The gonadotroph origin of null cell adenomas.

Objective: The term "null cell" adenoma was first proposed in 1980 to designate pituitary adenomas lacking clinical, biochemical and morphological markers to disclose their cell origin.

Methods: The aim of this study was to investigate the presence of α- and β-gonadotropin subunits in clinically nonfunctioning pituitary tumors, which were initially immunonegative and thus diagnosed as null cell adenomas. For this reason, we reapplied immunohistochemistry using a more sensitive method comprising a tyramide signal amplification technique, combined with a polymer antibody immunohistochemical detection system.

Results: With this approach, all these previously negative tumors became positive for α- and β-gonadotropin hormone subunits.

Conclusions: Our results prove that so-called "null cell" adenomas produce α-SU or/and β-FSH or β-LH and therefore are gonadotrph adenomas in origin.