Introduction: Although active gonadotropin-secreting pituitary adenomas are considered very rare, the vast majority of pituitary tumours diagnosed as “non-functioning” express gonadotropins or their free β or α subunits. However, systemic investigations comparing the serum concentrations of follitropin (FSH), lutropin (LH), and α–subunit (αSU) before surgery with the immunoreactivity of the respective substances in the excised tumours are still lacking.

Material and methods: Immunostaining of FSH, LH, and αSU was compared in 43 surgically removed gonadotropin — expressing pitu­itary adenomas with serum concentrations of the above-mentioned substances before surgery in the same patients.

Results: The serum concentrations of FSH were elevated (> 11.6 mU/mL) in 8/12 (66.7%) cases of FSH-positive adenomas. By contrast, in FSH–negative tumours the elevation of FSH is absent. Moreover, only 1/25 (4%) patients with LH–positive adenoma had the elevated serum concentration of LH (51.5 mU/mL). The overproduction of LH was not observed in adenomas expressing free β LH or in LH-negative tumours. In patients with αSU-positive adenomas elevated serum levels of αSU were observed in 3/15 (20%) cases. No αSU elevations were observed in patients with αSU–negative adenomas. The mean serum FSH, LH, and αSU concentrations were higher in patients with FSH, LH, and/or αSU immunopositive tumours in comparison with immunonegative. However, the differences are not statistically significant.

Conclusions: Although “silent” gonadotropinomas constitute a frequent subtype of pituitary adenomas, the “active” subtype (i.e. manifesting by gonadotropin excess) are rare (approx. 4% of all pituitary adenomas). Gonadotropinomas are difficult to diagnose before surgery. The measurement of gonadotropins including αSU is needed but often not sufficient for presurgical diagnosis.