Cause of Tumors Isn’t Yet Known

Uterine fibroids, also called leiomyomas, myomas or fibromas, are rubbery nodules that begin as irregular cells in the muscular layers of the uterus. Benign growths, they affect up to a quarter of all women younger than 50, especially women in their 30s and 40s.

They usually grow slowly and erratically into smooth muscle bound by fibrous connective tissue, varying in size from a pinhead to a watermelon.

No one knows what causes fibroids, but experts believe estrogen stimulates their growth: They do not occur before puberty; they grow larger on the birth control pill and during pregnancy, and disappear or shrink with menopause, although they can come back if a woman goes on hormone replacement therapy.

Some believe environment may also play a role, because African women have a lower incidence of fibroids than African American women, half of whom in their 30s and 40s will have fibroids.

There are three types of fibroids: submucous, which grow under the lining of the uterus, called the endometrium; intramural, which expand within the wall of the uterus; and subserous, which grow out from the outer wall of the uterus. Sometimes a fibroid will grow at the end of a thin stalk that remains attached to the uterine wall; this is called a pedicule.

Many fibroids cause no symptoms, so women don’t know they have them until a doctor does an internal exam.

The most common symptom is heavy menstrual bleeding, which can cause anemia and weakness. If large enough, they can push against a ureter, which carries urine from the kidney, or against the bladder or bowel and cause incontinence or constipation. They also can cause the stomach to expand--most doctors refer to the size of the tumor by comparing it to a certain point in pregnancy.

Fibroids that block the fallopian tubes or distort the cervix, the opening into the uterus, may prevent some women from becoming pregnant or can cause miscarriage or early delivery.

Rapidly growing fibroids worry some doctors who fear that the presence of a large fibroid makes it difficult for the doctor to feel the ovaries during an exam or may signal uterine cancer. But others say that ovarian cancer and uterine cancer are rare in women under 50, and ultrasound can be used to look at the uterus and ovaries for signs of cancer.