Neural tube defects

Neural tube defects

Definition NTDS are serious birth defects caused by the incomplete closure of the neural tube very early in pregnancy. By definition, the neural tube is a bundle of nerves or a thin sheath that eventually closes to form the brain at its anterior end and spinal cord at its posterior end. This closure should occur around the 28th day after conception, failing which parts of the brain or spinal cord do not form properly and fail to function.

The most common forms of NTDs or neural tube defects are spina bifida, characterized by incomplete development of spine, brain and/or meninges and anencephaly, characterized by absence of a cranial bones. Without protection of cranial bones neural tissue/brain washes and remnant brain tissue remains.

Incidence

NTD affects 2.6 percent per 1000 of birth, with spina bifida and anencephaly accounts for 95 % of all NTD

Cause

Folic acid (vit B9 ) deficiency is cause of neural tube defects in majority of cases. Supplementation of Folic acid in preconeception and first few few months of pregnancy can prevents these defects. No wonder NTD'S are most prevelent in low socio-economic strata.

Diagnosis

Most NTDs can be detected during pregnancy by one of three different prenatal tests:

1. Maternal Serum Alpha Fetoprotein (MSAFP), a screening test that is performed on a pregnant woman's blood at approximately 16-18 weeks of pregnancy
   
   
2. High Resolution Ultrasound, which may detect an NTD visually after approximately 18 weeks of pregnancy. Some severe forms of NTDs such as anencephaly may be detected earlier than 16 weeks
   
   
3. Amniocentesis, a test that samples the amniotic fluid (fluid that surrounds the baby) after 15 weeks of pregnancy.
   

MSAFP are costly test while amniocentesis

is invasive test and carries risk of abortion. Ultrasound is noninvasive,safe cheap procedure which can be done after 12 weeks to rule out acrania and 16-18 weeks for anencephaly. Anencephaly is associated with polyhdroaminos due to loss of control by pituitary.

Frog eye sign or Mickey mouse sign is due to bulging eye and loss of brain tissues.

Residual brain tissue can be seen.