This was a 2nd gravida lady of age 28 years , without history of consanguinity. She was referred for a 2nd opinion for anencephaly . She was in her 18th week of gestation.
The following images were obtained .
Anencephaly is the most severe form of neural tube defect and is lethal.
Embryologically , it is failure of closure of rostral neuropore.
Depiction of various waves of neural tube closure in human embryos. There are thought to be at least five waves of closure in normal human embryogenesis. Anencephaly is thought to represent failure of Wave 2, myelomeningocele a failure at the junction of Waves 4 and 5 (representing the junction of primary and secondary neurulation). From Gilbert SF, 2003.
Anencephaly is recognised as failure of development of skull vault. The underlying brain tissue is disorganised, often asymmetric and incompletely formed.
From when can we identify by ultrasound ?
From 12 weeks onwards – Ossification of the skull vault is normally present from 12 weeks of gestation and anencephaly should not be diagnosed before this time.
The sequence of events could be exencephaly or arcania ( where the skull vault is absent with cerebral tissue present ) in the earlier stages and later anencephaly ( where the apart from the absent skull vault, the cerebral tissue is disorganised ).
ROLE OF FOLIC ACID:
The cause of anencephaly is disputed.
Folic acid has been shown to be important in neural tube formation since at least 1995, and as a subtype of neural tube defect, folic acid may play a role in anencephaly. Studies have shown that the addition of folic acid to the diet of women of child-bearing age may significantly reduce, although not eliminate, the incidence of neural tube defects. Therefore, it is recommended that all women of child-bearing age consume 0.4 mg of folic acid daily, especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%. It is not advisable to wait until pregnancy has begun, since, by the time a woman knows she is pregnant, the critical time for the formation of a neural tube defect has usually already passed. A physician may prescribe even higher dosages of folic acid (4 mg/day) for women having had a previous pregnancy with a neural tube defect.
Studies show that a woman who has had one child with a neural tube defect such as anencephaly has about a 3% risk of having another child with a neural tube defect,as opposed to the background rate of 0.1% occurrence in the population at large.Genetic counseling is usually offered to women at a higher risk of having a child with a neural tube defect to discuss available testing.
It is known that people taking certain anticonvulsants and people with insulin-dependent diabetes have a higher risk of having a child with a neural tube defect.
Anencephaly and other physical and mental deformities have also been blamed on a high exposure to such toxins as lead, chromium, mercury, and nickel.
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