Obstetric imaging: lambda sign in twins: practice question

A Radiology 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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Radiology · Obstetric imaging: lambda sign in twins

Sample item

A first trimester ultrasound of twin pregnancy shows a triangular projection of placental tissue extending into the base of the intertwin membrane. What does this indicate?

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

The answer and the reasoning

B. Dichorionic diamniotic twins

The lambda or twin peak sign is a wedge of chorionic tissue between the two layers of the membrane and denotes dichorionic twins. Monochorionic diamniotic twins show a thin T-shaped junction instead.

Option by option

  • A. Monochorionic monoamniotic twins

    Monoamniotic twins have no dividing membrane.

  • B. Dichorionic diamniotic twins (correct)

    Correct. The lambda sign denotes dichorionic twins.

  • C. Conjoined twins

    Conjoined twins have no separating membrane and share body parts.

  • D. Monochorionic diamniotic twins

    Monochorionic diamniotic twins show the T sign.

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 Radiology question

What is the answer to this Radiology question?

The best answer is B, Dichorionic diamniotic twins. The lambda or twin peak sign is a wedge of chorionic tissue between the two layers of the membrane and denotes dichorionic twins.

Why is "Monochorionic monoamniotic twins" not the answer?

Monoamniotic twins have no dividing membrane.

Why is "Conjoined twins" not the answer?

Conjoined twins have no separating membrane and share body parts.

Why is "Monochorionic diamniotic twins" not the answer?

Monochorionic diamniotic twins show the T sign.

What concept does this question test?

It tests Obstetric imaging: lambda sign in twins in Radiology. Monochorionic diamniotic twins show a thin T-shaped junction instead.

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 Obstetric imaging: lambda sign in twins?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology 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.