Brain and spinal cord trauma

Lesion

A blow or a sudden stop can crack the skull, bruise the brain where it hits bone, shear axons deep inside, or crush the spinal cord.

Updated Nov 12, 2026

Key points

Contusions favour the crests of gyri on the orbitofrontal and temporal poles, where brain meets rough bone; old contusions are yellow-brown depressed scars (plaques jaunes).
Coup lesion under the impact, contrecoup lesion opposite it when the moving head stops suddenly.
Diffuse axonal injury: axonal swellings (spheroids, beta-amyloid precursor protein positive) in the corpus callosum, internal capsule and brainstem; causes coma without a mass.
Concussion: brief loss of function without visible structural damage; repeated concussions raise the risk of chronic traumatic encephalopathy.
Chronic traumatic encephalopathy: perivascular tau tangles at the depths of sulci, with atrophy and cognitive and mood decline.
Spinal cord injury above C4 can stop breathing; neurogenic shock and autonomic dysreflexia complicate high lesions.

What it is

Mechanical forces injure the CNS in predictable ways. Direct impact fractures the skull and bruises the cortex under the blow (coup) and on the opposite side (contrecoup). Rotational acceleration shears long axons in the white matter (diffuse axonal injury). Repeated mild injuries, as in contact sports, can lead to a tau-based degeneration (chronic traumatic encephalopathy). In the spine, fractures and dislocations crush the cord, and the level sets the deficit.

Structure

Skull fractures: linear, depressed or basilar; a basilar fracture gives CSF leak from nose or ear and bruising behind the ear or around the eyes.
Acute contusion: wedge-shaped hemorrhage and necrosis at the gyral crest, with edema; later macrophages and gliosis leave a depressed scar.
Laceration: torn brain from a penetrating object or bone fragment.
Cord injury: acute hemorrhagic necrosis at the level, later a cystic gliotic segment, with ascending and descending tract degeneration.

Step by step

The head is struck or stops suddenly; the brain moves inside the skull.
Brain surfaces hit bony ridges and bruise at the impact and the opposite side.
Rotation stretches long axons; transport stops and the axon swells into a spheroid.
Edema, bleeding and raised pressure add secondary injury.
Repeated mild trauma leaves abnormal tau that spreads over years.

Types of parenchymal brain injury

Injury	Force	Pathology	Clinical picture
Concussion	Sudden acceleration or impact	No visible lesion	Brief loss of consciousness or confusion, amnesia
Contusion	Impact against bone	Bruise at gyral crests (coup and contrecoup)	Focal deficit, seizures
Laceration	Penetration or bone fragment	Torn tissue with bleeding	Focal deficit, infection risk
Diffuse axonal injury	Rotational acceleration	Axonal spheroids in deep white matter and brainstem	Immediate coma, persistent vegetative state
Chronic traumatic encephalopathy	Repeated mild injuries	Perivascular tau at sulcal depths, atrophy	Memory, mood and behaviour decline years later

Clinical notes

Glasgow Coma Scale and CT guide early care; secondary injury from hypoxia and hypotension worsens outcome.
Abusive head trauma in infants combines subdural hematoma, retinal hemorrhages and diffuse brain injury.

Test yourself

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

What is a contrecoup contusion?

A bruise of the brain on the side opposite the impact, formed when the moving head stops suddenly and the brain strikes the far inner skull.

Which stain highlights axonal swellings in diffuse axonal injury?

Immunostaining for beta-amyloid precursor protein, which accumulates where axonal transport stops.

What protein defines chronic traumatic encephalopathy?

Hyperphosphorylated tau, in perivascular deposits at the depths of cortical sulci.

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Traumatic Brain Injury (StatPearls (NCBI Bookshelf), 2026).

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Representative model, for educational purposes only.