Thorax: thoracic duct: 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 · Thorax: thoracic duct

Sample item

A 55-year-old man develops a milky pleural effusion with a triglyceride level of 420 mg/dL on the fifth day after transthoracic oesophagectomy. The thoracic duct was injured in the lower thorax, below the level where it crosses to the left. On which side is the chylothorax most likely to form?

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

The answer and the reasoning

B. Right side, because the duct lies on the right of the vertebral column below T5

The thoracic duct begins at the cisterna chyli, enters the thorax through the aortic hiatus and ascends on the right side of the vertebral column between the azygos vein and the aorta. It crosses to the left at about the level of T5, so injury below T5 leaks chyle into the right pleural space, and injury above T5 leaks into the left. Its termination at the left venous angle does not decide the side of a lower injury.

Option by option

  • A. Left side, because the duct opens into the left venous angle

    The termination at the left venous angle is relevant to injuries in the neck or upper thorax, not to a lower thoracic injury.

  • B. Right side, because the duct lies on the right of the vertebral column below T5 (correct)

    Correct. Below T5 the duct is still right-sided, so leaked chyle enters the right pleural cavity.

  • C. Bilateral, because the cisterna chyli feeds both pleural cavities

    The cisterna chyli lies in the abdomen and the duct is a single channel, so the effusion is not bilateral.

  • D. Left side, because the duct lies directly behind the left lung hilum

    The duct is not related to the left hilum at this level; it lies in the posterior mediastinum on the right.

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 B, Right side, because the duct lies on the right of the vertebral column below T5. The thoracic duct begins at the cisterna chyli, enters the thorax through the aortic hiatus and ascends on the right side of the vertebral column between the azygos vein and the aorta.

Why is "Left side, because the duct opens into the left venous angle" not the answer?

The termination at the left venous angle is relevant to injuries in the neck or upper thorax, not to a lower thoracic injury.

Why is "Bilateral, because the cisterna chyli feeds both pleural cavities" not the answer?

The cisterna chyli lies in the abdomen and the duct is a single channel, so the effusion is not bilateral.

Why is "Left side, because the duct lies directly behind the left lung hilum" not the answer?

The duct is not related to the left hilum at this level; it lies in the posterior mediastinum on the right.

What concept does this question test?

It tests Thorax: thoracic duct in Anatomy. It crosses to the left at about the level of T5, so injury below T5 leaks chyle into the right pleural space, and injury above T5 leaks into the left. Its termination at the left venous angle does not decide the side of a lower injury.

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 Thorax: thoracic duct?

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.