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Contusions, coup–contrecoup and diffuse axonal injury

  • Finding

Bruises of the brain and damage to its nerve fibres show how the head moved, and they explain deaths that come hours or days after the injury.

Updated

What it is

Brain injury is either focal or diffuse. Contusions are bruises of the cortex: under the impact (coup) or on the opposite side (contrecoup). Contrecoup contusions are typical when the moving head hits a fixed surface, as in a fall onto the back of the head, which bruises the frontal and temporal poles. Diffuse axonal injury is damage to nerve fibres from rotation of the head; the person is usually unconscious from the start, and it is confirmed under the microscope. Many deaths are delayed: the brain swells, pressure rises, the brain herniates and the brainstem bleeds secondarily; lack of oxygen adds its own damage. For the forensic doctor this pattern helps tell a fall from a blow and links a later death to the original injury.

How to tell it apart

  • Contrecoup contusions point to a fall, but they do not prove it; the whole pattern counts.
  • Axonal damage from lack of oxygen or poor perfusion can look like traumatic axonal injury: the distribution and the history separate them.
  • Amyloid precursor protein staining usually needs a few hours of survival to become visible; very rapid deaths may show none.
  • Hypertensive brain bleeding in older people can be confused with a traumatic contusion haematoma.

How to recognise it

  • Contusions: small haemorrhages on the crests of the gyri, later becoming yellow-brown depressed scars.
  • Sites: frontal poles, orbital surfaces, temporal poles, where the brain meets rough bone.
  • Diffuse axonal injury: small bleeds in the corpus callosum and upper brainstem; microscopic axonal swellings.
  • Herniation: grooving of the uncus or cerebellar tonsils; secondary bleeding in the midbrain and pons.

How it forms

  • Coup: the skull bends in and strikes the brain beneath.
  • Contrecoup: when the moving head stops, the brain lags behind and is damaged on the opposite side.
  • Rotational acceleration shears axons between areas of different density.
  • Swelling, hypoxia and raised pressure add secondary injury after the first blow.

Step by step

  1. Record the site of the scalp impact and the site of each contusion: same side (coup) or opposite (contrecoup).
  2. Fix the brain where possible before slicing to see small lesions.
  3. Sample corpus callosum, brainstem and contusions for histology and immunohistochemistry.
  4. Correlate with the survival time and the clinical course in the medical record.

Next step: what to do and document

  • Record whether the patient was unconscious from the start or lost consciousness later; this distinguishes diffuse injury from an expanding clot.
  • Document hypoxia, low blood pressure and seizures with their times: they add brain damage and matter for causation.
  • Keep the first and later CT and MRI images; they show contusions blossoming and swelling over time.
  • If the patient dies days or weeks later, state in the record that the death followed the injury and report it as a violent death.
  • Write findings without concluding the mechanism: «right frontal contusion with left occipital scalp swelling».

Common mistakes

  • Taking contrecoup contusions as proof of a fall without looking at the rest of the evidence.
  • Calling a delayed death «natural» because the immediate cause was pneumonia or brain swelling.
  • Expecting axonal injury staining in a death within minutes.
  • Mistaking a hypertensive haemorrhage for a contusion, or the reverse.

Test yourself

Think of the answer, then tap the question to see it.

A man falls backwards and strikes his occiput. Where are contrecoup contusions expected?

On the frontal and temporal poles and the orbital surfaces of the frontal lobes, opposite the impact.

What force causes diffuse axonal injury, and how is it confirmed?

Rotational acceleration of the head; it is confirmed under the microscope by axonal swellings, often with amyloid precursor protein staining.

Why might axonal injury staining be negative in a death within minutes?

The marker accumulates over a few hours of survival; very rapid deaths may not show it.

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Educational content on forensic and legal medicine; not legal advice and no substitute for the technical guides of Colombia's National Institute of Legal Medicine and Forensic Sciences. Laws change: each page links the official text and says when it was last checked. For a real case, follow the guide in force and ask the competent authority.

Sources: Contrecoup Brain Injury (StatPearls Publishing (NCBI Bookshelf), 2025); Diffuse Axonal Injury (StatPearls Publishing (NCBI Bookshelf), 2025); Cerebral Contusion (StatPearls Publishing (NCBI Bookshelf), 2025); Diagnostic Problems in Diffuse Axonal Injury (Diagnostics (PMC), 2020); Brain Herniation (StatPearls Publishing (NCBI Bookshelf), 2026).

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