Traumatic Brain Injury in Litigation: Mechanism, Symptom, and the Causation Gap

Most traumatic brain injury litigation is fought in the mild range — injuries where the diagnostic criteria are met at the time of the event, the imaging is normal, and the claim rests on whether symptoms reported months later are still being caused by a brain that, by every clinical measure, should have healed. The defense calls it overreach. The plaintiff calls it dismissal. The careful answer lives in a narrow set of facts that the record either supports or does not.

The Spectrum of Severity

Traumatic brain injury is not one diagnosis. It is a range, and the expected clinical course, prognosis, and evidentiary weight differ meaningfully across it.

Mild TBI — clinical concussion — is defined by the American Congress of Rehabilitation Medicine and echoed by the VA/DoD Clinical Practice Guidelines and the Concussion in Sport Group's Amsterdam Consensus.¹²³ The criteria require at least one of: loss of consciousness up to thirty minutes, post-traumatic amnesia up to twenty-four hours, alteration in mental state at the time of injury, or transient focal neurological deficits. A Glasgow Coma Scale of 13–15 at thirty minutes post-injury or on initial evaluation is part of the definition.

Moderate TBI is typically GCS 9–12, loss of consciousness from thirty minutes to twenty-four hours, or post-traumatic amnesia lasting one to seven days. Severe TBI carries GCS of 8 or less, loss of consciousness beyond twenty-four hours, or amnesia beyond a week. Moderate and severe injuries usually produce objective neuroimaging findings and have clearer causation pathways. The litigated cases, overwhelmingly, are mild.

The Imaging Question

The most common source of confusion in TBI litigation is what to make of a normal scan. CT and conventional MRI are designed to detect structural pathology — hemorrhage, contusion, edema, skull fracture. In mild TBI, these studies are frequently normal. That absence is not evidence that no injury occurred.

Concussion is, mechanistically, a functional disturbance rather than a gross structural lesion — neurometabolic disruption, axonal strain, transient neurochemical dysfunction, none of which conventional imaging resolves.⁴ This is why the diagnosis is made clinically, from the record of the event, and why imaging obtained days or weeks later is not the primary evidentiary instrument.

Two cautions are worth stating plainly. A normal CT or MRI does not exclude mild TBI — but neither does it prove that ongoing symptoms are caused by brain injury. Advanced techniques — diffusion tensor imaging, functional MRI, resting-state connectivity studies — are sometimes offered as evidence of injury at the individual level. Their forensic application remains contested: these modalities have not been validated for individual-case adjudication, and their sensitivity to subclinical signal raises specificity questions that a thoughtful expert has to engage, not wave past.⁴

Mechanism and Its Limits

In personal injury cases, the mechanism of injury is often where the fight is staged. Defense experts may argue that the forces were insufficient to produce a brain injury. Plaintiff experts may argue the opposite. Both positions deserve scrutiny.

Biomechanical thresholds for concussion are not absolute. Rotational acceleration of the head appears more predictive of brain injury than linear acceleration, but individual susceptibility varies with neck strength, head position at impact, prior concussion history, and factors that are not fully characterized. Low-speed motor vehicle collisions, falls from standing height, and ordinary sports impacts have all been documented to produce concussion in some individuals and no injury at all in others.

The analytically useful question is not whether a given mechanism can cause TBI in the abstract. That question almost always resolves toward yes. The useful question is whether this patient, on this day, experienced signs and symptoms consistent with TBI at the time of the event. Mechanism analysis should inform clinical correlation, not substitute for it.

When Symptoms Persist

Most patients with mild TBI recover fully within days to weeks. The WHO Collaborating Centre Task Force on Mild Traumatic Brain Injury established decades ago, and subsequent guidelines have reaffirmed, that the expected trajectory is resolution, not chronic impairment.⁵⁶ When symptoms persist beyond the typical recovery window — often defined at three months — the differential diagnosis expands, and the careful expert expands with it.

Several conditions can produce or perpetuate post-concussion-type symptoms:

• Mood disorders. Depression and anxiety are both common after any significant trauma and are individually capable of producing fatigue, concentration difficulty, sleep disturbance, and irritability.
• Sleep dysfunction. Primary sleep disorders, or pain-driven sleep disruption, impair cognition in patterns that overlap substantially with post-concussion complaints.
• Cervicogenic contributions. A neck injury sustained in the same traumatic event can produce headache, dizziness, and concentration difficulty that mimic or amplify concussion symptoms.
• Preexisting conditions. ADHD, migraine, prior concussion, learning disability, and chronic pain syndromes predispose to prolonged symptoms and are frequently misattributed to a new injury when the baseline was never established.
• Psychological and contextual factors. Expectation of impairment, litigation stress, and — where relevant — secondary gain can influence symptom reporting. These are legitimate considerations, but they require careful evaluation rather than presumption.⁷

Whether persistent symptoms reflect the TBI itself, a comorbidity, a preexisting condition, or some combination is a question of probability. A defensible causation opinion works through the alternatives rather than around them.

Neuropsychological testing is often obtained to document cognitive impairment, and it provides objective data — attention, memory, processing speed, executive function — on domains plausibly affected by brain injury. But the interpretation is not the test score. Performance is affected by effort, mood, sleep, medication, and pain, not only by brain pathology. Modern neuropsychological evaluations embed performance validity tests and symptom validity tests specifically to assess whether results reliably reflect the patient's true abilities, and contemporary literature supports using multiple validity measures rather than relying on any single index.⁸ Baseline testing — such as ImPACT in sports concussion programs — is genuinely useful for comparison, but is rarely available in litigation. Without a baseline, neuropsychological findings have to be read against the full clinical picture: acute injury characteristics, recovery trajectory, and the specific confounders present in this patient.

Reading the Record

A defensible TBI causation opinion does not rest on the fact that a traumatic event occurred and the patient has symptoms. It rests on the record, and it answers a small number of specific questions:

• Did the patient meet diagnostic criteria for TBI at the time of injury? That requires documented alteration of consciousness, amnesia, or acute neurological findings — not a headache reported days later, and not a symptom inventory filled out after counsel was retained.
• Is the symptom profile consistent with TBI? Reported symptoms should align with known patterns of post-concussion impairment and should have emerged in temporal proximity to the injury, with a trajectory the literature recognizes.
• Are alternative explanations engaged, not dismissed? Preexisting conditions, comorbidities, and contextual factors should be named and worked, not left as footnotes for the other side to exploit.
• Is the claimed impairment proportionate to the documented injury? Profound, permanent disability following an uncomplicated mild TBI warrants careful scrutiny — and when the literature on uncomplicated mild TBI shows near-universal recovery within months, a disability claim has to account for why this patient is the exception.⁹

The useful question in a TBI case is almost never whether the event could have caused an injury. The answer is usually yes. The useful question is whether it did, in this patient, on this day, in a way the record documents. The cases that hold up in deposition are the ones where the expert has already conceded everything the record does not support, and built what remains from what does.

References

Footnotes

1. Menon DK, Schwab K, Wright DW, Maas AI; Demographics and Clinical Assessment Working Group of the International and Interagency Initiative toward Common Data Elements for Research on Traumatic Brain Injury and Psychological Health. Position statement: definition of traumatic brain injury. Arch Phys Med Rehabil. 2010;91(11):1637–1640. doi:10.1016/j.apmr.2010.05.017 ↩

2. Patricios JS, Schneider KJ, Dvorak J, et al. Consensus statement on concussion in sport: the 6th International Conference on Concussion in Sport–Amsterdam, October 2022. Br J Sports Med. 2023;57(11):695–711. doi:10.1136/bjsports-2023-106898 ↩

3. American Congress of Rehabilitation Medicine, Brain Injury Interdisciplinary Special Interest Group. Definition of mild traumatic brain injury. J Head Trauma Rehabil. 1993;8(3):86–87. ↩

4. Bigler ED. Neuroimaging biomarkers in mild traumatic brain injury (mTBI). Neuropsychol Rev. 2013;23(3):169–209. doi:10.1007/s11065-013-9237-2 ↩ ↩²

5. Management of Concussion-Mild Traumatic Brain Injury Working Group. VA/DoD Clinical Practice Guideline for the Management and Rehabilitation of Post-Acute Mild Traumatic Brain Injury. Version 3.0. Washington, DC: Department of Veterans Affairs, Department of Defense; 2021. ↩

6. Carroll LJ, Cassidy JD, Peloso PM, et al. Prognosis for mild traumatic brain injury: results of the WHO Collaborating Centre Task Force on Mild Traumatic Brain Injury. J Rehabil Med. 2004;(43 Suppl):84–105. doi:10.1080/16501960410023859 ↩

7. Silverberg ND, Iverson GL. Etiology of the post-concussion syndrome: Physiogenesis and psychogenesis revisited. NeuroRehabilitation. 2011;29(4):317–329. doi:10.3233/NRE-2011-0708 ↩

8. Larrabee GJ, Rohling ML, Meyers JE. Use of multiple performance and symptom validity measures: Determining the optimal per test cutoff for determination of invalidity. Clin Neuropsychol. 2019;33(8):1356–1372. doi:10.1080/13854046.2019.1614227 ↩

9. Iverson GL, Lange RT, Wäljas M, et al. Outcome from Complicated versus Uncomplicated Mild Traumatic Brain Injury. Rehabil Res Pract. 2012;2012:415740. doi:10.1155/2012/415740 ↩