Cranial nerves: abducens: 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 · Cranial nerves: abducens

Sample item

A child with a posterior fossa tumour and raised intracranial pressure has diplopia worsening on looking to the left, with the left eye unable to abduct. The nerve involved is described as a 'false localising sign' because of:

AIts long intracranial course and sharp bend over the petrous apexBIts crossing of the tentorial notch beside the posterior cerebral arteryCIts position in the lateral wall of the cavernous sinusDIts passage through the superior orbital fissure with the ophthalmic vein

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

The answer and the reasoning

A. Its long intracranial course and sharp bend over the petrous apex

The abducens nerve has the longest intracranial course of the cranial nerves and angles over the petrous temporal bone. Downward displacement of the brainstem in raised intracranial pressure stretches it, producing a lateral rectus palsy that does not localise the tumour.

Option by option

A. Its long intracranial course and sharp bend over the petrous apex (correct)
Correct. Stretching of this long course causes the palsy in raised intracranial pressure.
B. Its crossing of the tentorial notch beside the posterior cerebral artery
The oculomotor nerve, not the abducens, passes close to the posterior cerebral artery at the tentorial notch.
C. Its position in the lateral wall of the cavernous sinus
In the cavernous sinus the nerve lies free in the sinus beside the carotid, not in the lateral wall, and this is not the usual reason for raised pressure palsy.
D. Its passage through the superior orbital fissure with the ophthalmic vein
All the ocular motor nerves pass through the superior orbital fissure, which does not explain a false localising 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.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Its long intracranial course and sharp bend over the petrous apex. The abducens nerve has the longest intracranial course of the cranial nerves and angles over the petrous temporal bone.

Why is "Its crossing of the tentorial notch beside the posterior cerebral art…" not the answer?

The oculomotor nerve, not the abducens, passes close to the posterior cerebral artery at the tentorial notch.

Why is "Its position in the lateral wall of the cavernous sinus" not the answer?

In the cavernous sinus the nerve lies free in the sinus beside the carotid, not in the lateral wall, and this is not the usual reason for raised pressure palsy.

Why is "Its passage through the superior orbital fissure with the ophthalmic…" not the answer?

All the ocular motor nerves pass through the superior orbital fissure, which does not explain a false localising sign.

What concept does this question test?

It tests Cranial nerves: abducens in Anatomy. Downward displacement of the brainstem in raised intracranial pressure stretches it, producing a lateral rectus palsy that does not localise the tumour.

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 Cranial nerves: abducens?

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.