Embryology: tetralogy of Fallot: 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: tetralogy of Fallot

Sample item

A cyanotic infant has a systolic ejection murmur and a boot-shaped heart on radiography. Echocardiography confirms tetralogy of Fallot. Which embryological defect underlies the four features?

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

The answer and the reasoning

B. Anterosuperior displacement of the infundibular (conal) septum

In tetralogy of Fallot the infundibular septum is displaced anteriorly and superiorly, which narrows the right ventricular outflow and creates a malaligned ventricular septal defect with an overriding aorta. Right ventricular hypertrophy follows from the outflow obstruction. Neural crest cell abnormalities are implicated in this misalignment.

Option by option

  • A. Failure of the endocardial cushions to fuse with the septum primum

    Failure of cushions to fuse with the septum primum causes an ostium primum atrial septal defect.

  • B. Anterosuperior displacement of the infundibular (conal) septum (correct)

    Correct. The displaced septum produces pulmonary stenosis, a VSD, an overriding aorta and right ventricular hypertrophy.

  • C. Failure of the truncal ridges to fuse to divide the truncus

    Failure of the truncal ridges to fuse causes persistent truncus arteriosus.

  • D. Failure of the aorticopulmonary septum to spiral

    Failure of the septum to spiral causes transposition of the great arteries.

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, Anterosuperior displacement of the infundibular (conal) septum. In tetralogy of Fallot the infundibular septum is displaced anteriorly and superiorly, which narrows the right ventricular outflow and creates a malaligned ventricular septal defect with an overriding aorta.

Why is "Failure of the endocardial cushions to fuse with the septum primum" not the answer?

Failure of cushions to fuse with the septum primum causes an ostium primum atrial septal defect.

Why is "Failure of the truncal ridges to fuse to divide the truncus" not the answer?

Failure of the truncal ridges to fuse causes persistent truncus arteriosus.

Why is "Failure of the aorticopulmonary septum to spiral" not the answer?

Failure of the septum to spiral causes transposition of the great arteries.

What concept does this question test?

It tests Embryology: tetralogy of Fallot in Anatomy. Right ventricular hypertrophy follows from the outflow obstruction. Neural crest cell abnormalities are implicated in this misalignment.

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: tetralogy of Fallot?

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.