Thyrotropin-producing pituitary adenoma discovered as a pituitary incidentaloma

A 46-year-old woman with incidentally discovered thyrotropin (TSH)-producing pituitary adenoma showed endocrine data which was consistent with TSH-producing pituitary tumor. However, she showed only slight hyperthyroidism and the oversecretion and autonomous secretion of TSH from the tumor seemed to be limited from the results of several endocrine examinations. Immunohistochemical examination revealed that not only TSH-beta and TSH-alpha but also prolactin and growth hormone synthesizing cells were present in the tumor tissue. Pituitary-transcription activator 1 (Pit-1) immunoreactivity was also detected in the adenoma cell nuclei. It was conceivable that the presented TSH-producing adenoma clinically located close to the non-functioning adenoma and Pit-1 may have played an important role in the multidirectional differentiation or development of this tumor.