FSHB and adenoma: Most CNFPA are of gonadotrophic differentiation as they immunostain for α-subunit, LHβ and/or FSHβ and are conditioned by the transcription factor NR5A1 but also include silent corticotroph, somatotroph or lactotroph adenomas as well as null cell adenomas, which do not immunostain for any known hormone [3, 4].