Beyond the Scan: Evaluating Diffuse Axonal Injury in Litigation

The Clinical Challenge of ‘Normal’ Imaging

In neurology medico-legal practice, the absence of radiological abnormalities on conventional CT or standard 1.5T/3T MRI does not exclude the presence of diffuse axonal injury (DAI). DAI represents a spectrum of traumatic brain injury resulting from rotational or shearing forces, causing microscopic disruption of axons. When these injuries occur at a scale below the sensitivity of standard imaging protocols, identifying the anatomical substrate for persistent post-concussive symptoms requires a careful reconciliation of clinical observations with structural possibilities.

For solicitors and insurers, this presents an evidentiary challenge. Under the ordinary rules of causation, the burden rests on the claimant to demonstrate that the TBI is the material cause of the reported cognitive or behavioural sequelae. Where scan reports are unremarkable, experts must differentiate between the physiological consequences of microscopic trauma and other potential aetiologies, including psychological reactions to trauma or pre-existing neurodegenerative markers.

Differential Diagnosis and Symptom Validity

Distinguishing between the sequelae of DAI and other clinical presentations is essential for robust litigation outcomes. A critical area of dispute involves Functional Neurological Disorder (FND), where symptoms may mimic organic damage. Expert opinion relies on a comprehensive evaluation of positive clinical signs to identify functional presentations. Diagnostic overreach, wherein functional symptoms are incorrectly attributed to minor DAI, remains a potential pitfall that experts must address by applying established clinical pathways in traumatic brain injury cases.

Similarly, the evaluation of cognitive impairment must account for the baseline neuropsychological profile. The assumption that every cognitive deficit following a traumatic event is a direct result of that event can lead to errors in apportionment. Causation analysis requires a thorough review of pre-incident medical history, looking for evidence of emerging neurodegenerative conditions or vascular issues that may have contributed to the current clinical picture.

The Role of the Expert under CPR Part 35

The expert’s primary duty is to the court, as stipulated in CPR 35.3. In cases involving DAI, this duty often requires the expert to manage expectations regarding the limitations of objective diagnostic evidence. An expert may be instructed to provide a condition and prognosis report, which requires an objective assessment of the Glasgow Outcome Scale (Extended) scores and a functional assessment of the claimant’s current limitations compared to their pre-morbid state.

When parties instruct separate experts, the court may direct them to engage in discussions under CPR 35.12 to narrow the issues. This process, which may culminate in a joint statement, is useful for identifying areas of agreement regarding the diagnosis—or the lack thereof—and the underlying mechanisms of the injury. Where the court directs the appointment of a single joint expert, that expert is instructed under CPR 35.8. It is imperative that the expert remains independent throughout these processes, focusing on the evidence at hand rather than the adversarial requirements of the parties. If complex disagreements persist, the expert may seek further directions from the court under CPR 35.14.

Practical Considerations for Litigation

Solicitors should focus on the following areas when managing cases involving potential DAI:

• Precision in Instructions: Ensure the expert is provided with a full chronological history, including all prior neurological or psychiatric consultations.
• Focus on Functional Impact: The evaluation should centre on the claimant’s ability to engage in activities of daily living, capacity assessments under the Mental Capacity Act 2005, and behavioural changes that may not be captured by standardised cognitive testing.
• Review of Imaging Protocols: Clarify whether the original imaging was limited to routine sequences or if specific diffusion-weighted or susceptibility-weighted imaging was performed, which may be more sensitive to micro-haemorrhages associated with DAI.
• Expert Neutrality: The probative value of an expert report in court relies on the clinician’s adherence to standard practice—ensuring the opinion is supported by a responsible body of neurological peers and withstands logical scrutiny.