What are uterine fibroids?
Uterine fibroids are growths made of smooth muscle cells and other tissue that develop within the wall of the uterus.
Fibroids may grow as a single tumor or in clusters. A single fibroid can be microscopic in size or can grow to eight inches or more across. In many cases, a single uterus can contain many fibroids. Most fibroids range from about the size of a large marble to slightly smaller than a baseball.1
Bunches or clusters of fibroids are often of different sizes. Not all fibroids grow, and some may shrink, or remain constant over time.2
Health care providers categorize fibroids based on where in the uterine wall they grow:
- Submucosal (pronounced sub-myoo-KOH-sul) fibroids grow just underneath the uterine lining and into the endometrial cavity.
- Intramural (pronounced intra-MYUR-ul) fibroids grow in between the muscles of the uterus.
- Subserosal (pronounced sub-sur-OH-sul) fibroids grow on the outside of the uterus.
Some fibroids grow on stalks that grow out from the surface of the uterus or into the cavity of the uterus. These are called pedunculated (pronounced ped-UN-kyoo-lay-ted) fibroids.
- Agency for Healthcare Research and Quality (AHRQ). (2007). Management of uterine fibroids: An update of the evidence (AHRQ Publication No. 07-E011). Retrieved December 8, 2011, from http://archive.ahrq.gov/downloads/pub/evidence/pdf/uterupdate/uterup.pdf (PDF - 343 KB) [top]
- Peddada, S. D., Laughlin, S. K., Miner, K., Guyon, J.-P., Haneke, K., Vahdat, H. L., et al. (2008). Growth of uterine leiomyomata among premenopausal black and white women. Proceedings of the National Academy of Sciences of the United States of America, 105, 19887–19892. Retrieved April 11, 2012, from http://www.pnas.org/content/105/50/19887.long [top]