Neuroanatomy: midbrain syndromes: 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 · Neuroanatomy: midbrain syndromes

Sample item

A man has a right oculomotor palsy with a dilated pupil and a coarse tremor of the left arm. There is no weakness. Which lesion is most likely?

ALeft subthalamic nucleusBRight paramedian ponsCRight cerebral peduncleDRight midbrain tegmentum involving the red nucleus

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

The answer and the reasoning

D. Right midbrain tegmentum involving the red nucleus

Benedikt syndrome is an ipsilateral oculomotor palsy with contralateral tremor, from a lesion in the midbrain tegmentum that involves the red nucleus and the third nerve fascicle. Weber syndrome, in contrast, is caused by involvement of the cerebral peduncle and gives contralateral hemiparesis.

Option by option

A. Left subthalamic nucleus
A subthalamic lesion causes contralateral hemiballismus without a third nerve palsy.
B. Right paramedian pons
A pontine lesion would affect the sixth and seventh nerves, not the third.
C. Right cerebral peduncle
A peduncular lesion produces contralateral hemiparesis, which is absent here.
D. Right midbrain tegmentum involving the red nucleus (correct)
Correct. Third nerve palsy with contralateral tremor localises to the red nucleus.

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 D, Right midbrain tegmentum involving the red nucleus. Benedikt syndrome is an ipsilateral oculomotor palsy with contralateral tremor, from a lesion in the midbrain tegmentum that involves the red nucleus and the third nerve fascicle.

Why is "Left subthalamic nucleus" not the answer?

A subthalamic lesion causes contralateral hemiballismus without a third nerve palsy.

Why is "Right paramedian pons" not the answer?

A pontine lesion would affect the sixth and seventh nerves, not the third.

Why is "Right cerebral peduncle" not the answer?

A peduncular lesion produces contralateral hemiparesis, which is absent here.

What concept does this question test?

It tests Neuroanatomy: midbrain syndromes in Anatomy. Weber syndrome, in contrast, is caused by involvement of the cerebral peduncle and gives contralateral hemiparesis.

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 Neuroanatomy: midbrain syndromes?

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.