Pituitary tumors arise from the pituitary gland within the base of the skull. These tumors are almost always benign. Symptoms arise when these tumors secrete hormones or become large enough to compress adjacent structures. Rarely, these tumors may spontaneously hemorrhage.

As these tumors enlarge, the normal pituitary function is destroyed. This produces various hormonal deficiencies, since the pituitary controls the action of other endocrine glands within the body. Pressure on near-by structures  can produces double vision and facial numbness. The nerves of vision, the optic nerves, are directly above the pituitary gland and upward growth of pituitary tumors frequently causes progressive visual loss. This visual loss is typically begins from each side of the field of vision leading to tunnel vision and then blindness.