Embryology: neural tube closure: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Embryology: neural tube closure

Sample item

A fetus at 20 weeks has an absent cranial vault, with raised maternal serum alpha-fetoprotein and polyhydramnios. Which developmental event failed, and what is the mechanism of the polyhydramnios?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Closure of the cranial neuropore in the fourth week; impaired fetal swallowing

Anencephaly results from failure of the cranial neuropore to close at about day 25. The fetus cannot swallow adequately because of the absent brainstem control, so amniotic fluid builds up, and the exposed neural tissue leaks alpha-fetoprotein into the amniotic fluid and maternal serum. Periconceptional folic acid reduces the risk.

Option by option

  • A. Closure of the caudal neuropore; leak of fluid through the placental membrane

    Caudal neuropore failure gives a lumbosacral defect, and the placenta does not cause the fluid excess.

  • B. Closure of the cranial neuropore in the fourth week; impaired fetal swallowing (correct)

    Correct. Cranial neuropore failure causes anencephaly, and defective swallowing causes polyhydramnios.

  • C. Closure of the caudal neuropore in the fourth week; fetal polyuria

    Caudal neuropore failure causes spina bifida, and polyhydramnios is not due to polyuria here.

  • D. Fusion of the neural crest cells in the sixth week; increased fetal urine output

    Neural crest cells are not fused in the neural tube closure, and urine output is not increased.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is B, Closure of the cranial neuropore in the fourth week; impaired fetal swallowing. Anencephaly results from failure of the cranial neuropore to close at about day 25.

Why is "Closure of the caudal neuropore; leak of fluid through the placental…" not the answer?

Caudal neuropore failure gives a lumbosacral defect, and the placenta does not cause the fluid excess.

Why is "Closure of the caudal neuropore in the fourth week; fetal polyuria" not the answer?

Caudal neuropore failure causes spina bifida, and polyhydramnios is not due to polyuria here.

Why is "Fusion of the neural crest cells in the sixth week; increased fetal u…" not the answer?

Neural crest cells are not fused in the neural tube closure, and urine output is not increased.

What concept does this question test?

It tests Embryology: neural tube closure in Anatomy. The fetus cannot swallow adequately because of the absent brainstem control, so amniotic fluid builds up, and the exposed neural tissue leaks alpha-fetoprotein into the amniotic fluid and maternal serum. Periconceptional folic acid reduces the risk.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Embryology: neural tube closure?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.