A uterine fibroid (also uterine leiomyoma, myoma, fibromyoma, leiofibromyoma, fibroleiomyoma, and fibroma) 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.
Uterine fibroids is the major 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 uterine leiomyomatosis. The malignant version of a fibroid is uncommon and termed a leiomyosarcoma.
About 20–40% of women will be diagnosed with leiomyoma. Estrogen
receptors on fibroids cause them to respond to estrogen stimulation
during the reproductive years. During hypoestrogenic states, such as
after menopause, leiomyoma are expected to shrink. Leiomyoma are more
common in overweight women (because of increased estrogen from adipose
Uterine fibroids appear as round, well circumscribed (but
not encapsulated), solid nodules that are white or tan, and show
whorled appearance on histological section.
The size varies, from microscopic to lesions of
considerable size. Typically lesions the size of a grapefruit or bigger
are felt by the patient herself through the abdominal wall.
Microscopically, tumor cells resemble normal cells
(elongated, spindle-shaped, with a cigar-shaped nucleus) and form
bundles with different directions (whorled).
These cells are uniform in size and shape, with scarce
mitoses. There are three benign variants: bizarre (atypical); cellular;
and mitotically active.
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 agonists as part of treatment are currently
In very rare cases, malignant (cancerous) growths, leiomyosarcoma, of the myometrium can develop.
Fibroids that lead to heavy vaginal bleeding lead to anemia and iron
deficiency. Due to pressure effects gastrointestinal problems are
possible such as constipation and bloatedness. Compression of the
ureter may lead to hydronephrosis. Fibroids may also present alongside
endometriosis, which itself may cause infertility.Adenomyosis may be
mistaken for or coexist with fibroids.
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Last Updated: Feb 1, 2011