CTE is categorized into four stages based on the extent and distribution of tau pathology:
Stage I: Sparse, focal perivascular neurofibrillary tangles, primarily in the sulcal depths of the frontal cortex. Stage II: Multiple foci of neurofibrillary tangles, with more widespread involvement of the frontal and temporal cortex. Stage III: Extensive tau pathology affecting the frontal, temporal, parietal, and insular cortices, often with hippocampal involvement. Stage IV: Severe tau pathology encompassing widespread cortical regions, including the brainstem and cerebellum.
