Pituitary tumours can release high amounts of ACTH, which in turn stimulates the adrenal glands to produce excess cortisol. Pituitary tumours that produce growth hormone cause excessive bone growth or disfigurement. Prolacinomas are tumours that overproduce prolactin and disturb reproductive functions. They are the most common pituitary tumour. A pituitary tumour may become quite large. As it grows, the tumour can press against and damage the normal part of the pituitary gland or the nerves that carry vision from the eyes. Sometimes impaired vision is the first sign of a pituitary tumour.
The cause of pituitary tumours remains unknown. Most pituitary tumours are sporadic - they are not genetically passed from parents to offspring.
Autopsy studies indicate that 25 percent of the population of the USA have small pituitary tumours, but that few of these are clinically significant. Clinically significant pituitary tumours affect the health of approximately 14 out of 100,000 people.