Paired twisted filaments: a new ultrastructural marker of human pinealomas?

Paired twisted filaments (PTF) forming helices are described in tumor cells of three human pinealomas. Each filament was 8.11 +/- 1.55 nm wide. The maximal width of the helix was 16.62 +/- 2.62 nm. The periodicity of the constrictions was 26.63 +/- 4.49 nm. These characteristics appeared original, suggesting protein filaments possibly specific of pinealocytes. The similarities and discrepancies between PTF and Alzheimer's paired helical filaments (PHF) are discussed.