Prolactinomas secrete excess prolactin and are the most common pituitary adenoma. The normal blood prolactin level is typically less than 20-25 ng/ml. In general, the prolactin level correlates with the size of the prolactinoma. 

In most women, prolactinomas are detected when they are smaller (microadenomas) and the prolactin level is moderately elevated (50 - 300 ng/ml). A relatively small elevation in prolactin will cause irregular menstrual periods or amenorrhea and galactorrhea. In contrast, in men prolactinomas are typically detected when they are larger (macroadenomas), with prolactin levels over 500 - 1000 ng/ml. Most men with a prolactinoma have some degree of pituitary failure (hypopituitarism), especially hypogonadism. Women and men also typically have a reduced sex drive (decreased libido) and weight gain. With larger tumors, headaches and visual loss (from compression of the optic nerves or optic chiasm) can occur. A minority of patients with large tumors may have hemorrhage into a tumor (pituitary apoplexy) causing rapid onset of headache, visual loss, double vision, and pituitary failure.

Prolactinomas are typically diagnosed because of problems related to high prolactin and associated hypogonadism or with macroprolactinomas, prolactinomas may cause headaches, visual loss or bleeding (apoplexy).
Hormonal diagnosis: A prolactinoma is diagnosed by demonstrating elevated blood prolactin levels. A prolactin level of over 150-200 ng/ml is almost always due to a prolactinoma. However, moderate prolactin elevations (30-200 ng/ml) can occur from other causes such as pregnancy, stress (discomfort, exercise), low thyroid function (hypothyroidism), kidney or liver failure and medications (e.g., haloperidol, antidepressants, verapamil). An additional cause of high prolactin level is "stalk compression effect" from a pituitary or brain tumor that compresses the pituitary stalk. Other adenomas, craniopharyngiomas, Rathke’s cleft cysts and other brain tumors may cause modest prolactin in the range of 40 – 150 ng/ml.

Imaging: Prolactinomas can be best visualized on a pituitary MRI performed with and without gadolinium. 

Medical therapy: In general, the first line of treatment for patients with a prolactinoma is medication rather than transsphenoidal surgery. Approximately 80% of patients will have prolactin levels restored to normal with dopamine agonist therapy and many will have marked tumor shrinkage. The most commonly used agent is cabergoline (Dostinex) which has replaced bromocriptine (Parlodel) as the drug of choice given cabergoline’s higher success rate and lower side-effect rate. Most women have return of menses and many become fertile again. Tumor shrinkage will often results in rapidly improved vision and headache resolution. Dostinex is taken only twice per week and generally has few side effects. It is also effective in patients whose prolactinomas are resistant to bromocriptine therapy. The usual starting dose is 0.5 mg twice per week and may be increased up to 1.0 mg twice per week. Bromocriptine, if used, should be started at a low dose to minimize nausea and other gastrointestinal side effects, usually 2.5 mg tablet per day at mealtime. The dose is then increased over several days or weeks to a daily maximum usually no exceeding 10 mgs.

Recent reports indicate that long-term high-dose therapy with a dopamine agonist like cabergoline or bromocriptine can result in heart disease that affects the valves specifically. Although the risk of valvular heart disease appears to be low with standard doses of cabergoline and bromocriptine used to treat prolactinomas, it remains a potential risk.

Transsphenoidal Surgery: Endonasal tumor removal is a reasonable first-line therapy in patients with micro-prolactinomas that do not invade the cavernous sinus and whose prolactin level is less than 250 ng/ml. In these patients, long term remission is generally 80-90%. Surgery is also effective for lowing prolactin levels in patients intolerant of Dostinex. However, for macroadenomas, the cure rate is generally low. In men with large invasive prolactinomas it average less than 30%. Even in patients with long-standing visual loss, dopamine agonist therapy can be tried first. However, if visual loss has occurred rapidly over less than 2 weeks, or if the MRI shows hemorrhage or degeneration in the tumor, endonasal surgery is generally recommended. For the minority of patients who do not respond well to dopamine agonist therapy with cabergoline, surgery should generally be performed within 6 months of starting therapy. After more than 6 months of such therapy the tumor may become more fibrotic and difficult to remove.

Radiosurgery (SRS) or Stereotactic Radiotherapy (SRT): Because most patients with prolactinomas respond so well to dopamine agonist therapy and/or surgery, radiation therapy is rarely required.