discoloration over lumbar area.
Outer part of vertebrae not completely joined.
Spinal cord and covering (meninges) usually undamaged.
Hair often at site of defect

MENINGOCELE:

MYELOMENINGOCELE :

Outer part of vertebrae split. Spinal cord and meninges damaged and displaced through opening. Usually hydrocephalus
Saccular protrusion containing neural placode and CSF.
Surface covered by arachnoid but no dura nor skin.
The sac appears yellow with fragile vessels.
Nerve roots pass into the sac.
Spine tethered by bony defect

LARGE OCCIPITAL ENCEPHALOCELE:

DIAGNOSIS:

In the first half of pregnancy:

Around 10 week

Absence of cranial vault
Angiomatous, brain tissue.
Accurate ancephaly diagnosis
↑MSAFP :Open neural tube defects(15–20 weeks)
Neural tube defects are associated with high levels of Acetylcholinesterase.
In the latter half of pregnancy
Diagnosis is difficult especially when associated with hydramnios.
Inability to locate the fetal head on abdominal palpation arouses the suspicion.
Confirmation is done by sonography

COMPLICATIONS:

Hydramnios (70%),
Malpresentation—face or breech
Premature labor, especially when associated with hydramnios,
Tendency of postmaturity,
Shoulder dystocia,
Obstructed labor if the head and shoulders try to engage together because of short neck.

MANAGEMENT:

If confirmed before 20 weeks: Termination of pregnancy is to be done.
If diagnosed in late pregnancy:Termination is to be done.
Uterus is most often refractory to oxytocin as a result of insufficient production of its precursor cortisol from fetal adrenals.
Use of prostaglandin vaginal gel (PGE2) h
During labor, there is tendency of delay.
Shoulder dystocia should be managed by cleidotomy.

PREVENTION:

Folic acid supplementation beginning 1 month before conception to about 12 weeks of pregnancy has reduced the incidence of NTD significantly (85%).
A dose of 4 mg daily is recommended.
Risk of recurrence is about 2% in subsequent pregnancy.

Exam Question

Pre-conceptional intake of Folate results in decrease in incidence of neural tube defect
Myelomeningocele, Anencephaly & Encephalocele are neural tube defect
↑Acetylcholinesterase is a marker for neural tube defects
Acetylcholinesterase is the Most useful maternal serum test used for distinguishing open neural tube defects and ventral wall defect in a fetus
Sodium valproate causes open neural tube defect
Neural tube defects are Multifactorial
Facial presentation, Increased alpha-fetoprotein & Polyhydramnios are seen in anencephaly
Anencephaly is best diagnosed using USG
Most common presentation in anencephaly is Face
Banana sign seen in the fetal brain Spina bifida
Most common birth defect in north India is Neural tube defects (Spina bifida)
Widened neural foramen can be seen in MRI/CT appearance of lateral meningocele
Sonographic finding of Spina bifida Ventriculomegaly & Obliteration of cisterna magna
Anencephaly can be diagnosed in first trimester by ultrasound
Neural tube defect is best detected by Amniocentesis
Commonest site of meningocele is Lumbosacral
Accurate diagnosis of anencephaly on ultrasound can be done at 10 weeks of gestation
Shoulder dystocia is seen predominantly in Anencephaly

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