Types of Fibroids
Uterine fibroids, the most prevalent benign pelvic tumor in women, are estimated to affect more than 70% of reproductive-age women. Although all uterine fibroids arise from myometrium, they are classified by their location in the uterus. Uterine fibroids fall into three major clinical categories: subserosal, submucosal, and intramural. A fourth type, pedunculated fibroids, are characterized by their structure and behavior, rather than their location. In addition to their different positions in relation to the uterus, fibroid types vary in terms of associated symptoms, as well as their potential impact on reproductive functions, including fertility.
Subserosal fibroids are located on the outer wall of the uterus and protrude into the abdominal cavity. The most common of the three types, approximately 55% of uterine fibroids can be classified as subserosal. As subserosal fibroids grow outward, they can press against surrounding organs, causing what are known as “bulk symptoms”—pelvic pain, pressure, and urinary symptoms being common examples. Large subserosal fibroids that push on the bowel, pelvic wall, or vagina can result in painful bowel movements or intercourse.
The second category, submucosal fibroids, grow on the inside of the uterus, protruding into the uterine cavity. While submucosal fibroids are the least common type, comprising only 5% of cases, they are the most likely to be symptomatic. They are typically responsible for the heavy bleeding that many fibroid patients experience; this bleeding occurs because submucosal tumors disrupt the endometrial lining of the uterus and, when particularly large, can distort or enlarge the uterine cavity.
Whereas subserosal and submucosal fibroids grow from the wall of the uterus, the third type of fibroid, intramural, grows within the muscular layers of the uterine wall. Symptoms related to intramural fibroids include heavy bleeding, pressure and pain, depending on their size and location within the uterine wall. Enlarged intramural fibroids located close to the uterine cavity can change the shape of the uterus and interfere with menstrual and reproductive functions.
By disrupting the reproductive mechanism of the uterus in certain ways, submucosal and intramural fibroids can affect a woman’s fertility; large intramural fibroids, for example, can press into the fallopian tubes, interfering with ovulation. Having fibroids inside the wall or cavity of the uterus has also been shown to decrease the chance of success with in vitro fertilization (IVF), particularly if they are larger than 5 cm.
Pain is a common symptom of uterine fibroids, though the nature and severity can vary. A particular type of fibroid is especially painful, however: pedunculated tumors, which are connected to the uterus by a thin stalk, can easily twist, causing extreme pain. As they develop, submucosal and subserosal fibroids can become pedunculated.
Fibroids don’t tend to occur singularly: In fact, the average affected uterus has 6 to 7 fibroid tumors, and they can develop in different locations simultaneously. Moreover, while the clinical classification separates fibroids into distinct types by location, in reality, most fibroid tumors are “hybrids”; for example, a fibroid that is predominantly intramural can extend past the endometrium and protrude into the uterine cavity, rendering it a hybrid of the intramural-submucosal types. As a result, multiple diagnostic methods may be required to determine the actual size and location of all existing fibroids.
- Center for Uterine Fibroids, “What Are Fibroids”, Fibroids.net. Retrieved May 4, 2015 from http://www.fibroids.net/fibroids.html
- Galen, D. et. al, “Does Menstrual Bleeding Decrease After Ablation of Intramural Myomas? A Retrospective Study”, Journal of Minimally Invasive Gynecology. May 2013; Vol 20(6): 830-835
- “Fibroid Tumors.” [Video]. American Society for Reproductive Medicine, 21 Feb. 2012. Retrieved April 28, 2015, from https://www.youtube.com/watch?v=eSJ-ztQ97Og
- Wilde, S. and Scott-Barret, S. “Radiological Appearances of Uterine Fibroids”, Indian Journal of Radiology and Imaging. Aug 2009; Vol 19(3): 222–231. doi: 10.4103/0971-3026.54887
- Burbank, F. Fibroids, Menstruation, Childbirth, and Evolution, p. 106. Wheatmark, 2009. Tucson, AZ.