Neuroanatomy: tonsillar herniation: 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: tonsillar herniation

Sample item

A patient with a large cerebellar tumour and raised intracranial pressure collapses minutes after a lumbar puncture, with irregular breathing progressing to apnoea and bradycardia. Which event best explains the collapse?

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

The answer and the reasoning

C. Tonsillar herniation compressing the medulla

Lowering lumbar CSF pressure in the presence of a posterior fossa mass can push the cerebellar tonsils into the foramen magnum. This compresses the medulla and its respiratory and cardiovascular centres, causing apnoea and bradycardia.

Option by option

  • A. Uncal herniation through the tentorial notch

    Uncal herniation compresses the oculomotor nerve and midbrain, causing a dilated pupil and hemiparesis before respiratory failure.

  • B. Subfalcine herniation of the cingulate gyrus

    Subfalcine herniation compresses the anterior cerebral artery and causes leg weakness, not apnoea.

  • C. Tonsillar herniation compressing the medulla (correct)

    Correct. The tonsils wedge into the foramen magnum and squeeze the medullary cardiorespiratory centres.

  • D. Upward herniation of the cerebellar vermis

    Upward vermis herniation compresses the midbrain and is a less likely result of lumbar CSF removal.

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 C, Tonsillar herniation compressing the medulla. Lowering lumbar CSF pressure in the presence of a posterior fossa mass can push the cerebellar tonsils into the foramen magnum.

Why is "Uncal herniation through the tentorial notch" not the answer?

Uncal herniation compresses the oculomotor nerve and midbrain, causing a dilated pupil and hemiparesis before respiratory failure.

Why is "Subfalcine herniation of the cingulate gyrus" not the answer?

Subfalcine herniation compresses the anterior cerebral artery and causes leg weakness, not apnoea.

Why is "Upward herniation of the cerebellar vermis" not the answer?

Upward vermis herniation compresses the midbrain and is a less likely result of lumbar CSF removal.

What concept does this question test?

It tests Neuroanatomy: tonsillar herniation in Anatomy. This compresses the medulla and its respiratory and cardiovascular centres, causing apnoea and bradycardia.

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: tonsillar herniation?

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.