Fibroids are benign tumours that grow inside the uterus, or within the uterine wall. More than 99% of fibroids are benign, and these benign tumours cannot become cancerous. In addition, having fibroids doesn't increase the risk that a woman will develop uterine cancer.
Estimates of the number of women affected by fibroids vary: some are as low as 30% of women aged 40 to 60 years old. Other estimates say that up to 70% to 80% of women may have fibroids by the time they reach 50 years of age. However, because only around one-third of fibroids ever grow large enough to cause symptoms, or be detected by a doctor, most women are not diagnosed.
Exactly what causes fibroids to develop is unknown. However, it is thought that fibroids develop from abnormal muscle cells, and that the presence of oestrogen enables the rapid growth of a single abnormal cell into a fibroid tumour.
Types of Fibroids
There are several different kinds of fibroids. The different types are classified according to where they are located in the uterus.
Intramural fibroids are the most common type of fibroid. These are fibroids that grow within the wall of the uterus. Of the four different kinds of fibroids, intramural fibroids are the least likely to cause severe symptoms or to interfere with fertility.
However, if they grow large enough, intramural fibroids can cause the uterus to bulge outward, and cause visible abdominal swelling. When they grow this large they can cause pain and bleeding, and may reduce fertility in some women. In some cases, an intramural fibroid can grow large enough to become a submucosal or subserosal fibroid.
Subserosal fibroids grow outside the uterus, beneath the outer tissue layer of the uterus. These can become pedunculated, which means they develop a stalk. They can grow to a large size and protrude quite far from the outside of the uterine wall. However, due to the location of these fibroids within the abdominal cavity, they tend to cause the least problematic symptoms.
Submucosal fibroids grow within the uterus, in the muscle underneath the uterine lining. Because they grow within the endometrium of the uterus, they tend to be the type of fibroid that leads to the most problems. For example, of the four different kinds they are the most likely to cause the heaviest bleeding during and between periods.
These fibroids can grow into the uterine cavity, and may also develop a stalk. If they grow large enough, these fibroids can sometimes start to protrude through the cervix and into the vagina.
Cervical fibroids develop within the cervix, or neck of the uterus. These tend to be the most easily diagnosed, because they can often be seen and felt by a doctor during a pelvic examination. Cervical fibroids are also the most likely to cause pain during sexual intercourse, and the most likely to become infected. If a cervical fibroid grows large enough it can cause partial blockage of the urinary track.
Cervical fibroids are quite rare, and when they do develop it usually indicates that there are other fibroids present within the uterus.