Uterine fibroids are common, non-cancerous growths that develop from the muscle tissue of the uterus. As living tissues, they require a blood supply to grow. Medical imaging, particularly ultrasound, is a primary method used to evaluate these growths. An ultrasound can confirm the presence of fibroids and provide information about their size, location, and vascularity.
How Ultrasound Visualizes Blood Flow
A standard ultrasound, known as B-mode or 2D imaging, produces the familiar black-and-white picture of anatomical structures. This modality is effective for identifying the presence, size, and shape of fibroids, but it does not show the movement of blood. To visualize blood flow, a specialized function called Doppler ultrasound is employed during the examination.
Doppler ultrasound technology works by measuring the frequency shift of sound waves as they reflect off moving red blood cells. The most commonly used type is Color Doppler, which overlays a color map onto the black-and-white image. These colors represent the direction of blood flow relative to the ultrasound transducer; red indicates flow towards the probe and blue signifies flow away from it.
For situations where blood flow is very slow, another mode called Power Doppler can be used. Power Doppler is more sensitive than Color Doppler in detecting low-velocity flow but does not provide directional information. It registers the presence of moving blood cells and displays it as a solid color, making it useful for confirming whether a growth has any detectable blood supply.
Common Blood Flow Patterns in Fibroids
The blood supply to a fibroid is a strong indicator of its metabolic activity and status. For a benign uterine fibroid, the most common finding on a Doppler ultrasound is a pattern of peripheral vascularity. This appears as a distinct ring of blood vessels encircling the outer boundary of the growth. This pattern occurs because fibroids derive their blood supply from the uterine arteries that feed the surrounding healthy uterine tissue.
This peripheral pattern is a reassuring sign often associated with a standard, benign leiomyoma. The density of this outer ring of vessels can vary, with some fibroids showing a rich, dense network and others a more sparse supply. This variation can influence their growth rate and the symptoms they cause.
Conversely, some fibroids may show very little or no detectable blood flow on a Doppler ultrasound. This often signifies that the fibroid is undergoing degeneration. Degeneration happens when a fibroid outgrows its blood supply, causing its central tissues to break down due to a lack of oxygen. A fibroid with minimal flow is often considered less active and may be stable in size or even shrinking.
Distinguishing Fibroids from Other Conditions
While the vast majority of muscular tumors in the uterus are benign fibroids, a primary goal of diagnostic imaging is to look for features that might suggest a different, more serious condition. The pattern of blood flow is one of several clues used to differentiate a benign fibroid from a rare uterine cancer, such as a leiomyosarcoma.
Malignant sarcomas tend to develop their own internal blood supply through a process called neoangiogenesis, resulting in a chaotic and disorganized vascular pattern. Instead of a neat peripheral ring of vessels, a sarcoma may show prominent blood vessels scattered throughout the core of the tumor. This internal, haphazard vascularity is considered a suspicious finding that warrants further investigation.
Blood flow patterns on an ultrasound are not a definitive diagnosis for cancer. These findings are interpreted in the context of other factors, including the patient’s age, symptoms, and how quickly the growth is changing in size. If an ultrasound reveals atypical vascularity or other concerning features, a physician may recommend additional imaging, such as an MRI, or a biopsy to make an accurate diagnosis.
How Blood Flow Information Influences Treatment
Understanding a fibroid’s vascularity has direct and practical implications for treatment planning. The amount and location of blood flow help guide the choice of intervention, as the success of different treatments can depend heavily on the tumor’s blood supply.
For example, Uterine Fibroid Embolization (UFE) is a minimally invasive procedure that works by cutting off the blood supply to the fibroids. During UFE, tiny particles are injected into the uterine arteries to block the small vessels feeding the growths, causing them to shrink and die. A detailed pre-procedure map of this blood flow from an ultrasound or MRI is important for the success of the embolization. A fibroid with a very rich blood supply is often an excellent candidate for this treatment.
In cases where surgical removal of a fibroid, known as a myomectomy, is planned, knowing its vascularity helps the surgeon prepare. A highly vascular fibroid may have a higher risk of significant bleeding during the operation. This knowledge allows the surgeon to take proactive measures to control blood loss, such as using specific medications or surgical techniques, ensuring a safer procedure.