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 35-year-old woman has a stroke, and echocardiography with bubble study shows a small right-to-left shunt at the atrial level with a flap-like valve. What is the embryological basis?

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

The answer and the reasoning

D. Failure of fusion of septum primum with septum secundum after birth

Before birth the foramen ovale is formed by the overlap of septum primum and septum secundum. After birth the left atrial pressure rises and normally presses septum primum against septum secundum. In about 25% of adults they stay unfused, giving a probe-patent foramen ovale and risk of paradoxical embolism.

Option by option

  • A. Persistent left superior vena cava

    A persistent left superior vena cava drains to the coronary sinus and does not cause an atrial shunt.

  • B. Excessive resorption of the septum secundum

    Excess resorption of septum primum, not secundum, produces an ostium secundum defect.

  • C. Failure of the endocardial cushions to fuse

    Endocardial cushion failure gives an ostium primum defect with an atrioventricular canal.

  • D. Failure of fusion of septum primum with septum secundum after birth (correct)

    Correct. Persisting non-fusion leaves a patent foramen ovale allowing paradoxical embolism.

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 D, Failure of fusion of septum primum with septum secundum after birth. Before birth the foramen ovale is formed by the overlap of septum primum and septum secundum.

Why is "Persistent left superior vena cava" not the answer?

A persistent left superior vena cava drains to the coronary sinus and does not cause an atrial shunt.

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

Excess resorption of septum primum, not secundum, produces an ostium secundum defect.

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

Endocardial cushion failure gives an ostium primum defect with an atrioventricular canal.

What concept does this question test?

It tests Embryology: atrial septation in Anatomy. After birth the left atrial pressure rises and normally presses septum primum against septum secundum. In about 25% of adults they stay unfused, giving a probe-patent foramen ovale and risk of paradoxical embolism.

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: 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.