A uterine fibroid is a benign (non-cancerous) tumor that originates from the smooth muscle layer (myometrium) and the accompanying connective tissue of the uterus. Fibroids are the most common benign tumors in females and typically found during the middle and later reproductive years. While most fibroids are asymptomatic, they can grow and cause heavy and painful menstruation, painful sexual intercourse, and urinary frequency and urgency. Symptoms caused by uterine fibroids are a very frequent indication for hysterectomy in the US.Fibroids are often multiple and if the uterus contains too many leiomyomatas to count, it is referred to as diffuse uterine leiomyomatosis. The malignant version of a fibroid is uncommon and termed a leiomyosarcoma

About 20-40% of women will be diagnosed with leiomyoma but only a fraction of those will cause problems or require treatment.

The condition is about twice as common in black women as white women.

Leiomyoma are more common in overweight women (perhaps because of increased estrogen from adipose aromatase activity).Fibroids are dependent on estrogen and progesterone to grow and therefore relevant only during the reproductive years, they are expected to shrink after menopause.

For decades estrogen has been known to stimulate fibroids, but more recent studies have also revealed a possible role of progesterone and progestins to fibroid growth as well,and applicability of progestin antagonists as part of treatment are currently being considered.

Genetic and hereditary causes are being considered and several epidemiologic findings indicate a strong genetic influence. First degree relatives have a 2.5-fold risk, and nearly 6-fold risk when considering early onset cases. Monozygotic twinshave double concordance rate for hysterectomy compared to dizygotic twins.

In very rare cases, malignant (cancerous) growths, leiomyosarcoma, of the myometrium can develop.

Growth and location are the main factors that determine if a fibroid leads to symptoms and problems.A small lesion can be symptomatic if located within the uterine cavity while a large lesion on the outside of the uterus may go unnoticed. Different locations are classified as follows:

Intramural Fibroids are located within the wall of the uterus and are the most common type; unless large, they may be asymptomatic. Intramural fibroids begin as small nodules in the muscular wall of the uterus. With time, intramural fibroids may expand inwards, causing distortion and elongation of the uterine cavity.

Subserosal fibroids are located underneath the mucosal (peritoneal) surface of the uterus and can become very large. They can also grow out in a papillary manner to become pedunculated fibroids. These pedunculated growths can actually detach from the uterus to become a parasitic leiomyoma.

Submucosal fibroids are located in the muscle beneath the endometrium of the uterus and distort the uterine cavity; even small lesion in this location may lead to bleeding and infertility. A pedunculated lesion within the cavity is termed an intracavitary fibroid and can be passed through the cervix.

Cervical fibroids are located in the wall of the cervix (neck of the uterus). Rarely fibroids are found in the supporting structures (round ligament, broad ligament, or uterosacral ligament) of the uterus that also contain smooth muscle tissue.

Fibroids may be single or multiple. Most fibroids start in an intramural location, that is the layer of the muscle of the uterus. With further growth, some lesions may develop towards the outside of the uterus or towards the internal cavity. Secondary changes that may develop within fibroids are hemorrhage, necrosis, calcification, and cystic changes.

Generally, symptoms relate to the location of the lesion and its size (mass effect). Important symptoms include abnormal gynecologic hemorrhage, heavy or painful periods, abdominal discomfort or bloating, painful defecation, back ache, urinary frequency or retention, and in some cases, infertility.There may also be pain during intercourse, depending on the location of the fibroid. During pregnancy they may be the cause of miscarriage, bleeding, premature labor, or interference with the position of the fetus.

Fibroids, particularly when small, may be entirely asymptomatic. The U.S. Department of Health & Human Services states that “Fibroids are almost always benign (not cancerous). Rarely (less than one in 1,000) a cancerous fibroid will occur. This is called leiomyosarcoma. Doctors think that these cancers do not arise from an already-existing fibroid. Having fibroids does not increase the risk of developing a cancerous fibroid. Having fibroids also does not increase a woman’s chances of getting other forms of cancer in the uterus.

While fibroids are common, they are not a typical cause for infertility accounting for about 3% of reasons why a woman may not have a child.Typically in such cases a fibroid is located in a submucosal position and it is thought that this location may interfere with the function of the lining and the ability of the embryo toimplant.Also larger fibroids may distort or block the fallopian tubes.