Uterine Fibroids (Leiomyomas)

Uterine fibroids, also called leiomyomas or myomas, are benign smooth-muscle tumors arising from the myometrium of the uterus. They are the most common pelvic tumors in women of reproductive age and, although often asymptomatic, can cause heavy menstrual bleeding, pelvic pressure, bulk symptoms, and reproductive problems depending on their size, number, and location.

Definition

A uterine fibroid (leiomyoma) is a benign, monoclonal tumor of uterine smooth muscle and extracellular matrix arising in the myometrium, classified by location as submucosal, intramural, or subserosal.

Scope

This entry covers fibroids as a benign clinical entity: what they are, how they are thought to develop, where they sit within the uterus, how they present, and how they are classified — including their place within the FIGO PALM-COEIN system for abnormal uterine bleeding. It is a reference overview and does not provide treatment recommendations.

Core questions

• What distinguishes a benign uterine leiomyoma from malignant uterine smooth-muscle tumors?
• How does fibroid location (submucosal, intramural, subserosal) relate to symptoms such as bleeding and bulk effects?
• Why are fibroids considered estrogen- and progesterone-dependent, and how does this shape their natural history?

Key concepts

• Benign smooth-muscle (myometrial) tumor
• Monoclonal origin
• Submucosal, intramural, and subserosal location
• Estrogen and progesterone dependence
• Heavy menstrual bleeding and bulk symptoms
• FIGO leiomyoma subclassification

Mechanisms

Fibroids are thought to arise from a single transformed myometrial smooth-muscle cell that proliferates clonally, producing a firm, well-circumscribed tumor of smooth muscle and abundant extracellular matrix. Their growth is dependent on the ovarian steroids estrogen and progesterone, which is consistent with their occurrence during the reproductive years and tendency to regress after menopause; genetic alterations have also been implicated in many tumors. Location largely determines the clinical picture: submucosal lesions that distort the endometrial cavity are most associated with heavy menstrual bleeding, whereas larger intramural and subserosal lesions tend to produce pressure and bulk symptoms.

Clinical relevance

Fibroids are a leading cause of heavy menstrual bleeding and of benign pelvic masses, and they are one of the most common indications recorded for gynecologic surgery. They are also relevant to fertility and pregnancy when they distort the uterine cavity. This entry describes the condition and how it is classified for reference; it is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Fibroids are very common: a systematic review of the epidemiology reported a wide range of prevalence estimates that rise with age through the reproductive years, with substantial cumulative incidence by the later reproductive decades. Reported figures vary considerably with the population studied and whether diagnosis was based on symptoms, imaging, or pathology.

History

Leiomyomas have long been recognized as common uterine tumors, and their classification has been refined as imaging and surgery allowed precise localization within the uterine wall. The 2011 FIGO classification, revised in 2018, introduced a standardized leiomyoma subclassification within the PALM-COEIN framework, improving how submucosal, intramural, and subserosal lesions are described in research and practice.

Seminal works

• stewart-2017
• parker-2007
• munro-2018

Frequently asked questions

Are uterine fibroids cancerous?

No. Fibroids are benign smooth-muscle tumors and are distinct from the rare malignant uterine smooth-muscle tumors. They do not invade or metastasize, though they can cause significant symptoms.

Why do fibroid symptoms depend on location?

Submucosal fibroids that bulge into and distort the endometrial cavity are most strongly linked to heavy menstrual bleeding, while larger intramural and subserosal fibroids tend to cause pelvic pressure and bulk-related symptoms.