Family doctor

What are uterine fibroids?

Uterine fibroids are benign tumours formed from the muscular layer in the uterus. Also known as uterine leiomyomas or myomas, fibroids are the most common solid pelvic tumours in women. As benign tumours, fibroids are not cancerous (i.e. they do not spread beyond the uterus) and only extremely rarely develop into malignant tumours (cancer).

 Fibroids are classified according to where in the uterus they form: either in the wall of the uterus itself (intramural), beneath the inner lining of the uterus (submucosal) or beneath the outer covering of the uterus (subserosal). In fact, most fibroids are a combination of these types.

 Who gets fibroids?

Fibroids are found in about 25% of women of reproductive age during pelvic examinations, but probably occur in even more: careful examination of surgical uterine specimens demonstrates that over 80% have fibroids. However, symptoms occur in only 20-50% of those with fibroids, usually in women in their 30s or 40s. There are increasing reports of women continuing to have, or developing symptoms, whilst taking hormone replacement therapy in menopause.

  What causes fibroids?

The exact cause of fibroids is not well understood, although various factors have been recognised as being important in their development. The hormones estrogen and progesterone have a role in the formation of fibroids. Growth factors and gene mutations are also involved in fibroid development. The latter explains the hereditary predisposition for fibroids seen in families.

 (Although the levels of estrogen and progesterone are high in both the oral contraceptive and during pregnancy, they remain protective against the risk of developing fibroids. This is perhaps because there is no fluctuation in the high hormone levels during oral contraceptive use or pregnancy, whereas hormone levels fluctuate widely during the normal menstrual cycle.)

 What are the symptoms of fibroids?

Many women have no symptoms from their fibroids at all. However, fibroids may produce three main types of symptoms in 20-50% of cases: abnormal menstrual bleeding, pressure and pain, and reproductive problems.

 The abnormal bleeding associated with fibroids usually occurs during the normal time in the menstrual cycle, but it is prolonged ('menorrhagia') and/or the flow is heavier than normal ('hypermennorhoea'). Bleeding at other times (i.e. not during a period) is NOT characteristic of fibroids and should always be thoroughly investigated. Prolonged or heavy menstrual bleeding may cause iron-deficiency anaemia. It is also often socially embarrassing and can interfere with work, because of the need to change sanitary protection frequently.

 Fibroids can cause pelvic pressure symptoms either because they increase the size of the uterus, or because they press on nearby organs. Fibroids as big as a 20-week pregnancy are not uncommon. Those arising in the anterior (front) part of the uterus may put pressure on the bladder &endash; causing urinary frequency &endash; whilst those in the posterior (back) part of the uterus may cause constipation, due to pressure on the large bowel. Pain may occur if the fibroid degenerates, or if it arises on a stalk from the uterus and then twists on that stalk ('torsion').

 Reproductive problems may occur, especially if the fibroid distorts the cavity of the uterus. These include recurrent miscarriage, infertility, premature labour, or complications of labour (such as abnormal presentation of the fetus). Many of these problems are directly related to the size of the fibroid. If the placenta develops over a fibroid, there is an increased risk of the placenta 'breaking away' (placental abruption').

 How are fibroids diagnosed?

Fibroids can be suspected if the uterus feels enlarged, irregular and mobile during a pelvic examination. The diagnosis is usually confirmed by ultrasound examination of the pelvis. Magnetic resonance imaging (MRI) gives a clearer image of the uterus, but the additional cost does not usually justify its use in diagnosing fibroids. Other studies that are used to help diagnose fibroids include hysteroscopy (insertion of a thin telescope into the uterus via the vagina and cervix) and hysterosalpingography (dye-study x-rays of the uterus and fallopian tubes).

 How are fibroids treated?

Because fibroids are not malignant, they do not require treatment unless they cause symptoms. The main method of treating fibroids is to surgically remove them. Hysterectomy (removal of the uterus) is the most common technique used, and may be the best option in women who have completed their childbearing.

 For women who wish to have more children, myomectomy may be performed. This involves removal of the fibroid itself, with preservation of the uterus. Myomectomy can be performed via an abdominal incision, using a laparoscope, or via the vagina/cervix, depending on the size and location of the fibroid. There is a slight risk of uterine rupture during subsequent pregnancies after laparoscopic myomectomy. It is important to note that 25-51% of fibroids recur after myomectomy, and that 11-26% of patients need a further operation.

 Newer surgical treatments include endometrial ablation (in which the lining of the uterus is removed) and uterine-artery embolization (in which the uterine artery is blocked). Both are used to control excessive menstrual bleeding, but the former is reserved for those who have completed childbearing.

 GnRH agonists are the most common medical (i.e. nonsurgical) therapy available for the treatment of fibroids. They induce a state of low estrogen levels, (hormonally similar to the menopause) which in turn reduces the size of the fibroids and decreases the volume of the uterus. Most women also stop having periods while taking GnRH agonists. This allows those with iron-deficiency anaemia secondary to heavy/prolonged menstrual bleeding to significantly increase their iron stores and correct their anaemia. However, prolonged usage of GnRH agonists may cause bone loss/osteoporosis and other symptoms of the low estrogen state. Unfortunately, once these drugs are stopped, the uterine size again increases and menses resumes. Consequently, they are most useful in reversing anaemia and decreasing uterine size in the short term, thus preparing a woman for surgery.

 Other medical therapies include androgenic (male hormone-like) drugs and progesterone-type agents. However, these do not consistently decrease the size of the fibroids or uterus, and they often don't successfully control abnormal menstrual bleeding. There is also ongoing research into combinations of drugs that may be beneficial without the adverse effects associated with using GnRH agonists alone.

 Bibliography:

Feldman S, Stewart EA. The Uterine Corpus. In: Ryan KJ, Berkowitz RS, Barbieri RL, Duanif A, eds. Kistner's Gynecology & Women's Health:, 7th ed. St Louis: Mosby Inc, 1999: 121-42

Stewart EA. Uterine fibroids. Lancet 2001;357(9252):293-8