What is it?

A benign, non-cancerous, pituitary gland tumor is a type of growth that will not spread outside your gland to the rest of your body. It may grow locally, and cause problems because of it, but it is usually not a life-threatening disease.
The Pituitary gland, or hypophysis, is a pea size organ located right below you brain. Its main job is to secrete different hormones to your blood- each group of cells secretes a different type of hormone.
An abnormal growth of the pituitary gland can lead to a high or low level of hormones. Another effect of this overgrowth appears if it presses nearby parts of your brain and causes nerve damage, most commonly the one responsible for your vision.
A Prolactinoma is the most common overgrowth of the pituitary. It secrets the hormone prolactin.
This overgrowth is benign, not cancerous, but it can cause different symptoms.