Types of Fibroids

By Dr. Kenosha Gleaton, OBGYN

Fibroids occur in over 77% of all people assigned female at birth (AFAB) and can vary widely in size, shape, and location. [1-2] While researchers are still trying to learn more about them, we do have a basic understanding of the different types, treatments, and symptoms associated with uterine fibroids. 

What are Fibroids?

Leiomyomas, also known as myomas or uterine fibroids, are growths found in or around the uterus. Fibroids are the most common type of noncancerous tumors found in people AFAB of reproductive age. [1-2] Not everyone with fibroids will experience symptoms, but others may notice pain, abnormal bleeding, pressure, cramping, or reduced fertility. Research is still ongoing to better understand the causes, treatments, and health effects of uterine fibroids. [1-2] 

Causes and Risk Factors of Fibroids

There is no exact cause of fibroids, but research supports a few different hypotheses. We know that genetics likely play a role, as studies have found that many people with uterine fibroids have specific genetic mutations that may impact the growth of fibroids. [2] The overproduction of certain genes is also associated with increased fibroid size. 

Another hypothesis is that the hormones estrogen and progesterone contribute to the growth of fibroids. It’s common for fibroids to shrink during and after menopause, when we see a decrease in these hormone levels. [1] There is also data that links major stresses, micronutrients, growth hormones, and more to the formation of fibroids. [1-3] 

There are some risk factors that may increase someone’s chances of developing uterine fibroids, such as [1,4]:

• Age: Fibroids are most commonly seen in AFAB people aged 30 to 40.
• Obesity
• Race: Black women are more likely to have fibroids than white women
• Family history of fibroids
• Vitamin D deficiency (learn more about vitamin D and fibroids)
• High blood pressure
• Use of soybean milk

Multiple successful pregnancies and the long-term use of hormonal contraceptives are associated with a decreased risk of uterine fibroids. [4] 

How are Fibroids Diagnosed?

Fibroids are sometimes discovered during a regular pelvic exam or a gynecologic exam. Some people may seek out a healthcare provider because they are experiencing symptoms such as pelvic pain or heavy bleeding. [5] If fibroids are suspected, a healthcare provider may conduct one or more tests to confirm and determine the size or location of the fibroids [5]:

• Ultrasound: A non-invasive imaging test that uses sound waves to create an image of the internal organs
• Magnetic resonance imaging (MRI): More detailed imaging test that uses magnets and radio waves.
• Computed tomography (CT): Uses X-ray to view detailed images of the internal organs
• Hysteroscopy and laparoscopy: These are minimally invasive options that require making small incisions along the abdomen or passing a scope through the vagina and into the uterus. These allow the healthcare provider to view the inside of your body with a camera to better determine the size and location of fibroids or other tissues and organs. 
• Hysterosalpingography (HSG): This is a detailed X-ray using contrast material to get a better view of the organs. This is often used in those undergoing infertility evaluation. 
• Sonohysterography: Another imaging test that uses a transvaginal catheter. Saline is injected into the uterine cavity to give a clearer image of the organs. 

It is usually fairly easy for healthcare providers to differentiate between the types of fibroids with MRI or other tests. Even small fibroids with a diameter of 5 mm are distinguishable. [6]

What Are the Different Types of Fibroids?

Fibroids can range in size, location, and shape, and may require different treatments or lead to different symptoms. Typically fibroids are classified according to their location, of which there are three categories: submucosal, intramural, or subserosal. [6] Here’s a breakdown of the different types of fibroids. 

Exophytic Fibroids

There are two key locations where fibroids can grow, either inside the uterine wall or outside of the uterine wall. Fibroids that are able to extend beyond the surface of the uterus, or are otherwise not contained inside the uterine wall, are sometimes classified as exophytic fibroids. 

Subserosal

Subserosal fibroids are an example of exophytic fibroids, growing from the outer wall of the uterus and into the pelvis and surrounding space. [6] Subserosal fibroids sometimes grow relatively large and can develop a stalk that attaches to the uterus, known as a pedunculated fibroid (picture a mushroom-like shape). [5] While rare, some of these pedunculated fibroids can twist, causing severe pain. 

Submucosal

Submucosal fibroids can also project outside of the uterine tissue. These are the least common type of myoma, accounting for approximately 5% of all fibroids. [6] Although these aren’t as common, they are the most likely to cause symptoms. Submucosal fibroids can grow into the endometrial cavity, can occasionally become pedunculated, and may even prolapse (drop-down or bulge) into the cervical canal or vagina. [6] 

Intramural

Intramural fibroids are another common type and are often asymptomatic, meaning they don’t cause any symptoms. [6] Intramural fibroids are embedded in the wall of the uterus rather than the uterine cavity or outside of the uterus. Intramural fibroids have the potential to compress the fallopian tubes, which may negatively impact fertility. [6] 

What is the Most Common Type of Fibroid?

There is mixed information about the most common type of fibroid. A 2015 publication by The American Society for Reproductive Medicine states that subserosal fibroids are the most common type, making up approximately 55% of fibroids. [7] However, a study from 2009 and USA Fibroid Centers suggest that intramural fibroids are the most common type of fibroid. [6,8] Symptoms are more likely to appear with subserosal fibroids than intramural fibroids, which may play a role in the underreporting of intramural fibroids. What most experts seem to agree on is that submucosal fibroids are the least common fibroid type. [6-8] 

Does Treatment Vary for Fibroid Types?

Treatment options do vary depending on the severity of the symptoms, location, family planning goals, and size. [1,5] Treatment isn’t always necessary either unless the fibroids are causing discomfort or impacting fertility outcomes. Some common treatment options include hormonal medications, myomectomy (removal of the fibroids while leaving the uterus intact), hysterectomy (total removal of the uterus), ablation (destroying the lining of the uterus), embolization (blocking blood flow to the fibroids in hopes of shrinking them), and others. [1,5] There are also methods for reducing symptoms and severity of fibroids, such as pain medications, warm compresses, and rest. [9] Some data also suggest that vitamins D, A, B3, E, and K may be useful for improving the size and symptoms of fibroids. [10] You should speak to your healthcare provider about the best treatment option for you. 

Key Takeaways

• Fibroids are noncancerous growths or tumors found in or around the uterus. 
• Fibroids are very common in females of reproductive age.
• There isn’t an exact cause of fibroids, but some potential causes include hormones, genetics, stresses, and micronutrients. 
• Fibroids can be diagnosed through various imaging tests and are sometimes discovered during a pelvic exam. 
• The three types of fibroids include submucosal, subserosal, and intramural. 
• Submucosal fibroids are the least common type of fibroid but the most likely to cause symptoms. Submucosal fibroids can extend into the uterine cavity. 
• Intramural fibroids are a common type of fibroid and are found within the muscular uterine wall. 
• Subserosal fibroids are another common type of fibroid, they grow from the outer wall of the uterus. 
• Treatment for fibroids can vary depending on symptoms, size, shape, and fertility goals. 

References:

1. Patient FAQ: Uterine fibroids. FAQ074. American Congress of Obstetricians and Gynecologists. July 2022. Retrieved June 2023. URL.
2. Segars JH, Parrott EC, Nagel JD, et al. Proceedings from the Third National Institutes of Health International Congress on Advances in Uterine Leiomyoma Research: comprehensive review, conference summary and future recommendations. Hum Reprod Update. 2014;20(3):309-333. doi:10.1093/humupd/dmt058
3. Uterine Fibroids. NIH. Office of Communications. November 2 2018. URL. 
4. Risk Factors of Uterine Fibroids. NIH. Office of Communications. November 2 2018. URL. 
5. Uterine Fibroids. Cleveland Clinic. August 24 2020. URL. 
6. Wilde S, Scott-Barrett S. Radiological appearances of uterine fibroids. Indian J Radiol Imaging. 2009;19(3):222-231. doi:10.4103/0971-3026.54887
7. Fibroids and Fertility. American Society for Reproductive Medicine. ReproductiveFacts.org. Revised 2015. URL. 
8. Intramural Fibroid: Symptoms and Treatment. USA Fibroid Centers. July 4, 2022. URL. 
9. Living with uterine fibroids. NIH. Medline Plus. January 10 2022. URL. 
10. Ciebiera M, Ali M, Zgliczyńska M, Skrzypczak M, Al-Hendy A. Vitamins and Uterine Fibroids: Current Data on Pathophysiology and Possible Clinical Relevance. Int J Mol Sci. 2020;21(15):5528. Published 2020 Aug 1. doi:10.3390/ijms21155528