[Challenges of Diagnostic Imaging of Chronic Traumatic Encephalopathy]

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive mild traumatic brain injury (rmTBI). Clinically, CTE experienced by athletes with rmTBI can lead to long-term neurological impairment, including memory disturbances, Parkinsonism, behavioral changes, speech irregularities, and gait abnormalities, formerly described as punch-drunk syndrome and dementia pugilistica. CTE has gained significant public interest owing to dramatic cases involving retired professional athletes wherein severe behavioral problems and tragic incidents were reported. However, no reliable biomarkers of late-onset neurodegenerative diseases following TBI are available, and a definitive diagnosis can only be made via postmortem neuropathological examination. CTE is characterized by abnormal accumulation of hyperphosphorylated tau proteins. Neuropathological studies have revealed that CTE demonstrates a unique pattern of tau pathology in neurons and astrocytes and accumulation of other misfolded proteins such as TDP-43. Furthermore, gross pathological findings were revealed, especially in severe CTE. Thus, we hypothesized that objective neuroimaging patterns linking the history of rmTBI or CTE might be established using tau positron emission tomography (PET) and magnetic resonance imaging (MRI). In this review, we present the clinical and neuropathological features of CTE and our efforts to develop a prenatal diagnostic method using MRI and tau PET. The unique findings of tau PET images and various signal and morphological abnormalities on conventional MRI in retired athletes with rmTBI may be useful in diagnosing CTE.