Leiomyomas are the most common tumor of the female genital tract and the most common cause of enlargement of the nonpregnant uterus. The incidence is as high as 40% in women greater than 35 years old (Brant). African American women are two times more likely than Caucasian women to have fibroids when older than 30 years old (Laing, et al ). They are composed of smooth muscle arranged in whorls in combination with varying amounts of fibrous tissue. These benign neoplasms enlarge and regress with estrogen levels. Symptoms can range from “menorrhagia, dysmenorrhea, irregular uterine bleeding, pelvic pain, infertility, and the discomfort of a large pelvic mass” (Brant). The location may be intramural (confined to myometrium), submucosal (projects into uterine cavity) or subserosal (projects from the peritoneal surface). Intramural fibroids are the most common type and tend to distort the contour of the uterus. Submucosal fibroids cause distortion and compression of the endometrium. Subserosal fibroids may be pedunculated and may present as an adnexal mass. Large fibroids do not interfere with pregnancy or vaginal delivery except when located in the lower uterine segment or cervix (Rumack).
Sonographic findings are typically a heterogeneous, hypoechoic mass that is well circumscribed. However, numerous small fibroids may give the myometrium a heterogeneous appearance. Acoustic attenuation secondary to dense fibrosis makes size estimation difficult. Variants include calcific, cystic, fatty, or hemorrhagic degeneration. Cystic degeneration tends to begin centrally. Hemorrhagic infarction tends to occur during periods of rapid growth, such as during pregnancy, when they may tend to outgrow their blood supply. Calcifications may occur in older women and tend to start in the periphery.
Different approaches may be necessary to better characterize lesions. Transvaginal ultrasound helps differentiate submucosal versus intramural lesions and can detect small fibroids. It may also be diagnostic in differentiating adnexal masses from pedunculated subserosal lesions. Transabdominal ultrasound gives a larger field of view to detect subserosal and pedunculated fibroids. Sonohysterography is useful to delineate submucosal leiomyomas from endometrial lesions.