Traumatic brain injury (TBI) produces some of the most distinctive and clinically urgent neuropathologic findings. The patterns reflect the mechanism of injury — contusion at sites of impact (coup) and at the opposite pole (contrecoup), diffuse axonal injury (DAI) from rotational acceleration, intracranial hemorrhages of different types reflecting which compartment is bleeding, and secondary injury from edema, hypoxia, and hypotension. Recognition of these patterns at imaging and at autopsy is essential for understanding the patient’s clinical state and forensic evaluation. This page covers the major TBI pathologies.

Primary Brain Injuries

Contusion

Focal damage to the brain surface from direct impact:

  • Coup contusion: at the site of impact.
  • Contrecoup contusion: at the opposite pole; often more severe than coup; classical of acceleration-deceleration injury (motor vehicle accident, fall).
  • Common sites: orbital frontal, temporal poles, perirolandic — areas where the brain strikes against bone.
  • Pathology: hemorrhagic damage to cortex and underlying white matter; later cyst formation and gliosis.

Diffuse Axonal Injury (DAI)

Stretching and shearing of axons from rotational acceleration. Pathology:

  • Axonal swellings (“retraction balls” or “axonal swellings”): characteristic; visible on H&E within hours to days; better visualized with β-amyloid precursor protein (β-APP) IHC.
  • Multifocal, scattered, often in white matter, corpus callosum, brainstem (rostral pontomesencephalic).
  • Wallerian degeneration of disrupted axons over time.
  • Microhemorrhages at gray-white junction, corpus callosum, dorsolateral brainstem.
  • Microglial reaction.
  • Imaging: T2/FLAIR or SWI hyperintensities at gray-white junction, corpus callosum, brainstem.

Brainstem Injury

Dorsolateral pontomesencephalic shearing common in severe TBI; substrate of coma.

Intracranial Hemorrhages

Epidural Hematoma

  • Blood between dura and skull.
  • Usually arterial (middle meningeal artery; temporal fracture).
  • Lens-shaped (biconvex) on CT; does not cross suture lines.
  • Classic clinical course: lucid interval followed by rapid deterioration.
  • Neurosurgical emergency.

Subdural Hematoma

  • Blood between dura and arachnoid.
  • Usually venous (bridging veins).
  • Crescent-shaped on CT; crosses suture lines.
  • Common in elderly (brain atrophy stretches veins) and alcoholics.
  • Acute: bright on CT; high mortality if large.
  • Subacute (3 days – 3 weeks): isodense; harder to see on CT.
  • Chronic: hypodense; older adults; may evolve from minor trauma.

Subarachnoid Hemorrhage (Traumatic)

  • Blood in subarachnoid space from cortical surface injury.
  • Distinguished from aneurysmal SAH by location (convexity rather than basal cisterns), traumatic context, and associated injury.

Intracerebral Hemorrhage / Traumatic Hemorrhagic Contusion

  • Hemorrhage within brain parenchyma at site of contusion.
  • Can expand over days.

Intraventricular Hemorrhage

From extension of contusion or from shearing injury of subependymal veins.

Secondary Injuries

  • Edema: cytotoxic + vasogenic; peaks 3-5 days; cause of clinical deterioration.
  • Increased ICP and herniation: from mass effect of contusion, hemorrhage, edema.
  • Cerebral hypoperfusion: from hypotension, increased ICP.
  • Hypoxia: from respiratory compromise.
  • Infarction: secondary to compression, herniation, or vascular injury (carotid/vertebral artery dissection from trauma).
  • Duret hemorrhages: brainstem from severe central herniation.
  • Skull fractures: linear, depressed, basilar; CSF leak with basilar fracture.

Penetrating Trauma

  • Tract of damage along projectile path.
  • Hemorrhage along tract.
  • Infection risk (especially with depressed skull fractures or retained foreign body).
  • Late complications: epilepsy, focal deficits.

Pediatric Considerations

  • Abusive head trauma (“shaken baby syndrome”): retinal hemorrhages + subdural hemorrhages + sometimes axonal injury, without external signs. Forensic implications. Triad alone is insufficient diagnosis; clinical context matters.
  • Pediatric DAI patterns can differ.

Forensic Considerations

  • Timing of injury: depend on cellular evolution (red neurons in 4-12 hours; macrophages in days; gliosis in weeks).
  • Mechanism: pattern of injury (coup/contrecoup vs DAI vs penetrating) informs mechanism.
  • Dating subdural hematomas by color, organization stage, and histology.

Chronic Sequelae of TBI

  • Encephalomalacia at sites of contusion / infarction.
  • Hemosiderin staining of cyst walls (Prussian blue positive).
  • Atrophy of affected regions; ex vacuo ventricular dilation.
  • Wallerian degeneration in tracts.
  • Post-traumatic epilepsy (seizure focus at contusion or gliotic scar).
  • Chronic traumatic encephalopathy (CTE) — separate page; from repetitive TBI.

Imaging Patterns

  • Acute: CT for hemorrhage and mass effect; MRI may be deferred.
  • Subacute: MRI for DAI (SWI/GRE for microbleeds at gray-white junction), contusion, axonal damage.
  • Chronic: MRI shows encephalomalacia, hemosiderin, atrophy.

🔍 Did You Know?

The classical “lucid interval” of epidural hematoma — a period of consciousness between an initial loss of consciousness at the time of injury and a subsequent rapid deterioration — is one of the most clinically critical patterns in traumatic neurology. The mechanism: a temporal bone fracture lacerates the middle meningeal artery, with arterial blood accumulating in the epidural space over minutes to hours. The initial loss of consciousness from the concussion resolves transiently as the patient awakens, but the expanding hematoma eventually compresses the brain, causes herniation, and produces rapid deterioration. The lucid interval can last from 30 minutes to several hours, and the patient may seem entirely well during this time. The clinical implication is stark: any patient with head trauma, even one who appears initially well after a brief loss of consciousness, requires CT imaging if there is any concern about underlying epidural hematoma. The classic teaching is that epidural hematomas are surgical emergencies — neurosurgical evacuation can produce dramatic recovery, while delay can produce permanent neurologic damage or death. The recognition of this pattern has saved countless lives. The same urgency does NOT apply to most acute subdural hematomas (which often arise from venous bleeding, evolve more slowly, and may not require emergent evacuation), but the pattern of acute deterioration after a lucid interval should always prompt immediate imaging. The lesson: in head trauma, the patient who seems well 30 minutes after the injury is not necessarily out of danger.

Pitfalls and Pearls

  • Coup-contrecoup contusions: orbital frontal, temporal poles, perirolandic predilection.
  • Diffuse axonal injury (DAI): rotational shearing; axonal swellings + microhemorrhages at gray-white junction, CC, brainstem.
  • β-APP IHC: best for visualizing acute axonal injury.
  • Epidural hematoma: arterial; lens-shaped; lucid interval; emergency.
  • Subdural hematoma: venous; crescent; crosses sutures; elderly + alcoholic at risk.
  • Acute SDH: bright on CT; subacute: isodense (hardest to see); chronic: hypodense.
  • Traumatic SAH: convexity location vs basal aneurysmal.
  • Edema peak at 3-5 days: clinical deterioration window.
  • Duret hemorrhages: from severe central herniation; brainstem.
  • Penetrating injury: tract damage + infection risk + late epilepsy.
  • Abusive head trauma: subdural + retinal hemorrhages; forensic implications.
  • Carotid/vertebral dissection: from trauma; image vasculature.
  • Wallerian degeneration: of axons whose cell bodies are damaged; manifests in distant tracts over weeks.
  • Post-traumatic epilepsy: from gliotic scar at contusion.

References

  1. Love S, Budka H, Ironside JW, Perry A, eds. Greenfield’s Neuropathology. 9th ed. CRC Press; 2015.
  2. Maas AI, Stocchetti N, Bullock R. Moderate and severe traumatic brain injury in adults. Lancet Neurol. 2008;7(8):728-741.
  3. Smith DH, Meaney DF. Axonal damage in traumatic brain injury. Neuroscientist. 2000;6(6):483-495.
  4. Bullock MR, Chesnut R, Ghajar J, et al. Surgical management of acute epidural hematomas. Neurosurgery. 2006;58(3 Suppl):S7-S15.
  5. Stein DM, Brenner M, Hu PF, Yang S, Hauschild EC, Stansbury LG. Timing of intracranial hypertension following severe traumatic brain injury. Neurocrit Care. 2013;18(3):332-340.