Prolactinoma

Overview

A prolactinoma is a benign or noncancerous tumor of the pituitary gland, a pea-sized gland at the base of the brain that makes hormones.

Prolactinomas increase the production of prolactin, which is responsible for milk production, lactation, and certain breast tissue development. As the tumor grows, it can cause very high levels of prolactin in your blood.

Prolactinomas are the most common type of hormone-producing pituitary tumors. Doctors can often treat them with prescription medicines alone. These medications, called cabergoline and bromocriptine, effectively lower prolactin levels and can, in most cases, shrink the tumor. In some exceptional cases, your care team may recommend surgery, radiation therapy, or both.

What causes prolactinoma?

The exact cause of prolactinomas is unknown, but there are several possible causes, like:

• Genetic conditions can increase the risk of developing a prolactinoma, including multiple endocrine neoplasia types one and four and familial isolated pituitary adenomas (FIPAs)
• Mutations in the cells of the pituitary gland, resulting in a large number of cells and causing the production of too much prolactin

Producing too much prolactin (hyperprolactinemia) can also occur for reasons other than a prolactinoma, including:

• Chest wall injuries
• Medications
• Other types of pituitary tumors
• Kidney and liver disease
• Underactive thyroid gland
• Pregnancy and breastfeeding

In men, prolactinoma symptoms can look like:

• Impotence
• Decreased size of testicles
• Decreased beard growth
• Muscle weakness
• Breast enlargement
• Milk production and secretion (galactorrhea)
• Infertility
• Headache
• Vision changes (severe cases only)

It’s possible to have a prolactinoma but not to show any symptoms. Between 5 to 10 percent of adults will fall into this category, although asymptomatic prolactinomas are more common in men than in women.

As a whole, women tend to report their symptoms earlier than men because their symptoms are more outwardly observable—abrupt changes to their menstrual cycle or discharge from their breasts when they’re not pregnant or breastfeeding. But for women who are on hormonal birth control, hormone therapy, or are post-menopausal, these same symptoms might not occur, thus making the reporting of these symptoms less likely.

Prolactinoma Diagnosis

Diagnosing a prolactinoma can be challenging because prolactin levels can be high for reasons besides a tumor—think pregnancy, stress, or a thyroid disorder.

The most common diagnostic tools for prolactinoma involve two procedures:

1. Blood Testing. Your doctor can perform a blood test to determine if abnormally high prolactin levels are present. A standard level of prolactin is less than 20 nanograms per milliliter. In comparison, a level of more than 150-200 nanograms per milliliter strongly suggests a prolactinoma.
2. Imaging. If your blood test shows elevated levels of prolactin, your doctor will order a magnetic resonance imaging (MRI) scan to determine the location of the tumor in your pituitary region.

After these two procedures, other diagnostic tests may be enlisted, like a visual field test to check for optic nerve compression or a bone densitometry scan to look for evidence of osteoporosis.

Doctors classify prolactinomas by their size. A microprolactinoma is a tumor less than 1 cm in diameter that generally responds to treatment. A macroprolactinoma is a tumor greater than 1 cm in diameter that responds to treatment but may require more aggressive therapy.

What if I’m pregnant and diagnosed with a prolactinoma?

If you’re pregnant and are diagnosed with a prolactinoma, your doctor will carefully monitor the tumor to observe any changes in size. Regular vision tests will also be performed during your pregnancy, as the size of the tumor may increase and impinge on the optic nerves, which connect the eye to the brain, causing visual field defects. 

For women who wish to become pregnant and already have a prolactinoma, we encourage you to talk with your provider. Those with a small prolactinoma, or microprolactinoma, can expect a healthy pregnancy. Those with larger prolactinomas, or macroprolactinomas, may need to be treated medically first and followed up closely. In rare cases, it may be advisable to consider surgery before becoming pregnant.

Prolactinoma Treatments

Generally, the first line of treatment for prolactinoma is medical rather than surgical. Whichever treatment your medical team recommends, it will be important to regularly monitor your prolactin levels and the size of your prolactinoma.

Using precise instruments, the neurosurgeon enters the nasal cavity and creates an opening in the sphenoid bone. Further openings create a hole in the sella turcica, the bone that cradles and protects the pituitary gland.

Once the tumor appears in the operative field, removal occurs. Your neurosurgeon will use high magnification to help distinguish the tumor from normal pituitary tissue. After the tumor has been removed, the tumor cavity is cleaned and sealed off.

The surgery aims to minimize pain, discomfort, and trauma to the tissue surrounding your pituitary gland while maximizing your chance for a quick and uneventful recovery. Most prolactinoma patients can return home the day after their surgery.