Normal neural tube closure process
The formation of the embryonic nervous system includes critical stages during which the neural tube neuropores close. This process proceeds in strictly defined directions and involves different parts of the embryo.
Normally, there are two major events:
- Closure of the anterior neuropore: the neural tube opening located at the anterior (cranial) end of the embryo must fully close.
- Closure of the posterior neuropore: a similar process occurs at the posterior end of the embryo, where the opening must also seal completely.
Any disruption in these processes leads to severe anatomical defects.
Anterior (cranial) end defects
If the anterior neuropore remains open and fails to close on time, a severe anomaly develops — anencephaly (Anencephaly).
The main characteristic of this malformation is the absence of telencephalic structures in the fetus. This disorder is one of the most well-known neural tube defects. According to statistics, this embryogenesis failure is recorded with a frequency of 0.1% of all pregnancies.
Posterior end defects
Disorders in the posterior neuropore region lead to the development of a pathology known as Spina bifida (specifically in the form of myelomeningocele).
The mechanism of this malformation can develop according to two scenarios:
- The posterior neuropore initially remains open.
- The opening closes successfully, but then undergoes reopening.
As a result of these disorders, a characteristic clinical picture is formed — a cystic spinal cleft.
Comparative characteristics of defects
For easier memorization, the main differences between the pathologies are presented in the table below:
| Sign | Anencephaly | Spina bifida (Myelomeningocele) |
|---|---|---|
| Localization of failure | Anterior end (cranial region) | Posterior end |
| Nature of the disorder | Neuropore remains open | Neuropore is open or reopens |
| Main manifestation | Absence of the telencephalon | Cystic spinal cleft |
Briefly: answers to topical questions
Which vitamin deficiency increases the risk of neural tube defects?
The risk of neural tube defects increases with folic acid deficiency.
To prevent this fetal pathology, patients are recommended supplementation (additional intake) of this vitamin:
- Folic acid — prescribed to women planning pregnancy and pregnant women (first 12 weeks) at a dose of 400–800 mcg per day.
- Folic acid — prescribed at a dose of 4 mg/day when taking valproic acid and carbamazepine, which additionally increase the risk of neural tube defects.
PAK-ZAS: Anterior (Peredny) — Anencephaly (Telencephalon), Posterior (Zadny) — Spina bifida.
Class and exam questions
What normally happens to the anterior neuropore?
During normal embryogenesis, the anterior neuropore at the rostral end of the embryo closes completely.
What is the anatomical essence of anencephaly?
This is a malformation in which the anterior neuropore remains open, leading to the absence of the telencephalon in the fetus.
What are the mechanisms of Spina bifida development?
The pathology occurs if the opening at the posterior end of the embryo fails to close, or if it reopens after initial closure.
How common is anencephaly?
According to statistics, this anterior neuropore pathology occurs in 0.1% of all pregnancies.
What else to study on this topic
- Normal stages of telencephalon formation
- Mechanisms of secondary reopening of the posterior neuropore
- Clinical manifestations of myelomeningocele
- Critical periods of nervous system embryogenesis
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