Uterine fibroids, also called leiomyomas or myomas, are noncancerous growths of the smooth muscle of the uterus. They are the most common benign pelvic tumors in women — affecting up to 70% of women by age 50 — and range from small, asymptomatic nodules to large masses that distort the uterine cavity and cause significant bleeding, pain, and infertility.
Uterine fibroids frequently coexist with and can be confused with adenomyosis — a condition in which endometrial glands grow into the uterine muscle — which produces similar heavy bleeding and pelvic pain but requires a different treatment approach. MRI is the only imaging modality that reliably distinguishes the two. Chronic unopposed estrogen — the same hormonal driver of fibroids — also underlies the risk of endometrial cancer, making abnormal uterine bleeding in a fibroid patient always warrant endometrial evaluation. Fibroids can mimic pelvic congestion syndrome with pressure and pelvic heaviness, and large fibroids compressing adjacent structures may worsen pelvic organ prolapse.
Causes
Hormonal influence.
Estrogen and progesterone are the primary drivers of fibroid growth — fibroid tissue expresses significantly higher concentrations of estrogen and progesterone receptors than surrounding normal myometrium, making it disproportionately sensitive to hormonal stimulation. This explains the characteristic lifecycle of fibroids: they develop during the reproductive years when estrogen levels are high, often grow rapidly during pregnancy (when estrogen and progesterone surge), and typically shrink significantly after menopause when ovarian hormone production ceases. The growth signal is further amplified by growth factors including EGF, IGF-1, and TGF-? produced locally within fibroid tissue. Individual fibroids are monoclonal — each arises from a single mutated smooth muscle cell — and different fibroids within the same uterus are genetically distinct, explaining the variable growth rates and treatment responses seen within the same patient.
Other contributing factors.
Genetics play a major role — a woman with an affected first-degree relative has approximately 2.5 times the risk of developing fibroids. African-American women are disproportionately affected: fibroids are 2–3 times more prevalent, develop approximately 10 years earlier, tend to be larger and more numerous, cause more severe symptoms, and are associated with higher rates of hysterectomy in this population — a significant health disparity with incompletely understood etiologic contributors. Early menarche, obesity (which increases peripheral estrogen production from adipose tissue), vitamin D deficiency (fibroids have significantly lower vitamin D receptor expression), hypertension, and a diet high in red meat are recognized risk factors. Pregnancy — particularly multiple pregnancies — and long-term use of combined oral contraceptives appear to be associated with lower fibroid risk, possibly through their effects on estrogen cycling.
Symptoms
Approximately 50% of fibroids are asymptomatic and discovered incidentally on pelvic examination or imaging performed for another reason. Symptom severity depends heavily on fibroid size, number, and — most importantly — location within the uterus. Heavy menstrual bleeding (menorrhagia) is the most common symptom and occurs primarily with submucosal or intramural fibroids that distort the uterine cavity, disrupting normal hemostatic mechanisms and endometrial shedding. Bleeding is often heavy enough to cause iron-deficiency anemia. Pelvic pain and pressure, abdominal bloating, urinary frequency or urgency (from bladder compression by anterior fibroids), constipation (from rectal compression by posterior fibroids), low back pain, and dyspareunia are additional complaints. A large uterus from multiple fibroids may produce a palpable lower abdominal mass. Reproductive effects include infertility — particularly with submucosal fibroids that distort the endometrial cavity — recurrent pregnancy loss, preterm labor, placental abruption, fetal malpresentation, and an increased cesarean section rate.
Diagnosis
Fibroids are often first suspected during pelvic examination when the uterus feels enlarged, irregular, or nodular. Pelvic ultrasound is the standard initial imaging test and identifies most fibroids as well-defined hypoechoic masses within the myometrium. However, ultrasound has recognized limitations with multiple fibroids, large uteri, and the posterior uterus, where fibroids are commonly underestimated in number and size.
An MRI of the pelvis is the most accurate imaging study for fibroids and is essential when treatment planning is the goal. MRI precisely maps the number, size, location (submucosal, intramural, subserosal, pedunculated, cervical), and relationship of every fibroid to the endometrial cavity and serosa — information critical for selecting the appropriate procedure. The characteristic MRI appearance of a fibroid is a well-defined, T2-hypointense (dark) round mass within the myometrium, reflecting the densely packed smooth muscle and collagen. Degenerated fibroids (which have outgrown their blood supply) show variable T2 signal and peripheral or central necrosis — an important distinction because degenerated fibroids respond poorly to uterine fibroid embolization (UFE). MRI is the only imaging study that reliably distinguishes fibroids from adenomyosis — which appears as diffuse myometrial thickening with ill-defined T2-bright foci rather than a discrete mass — a distinction that fundamentally changes the treatment approach. MRI also identifies features suspicious for the rare uterine leiomyosarcoma, which can masquerade as a rapidly growing fibroid.
Classification
Fibroids are classified by location within the uterus using the FIGO (International Federation of Gynecology and Obstetrics) leiomyoma subclassification system, which directly guides treatment selection.
- Type 0 — Pedunculated submucosal: Entirely within the uterine cavity, attached by a stalk. Treated by hysteroscopic resection.
- Type 1 — Submucosal (<50% intramural): Bulging significantly into the uterine cavity. Strongly associated with heavy bleeding and infertility. Treated hysteroscopically when possible.
- Type 2 — Submucosal (?50% intramural): Majority in the myometrium but distorting the cavity. May require combined hysteroscopic and laparoscopic approach.
- Types 3–5 — Intramural: Entirely within the myometrium, ranging from cavity-abutting (Type 3) to purely intramural (Type 4) to serosa-abutting (Type 5). The most common fibroid location. Treated with myomectomy or UFE.
- Types 6–7 — Subserosal: Protruding from the outer uterine surface, ranging from serosa-distorting (Type 6) to pedunculated (Type 7). Cause pressure symptoms rather than bleeding. Well-suited to laparoscopic myomectomy or UFE.
- Type 8 — Cervical / parasitic: Arising from the cervix or detached from the uterus (parasitic). Rare; requires individualized surgical planning.
Treatments
Treatment depends on symptom severity, fibroid number, size and location, desire for future fertility, proximity to menopause, and patient preference. MRI findings are central to selecting the most appropriate intervention.
Observation: Asymptomatic fibroids require no treatment — regular monitoring with annual pelvic examination or imaging confirms stability. Women approaching menopause who are tolerating symptoms can reasonably defer intervention, as fibroids typically regress significantly after the menopause-related estrogen decline.
Medical management.
The levonorgestrel-releasing IUD (Mirena) reduces heavy menstrual bleeding effectively and is an excellent option for women with intramural or subserosal fibroids without significant cavity distortion. Combined oral contraceptives and oral progestins manage bleeding but do not shrink fibroids. GnRH agonists (leuprolide) induce a temporary menopausal state that shrinks fibroids by 30–50% over 3–6 months — useful as preoperative preparation to reduce fibroid size, restore hemoglobin before surgery, or as a bridge to natural menopause. GnRH antagonists (elagolix, relugolix) offer a newer oral option with faster onset and no initial flare effect. Tranexamic acid reduces menstrual blood loss without affecting fibroid size. Iron supplementation corrects fibroid-related anemia.
Uterine fibroid embolization (UFE).
UFE is a minimally invasive image-guided procedure performed by an interventional radiologist. Microspheres (polyvinyl alcohol particles or tris-acryl gelatin beads) are injected through a femoral artery catheter into the uterine arteries to occlude blood flow to all fibroids simultaneously, causing ischemic infarction and progressive shrinkage over 3–6 months. UFE treats all fibroids at once — regardless of number — preserves the uterus, and has high patient satisfaction rates with symptom relief comparable to myomectomy for most fibroid types. Submucosal fibroids may not respond as well, and UFE is not recommended for women actively pursuing pregnancy, as its effect on subsequent fertility and pregnancy outcomes remains uncertain. Preoperative MRI is essential to assess fibroid vascularity and exclude degenerated fibroids that will not respond to embolization.
MR-guided focused ultrasound (MRgFUS).
This entirely noninvasive treatment uses high-intensity focused ultrasound beams guided by real-time MRI to thermally ablate fibroid tissue without incisions or radiation. MRI simultaneously monitors tissue temperature to ensure complete treatment and protect surrounding structures. MRgFUS is suitable for selected patients with a limited number of T2-hypointense (non-degenerated) fibroids of appropriate size and location accessible to the ultrasound beam — specifically excluding anterior abdominal scar tissue, bowel loops in the beam path, and fibroids abutting the endometrium. The noninvasive nature makes it an attractive option for carefully selected patients who wish to avoid any invasive procedure.
Myomectomy.
Surgical removal of individual fibroids while preserving the uterus is the preferred approach for women who wish to maintain fertility. The surgical approach depends entirely on fibroid location and number as determined by MRI: hysteroscopic resection for submucosal fibroids (Types 0–2), laparoscopic or robotic myomectomy for subserosal and intramural fibroids of appropriate size, and open (laparotomy) myomectomy for very large, numerous, or deeply intramural fibroids. Myomectomy carries a 15–30% fibroid recurrence rate at 5 years — arising from new fibroids growing from remaining normal myometrium — and repeat procedures are sometimes needed.
Hysterectomy.
Removal of the uterus is the definitive and only curative treatment for fibroids and is appropriate for women with severe symptoms who have completed childbearing and prefer a permanent solution. Minimally invasive approaches (laparoscopic, robotic, or vaginal) are used when feasible. The ovaries are typically preserved in premenopausal women unless there is an independent indication for their removal, avoiding surgical menopause.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Pelvis MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.