Fibroids
Synonyms/Description
Leiomyoma, myoma, fibromyoma, and uterine fibroma
Etiology
Fibroids are the most common benign pelvic tumor in women. The prevalence in women age 50 and older is estimated at 80% in African Americans and up to 70% in Caucasians. Others have estimated a lower incidence (up to 50% of perimenopausal women).
Myomas are thought to be monoclonal and originate from a single myocyte that undergoes somatic mutation as it grows. Cytogenetic anomalies are found in 40% of fibroids. Estrogen and progesterone are known to stimulate the growth of fibroids. Although many fibroids are asymptomatic, others may cause bleeding, pain, mass effect, urinary frequency, constipation, pregnancy loss, and infertility. The presence of symptomatic fibroids is the most common indication for hysterectomy.
Ultrasound Findings
Fibroids are typically solid masses, which are sonographically hypoechoic or isoechoic with the surrounding myometrium. They are well circumscribed, with acoustic shadowing, often with a pattern of stripes or swirls caused by these shadows. They can be calcified, often with a circumferential pattern of calcification. If they degenerate, they can have central cystic portions. Color Doppler findings of fibroids are variable. Some fibroids have abundant flow and others scant; therefore there is no Doppler flow pattern specific to fibroids. Doppler is helpful to map the blood flow to the fibroid. If it is pedunculated, it may be confused with an ovarian mass.
Fibroids are further described by their location in the uterus.
Intramural
Fibroids are most commonly intramural and occur within the confines of myometrium.
Submucosal
A fibroid that protrudes into the endometrial cavity is submucosal. These can occasionally be pedunculated into the cavity and slide down into the cervix as the uterus tries to expel it. Three-dimensional ultrasound and sonohysterography can be very helpful in outlining the extent of the submucosal component of the fibroid within the cavity.
Subserosal
A fibroid that indents the serosal surface and gives a bumpy appearance of the outside of the uterus is subserosal.
Pedunculated
A fibroid that has grown from a subserosal fibroid outward and remains tethered to the uterus by a pedicle is considered pedunculated. Occasionally these can pick up vascularity from outside organs and become parasitic, no longer connected to the uterus, making the sonographic diagnosis more difficult.
Degenerating
Discrepancy between the rate of growth of the myoma and its blood supply can lead to an infarction of part (most often the center) of the myoma. The degenerating fibroid has a variable manifestation, the most common being a donut-appearing mass with a cystic center and a thick wall, located within the confines of the uterus. The acute infarction leads to severe pain and is more common during pregnancy. Some degenerating fibroids can mimic ovarian cystic masses, especially if they are pedunculated and multiseptate in appearance.
Differential Diagnosis
The differential diagnosis of fibroids depends on the location and appearance of the uterine mass. A fibroid that contains cystic areas and abundant blood flow may be indistinguishable sonographically from a uterine sarcoma (see Sarcoma
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