FSH-producing pituitary neuroendocrine tumor as a cause of ovarian hyperstimulation syndrome.

Functioning gonadotroph tumors are very rare neuroendocrine tumors of pituitary origin. Women of reproductive age presenting with bilateral multi-cystic ovarian enlargement, irregular menstrual cycles, and hyperestrogenemia under unsuppressed follicle-stimulating hormone (FSH) levels should be evaluated for FSH-producing tumor. Raising awareness of OHSS due to functioning gonadotroph tumors is crucial to prevent unnecessary ovarian surgery. Comprehensive histological analysis may provide useful information to better understand the characteristics of functioning gonadotroph tumors.