Figure 23. Oncocytomas represent silent gonadotroph adenomas with extensive oncocytic change. The tumor cells are arranged solid nests, and contain abundant granular eosinophilic cytoplasm (a). Immunohistochemistry identifies SF-1 nuclear reactivity and cytoplasmic staining for α-subunit as well as β-subunits of the gonadotropins, e.g. β-FSH in this tumor (b).