Neural tube defects

A neural tube defect (NTD) refers to incomplete closure of the neural tube in very early pregnancy. 

 The neural tube comprises of a bundle of nerve sheath which closes to form brain at the anterior end and spinal cord at posterior end. The closure should occur at around the 28^th day of conception failing which brain or spinal cord doesn't form properly.

Most common form of neural tube defects are 

• spina bifida 
• anencephaly / exencephaly

Spina bifida can involve the spine, brain and / or meninges while anencephaly is absence of cranial bones.

Other rare types include

• iniencephaly

Epidemiology

Neural tube defects affect approximately 2 -  5 per 1000 pregnancies with spina bifida and anencephaly accounting for 95% of these ^{reference required}.

Pathology

Causes

Folic acid deficiency is a major cause of anencephaly. By giving supplementation of Folic acid in early pregnancy this defect can be prevented. It is more prevalent in developing countries and in mothers of low socio-economic status.

Associations

• maternal diabetes *

Markers

• elevated materal serum alpha-fetoprotein (MSAFP) levels 
• elevated amniotic fluid acetylcholinesterase (AChE) levels : in an open neural tube defect  ³

Radiographic features

These are different for each entity and best discussed under each sub type.

Diagnosis

Most neural tube defects can be diagnosed by one of the following tests

• maternal serum alpha fetoprotien (MSAFP) : a screening test performed in the pregnant woman serum during 16 - 18 weeks of pregnancy (elevated)
• amniocentesis : invasive procedure, performed during 15 weeks of pregnancy
• antenatal ultrasound : allows detection of anencephaly / acrania at 12 weeks of pregnancy

Treatment and prognosis

Both the management and prognosis is heavily dependent on the type of neural tube defect. The risk for a subsequent pregnancy is thought to be ~ 5 - 10 %.