Prolactinomas or lactotroph cell tumours (Fig. 2.4) are the most common pituitary tumours, accounting for approximately fifty per cent of all such tumours. For many years, these tumours were considered to be nonfunctioning; however, with the discovery of human prolactin, and with the development of radioimmunoassays, it has become clear that most of these so-called nonfunctioning pituitary tumours are prolactinomas.
