Embryology: conotruncal septation: 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.

Try it

Anatomy · Embryology: conotruncal septation

Sample item

A newborn has hypocalcaemic seizures, an absent thymic shadow on chest radiograph and a single arterial trunk leaving the heart. Which embryological structures failed to develop normally?

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

The answer and the reasoning

C. Neural crest cells migrating to the third and fourth pharyngeal pouches and conotruncal ridges

Neural crest cells contribute to the aorticopulmonary septum dividing the truncus arteriosus, and to the mesenchyme of the thymus and parathyroids. Their failure of migration (22q11.2 deletion, DiGeorge syndrome) gives persistent truncus arteriosus, thymic hypoplasia and hypocalcaemia from absent parathyroid glands.

Option by option

  • A. Endocardial cushions of the atrioventricular canal

    Endocardial cushion defects cause atrioventricular septal defects and are linked to Down syndrome.

  • B. The left horn of the sinus venosus

    The left sinus venosus horn forms the coronary sinus and does not explain thymic or parathyroid absence.

  • C. Neural crest cells migrating to the third and fourth pharyngeal pouches and conotruncal ridges (correct)

    Correct. Neural crest abnormalities explain the cardiac, thymic and parathyroid defects together.

  • D. Septum primum and septum secundum

    Septum primum and secundum defects cause atrial septal defects without these features.

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.

More Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Neural crest cells migrating to the third and fourth pharyngeal pouches and conotruncal ridges. Neural crest cells contribute to the aorticopulmonary septum dividing the truncus arteriosus, and to the mesenchyme of the thymus and parathyroids.

Why is "Endocardial cushions of the atrioventricular canal" not the answer?

Endocardial cushion defects cause atrioventricular septal defects and are linked to Down syndrome.

Why is "The left horn of the sinus venosus" not the answer?

The left sinus venosus horn forms the coronary sinus and does not explain thymic or parathyroid absence.

Why is "Septum primum and septum secundum" not the answer?

Septum primum and secundum defects cause atrial septal defects without these features.

What concept does this question test?

It tests Embryology: conotruncal septation in Anatomy. Their failure of migration (22q11.2 deletion, DiGeorge syndrome) gives persistent truncus arteriosus, thymic hypoplasia and hypocalcaemia from absent parathyroid glands.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: conotruncal septation?

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.