Neuroimaging: Kernohan notch: practice question

A Radiology 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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Radiology · Neuroimaging: Kernohan notch

Sample item

A man with a large right subdural haematoma has right-sided hemiparesis, on the same side as the lesion. MRI shows an indentation and signal change in the left cerebral peduncle. What explains this false-localising sign?

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

The answer and the reasoning

B. Midbrain pushed against the tentorial edge, compressing the contralateral peduncle

A large mass shifts the midbrain across, and the opposite cerebral peduncle is crushed against the free edge of the tentorium, producing a notch. Because the corticospinal fibres have not yet decussated, the weakness is on the same side as the mass.

Option by option

  • A. Infarction of the right posterior cerebral artery

    A right PCA infarct causes visual field defects rather than hemiparesis.

  • B. Midbrain pushed against the tentorial edge, compressing the contralateral peduncle (correct)

    Correct. The peduncle opposite the mass is pressed on the tentorium, giving ipsilateral weakness.

  • C. Injury to the spinal cord at the cervical level

    A cervical injury would produce limb signs in all four limbs, not only one side.

  • D. Direct compression of the ipsilateral corticospinal tract by the haematoma

    Compression of the ipsilateral tract would cause weakness on the opposite side, the usual pattern.

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 Radiology question

What is the answer to this Radiology question?

The best answer is B, Midbrain pushed against the tentorial edge, compressing the contralateral peduncle. A large mass shifts the midbrain across, and the opposite cerebral peduncle is crushed against the free edge of the tentorium, producing a notch.

Why is "Infarction of the right posterior cerebral artery" not the answer?

A right PCA infarct causes visual field defects rather than hemiparesis.

Why is "Injury to the spinal cord at the cervical level" not the answer?

A cervical injury would produce limb signs in all four limbs, not only one side.

Why is "Direct compression of the ipsilateral corticospinal tract by the haem…" not the answer?

Compression of the ipsilateral tract would cause weakness on the opposite side, the usual pattern.

What concept does this question test?

It tests Neuroimaging: Kernohan notch in Radiology. Because the corticospinal fibres have not yet decussated, the weakness is on the same side as the mass.

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 Neuroimaging: Kernohan notch?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology 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.