Uterine Fibroid Embolization - Fibroids Background Information

What are Fibroids?

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Fibroids are benign tumors of smooth muscle, which is the type of muscle that makes up the uterus. They are also called leiomyomas or myomas. Fibroids may arise in different parts of the uterus, as shown in the figure.

Fibroids are named according to their position within the uterus; submucosal, intramural, and subserosal. A submucosal fibroid lies just under the inner lining of the uterus, which is called the endometrium. Some of these fibroids grow on a stalk. These are referred to as "pedunculated". An intramural fibroid that lies completely within the muscular wall of the uterus ("intra" means within and "mural" means wall). A serosal or subserosal fibroid lies on the outer part of the uterus, just under the covering of the outside of the uterus, which is called the serosa. Subserosal fibroids may also grow on a stalk and be called pedunculated.

Abnormal bleeding is usually caused by submucosal or intramural fibroids. Intramural and subserosal fibroids are the usual cause of pelvic pain, back pain, and the generalized pressure that many patients experience.

Who gets fibroids?

All women are at risk of getting fibroids. Uterine fibroids are the most common tumors of the female genital tract. They occur in 20 to 25 % of women of childbearing age. The presence of fibroids is the most common reason for a woman to have a hysterectomy in this country, totaling approximately 200,000 each year. In addition, many patients suffer symptoms from fibroids but never undergo a hysterectomy.

African-Americans are as much as 3.2 times as likely to develop fibroids as Caucasians. There is some variation among other racial groups. The reason for this increased risk is not known, although genetic variability is presumed to be a significant factor. While fibroids may appear in patients in their twenties, most patients do not have any symptoms until their late thirties or forties.

What causes fibroids?

The cause for fibroid development is not known. Leiomyomas arise after menarche (beginning of menstruation in adolescence) and regress after menopause, which suggests that the development of fibroids is dependent on the presence of hormones (primarily estrogen). But the triggering event for the development of the fibroid is not known and the interaction of the various hormones and growth factors likely to be involved is not well understood.

Once fibroids appear, their growth rate is also dependent on estrogen, progesterone and possibly other hormones. Growth rates vary greatly among women and the exact cause for this variability is not known, making the prediction of the behavior of fibroids very difficult.

Symptoms

Most leiomyomas do not cause symptoms. While 25% of women develop fibroids during their lives, only 10 to 20% of these women have symptoms. Therefore, only a minority of women ever require treatment.

Heavy Menstrual Bleeding

The most common symptom associated with fibroids is abnormal bleeding, which typically presents as heavy menstrual bleeding, often with clot formation. Anemia (low blood count) is a common side effect. The medical term for heavy menstrual bleeding is menorrhagia (pronounced men-o-ray-ja). As the bleeding severity increases, clot passage with the menstrual period commonly occurs. The clots form because the blood stays in the uterus long enough to clot prior to being expelled into the vagina. As these clots pass, they may cause severe menstrual cramping.

How fibroids cause abnormal bleeding is not known. Fibroids are believed to alter muscular contraction of the uterus, which may prevent the uterus from controlling the degree of bleeding during a patient's period. In addition, it has been shown that fibroids compress veins in the wall of the uterus. This results in dilation of the veins of the uterine lining. As the pressure in these veins increases, the the lining of the uterus becomes engorged. This may result in heavy bleeding during a menstrual period. It may also contribute to abnormal bleeding.

Heavy menstrual bleeding is usually caused by fibroids deep within the wall of the uterus (intramural) or those just under the inner lining of the uterus (submucosal). Very small fibroids in the wall of the uterus or fibroids in the outer part of the uterus (subserosal) usually do not cause abnormal bleeding.

There are many other potential causes of heavy menstrual bleeding and so a careful gynecologic history and physical examination is an important part of the evaluation of a patient with heavy bleeding. Just because a patient has fibroids, it does not mean that the fibroids are the cause of abnormal bleeding. Other causes include endometrial hyperplasia (an abnormal thickening of the uterine lining), endometrial polyps, adenomyosis, and even uterine cancer. The likelihood of these causes can often be determined based on a gynecologic history and physical examination, but on occasion additional tests may be needed.

Pelvic Pain and Pressure

Another symptom is pelvic pain. On rare occasions, a fibroid may suddenly degenerate (spontaneously shrink and scar due to decrease in blood supply). This is a painful process that may last several days or weeks. This type of severe pain is unusual. Severe or burning pain during a menstrual cycle is perhaps more commonly caused by other conditions, such as endometriosis. However, because of the broad range of presenting symptoms of fibroids, gynecologic evaluation is needed to confirm the diagnosis.

If fibroids cause symptoms related to the pressure they exert on other structures, they most commonly cause a sensation of pressure or discomfort in the pelvis. This may feel like heaviness, bloating, a dull ache, or mild tenderness of the fibroids themselves. The discomfort may be greater with exercise, while bending over or during sexual intercourse. As fibroids grow, they may compress nerves that supply the pelvis and the legs, causing pain in the back, flank, or legs. Patients also report increasingly severe menstrual cramps with the growth of their fibroids.

Urinary Symptoms and Other Symptoms

Pressure on the urinary system also may be caused by fibroids. Typically, this results in urinary frequency (increased frequency of urination, including the need to get up at night to urinate). Fibroids may also contribute to incontinence (urine leakage) or rarely, they may partially block the outflow of the bladder, making it difficult to empty the bladder. Occasionally, an enlarged uterus may press on other urinary structures resulting in partial blockage of the urine flow from the kidneys. On occasion, fibroids may also cause rectal pain or pressure.

Many of these symptoms may be cyclic, worse in the days leading up to the menstrual period and during the period. If the fibroids get large enough, the pressure and discomfort they cause may occur at any time.

Fibroids and Fertility

It has often been suggested that infertility and/or repeated miscarriage can be caused by fibroids. However, the statistical evidence for infertility is lacking and other factors are more likely to cause infertility in fibroid patients. Some researchers have suggested that the presence of fibroids may predispose a patient to miscarriage, but again firm statistical evidence to support this possibility is not yet available. There have been studies in infertile women in whom the only identifiable cause is the presence of fibroids. After myomectomy (surgical removal of the fibroids, leaving the uterus in place), these studies have shown that 40 to 60 % of these women have been able to become pregnant. However, because large studies have not been completed and infertility may have many causes, it is imprudent to assume that fibroids are the cause without a careful evaluation for other problems.

Fibroids and the Risk of a Malignant Tumor

A common question is whether a large mass in the uterus, presumed to be a benign fibroid, could be a malignant tumor. The answer is yes, although these tumors, called leiomyosarcomas, are very rare. They occur in about 1 in 1000 cases. Based on recent genetic studies, it does not appear that these malignant tumors result from a preexisting benign tumor. It appears that they arise separately from any existing fibroids.

The problem is that it can be impossible to tell a benign fibroid from a malignant tumor without surgery. No imaging test, such as ultrasound or MRI, can reliably distinguish these tumors. There is no blood test that can detect them. By history, they are often suspected when a presumed fibroid grows very rapidly. However, the majority of rapidly growing "fibroids" are just that, benign fibroids.

Biopsy also cannot reliably distinguish benign from malignant tumors of the uterus, because the sample may be taken from a relatively benign appearing portion of the mass.

Unfortunately, the reliable means of detecting malignant solid tumors of the uterus is surgery. This would either be by removal of the fibroids alone (myomectomy) or hysterectomy. Hysterectomy, with surgical removal of lymph nodes near the uterus is the primary treatment for leiomyosarcoma.