Types of Fibroids and the Fibroid Classification System
The most widely accepted uterine fibroid classification system is the International Federation of Gynecology and Obstetrics system, abbreviated FIGO. This system breaks and classifies the fibroid types based on anatomic location within the uterus. These locations are submucosal, myometrial, and subserosal. Fibroids in each anatomic location are then subcategorized based on what percentage of the fibroid resides within certain boundaries.
Submucosal fibroids are located within the innermost layer that lines the uterus, called the endometrium. This is the layer of the uterus that sheds during a woman’s menstruation. Submucosal fibroids can cause severe bleeding and longer periods. This type of fibroid is also the most likely subtype to cause fertility issues. They alter the contour of the uterine cavity and can make it difficult for a pregnancy to take hold onto the wall of the uterus or can block the fallopian tube. This type of fibroid can often cause issues even when comparatively small.
Type 0: intracavitary (on a stalk, completely in the uterine cavity)
Type 1: Submucosal with less than 50% intramural extension
Type 2: Submucosal with greater than 50% intramural extension
Intramural fibroids are the most common type of fibroids. These are located within the middle layer of the uterus, which is composed of smooth muscle. Intramural fibroids can cause issues similar to that of submucosal fibroids. These include bleeding, fertility issues and pregnancy complications. These can also cause increased menstrual cramping. They also contribute more so to the size of the uterus, which can cause bulk symptoms such as bloating and frequent urination.
Type 3: 100% intramural, but contacts the endometrium
Type 4: 100% intramural, not touching the endometrium
Type 5: Intramural with less than 50% subserosal
Subserosal fibroids originate from the outer wall of the uterus. As these fibroids enlarge, they can put pressure on the adjacent structures in the pelvis, causing pain or other bulk symptoms, like abdominal fullness.
Type 6: Subserosal with less than 50% intramural
Type 7: Subserosal, pedunculated (dangling on a stalk)
Type 8: Other (cervical or detached from the uterus)
While we do not stress that every fibroid should be strictly classified according to the FIGO system, having a working knowledge of what is typically expected based on a fibroid location is useful. After all, there are many causes of uterine bleeding and various treatments for symptomatic uterine fibroids based on the size, location, symptoms, and number of fibroids.