Prolactinoma

Definitions & Key takeaways

A prolactinoma is a benign pituitary gland tumor that produces high levels of the hormone prolactin. Prolactin then suppresses the gonadotropin-releasing hormone resulting in symptoms like amenorrhea, galactorrhea, hypogonadism, gynecomastia, and erectile dysfunction in males. Treatment involves the use of dopamine agonist agents like bromocriptine which reduces the size of the tumor and lowers prolactin levels. In some cases, surgery or radiation therapy may also be required.

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Introduction0:00–0:19

With prolactinoma, prolactin refers to the endocrine hormone secreted by the pituitary gland and -oma refers to a tumor.
So a prolactinoma is a benign tumor, or adenoma, of the pituitary gland that secretes excess prolactin. Normally, the pituitary is a pea-sized gland, hanging by a stalk from the base of the brain.

Physiology0:19–2:31

It sits just behind the eyes near something called the optic chiasm, which is where the optic nerves cross. The anterior pituitary, which is the front of the pituitary gland, contains a few different types of cells, and each of which secretes a different hormone.
One group of cells in the anterior pituitary are called lactotrophs and they secrete prolactin. Prolactin stimulates breast milk production.
Another group of cells are the gonadotrophs and they secrete two gonadotropic hormones - luteinizing hormone, or LH, and follicle-stimulating hormone, or FSH, both of which stimulate the ovaries in women which make estrogen and stimulate the testes in men which make testosterone.
Prolactin release is controlled by something called the hypothalamus, which is a structure at the base of the brain just above the pituitary gland.
It makes two key hormones, thyrotropin-releasing hormone which increases prolactin release, and dopamine, which inhibits the prolactin release and actually overrides the stimulatory effect of thyrotropin-releasing hormone.
That’s why dopamine is known as prolactin-inhibiting factor, and why it’s constantly released to prevent prolactin release in anyone that’s not pregnant.
High levels of prolactin in the blood sends a negative feedback signal to the hypothalamus, making it release more dopamine which then decreases prolactin levels.
High levels of prolactin can also signal the hypothalamus to decrease the secretion of gonadotropin releasing hormone or GnRH.
Gonadotropin releasing hormone acts on the anterior pituitary to make follicle stimulating hormone and luteinizing hormone or FSH and LH.
Now, during pregnancy the anterior pituitary gland releases prolactin and the placenta releases human placental lactogen and progesterone, and all three of these hormones stimulate the growth of more glandular tissue in the breast to produce milk.

Pathology2:31–4:36

Prolactinomas are functional tumors, meaning they secrete high levels of prolactin, and they typically form when there’s a mutation in the lactotroph cells of the anterior pituitary that allows the cells to divide uncontrollably.
The key is in the size of these things. Prolactinomas that are less than 10 mm in diameter are considered microprolactinomas, whereas those greater than 10 mm are known as macroprolactinomas.
Now, macroprolactinomas can compress surrounding structures like the meninges, which is the protective layer overlying the brain and that typically causes pain when it’s stretched.
Also, an enlarged pituitary gland can compress the optic nerves as they cross at the optic chiasm. This can cause visual problems as well as affect a person’s ability to view things that are in the temporal, or the outermost portion, of the visual field in both eyes, and this is called “bitemporal hemianopia”.
Another name for this is tunnel vision because the center of your vision is clear but everything in the periphery is dark, kind of like looking through a tunnel, I suppose.
As well as all the local effects, the prolactin that gets secreted by the pituitary inhibits the hypothalamus from releasing gonadotropin releasing hormone, which leads to a decrease in follicle stimulating hormone and luteinizing hormone from the pituitary.
This results in less estrogen being produced in the ovaries, and less testosterone from the testes. Low levels of these sex hormones can cause inhibition of ovulation in women, and inhibition of spermatogenesis in men.
In women, estrogen is also really important because it prevents the activation and differentiation of bone cells called osteoclasts.
Osteoclasts normally break down bones and release the calcium into the blood. So with decreased estrogen levels, osteoclasts are free to proliferate and therefore women with prolactinomas are at an increased risk of fractures and osteoporosis.

Symptoms4:36–5:17

So, when it comes to symptoms people with small prolactinomas, or microprolactinomas, often have no symptoms at all, whereas those with large prolactinomas, macroprolactinomas, might have vision problems, like bitemporal hemianopia, or headaches where the meninges are stretched.
In women, excess prolactin causes galactorrhea, which is a milky nipple discharge, amenorrhea, which is missed menses, vaginal dryness, and brittle bones in old age.
in men, excess prolactin causes gynecomastia or breast enlargement and erectile dysfunction. And both sexes can experience decreased libido and infertility.

Diagnosis5:17–5:38

The diagnosis of a prolactinoma is typically based on elevated levels of prolactin in the blood. Sometimes there’s also excess thyrotropin-releasing hormone which may be stimulating the pituitary gland to secrete prolactin.
Often, an MRI can be done to visualize the prolactinoma and classify it based on size. To treat prolactinomas you can use medication or chop it out surgically.

Treatment5:38–6:13

Since dopamine inhibits prolactin release, a clever way to treat it medically is with dopamine agonists like bromocriptine and cabergoline can be used to inhibit prolactin release.
Now, surgery is usually only considered for individuals with macroprolactinomas or in individuals who fail medical therapy.
If complete resection of the prolactinoma is not possible or if prolactin levels remain elevated after surgery, radiation therapy can sometimes be useful.

Review6:13–7:46

OK, we made it, that’s it. So let’s just quickly whizz over the main points - Prolactinomas are benign tumors of the anterior pituitary that result in the excess secretion of prolactin.
Excess prolactin can cause a wide range of symptoms including galactorrhea, which is a milky discharge from the nipples, gynecomastia, which is breast tissue growth in men, amenorrhea, or missed menstrual periods and infertility.
It is typically treated either with dopamine agonists or with surgery.