Uterine fibroids (leiomyomas or myomas) are non-cancerous growths that form from the muscle tissue of the uterus. They affect a large percentage of women during their reproductive years, though many remain unaware they have them because they cause no symptoms. When symptoms such as heavy bleeding or pelvic pressure arise, the initial diagnosis typically uses a non-invasive imaging procedure: the ultrasound. Ultrasound provides a clear visualization of the uterus, allowing medical professionals to identify, measure, and characterize any suspicious masses present and guide patient care.
Why Ultrasound Is the Primary Diagnostic Tool
Ultrasound is the standard imaging modality for evaluating the uterus and diagnosing fibroids due to several practical advantages. The procedure is non-invasive, using sound waves instead of radiation, making it a safe option for nearly all patients. This safety profile allows it to be used repeatedly for monitoring purposes.
The equipment is widely available and the procedure is cost-effective compared to other detailed imaging methods like Magnetic Resonance Imaging (MRI). Ultrasound offers real-time imaging, allowing the technician and physician to view internal structures as the scan is performed. This capability is useful for examining masses from different angles.
The goals of the initial ultrasound scan are to confirm the presence of a mass, count the number of fibroids, and accurately measure their dimensions. Determining size and quantity is important for understanding potential symptoms. While smaller fibroids may be missed on a standard transabdominal scan, a transvaginal ultrasound provides a much closer view, improving the ability to detect and evaluate smaller fibroids.
Key Visual Signatures: How Fibroids Appear on Screen
Specific visual characteristics distinguish a fibroid from the surrounding healthy uterine tissue on an ultrasound screen. The appearance is described using echogenicity, which refers to how brightly the tissue reflects sound waves. Most uncomplicated fibroids appear hypoechoic, meaning they are darker than the normal uterine muscle (myometrium) because they reflect fewer sound waves.
Fibroids often have a heterogeneous, or mixed, echo texture, particularly when they grow larger than three centimeters. This mixed appearance is due to the varying composition, which includes muscle, fibrous tissue, and sometimes areas of degeneration. Fibroids are typically well-defined masses with distinct, rounded or lobulated borders, separating them visually from the uterine wall.
A hallmark sign of a fibroid is acoustic shadowing. Because fibroids are dense, they block sound waves, creating a dark, shadow-like area immediately behind the mass. This shadowing indicates that the mass is solid and fibrous. In older fibroids or those undergoing degeneration, bright spots (hyperechoic foci) may be visible due to calcification.
Classifying Fibroids Based on Their Location
Once identified, a fibroid’s location relative to the uterine wall is an important classification affecting symptoms and treatment planning. The three primary categories are named based on their position: submucosal, intramural, and subserosal. Intramural fibroids are the most common type, located entirely within the muscular wall of the uterus (myometrium).
Subserosal fibroids are located on the outer surface of the uterus, often projecting outward, and may be connected by a narrow stalk (pedunculated). These typically do not distort the uterine cavity, but large ones can press on nearby organs like the bladder. Submucosal fibroids are situated just beneath the endometrium, the inner lining of the uterus, and project into the uterine cavity.
Submucosal fibroids are often the most symptomatic, even when small, commonly causing heavy bleeding and fertility issues due to their proximity to the uterine lining. To get a clearer image of these masses, specialized saline infusion sonography (SIS) may be used. This technique involves instilling sterile saline into the uterus to expand the cavity, providing enhanced visualization for classifying the fibroid’s extension into the muscle wall.