Uterine fibroids, also known as leiomyomas, are non-cancerous growths that commonly develop in the muscular wall of the uterus. They vary significantly in size, number, and location. Understanding the results of an imaging test is often the first step for people seeking information about these growths. This article explains how ultrasound technology detects fibroids and what the visual information on the resulting images signifies.
The Role of Ultrasound in Diagnosis
Ultrasound is typically the first-line imaging modality used to diagnose uterine fibroids because it is widely available, cost-effective, and non-invasive. This technology uses high-frequency sound waves to create real-time pictures of the uterus and surrounding pelvic organs. It allows clinicians to confirm the presence of a mass, distinguish it from other pelvic conditions, and determine its initial characteristics.
Two primary methods are used for this examination: transabdominal and transvaginal ultrasound. The transabdominal approach uses a transducer placed on the lower abdomen, providing an overall view of the uterus and identifying larger fibroids. Conversely, the transvaginal ultrasound involves inserting a smaller probe into the vagina, providing a closer, higher-resolution image of the uterus. Transvaginal sonography generally offers superior detail and higher sensitivity for detecting fibroids compared to the transabdominal method alone.
Interpreting Ultrasound Images of Fibroids
Interpreting an ultrasound image involves looking for specific visual cues that indicate the presence of a fibroid. A classic fibroid typically appears as a solid, well-defined, and concentric mass within the uterine muscle. The density of the fibroid tissue causes sound waves to interact with it in a distinctive manner, which is visually represented.
One important visual characteristic is echogenicity, which describes how light or dark the mass appears relative to the surrounding tissue. Fibroids are often hypoechoic, meaning they appear darker than the normal uterine muscle because they absorb more sound waves. However, the internal composition can be heterogeneous or mixed, with some areas appearing brighter or hyperechoic due to internal changes like calcification.
Another defining feature is acoustic shadowing, which appears as a dark area immediately behind the fibroid mass. This shadowing occurs because the dense, solid nature of the fibroid strongly attenuates or blocks the sound waves. Calcification within an older fibroid appears as very bright spots and results in sharp, dense shadowing. These visual clues of shadowing and hypoechogenicity indicate that the mass is a dense, benign fibroid rather than a fluid-filled cyst or another type of growth.
Classifying Fibroids by Location and Appearance
The location of a fibroid significantly influences its appearance on an ultrasound image and is a primary factor in determining potential symptoms and treatment options. The International Federation of Gynecology and Obstetrics (FIGO) classification system categorizes fibroids based on their position relative to the layers of the uterine wall. The three main types are submucosal, intramural, and subserosal, each presenting a distinct image profile.
Intramural fibroids are the most common type and are located entirely within the myometrium, the muscular wall of the uterus. On ultrasound, they appear surrounded by muscle tissue, often causing the wall to bulge or become irregularly thickened.
Subserosal fibroids develop on the outer surface of the uterus, beneath the serosa layer. These growths push outward from the uterine wall, sometimes appearing as a distinct mass attached by a stalk, termed pedunculated. An ultrasound may show these fibroids predominantly outside the main body of the uterus, which can make them difficult to distinguish from other masses like ovarian tumors.
Submucosal fibroids are the least common but often the most symptomatic, as they are located directly beneath the endometrium, the inner lining of the uterine cavity. They are identified by how they protrude into and distort the endometrial cavity. A specialized procedure called saline infusion sonography, which fills the cavity with fluid, is often used to get a clearer, more precise image of the fibroid’s extent.
Measuring Size and Monitoring Changes
Beyond identifying a fibroid’s presence and location, ultrasound images are used for quantitative assessment, specifically measuring the size of the growth. Clinicians typically measure the fibroid in three dimensions—length, width, and depth—to calculate its estimated volume. This measurement provides a baseline for tracking the fibroid over time.
The volume calculation is important because the size of the fibroid is a determining factor for symptoms and treatment planning. While two-dimensional measurements are commonly used, three-dimensional ultrasound techniques offer a more accurate estimation of the total volume. Subsequent or serial ultrasounds are performed over time to monitor changes in size or internal structure. Documenting the growth rate helps healthcare providers decide whether observation is appropriate or if intervention is necessary.