Small nonfunctioning tumors (those that do not make hormones) may be asymptomatic. When these tumors enlarge, they may compress surrounding structures and cause a variety of symptoms, including visual loss, headaches and damage to the normal pituitary gland. Visual loss is typically characterized by loss of peripheral vision but can take other forms. Damage to the pituitary gland can result in hormone deficiencies. This is called "hypopituitarism.” Symptoms may result from loss of hormones, which include cortisol, thyroid hormone, estrogen or testosterone.

It is unknown why these tumors develop. What is known is that they are generally benign, usually slow growing and are often present for years before diagnosis. They are thought to arise from a mutation or mutations in a single pituitary gland cell, but it is unknown why or how this happens, except in a minority of very rare inherited syndromes. Research is ongoing in the MGB Pituitary Center into the causes of and treatments for these tumors.

Complications of non-functioning pituitary adenomas generally arise as they grow large and impinge on surrounding structures, including the optic (visual) system, the pituitary gland, and the brain. After surgical removal, visual symptoms will usually improve, hormone function improves in about 50% of cases, and headaches often, but not always, resolve.

Nonfunctioning pituitary tumors are usually diagnosed by MRI. Sometimes an MRI is performed because a patient presents with hormone deficiencies. Other times, it is ordered because of visual loss or headaches. If an MRI demonstrates a pituitary tumor, hormone evaluation by an endocrinologist with expertise in pituitary function is indicated to determine whether the tumor is secreting a hormone or causing hormone deficiencies. If the tumor is large enough to compress the optic chiasm or nerves (visual system), a prompt ophthalmologic exam, including formal visual field testing, is very important.

The primary treatment for nonfunctioning pituitary adenomas is transsphenoidal surgery. Studies have shown that outcomes are better when the surgery is performed by a surgeon experienced in this specific procedure. When the tumor cannot be fully removed by surgery or recurs after surgery, radiation may be recommended. Some small tumors can be followed closely with serial MRI imaging and treated only if the tumor enlarges. There is no effective medical treatment for nonfunctioning pituitary tumors, although this is an area under research investigation.