Types of Fibroids Explained
Fibroid Locations, Different Types, Sizes, & FIGO Classifications
Understanding fibroid anatomy and how they factor into fibroid symptoms is important. Learn about fibroid locations, different fibroid types, and fibroid size classifications. If you’ve been diagnosed with fibroids, your doctor has probably given you a brief explanation of how many fibroids you have, where your fibroids are located within your uterus, and how big (or small) they are. Your doctor may have even introduced you to specialized terms like ‘submucosal’ or ‘pedunculated’ to describe the specific anatomy of your fibroids. These fibroid attributes (location, type, and size classification) can have a major influence on your individual experience with fibroids, and can even preclude certain treatment options. Ask your doctor the right questions about fibroids.
Our fibroid specialists review what we know about fibroid anatomy and how it can affect symptoms and treatment options. We provide a detailed explanation of fibroid locations, fibroid types, and fibroid sizes so you can make sense of your diagnosis and your options.
Quick Navigation:
- Uterine Fibroid Classification
- Fibroid Types: Pedunculated, Intramural, Submucosal, Subserosal, Other
- Fibroid Size Classifications Explained
- How Does Fibroid Size & Location Affect Symptoms?
- How Does Fibroid Size & Location Affect Pregnancy & Fertility?
- How Does Fibroid Size & Location Affect Treatment Options?
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Adrianne S, October 2018
Fibroid Classification
Fibroid classification can be done in different ways, but the most widely adopted classification system is the one set by the International Federation of Gynecology and Obstetrics (FIGO). FIGO classifies fibroids based on the fibroids location in the uterus. According to FIGO fibroid classification, there are 9 types of fibroids, which are assigned numbers ranging from 0 to 8 [1]. These numbers describe the location of the fibroid relative to the three main layers of the uterus: the inner lining of the uterine cavity called the endometrium, the smooth muscle of the uterine wall called the myometrium, and the outer surface of the uterus known as the serous membrane. Size and number of fibroids are not currently included in existing staging systems, which assess fibroids primarily on their location [2]. Under the FIGO classification system, you’ll see that uterine fibroids are described as either pedunculated, submucosal, intramural, or subserosal.
FIGO Fibroids Classification
Fibroid Type | Description |
Type 0 | Pedunculated, intracavitary |
Type 1 | Submucosal, <50% intramural | 50%>
Type 2 | Submucosal, ≥50% intramural |
Type 3 | Contact with endometrium, 100% intramural |
Type 4 | Intramural |
Type 5 | Subserosal, ≥50% intramural |
Type 6 | Subserosal, <50% intramural50%> |
Type 7 | Subserosal, pedunculated |
Type 8 | Other (e.g., cervical, parasitic) |
Uterine Fibroid Types
Pedunculated Fibroids
Fibroid Type | Description |
Type 0 | Pedunculated, intracavitary |
Type 7 | Subserosal, pedunculated |
Intramural Fibroids
Fibroid Type | Description |
Type 3 | Contact with endometrium, 100% intramural |
Type 4 | Intramural |
Submucosal Fibroids
Fibroid Type | Description |
Type 1 | Submucosal, <50% intramural50%> |
Type 2 | Submucosal, ≥50% intramural |
Subserosal Fibroids
Fibroid Type | Description |
Type 5 | Subserosal, ≥50% intramural |
Type 6 | Subserosal, <50% intramural 50%> |
Other Types of Fibroids
Fibroid Type | Description |
Type 8 | Other (e.g., cervical, parasitic) |
Fibroid Sizes Explained
Fibroid Size Classification
Fibroid size classification is done to either estimate the fibroid volume, measure fibroid diameter on imaging studies, or to estimate the size of the enlarged uterus as a result of a growing fibroid. In one study, women with one or more fibroids had a median fibroid size of 5 cm3 by volume [4]. Small fibroids have diameters less than or equal to 20 mm and they enlarge the uterus to appear as it would at the 4th week of pregnancy. Average, medium-sized fibroids range between 20 and 60 mm in diameter and cause the uterus to appear as if it were at 10 or 11 weeks gestation. Large fibroids are greater than 60 mm in diameter and enlarge the uterus, making it comparable to a womb at 12 to 16 weeks gestation.
Fibroid Size and Type
Fibroid Size and Position
How Does Fibroid Size & Location Affect Symptoms?
Some large fibroids can exert pressure on surrounding organs and nerves, which can lead to more severe and noticeable symptoms. However, larger fibroids aren’t always associated with more symptoms like increased pain [4]. In one study, women with smaller intramural fibroids were more likely to report moderate or severe pain compared to patients without them [4].
Many women with uterine fibroids are able to become pregnant without a problem. However, certain types of fibroids can crowd the uterine cavity or distort the endometrium, causing complications. Some studies show that the risk of developing complications during pregnancy increases if a woman has uterine fibroids over 3 cm in diameter. However, women with large fibroids greater than 10 cm in diameter can achieve vaginal delivery approximately 70% of the time [3]. In general, complications such as miscarriage, c-section, preterm labor and postpartum hemorrhage can occur in approximately 10 to 40% of pregnancies when fibroids are present [10, 11].
How Does Fibroid Size & Location Affect Pregnancy & Fertility?
How Does Fibroid Size & Location Affect Treatment Options?
Medications
Uterine Fibroid Embolization
The ideal UFE candidate is a premenopausal woman with heavy menstrual bleeding and/or severe menstrual pain caused by intramural fibroids. UFE may not be efficacious if the only fibroid symptoms you have are bulk-related (i.e. pelvic pain or pelvic pressure) [14]. In addition, UFE isn’t the most suitable option for very large fibroids or women with a high number of fibroids, as symptom recurrence is likely to occur [14]. Pedunculated fibroids with a narrow stem (the stalk has a diameter less than 50% of the diameter of the largest fibroid) are considered to be relative contraindications for UFE because these fibroids may detach into the peritoneal or uterine cavities and cause infection [14].
The probability of needing a new surgical procedure in 2 to 5 years after UFE ranges from 15 to 32 percent compared to 7% for surgical procedures like myomectomy and hysterectomy [12]. Though successful pregnancies have been reported post-UFE, there are studies that show lower pregnancy and higher miscarriage rates compared to other treatments like myomectomy [9].
Myolysis
Myolysis does impact future fertility and pregnancies. As fibroid tissue is destroyed with myolysis, scar tissue can form in the endometrium. While some women may achieve successful pregnancies, there could be potential complications. Myolysis is not always a definitive treatment. Surgical intervention may be required down the line [12].
Endometrial Ablation
Pregnancy is not recommended after endometrial ablation. A single endometrial ablation procedure may require follow-up intervention in the future. A recent study compared the re-intervention rates for women after they underwent endometrial ablation, myomectomy, or uterine artery embolization to treat fibroids. One year after the initial procedure, the need for a second procedure was 12.4% for endometrial ablation, 4.2% for myomectomy, and 7.0% for uterine artery embolization [16,17].
Myomectomy
Myomectomy isn’t without its flaws, and isn’t always ideal for women with multiple large fibroids. Failure rates range from 14.5% to 30% at 3 to 4 years’ follow-up [9]. Between 10 and 25 percent of women will require a second fibroid surgery [15]. Still, many women choose myomectomy in order to preserve their uterus for future pregnancies. Most women who have myomectomy are able to have children afterwards.
Hysterectomy
Hysterectomy is the most definitive treatment available for uterine fibroids, particularly for women who have no desire to conceive [12]. It can be very effective for patients with extremely large fibroids or a large quantity of fibroids. However, after hysterectomy, once the uterus or parts of it are removed, pregnancy is no longer possible.
Surgical vs. Non-Surgical Fibroid Treatments: Which Is Best?
When it comes to fibroid treatment, we believe that less is more. A less invasive procedure means less trauma, less risk, and shorter recovery time. Learn more about why we opt for UFE, the least invasive treatment for uterine fibroids.
Uterine Artery Embolization
Fibroid Specialist in Los Angeles
Learn more about Los Angeles Fibroid Specialist Dr. Michael Lalezarian.
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[12] Mas A, Tarazona M, Dasí Carrasco J, Estaca G, Cristóbal I, Monleón J. Updated approaches for management of uterine fibroids. Int J Womens Health. 2017 Sep 5;9:607-617. doi: 10.2147/IJWH.S138982. PMID: 28919823; PMCID: PMC5592915.
[13] Khan AT, Shehmar M, Gupta JK. Uterine fibroids: current perspectives. Int J Womens Health. 2014 Jan 29;6:95-114. doi: 10.2147/IJWH.S51083. PMID: 24511243; PMCID: PMC3914832.
[14] van der Kooij S.M., Hehenkamp W. Uterine fibroids (leiomyomas): Treatment with uterine artery. UpToDate. Accessed February 2021.
[15] Stewart, E.A., Laughlin-Tommaso, S.K. Patient education: Uterine fibroids (Beyond the Basics). UpToDate. Accessed February 2021.
[16] Singh SS, Belland L. Contemporary management of uterine fibroids: focus on emerging medical treatments. Curr Med Res Opin. 2015;31(1):1-12.
[17] Davis MR, Soliman AM, Castelli-haley J, Snabes MC, Surrey ES. Reintervention Rates After Myomectomy, Endometrial Ablation, and Uterine Artery Embolization for Patients with Uterine Fibroids. J Womens Health (Larchmt). 2018;27(10):1204-1214.
[18] Munro MG. Endometrial ablation: where have we been? Where are we going?. Clin Obstet Gynecol. 2006;49(4):736-66.
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