What are Uterine Fibroids, Leiomyomas, Myomas or Fibromyomas?

Uterine fibroids are benign tumors that develop from the smooth muscle of the uterus.  It is also known as leiomyomas, myomas, or fibromyomas. Uterine fibroids are extremely common in women of childbearing age and usually regress after menopause. Although there may be symptoms such as heavy menstrual bleeding, sometimes there may be no symptom at all and a woman may be unaware that she has a fibroid.

Uterine fibroids are usually round in shape and  can grow to a massive size. It can occur as a single large growth or multiple smaller growths. Depending upon the size and location of the fibroid, it may lead to infertility or produce complications during pregnancy. Very rarely do uterine fibroids become cancerous.

How does a uterine fibroid develop?

Pathophysiology of Uterine Fibroids

The uterus is a pear-shaped organ composed of the body of the uterus on top and the cervix below, which connects at its lower end to the vagina. Extending from the upper part of the uterus on either side are the fallopian tubes. Near the end of each tube is an ovary.

The uterine wall is composed of smooth muscular tissue or myometrium, covered on the surface by a serous or peritoneal layer and on the inside by the mucosal layer known as endometrium. Hormones regulate the reproductive system in women and include :

  • Gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus.
  • GnRH stimulates the pituitary gland to produce follicle stimulating hormone (FSH) and luteinizing hormone (LH).
  • FSH and LH stimulate the ovaries to secrete estrogen and progesterone. The effects of these hormones are discussed further under female hormones.

The growth of uterine fibroids are hormone mediated. Estrogen, progesterone and growth factors play a role in tumor growth. Fibroids may grow rapidly during pregnancy due to the effect of hormones and are seen to regress after menopause. Drugs containing estrogen, such as oral contraceptives, may also cause fibroids to grow.

The term “fibroid” is often misleading since it does not contain any fibrous tissue but is made up entirely of smooth muscular tissue of the uterus. For this reason, the term “leiomyoma” is more accurate in describing the growth.  Fibroids start in the muscle layer of the uterus where a single muscle cell may reproduce repeatedly to form a pale, firm, rubbery mass which is clearly demarcated from the surrounding muscle tissue. The cut surface of a fibroid shows a characteristic whorled, spiral pattern of fibers.

The fibroid may be confined within the muscular layer of the uterus (intramural), or may grow on the surface of the uterus beneath the peritoneum (subserosal), or it may grow into the uterine cavity beneath the endometrium (submucosal). When the muscular action of the uterus attempts to expel the submucosal tumor, it can give rise to a fibroid polyp or a pedunculated fibroid.

These tumors are hormone mediated. Estrogen, progesterone and growth factors play a role in tumor growth. Fibroids may grow rapidly during pregnancy due to the effect of hormones and are seen to regress after menopause. Drugs containing estrogen, such as oral contraceptives, may cause fibroids to grow.

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