Injuries: diffuse axonal injury: practice question

A Forensic Medicine 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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Forensic Medicine · Injuries: diffuse axonal injury

Sample item

A 25-year-old motorcyclist is deeply unconscious from the moment of a high-speed crash. CT shows no mass lesion, and MRI later shows small haemorrhagic foci in the corpus callosum and the grey-white junction. What is the mechanism of this injury?

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

The answer and the reasoning

C. Rotational acceleration and deceleration, shearing the axons at the moment of impact

Diffuse axonal injury follows sudden rotational acceleration-deceleration, which produces shearing of axons at junctions between tissues of different density such as the corpus callosum and brainstem. Immediate prolonged coma with a near-normal CT is typical, and MRI (gradient-echo or susceptibility sequences) shows the small haemorrhages. It carries a poor prognosis when severe.

Option by option

  • A. A depressed bone fragment lacerating the cortex directly

    A depressed fragment would be seen on CT and causes focal rather than diffuse injury.

  • B. Rising intracranial pressure from a slowly expanding clot

    A slowly expanding clot would be visible on CT and would not cause immediate coma.

  • C. Rotational acceleration and deceleration, shearing the axons at the moment of impact (correct)

    Correct. Shearing of axons by rotational forces explains immediate coma without a mass lesion.

  • D. Hypoxic-ischaemic damage from hypotension after the crash

    Hypoxic-ischaemic injury is a secondary insult and does not produce callosal shear haemorrhages.

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 Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is C, Rotational acceleration and deceleration, shearing the axons at the moment of impact. Diffuse axonal injury follows sudden rotational acceleration-deceleration, which produces shearing of axons at junctions between tissues of different density such as the corpus callosum and brainstem.

Why is "A depressed bone fragment lacerating the cortex directly" not the answer?

A depressed fragment would be seen on CT and causes focal rather than diffuse injury.

Why is "Rising intracranial pressure from a slowly expanding clot" not the answer?

A slowly expanding clot would be visible on CT and would not cause immediate coma.

Why is "Hypoxic-ischaemic damage from hypotension after the crash" not the answer?

Hypoxic-ischaemic injury is a secondary insult and does not produce callosal shear haemorrhages.

What concept does this question test?

It tests Injuries: diffuse axonal injury in Forensic Medicine. Immediate prolonged coma with a near-normal CT is typical, and MRI (gradient-echo or susceptibility sequences) shows the small haemorrhages. It carries a poor prognosis when severe.

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 Injuries: diffuse axonal injury?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.