Tumors of the pituitary gland comprise a unique category of intracranial tumors. Although strictly speaking, not actually brain tumors at all, they often produce symptoms by extension into the region underneath the brain and compression of various neural structures. Most commonly involved are the optic nerves and optic chiasm (the location where some of these nerve fibers cross). These nerves transmit visual information from the retina in the eye to the central nervous system. Compression of the optic apparatus can result in blurring of the vision and loss of peripheral vision. If untreated this can progress to blindness in one or both eyes. Other nerves involved in eye movement can also be affected and very large tumors can cause a wide variety of neurological symptoms.

A second way that pituitary tumors can cause health problems is through disruption of the normal hormonal systems regulated by the pituitary gland. The pituitary is sometimes referred to as the "master gland", because many other endocrine glands such as the thyroid and adrenals are regulated by substances produced in or passing through the region of the pituitary. In fact, the pituitary and its related hormonal factors are responsible for a wide range of normal functions in the body. A pituitary tumor can produce symptoms by either over-production of some hormonal factor or by limiting production of others.