Cranial nerves: trochlear nerve palsy: 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.

Try it

Anatomy · Cranial nerves: trochlear nerve palsy

Sample item

After head trauma, a man has vertical diplopia that is worst when he looks down and inward, as in descending stairs. He keeps his head tilted to the left. Which lesion is most likely?

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

The answer and the reasoning

C. Right trochlear nerve palsy, with weakness of the right superior oblique

The superior oblique, supplied by the trochlear nerve, intorts the eye and depresses it when adducted. Loss causes vertical diplopia worse in downward gaze when adducted, and patients tilt the head away from the affected side to limit the double vision. The trochlear nerve is the thinnest cranial nerve and the only one to exit dorsally, so it is vulnerable to head trauma.

Option by option

  • A. Left trochlear nerve palsy, with weakness of the left superior oblique

    A left-sided palsy would produce a head tilt to the right.

  • B. Right oculomotor nerve palsy, with weakness of the right superior rectus

    An oculomotor palsy causes ptosis and a down-and-out eye, not isolated vertical diplopia.

  • C. Right trochlear nerve palsy, with weakness of the right superior oblique (correct)

    Correct. A leftward head tilt compensates for a right-sided superior oblique palsy.

  • D. Right abducens nerve palsy, with weakness of the right lateral rectus

    An abducens palsy causes horizontal diplopia, worse looking to the affected side.

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 Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Right trochlear nerve palsy, with weakness of the right superior oblique. The superior oblique, supplied by the trochlear nerve, intorts the eye and depresses it when adducted.

Why is "Left trochlear nerve palsy, with weakness of the left superior oblique" not the answer?

A left-sided palsy would produce a head tilt to the right.

Why is "Right oculomotor nerve palsy, with weakness of the right superior rec…" not the answer?

An oculomotor palsy causes ptosis and a down-and-out eye, not isolated vertical diplopia.

Why is "Right abducens nerve palsy, with weakness of the right lateral rectus" not the answer?

An abducens palsy causes horizontal diplopia, worse looking to the affected side.

What concept does this question test?

It tests Cranial nerves: trochlear nerve palsy in Anatomy. Loss causes vertical diplopia worse in downward gaze when adducted, and patients tilt the head away from the affected side to limit the double vision. The trochlear nerve is the thinnest cranial nerve and the only one to exit dorsally, so it is vulnerable to head trauma.

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 Cranial nerves: trochlear nerve palsy?

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.