Classification of Uterine Fibroids

Uterine fibroids are traditionally classified according to their anatomical location as intramural, submucosal or subserosal. In addition, fibroids may be pedunculated (attached to the uterus by a stalk). Some larger fibroids may have characteristics of each type. Fibroids are not always isolated as there are often several coexistent lesions; in cases of multiple fibroids, a detailed ‘mapping’ of each lesion is valuable from a surgical point of view, although this may not always define a precise clinical situation14.

Fibroids can vary in size from millimetres to over 10 centimetres, and this can have a considerable clinical impact on the patient, with larger fibroids tending to respond less to pharmaceutical interventions, requiring more invasive surgical treatment options15.

Classification of Uterine Fibroids14, 16

  • Intramural fibroids: are fibroids which normally do not distort the uterine cavity and have <50% protruding into the serosal surface of the uterus and are the most common type. They typically develop within the wall of the uterus, beginning as small nodules in the muscular wall of the uterus. With time, intramural fibroids may expand inwards, causing distortion and elongation of the uterine cavity. They typically give the uterus a globular feeling on examination (like early pregnancy). They increase overall blood flow to the uterus and if large can distort and enlarge the internal cavity, even if they do not encroach onto it.
  • Subserosal fibroids: are those were >50% of the fibroid protrudes out of the serosal surface of the uterus. A subserosal fibroid may be sessile or pedunculated. They can grow quite large, but do not typically affect the size of the uterine cavity. They are more likely to produce pressure symptoms than heavy menstrual bleeding or infertility.
  • Submucosal fibroids: are defined as fibroids, which distort the uterine cavity according to the classification by the European Society of Hysteroscopy. The classification of these fibroids is then further divided into three subtypes: pedunculated fibroids without intramural extension (type 0), sessile (fixed in one location) with intramural extension of fibroid <50% (type I), and sessile with an intramural extension of >50% (type II). The degree of intramural extension can be assessed by ultrasonography or by hysteroscopy by observing the angle between the fibroid and the endometrium at the attachment to the uterine wall.

Submucosal fibroids are the fibroid type most likely to interfere with fertility14.

Other types of less frequent fibroids are:

  • Cervical fibroids: are found in the ‘neck’ (cervix) of the uterus and are difficult to remove without damaging the surrounding area.
  • Intraligamentous fibroids: are fibroids which may grow from a subserosal location into the peritoneal folds of the broad ligaments.