In an interview with Good Housekeeping, the star revealed that the tumour, which is in her pituitary gland, will stop her having children.
"We live in a time and place where we think everything is possible. I don’t know if I would have gone on to have children. But as soon as someone says you can’t have something, you want it more than anything," she said.
“Sometimes it [the tumour] is big and makes me mad, and sometimes it’s small and is in the background. I have various tests now to make sure the side effects aren’t too onerous."
Thankfully the condition, known as prolactinoma, isn't life-threatening. But what else do we know about it?
What Is A Prolactinoma?
According to The Pituitary Foundation, a prolactinoma is a tumour found in the pituitary gland that produces prolactin. Prolactin is a hormone released by the pituitary gland that stimulates lactation (milk production) after childbirth.
Prolactinoma tumours come in various shapes and sizes, but the vast majority are less than 10mm in diameter.
What Are The Common Symptoms Of A Prolactinoma?
For women, a change in the frequency of periods or a loss of periods all together can be the first sign of a prolactinoma.
This is because "excessive prolactin interferes with the pituitary’s production of the hormones FSH and LH which control the menstrual cycle," The Pituitary Foundation explains.
A woman with a prolactinoma may also experience reduced interest in sex (low libido), vaginal dryness and discomfort during intercourse.
Infertility can be a symptom of a prolactinoma for some women. This is because the change in hormone levels may cause impaired egg release by the ovaries.
Having excess breast milk which sometimes leaks spontaneously is another common symptom.
As with women, high levels of prolactin caused by a prolactinoma reduces production of FSH and LH by the pituitary gland for men.
"This in turn lowers testosterone levels and may result in a reduced interest in sex and in impotence. Men may also have infertility due to a low sperm count," The Pituitary Foundation says.
Milk production by the male breast can also occur, but this is a very rare symptom.
How Is A Prolactinoma Treated?
Whatever the size of the prolactinoma, it is likely that doctors will prescribe tablets for treatment.
"Drugs known as dopamine agonists are the first line medication in patients presenting with a prolactinoma," The Pituitary Foundation says.
"These drugs are safe and well tolerated by most patients. To minimise any side effects, particularly dizziness on standing up, nausea and headaches they should be taken with food."
Prolactin levels often fall to normal within a few weeks of starting the treatment. In most women, this will mean that usual menstrual cycles resume, interest in sex is regained and fertility is restored.
Men often experience a raise in testosterone levels once they begin medication, which often improves sex drive and potency.