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.
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.
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.