Hypopituitarism

With hypopituitarism, “hypo” means under and “pituitarism” refers to the pituitary gland which normally secretes various endocrine hormones.

So hypopituitarism is the underproduction of hormones released by the pituitary gland, and the symptoms depend on which hormones are actually undersecreted.

If all of the pituitary hormones are affected, it’s called panhypopituitarism.

The pituitary is a pea-sized gland, hanging by a stalk from the base of the brain.

It sits just behind the eyes near the optic chiasm, which is where the optic nerves cross and the gland rests in a very small depression of the skull known as the sella turcica.

The pituitary gland produces and secretes hormones when it receives signals from another part of the brain called the hypothalamus.

Together, they form the hypothalamic-pituitary axis which regulates the release of all the major endocrine hormones.

The pituitary itself has two distinct parts: the anterior pituitary and the posterior pituitary.

The anterior pituitary, which is the front of the pituitary gland, contains a few different types of cells, each of which secretes a different hormone.

The largest group of cells are the somatotropes which secrete growth hormone, which goes on to promote tissue and organ growth.

The second largest cell group are the corticotrophs which secrete adrenocorticotropic hormone, or ACTH, which stimulates the adrenal glands to secrete cortisol, a hormone that controls the stress response, blood pressure, and metabolic regulation.

A smaller cell group are the lactotrophs which secrete prolactin.

Prolactin stimulates breast milk production, and also inhibits ovulation, which is when an egg cell is released from the ovary, and inhibits spermatogenesis, which is the development of sperm cells.

There are also thyrotrophs which are cells that secrete thyroid stimulating hormone, or TSH, that stimulate the thyroid gland.

And finally, there are the gonadotrophs which secrete two gonadotropic hormones - luteinizing hormone, or LH, and follicle-stimulating hormone, or FSH, both of which go on to stimulate the ovaries or testes.

The posterior pituitary, which is the back of the pituitary gland releases the antidiuretic hormone, or ADH, which is made by a part of the brain called hypothalamus.

ADH acts on the kidneys to decrease the amount of water lost in the urine.

The posterior pituitary also produces oxytocin which is responsible for uterine contractions during labor and milk letdown during breastfeeding.

Hypopituitarism can be the result of compression, tissue ischemia or infarction, and iatrogenic or medically-induced injuries. Let's start with compression.

Because the pituitary exists within the very confined space of the sella turcica, it’s very sensitive to changes in that space. Even the slightest bit of compression can interfere with the pituitary’s hormone production.

In adults, the most common cause of compression is a pituitary tumor or adenoma, and in children, the tumor is usually a craniopharyngioma.

Craniopharyngiomas are pituitary tumors that develop from the cells of Rathke’s pouch, a structure that normally develops into the anterior pituitary gland during fetal development.

In addition to solid tissue compressing the pituitary gland, liquid like cerebrospinal fluid can also have the same effect.

In empty sella syndrome, for example, the sella becomes filled with cerebrospinal fluid and it can make the pituitary shrink or flatten and ultimately become nonfunctional.

Hypopituitarism can also be due to pituitary apoplexy, which is a disorder where there is either severe bleeding such as a hemorrhage, or a loss of blood flow to the pituitary gland, known as infarction. The more common way is a hemorrhage.

The hemorrhage is usually caused by a pituitary adenoma, which is a benign tumor of the anterior pituitary gland.

Larger tumors demand more blood, and increased blood flow means increased pressure in the vessels, eventually causing them to rupture and bleed.