Recent Clinical and Pathophysiological Advances in Non-Functioning Pituitary Adenomas

Pituitary adenomas are being recognized and diagnosed with increasing frequency. One of the most common forms of pituitary lesion is the clinically non-functioning pituitary adenoma (NFPA), which is often diagnosed incidentally. The vast majority of pituitary adenomas are sporadic, but familial adenomas can occur in the multiple pituitary adenoma type 1 syndrome, in Carney complex or in familial isolated pituitary adenoma. Distinguishing NFPA from prolactinomas can occasionally cause a differential diagnostic problem due to the 'stalk effect'. NFPA often show hormone synthesis on tissue immunostaining without causing clinical symptoms. Most often these are silent gonadotroph adenomas, with silent corticotroph or somatotroph adenomas occurring less frequently. It is unclear why these silent adenomas do not release hormones at a clinically recognizable level, although it is probable that there is a continuum between fully functional and completely silent adenomas. Another intriguing feature of NFPAs is the lack of clinical response to somatostatin analogues, despite the presence of somatostatin receptors and an often good response in the in vitro setting. Temozolomide has been successfully used for the treatment of a few aggressive pituitary adenomas, and the response to this drug could be influenced by the expression of the DNA repair enzyme O-6-methylguanine DNA methyltransferase. The early diagnosis, prediction of long-term outcome and treatment of NFPAs remain a challenge for endocrinologists.