Defining Traumatic Brain Injury: A Spectrum of Severity

Traumatic brain injury (TBI) ranges from mild concussion to severe injuries associated with prolonged coma and permanent disability. This distinction matters because the expected clinical course, prognosis, and evidentiary requirements differ substantially across the spectrum.

Mild TBI (Concussion)

The American Congress of Rehabilitation Medicine (ACRM) defines mild TBI as a traumatically induced physiological disruption of brain function manifested by at least one of the following:

  • Loss of consciousness (up to 30 minutes)
  • Post-traumatic amnesia (up to 24 hours)
  • Alteration in mental state at the time of injury (confusion, disorientation)
  • Focal neurological deficits that may or may not be transient

Importantly, the Glasgow Coma Scale (GCS) score must be 13–15 at 30 minutes post-injury or upon initial evaluation. The VA/DoD Clinical Practice Guidelines and the Concussion in Sport Group (Berlin Consensus) use similar criteria.

Moderate and Severe TBI

Moderate TBI is typically defined by GCS 9–12, loss of consciousness from 30 minutes to 24 hours, or post-traumatic amnesia lasting 1–7 days. Severe TBI involves GCS ≤8, loss of consciousness exceeding 24 hours, or post-traumatic amnesia beyond 7 days.

These injuries usually produce objective neuroimaging findings and have clearer causation pathways in litigation.

The majority of litigated TBI cases involve mild TBI—where diagnostic criteria are met, but neuroimaging is often normal and long-term prognosis is generally favorable. This is precisely where disputes arise.

The Imaging Paradox: Normal Scans and Persistent Symptoms

One of the most common points of confusion in TBI litigation is the significance of normal neuroimaging. CT and conventional MRI are designed to detect structural abnormalities such as hemorrhage, contusion, edema, or skull fracture.

In mild TBI, these studies are frequently normal, which does not mean no injury occurred. Concussion is understood to be a functional disturbance rather than a gross structural lesion.

Advanced techniques such as diffusion tensor imaging (DTI) and functional MRI are sometimes offered as evidence of injury, but their use in individual case adjudication remains controversial. These modalities have not been validated for forensic application and raise concerns regarding specificity.

Key Point for Attorneys:

A normal CT or MRI does not disprove mild TBI, but it also does not prove that ongoing symptoms are caused by brain injury. Diagnosis rests on the clinical history at the time of injury, not on imaging obtained days or weeks later.

Mechanism of Injury: What the Biomechanics Do and Don't Tell Us

Biomechanical thresholds for concussion are not absolute. Rotational acceleration of the head appears more predictive of injury than linear acceleration, but individual susceptibility varies.

Low-speed motor vehicle collisions, falls from standing height, and sports impacts have all been documented to cause concussion in some individuals while leaving others unaffected.

The relevant question is not whether a mechanism can cause TBI in the abstract, but whether this patient experienced signs and symptoms consistent with TBI at the time of the event.

Post-Concussion Syndrome: Symptom Persistence and Alternative Explanations

Most patients with mild TBI recover within days to weeks. When symptoms persist beyond three months, the differential diagnosis expands.

  • Mood disorders: Depression and anxiety can independently cause cognitive and somatic symptoms.
  • Sleep dysfunction: Primary sleep disorders or pain-related disruption may impair cognition.
  • Cervicogenic factors: Neck injuries can mimic concussion symptoms.
  • Preexisting conditions: ADHD, migraine, prior TBI, and learning disabilities may contribute.
  • Psychological and motivational factors: Litigation stress and expectation effects may influence reporting.

Neuropsychological Testing: Utility and Limitations

Neuropsychological assessments provide objective data on attention, memory, processing speed, and executive function, but interpretation requires caution.

  • Performance can be influenced by effort, mood, sleep, medications, and pain
  • Performance and symptom validity tests help assess reliability of results
  • Baseline testing is valuable but often unavailable in litigation contexts

Causation in TBI Cases: Connecting the Dots

  • Did the patient meet diagnostic criteria at the time of injury?
  • Is the symptom profile consistent with TBI?
  • Are alternative explanations adequately considered?
  • Is the claimed impairment proportionate to injury severity?

Key Takeaways for Case Evaluation

  • TBI diagnosis requires documented acute findings
  • Normal imaging does not exclude mild TBI or prove causation
  • Biomechanics must be clinically correlated
  • Persistent symptoms may reflect comorbidities
  • Causation opinions must be medically proportionate

When Expert Review Is Warranted

  • Incomplete or ambiguous acute injury documentation
  • Persistent or atypical symptoms
  • Disputed mechanism of injury
  • Complex neuroimaging or neuropsychological findings
  • Preexisting conditions complicating attribution

Dr. Tobias B. Kulik is a board-certified neurologist with subspecialty certification in Vascular Neurology and Neurocritical Care, and a Certified ImPACT Consultant (CIC). He provides independent expert witness services in TBI-related cases for both plaintiff and defense counsel.

References

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  2. Patricios JS et al. Br J Sports Med. 2023.
  3. VA/DoD Clinical Practice Guideline for mTBI. 2021.
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  7. Bigler ED. Neuropsychol Rev. 2013.
  8. Larrabee GJ et al. Clin Neuropsychol. 2019.
  9. ACRM Brain Injury SIG. J Head Trauma Rehabil. 1993.