Head and neck: subclavian steal: 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 · Head and neck: subclavian steal

Sample item

A man has dizziness and left arm weakness during exercise, and the left brachial blood pressure is lower than the right. Imaging shows stenosis of the left subclavian artery proximal to the origin of the vertebral artery. What is the mechanism of the dizziness?

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

The answer and the reasoning

B. Retrograde flow in the left vertebral artery to supply the arm

In subclavian steal, a proximal subclavian stenosis lowers pressure beyond it, so blood from the contralateral vertebral artery passes through the basilar artery and flows backward down the ipsilateral vertebral artery into the arm. Arm exercise increases this diversion and causes brainstem ischaemia.

Option by option

  • A. Compression of the left vertebral artery in the foramina transversaria

    Compression in the transverse foramina is a mechanism of rotational vertebral insufficiency, not this scenario.

  • B. Retrograde flow in the left vertebral artery to supply the arm (correct)

    Correct. Reversal of flow in the ipsilateral vertebral artery steals blood from the brainstem.

  • C. Retrograde flow in the left common carotid artery

    The carotid system is not involved in the diversion past a subclavian stenosis.

  • D. Occlusion of the basilar artery by a thrombus

    Basilar thrombosis would cause persistent brainstem signs and does not produce a lower arm blood pressure.

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, Retrograde flow in the left vertebral artery to supply the arm. In subclavian steal, a proximal subclavian stenosis lowers pressure beyond it, so blood from the contralateral vertebral artery passes through the basilar artery and flows backward down the ipsilateral vertebral artery into the arm.

Why is "Compression of the left vertebral artery in the foramina transversaria" not the answer?

Compression in the transverse foramina is a mechanism of rotational vertebral insufficiency, not this scenario.

Why is "Retrograde flow in the left common carotid artery" not the answer?

The carotid system is not involved in the diversion past a subclavian stenosis.

Why is "Occlusion of the basilar artery by a thrombus" not the answer?

Basilar thrombosis would cause persistent brainstem signs and does not produce a lower arm blood pressure.

What concept does this question test?

It tests Head and neck: subclavian steal in Anatomy. Arm exercise increases this diversion and causes brainstem ischaemia.

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 Head and neck: subclavian steal?

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.