Uterine mass on ultrasound is common, with fibroids seen in the majority of women by the time of menopause. Ultrasound of the pelvis is commonly done to evaluate the uterus and ovaries. Pelvic pain, vaginal bleeding and abnormal physical exam are some of the more common reasons for doing a pelvic ultrasound.
By far, the most common mass is a leiomyoma or fibroid. Other less common masses include leiomyosarcoma, focal adenomyosis, ovarian or adnexal masses if a uterine tumor is pedunculated, and endometrial carcinoma. Differentiating some of these masses may not be possible with just an ultrasound. Additional options for imaging would be a pelvic MRI.
Uterine fibroids are often seen in symptomatic women and also commonly found in those who are imaged for other reasons. Fibroids are benign tumors composed of smooth muscle and connective tissue. They can range in size significantly with some occupying the entire uterus and even extending into the abdomen.
Uterine fibroids can have many appearances on ultrasound, most common as a solid mass darker than the uterus. Some fibroids can undergo degeneration and have cystic areas or internal bleeding. Some fibroids can have internal calcifications. Fibroids can be located in different parts of the uterus and even extend outside of it. There are many treatments some of which involve surgery and others are minimally invasive such as uterine artery embolization.
Uterine leiomyosarcoma is a cancer of the uterus. Unfortunately, this is often indistinguishable on imaging from a benign fibroid. Rarely, a benign fibroid can transform into a cancer. The distinction between fibroid and this tumor is often done under the microscope after surgery by a pathology doctor. This cancer has a poor prognosis. It is treated with surgery, radiation and chemotherapy.
Focal adenomyosis is another type of uterine mass. This is a condition where endometrial tissue ends up in the uterine wall. This is on the spectrum of endometriosis. Often this is indistinguishable from fibroid, although the borders are not as well defined.
Fibroids may be pedunculated or extending outside the uterus. Sometimes this can mimic a pelvic or ovarian mass. The key is to demonstrate that the mass is attached to the uterus. Also that the mass has the expected appearance of a fibroid. MRI of the pelvis can help in tough cases.
Endometrial cancer is most common in women after menopause. It often presents with vaginal bleeding. Ultrasound may demonstrate a thickened endometrium or mass. Fibroids that extend into the endometrial cavity can mimic cancer. Invasion into other structures makes cancer more likely. Biopsy of the endometrium is needed for the diagnosis.
Uterine masses are commonly found on ultrasound. The most common mass is a fibroid which is a benign tumor. Unfortunately, uterine cancer can have a similar appearance to fibroids. It can only be distinguished under the microscope. Fortunately it is rare. Other masses such as endometrial cancer and focal adenomyosis are some other possibilities.