What is a pituitary tumor?

A growth: A pituitary tumor is simply a growth on the pituitary. It's not cancerous but it could cause problems by increasing or decreasing pituitary hormone secretion. It can also cause visual problems if it's big enough.

Uncontrolled cells: The pituitary gland is full of very complex cells that are very reactive to factors from the brain and produce complex hormones that control many functions of the body. At times, these cells become uncontrolled and start to produce hormones in excess and grow too big. These cells form tumors that may cause severe problems with body regulation. Surgery is usually necessary.