Embryology: atrial 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.

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Anatomy · Embryology: atrial septation

Sample item

A child with Down syndrome has an atrial septal defect, left axis deviation on the electrocardiogram and mitral regurgitation caused by a cleft in the anterior mitral leaflet. Which developmental failure is responsible?

AFailure of the endocardial cushions to fuse with the septum primumBFailure of the septum primum and septum secundum to fuseCIncomplete incorporation of the right sinus horn into the right atriumDExcessive resorption of the septum primum

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

The answer and the reasoning

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

Endocardial cushion defects are common in Down syndrome and the ostium primum defect results when the cushions fail to meet the lower edge of the septum primum. The same cushions contribute to the mitral and tricuspid valves, so a cleft anterior mitral leaflet accompanies it. The conduction pathway is displaced, which explains the left axis deviation.

Option by option

A. Failure of the endocardial cushions to fuse with the septum primum (correct)
Correct. This is an ostium primum defect with a cleft mitral leaflet as part of an atrioventricular septal defect.
B. Failure of the septum primum and septum secundum to fuse
Failure of fusion of the two septa leaves a patent foramen ovale.
C. Incomplete incorporation of the right sinus horn into the right atrium
Abnormal incorporation of the sinus horn leads to a sinus venosus defect near the superior vena cava.
D. Excessive resorption of the septum primum
Excessive resorption of the septum primum causes an ostium secundum defect, which does not cause a cleft leaflet.

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.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Failure of the endocardial cushions to fuse with the septum primum. Endocardial cushion defects are common in Down syndrome and the ostium primum defect results when the cushions fail to meet the lower edge of the septum primum.

Why is "Failure of the septum primum and septum secundum to fuse" not the answer?

Failure of fusion of the two septa leaves a patent foramen ovale.

Why is "Incomplete incorporation of the right sinus horn into the right atrium" not the answer?

Abnormal incorporation of the sinus horn leads to a sinus venosus defect near the superior vena cava.

Why is "Excessive resorption of the septum primum" not the answer?

Excessive resorption of the septum primum causes an ostium secundum defect, which does not cause a cleft leaflet.

What concept does this question test?

It tests Embryology: atrial septation in Anatomy. The same cushions contribute to the mitral and tricuspid valves, so a cleft anterior mitral leaflet accompanies it. The conduction pathway is displaced, which explains the left axis deviation.

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: atrial 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.