Selective neurofibrillary degeneration of the hippocampal CA2 sector is associated with four-repeat tauopathies.

The CA2 sector of the hippocampus is relatively resistant to neurofibrillary tangles in aging and Alzheimer disease; however, some cases have selective neurofibrillary degeneration in CA2 with sparing of the more vulnerable CA1 sector. Cases such as this do not fit in the Braak and Braak staging scheme and can be considered to have an atypical pattern of neurofibrillary degeneration. We identified 24 atypical cases with an average age at death of 78.