Uterine fibroids are common, non-cancerous growths that develop within the uterus. Also known as leiomyomas, these benign tumors originate from the smooth muscle cells and connective tissue of the uterus. Ultrasound imaging serves as the primary diagnostic tool for identifying and characterizing these growths.
How Ultrasound Detects Fibroids
Ultrasound technology operates on the principle of high-frequency sound waves. A device called a transducer emits these sound waves, which travel through the body’s tissues and organs. When these waves encounter structures like fibroids, they bounce back to the transducer, which processes the reflected waves to create real-time images.
For detecting uterine fibroids, two main approaches are used: transabdominal ultrasound and transvaginal ultrasound. A transabdominal ultrasound involves moving the transducer over the lower abdomen, providing a broader view of the pelvic region and larger fibroids. A transvaginal ultrasound utilizes a smaller probe inserted gently into the vagina, offering a closer and more detailed view of the uterus, especially for smaller fibroids or those located deeper within the uterine wall.
Understanding Fibroid Appearance on Ultrasound
On ultrasound images, uterine fibroids appear as solid, well-defined masses. Their echogenicity, or how they reflect sound waves compared to surrounding tissue, is often hypoechoic, meaning they appear darker than the normal myometrium, or muscle wall of the uterus. However, fibroids can also be isoechoic (similar brightness) or hyperechoic (brighter) depending on their composition, such as the amount of fibrous tissue or calcification present.
Fibroids have a rounded or concentric shape with clear borders. They may exhibit acoustic shadowing, appearing as a darker area behind the fibroid due to the sound waves being absorbed or reflected. The location of a fibroid significantly influences its appearance: intramural fibroids are embedded within the uterine wall, subserosal fibroids protrude from the outer surface, and submucosal fibroids develop just beneath the uterine lining, potentially distorting the uterine cavity. Calcified areas within fibroids appear as bright, echogenic foci, often accompanied by dense posterior shadowing. Color Doppler ultrasound can also be used to assess blood flow, typically showing peripheral vascularity around the fibroid, although some may exhibit central blood flow.
What Information is Gathered from Ultrasound Images
Ultrasound images provide diagnostic data that medical professionals use to evaluate uterine fibroids. The scan accurately measures the dimensions of fibroids, typically in three planes, and can determine their number, although radiologists may report a range if numerous fibroids are present. The precise location of each fibroid, such as anterior, posterior, fundal (top of the uterus), cervical, or within specific layers of the uterine wall, is also identified.
Serial ultrasounds are used to monitor changes in fibroid size over time. While small changes may be due to measurement variability, an increase of about 20% in diameter or 29% in volume is generally considered indicative of true growth. Ultrasound also aids in differentiating fibroids from other uterine or pelvic conditions, such as adenomyosis, ovarian cysts, or endometrial polyps. The images reveal if fibroids are distorting the uterine cavity or impacting adjacent organs, which can influence symptoms and treatment decisions.
Preparing for and Undergoing a Fibroid Ultrasound
Preparation for a fibroid ultrasound varies depending on the type of scan. For a transabdominal ultrasound, patients are typically asked to arrive with a full bladder, as this helps to push the intestines out of the way and provides a clearer view of the uterus and fibroids. Drinking about 24 to 32 ounces of clear fluid an hour before the appointment is often recommended, and patients should avoid emptying their bladder until after this part of the exam.
During the transabdominal procedure, a gel is applied to the abdomen, and the sonographer moves the transducer over the skin, applying gentle pressure. For a transvaginal ultrasound, a full bladder is not required; patients are usually asked to empty their bladder beforehand. A small, lubricated transducer, covered with a protective sheath, is then gently inserted into the vagina.
Both scans are generally painless, though some pressure or mild discomfort may be felt. The entire procedure typically lasts between 15 to 30 minutes. After the scan, the gel is wiped off, and results are usually interpreted by a radiologist before being communicated to the patient by their doctor.