Clinical and histopathological characteristics of gonadotropin-producing pituitary adenomas.

The clinical and histopathological characteristics in six cases of gonadotropin-producing adenoma are presented. Definitive diagnosis was made by the determination of gonadotropin levels in culture medium. Several authors have reported that gonadotropin-producing adenomas are very rare; however, hormonal assay of adenoma cell culture medium may indicate the real incidence of gonadotropin-producing adenomas to be greater than is thought. In reported cases, practically no endocrinological symptoms have been found suggesting increased gonadotropin levels, and basal values of plasma gonadotropins have been reported as only slightly over the normal range. Gonadotropin-producing adenomas may have been misdiagnosed as nonsecreting adenomas. The clinical characteristics of gonadotropin-producing adenomas can be summarized as follows: 1) a tendency for more rapid growth than nonsecreting adenomas; 2) prominent suprasellar extension with marked enhancement on computerized tomography; and 3) diminished response of luteinizing hormone (LH) alone in response to LH-releasing hormone (LH-RH) stimulation, and the ratio of peak follicle-stimulating hormone to peak LH in the LH-RH stimulation test is more frequently over 1:1 in cases of gonadotropin-producing adenoma than in cases of nonsecreting adenoma and craniopharyngioma. Immunoperoxidase staining revealed two kinds of adenoma cells, one intensely and the other faintly stained. Abundant mitochondria and few secretory granules were characteristic electron microscopic features. Oncocytic transformation of adenoma cells was suggested by immunoperoxidase staining and the electron microscopic appearance, and may suppress the elevation of circulating plasma gonadotropin levels. Thus, hormonal assay of adenoma cell culture medium and immunoperoxidase staining are essential for definitive diagnosis of gonadotropin-producing adenomas.