Hypopituitarism is a condition characterized by an underactive pituitary gland, resulting in a deficiency of one or more hormones. This small gland at the base of the brain is often called the “master gland” because it regulates several other hormone-producing glands. Its hormones are responsible for managing growth, metabolism, reproductive function, and stress responses. When the pituitary fails to produce sufficient hormones, the functions of the glands it controls are compromised, and the specific consequences depend on which hormones are lacking.
Pituitary Tumors and Growths
The most prevalent cause of hypopituitarism is a tumor on or near the pituitary gland. Most of these are pituitary adenomas, which are benign growths. While not malignant, these tumors can cause harm as they expand. Their growth can compress and damage healthy pituitary tissue, disrupting the gland’s ability to produce and release hormones.
This pressure can also interfere with the gland’s blood supply, contributing to tissue damage. In some instances, a tumor may overproduce one hormone while compressing the cells responsible for others, creating a complex hormonal imbalance. Less commonly, other growths like craniopharyngiomas or cysts can develop in this region and exert similar damaging pressure.
Physical Damage and Trauma
Direct physical injury to the head or brain is a cause of pituitary dysfunction. Traumatic Brain Injury (TBI) from a severe blow to the head is an increasingly recognized factor. Such an impact can directly damage the pituitary gland or injure the pituitary stalk, which connects the gland to the hypothalamus. Damage to this stalk can interrupt the brain’s signals for hormone regulation.
Medical interventions can also lead to pituitary damage, known as iatrogenic injury. Brain surgery, especially to remove pituitary tumors, carries a risk of harming the surrounding gland tissue or its blood supply. This can compromise the function of the remaining gland.
Radiation therapy to the head or neck for treating cancers is another cause. The effects of radiation on the pituitary gland are often not immediate and can manifest slowly. Hypopituitarism can develop months or years after treatment, requiring long-term monitoring.
Diseases and Infections
The pituitary gland can be damaged by systemic diseases. In autoimmune conditions like lymphocytic hypophysitis, the body’s immune system mistakenly attacks pituitary cells. This inflammation causes the gland to swell and can destroy hormone-producing cells.
Infiltrative diseases cause hypopituitarism by allowing abnormal substances to accumulate within the gland. Conditions like sarcoidosis, which involves a buildup of inflammatory cells, and hemochromatosis, characterized by excess iron deposits, can disrupt the gland’s structure. This interferes with cellular processes and can lead to a progressive loss of hormone production.
Severe infections are a less common cause. Infections like tuberculosis or meningitis can spread to the brain and tissues surrounding the pituitary gland. The resulting inflammation and potential for abscess formation can cause direct and permanent damage to the gland.
Vascular and Blood Flow Problems
Disruptions in blood flow can cause hypopituitarism, as the gland requires constant oxygen to function. One related condition is Sheehan’s syndrome, a rare complication of childbirth. It occurs when a mother experiences severe blood loss, lowering blood pressure and depriving the pituitary of oxygen, which causes tissue death.
Another vascular event is pituitary apoplexy, a sudden condition involving bleeding into the pituitary gland or a blockage of its blood supply. It often happens in individuals with an undiagnosed pituitary tumor. The sudden hemorrhage increases pressure within the skull, causing severe headache, vision problems, and a swift decline in pituitary function, which is a medical emergency.
Congenital and Genetic Factors
In some cases, hypopituitarism is present from birth, known as congenital hypopituitarism. This occurs when the pituitary gland does not develop correctly during fetal growth. The causes are often genetic, from mutations in genes that guide pituitary formation or hormone synthesis.
These genetic changes can be inherited. The result can be a deficiency in a single pituitary hormone or a complete absence of multiple hormones. This form is identified in infancy or early childhood when a child fails to grow properly or shows signs of delayed puberty.