The pituitary gland is a small, pea-sized structure located at the base of the brain, residing within a bony pocket called the sella turcica. It acts as the central regulator of the body’s endocrine system, influencing nearly every physiological process by producing and controlling hormones. These chemical messengers regulate functions like growth, metabolism, reproduction, and the activity of other glands, including the thyroid and adrenals. Enlargement of this gland is most often caused by a slow-growing, non-cancerous growth known as a pituitary adenoma.
Immediate Risks and Mortality Associated with Pituitary Mass
The overall risk of death from an enlarged pituitary gland is low, especially when properly managed. Most pituitary adenomas are benign and highly treatable, meaning they do not spread to other parts of the body. The five-year survival rate for the majority of people diagnosed with a pituitary tumor is over 97%.
However, mortality risk is associated with severe, untreated cases or specific complications. Patients with non-functioning pituitary adenomas (NFAs) can have an increased standardized mortality ratio compared to the general population, often linked to long-term health issues from hormone deficiencies, such as cardiovascular and cerebrovascular diseases. Mortality can be higher in women and in individuals diagnosed at a younger age, tied to the long-term effects of hypopituitarism. This risk is concentrated in acute complications caused by the mass effect of the growth or a sudden hormonal imbalance. A timely diagnosis and consistent treatment plan are effective at mitigating these dangers.
How Enlargement Causes Life-Threatening Complications
An enlarged pituitary gland can become life-threatening through two main mechanisms: a mechanical “mass effect” on nearby brain structures or an acute “hormonal crisis.”
Mass Effect
The tight confines of the sella turcica mean that even a slow-growing mass can compromise surrounding areas. The most common mass effect is pressure on the optic chiasm, the point where the optic nerves cross, leading to progressive peripheral vision loss. More severely, a large growth, known as a macroadenoma, can extend upward to block the flow of cerebrospinal fluid, causing obstructive hydrocephalus. This results in a buildup of fluid within the brain, increasing intracranial pressure and leading to severe neurological decline. In extreme cases, a giant adenoma can exert pressure on the brainstem, which controls fundamental life functions such as breathing and consciousness.
Hormonal Crisis
The second, more acute mechanism is a hormonal crisis, most notably pituitary apoplexy. This is a medical emergency caused by sudden hemorrhage or infarction (loss of blood supply) within the growth. Symptoms include an abrupt, severe headache, vision loss, and a rapid decline in consciousness. Pituitary apoplexy is dangerous because it can cause acute adrenal insufficiency, also known as an Addisonian crisis. The sudden disruption prevents the production of adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to produce cortisol. A lack of cortisol leads to dangerously low blood pressure and shock, resulting in death within hours if high-dose corticosteroids are not administered immediately. Apoplexy can also lead to severe vascular complications, such as a stroke, by damaging the internal carotid arteries adjacent to the gland.
Identifying the Reasons for Pituitary Gland Enlargement
The vast majority of pituitary enlargements are caused by pituitary adenomas, which are classified as either functional or non-functional. This classification dictates the early symptoms and overall prognosis.
Functional Adenomas
Functional adenomas secrete an excess of one or more hormones, leading to specific endocrine disorders. Prolactinomas are the most common type, overproducing prolactin and often causing infertility or milk discharge. Other functional tumors produce growth hormone (GH), resulting in acromegaly or gigantism, or adrenocorticotropic hormone (ACTH), which causes Cushing’s disease.
Non-Functional Adenomas
Non-functional adenomas do not secrete a clinically significant amount of hormones. Instead, they cause issues primarily through the mechanical mass effect described previously. These tumors are often detected later because they do not cause noticeable symptoms until they grow large enough to compress the optic chiasm or other structures.
Less Common Causes
Other, less common causes of pituitary enlargement include:
- Rathke’s cleft cysts, which are benign fluid-filled sacs that can cause pressure effects.
- Inflammation of the gland, known as hypophysitis, which causes swelling and dysfunction.
- Long-term hypothyroidism.
- Normal pregnancy, as the body attempts to compensate for hormonal changes.
Management and Treatment to Mitigate Severe Outcomes
The risk of life-threatening complications is reduced by a timely therapeutic strategy tailored to the specific cause of the enlargement.
Medical Management
For prolactinomas, the first line of defense is medical management using dopamine agonist medications, such as cabergoline. These drugs can shrink the tumor and normalize hormone levels. Other functional tumors, like those causing acromegaly, may also be treated with medications such as somatostatin analogs to reduce hormone secretion and tumor size.
Surgery and Radiation
For most other adenomas, particularly large ones causing vision loss or mass effects, the primary treatment is surgical removal. The most common procedure is endoscopic transsphenoidal surgery, where the tumor is removed through the nose and sphenoid sinus, avoiding a craniotomy. This approach has low morbidity and mortality rates and is effective at decompressing neural structures. Radiation therapy, including stereotactic radiosurgery, is employed when surgery is incomplete or the tumor recurs.
Long-Term Care
Because treatment can sometimes damage remaining healthy tissue, many patients experience hypopituitarism. This requires lifelong hormone replacement therapy to prevent future hormonal crises. This ongoing management of deficiencies, such as the replacement of cortisol, is a necessary intervention that reduces the long-term risk of severe outcomes.