Uterine fibroids, also known as leiomyomas, are common, non-cancerous growths that develop in the wall of the uterus. They vary significantly in size, number, and location, sometimes causing symptoms like heavy bleeding and pelvic pressure. Diagnosis relies on ultrasound imaging, which allows medical professionals to visualize these growths and determine their characteristics. Because fibroids are living tissue, they require a constant blood supply to grow, making the assessment of their internal blood flow central to their evaluation.
Understanding Uterine Fibroids and Ultrasound Imaging
Uterine fibroids originate from the smooth muscle cells of the uterine wall and are classified based on their location. Submucosal fibroids bulge into the uterine cavity, intramural fibroids are located within the muscular wall, and subserosal fibroids project outward from the uterus. Standard ultrasound (2D or B-mode imaging) uses sound waves to create static, structural pictures of the uterus and any masses present.
B-mode ultrasound is effective for determining the size, shape, and location of the fibroids, which aids in diagnosis and treatment planning. However, it primarily provides structural information and does not visualize the dynamic movement of blood within the tissue. Fibroids require the uterine vascular network for oxygen and nutrients.
They are typically surrounded by a dense network of feeding vessels, often referred to as a pseudocapsule. Visualizing this complex vascular network requires specialized imaging beyond standard structural ultrasound.
Detecting Blood Flow with Doppler Ultrasound
To visualize the blood supply, medical practitioners use Doppler ultrasound techniques. Color Doppler uses color-coded signals overlaid on the B-mode image to show the direction and velocity of blood flow in real-time. Power Doppler detects slower blood flow, making it useful for visualizing smaller vessels within the fibroid.
Doppler methods reveal two main patterns of blood flow. Peripheral flow consists of prominent feeding vessels that encircle the fibroid, often seen as a vascular rim or “spoke-wheel” pattern. Intralesional or central flow represents the smaller vessels branching inward to supply the core.
Radiologists assign a vascularity grade based on the extent of color signal detected. A common system grades the fibroid from Grade 1 (minimal or no central flow) to Grade 3 (extensive central flow). This grading system provides an objective measure of the fibroid’s metabolic activity.
Clinical Meaning of Fibroid Vascularity
The degree of vascularity found on Doppler imaging is relevant to patient symptoms and clinical management. Fibroids with high vascularity (Grade 2 or Grade 3) are metabolically active and tend to exhibit faster growth rates. This increased blood supply is strongly associated with more severe symptoms, particularly heavy menstrual bleeding (menorrhagia).
High blood flow may contribute to menorrhagia by stimulating the development of new, fragile blood vessels in the adjacent uterine lining. Women with heavy bleeding often have fibroids with higher peak systolic velocity (PSV) and end-diastolic velocity (EDV) in their feeding vessels. Vascularity assessment is also important for planning minimally invasive procedures.
Uterine Fibroid Embolization (UFE) relies on blocking the blood flow to the fibroid. Highly vascular fibroids are candidates for this procedure, and flow assessment helps predict embolization success. Measuring parameters like the pulsatility index (PI) and resistive index (RI) provides insight into the resistance within the fibroid’s blood vessels, informing the treatment strategy.
What Happens When Blood Flow Stops: Fibroid Degeneration
Fibroid degeneration occurs when the fibroid’s blood supply is acutely compromised, leading to tissue death (infarction). This happens if a fibroid grows too rapidly for its feeding vessels, or if a pedunculated fibroid twists and cuts off its own blood supply. This sudden loss of oxygen and nutrients triggers the release of inflammatory chemicals, causing acute, severe pelvic pain.
On Doppler ultrasound, a degenerating fibroid shows a specific pattern consistent with a lack of blood flow. Imaging reveals a significantly reduced or complete absence of the color or power Doppler signal within the affected area. The structural B-mode image may also show a change in the fibroid’s texture, often appearing heterogeneous or cystic due to the dead tissue.
The pain is typically sudden and localized. While degeneration can cause the fibroid to shrink permanently, acute symptoms usually require medical management. The lack of detectable vascularity confirms this degenerative process.