Hypopituitarism

Definitions & Key takeaways

Hypopituitarism refers to the underproduction of any of the hormones released by the pituitary gland. If all of the pituitary hormones are underproduced, it's called panhypopituitarism. Hypopituitarism can be caused by tumors, pituitary hemorrhage or infarction, or accidental damage during radiation or surgery. Symptoms vary greatly depending on which hormones are impacted. Common symptoms include fatigue, weight gain, depression, low blood pressure, and problems with sexual function.

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Introduction0:00–0:27

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.

Physiology0:27–2:46

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.

Pathophysiology2:46–5:11

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.
The second, and less common way that hypopituitarism caused by pituitary apoplexy can develop is when there’s infarction of the pituitary gland.An example would be Sheehan’s syndrome which is commonly associated with pregnant women.
During pregnancy, there’s an increased demand for blood by the pituitary cells and coupled with excessive blood loss during childbirth, it leaves pituitary cells without adequate blood flow and they start to die.
If the blood flow isn't restored soon enough, more and more tissue dies, and over time, the pituitary gland shrinks, becomes scarred, and it can no longer effectively secrete hormones.Finally, there are iatrogenic causes of hypopituitarism like when there’s unintentional damage to the pituitary gland during radiation therapy or neurosurgery.Symptoms of hypopituitarism can vary greatly depending on which hormones become depleted.In general, luteinizing hormone, follicle- stimulating hormone, and growth hormone are lost before thyroid stimulating hormone and adrenocorticotropic hormone.

Symptoms5:11–7:26

So let’s go through these in order. Hyposecretion of follicle-stimulating and luteinizing hormone, together known as gonadotropins, can cause problems for men and women.
Women may experience oligomenorrhea, which is a decrease in their menstrual bleeding, or amenorrhea which is a complete absence of menstrual bleeding, and possible infertility.Men may experience loss of pubic hair and a reduction in muscle mass.Both men and women commonly complain of a diminished libido.Loss of gonadotropins is also seen in Sheehan syndrome, resulting in similar symptoms like absent menstruation, but the loss of prolactin also causes problems with postpartum lactation.
Moving on, a lack of adrenocorticotropic hormone causes adrenal insufficiency, or a lack of cortisol production by the adrenal glands and that leads to weight loss, delayed puberty, and low blood sugar and sodium levels.
Growth hormone deficiency results in a failure to grow in children, delayed puberty in adolescents, and lean body mass, and low bone density in adults.
Hypopituitarism can also cause hypothyroidism due to the diminished production of thyroid stimulating hormone with classic symptoms such as weight gain, constipation, hair loss, and low blood pressure.Finally, in addition to all the endocrine abnormalities seen in hypopituitarism, if there’s a tumor or fluid build up, it can cause local symptoms like increased intracranial pressure and headaches.
The pituitary gland is also close to the optic chiasm which is where the optic nerves cross. So any extra pressure in the area will press on these nerves and lead to visual field defects like bitemporal hemianopsia where the person suffers partial blindness in the lateral fields of both eyes.
Diagnosis of hypopituitarism is usually done by first assessing baseline levels of hormones in the morning, which accurately measure all the pituitary hormones except for growth hormone and adrenocorticotropic hormone because those hormones levels are more variable throughout the day.Next, it’s helpful to see how hormone levels change in response to a substance that should stimulate hormone release.

Diagnosis7:26–8:16

For example, administering insulin should cause a drop in blood sugar, which in turn stimulates the release of growth hormone and adrenocorticotropic hormone from the anterior pituitary.
If these hormone levels remain low despite the stimulatory effects of insulin, it may indicate hypopituitarism.Finally, MRI scans can help to look for possible causes of hypopituitarism, like tumors and hemorrhage.Treatment of hypopituitarism are based on correcting the underlying cause.

Treatment8:16–8:32

In the case of an adenoma, surgery can be performed to remove the tumor. Hormone replacement therapy might be needed if the pituitary damage is severe.
##SummaryAll right, as a quick recap: Hypopituitarism is the under-secretion of any of the hormones normally produced by the pituitary gland located at the base of the brain.

Review8:32–8:52

It is caused by tumors, pituitary hemorrhage or infarction, and by accidental damage during radiation or surgery. Lastly, it can be treated by hormone