Colorectal: closed loop obstruction: practice question

A General Surgery 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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General Surgery · Colorectal: closed loop obstruction

Sample item

A patient with a left colon carcinoma has massive caecal distension of 12 cm on film. Why is the caecum at highest risk of perforation?

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

The answer and the reasoning

B. Closed loop obstruction with a competent ileocaecal valve and the law of Laplace

If the ileocaecal valve is competent, the colon between valve and obstruction behaves as a closed loop. The caecum has the widest diameter and thinnest wall, so according to the Laplace law its wall tension is highest and it perforates first when diameter exceeds about 12 cm. Urgent decompression is needed.

Option by option

  • A. It contains no gas

    The caecum is typically full of gas in such obstruction.

  • B. Closed loop obstruction with a competent ileocaecal valve and the law of Laplace (correct)

    Correct. A closed loop and Laplace tension explain caecal rupture.

  • C. Its wall is the thickest

    The caecal wall is thin, not thick.

  • D. It has the best blood supply

    Distension compromises its blood supply.

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 General Surgery questions

Questions about this General Surgery question

What is the answer to this General Surgery question?

The best answer is B, Closed loop obstruction with a competent ileocaecal valve and the law of Laplace. If the ileocaecal valve is competent, the colon between valve and obstruction behaves as a closed loop.

Why is "It contains no gas" not the answer?

The caecum is typically full of gas in such obstruction.

Why is "Its wall is the thickest" not the answer?

The caecal wall is thin, not thick.

Why is "It has the best blood supply" not the answer?

Distension compromises its blood supply.

What concept does this question test?

It tests Colorectal: closed loop obstruction in General Surgery. The caecum has the widest diameter and thinnest wall, so according to the Laplace law its wall tension is highest and it perforates first when diameter exceeds about 12 cm. Urgent decompression is needed.

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 Colorectal: closed loop obstruction?

Learn classic signs and eponyms alongside what they diagnose. Then use the flashcards and the other General Surgery 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.