What is a uterine leiomyoma?

What is a Uterine Leiomyoma?

Uterine leiomyomas (also called fibroids or myomas) are benign smooth muscle tumors originating from the myometrium that represent the most common gynecologic tumors, affecting up to 70-80% of women by menopause. 1

Definition and Pathology

• Leiomyomas are benign, sex steroid-responsive, monoclonal tumors arising from individual myometrial smooth muscle cells 1
• The histology is virtually indistinguishable from normal myometrium, with highly variable cellularity 1
• These tumors grow in a spherical, nodular fashion with distinct demarcation from surrounding normal myometrium, reflecting their clonal origin 1
• They are well-vascularized tumors characterized by increased smooth muscle cell proliferation and collagen deposition 1

Epidemiology

• Leiomyomas are the most common soft-tissue tumors in the entire body, with clinical presentation in up to 25% of reproductive-age women 1, 2
• The true incidence is much higher, with estimates as high as 70% of white women and more than 80% of women of African ancestry having identifiable leiomyomas by menopause 1, 3
• They occur predominantly during reproductive years and are more common in African-American women 1
• Approximately 200,000 hysterectomies and 20,000 myomectomies are performed annually in the United States for symptomatic leiomyomata 1

Clinical Presentation

• Most women with fibroids are asymptomatic, but approximately 30% present with severe symptoms requiring intervention 3
• Symptomatic presentations include:
  • Menometrorrhagia (heavy or prolonged menstrual bleeding) 1
  • Dysmenorrhea and pelvic pain 1
  • Pelvic pressure symptoms 1
  • Compression of adjacent pelvic viscera (urinary frequency, constipation) 3
  • Reproductive failure and infertility 1
• Size does not correlate with symptoms: large tumors can be asymptomatic while small leiomyomata may cause massive uterine bleeding and pain 1

Pathophysiology

• Leiomyomas develop through complex interactions of genetic mutations, endogenous sex-steroid production, reproductive patterns, and environmental exposures 4
• Approximately one-third have clonal chromosomal aberrations, though these are not consistent between individual leiomyomata even in the same woman 4
• Growth factors including platelet-derived growth factor, heparin-binding epidermal growth factor, and transforming growth factor-β play regulatory roles in proliferation 1
• These tumors are hormone-responsive: many have limited growth potential and remain static until sex steroid levels decline at menopause 1

Distinguishing Benign from Malignant

• For practical purposes, leiomyomas should be considered benign in premenopausal women 1
• Leiomyosarcomas are rare, comprising only 0.1% of all uterine tumors 4, 5
• In postmenopausal women, particularly those in their seventh decade, 1.7% of presumed fibroids are actually leiomyosarcomas 1, 4, 5
• Histologic criteria for malignancy include increased mitoses (>10 per 10 high-power fields), cellular pleomorphism, and thrombotic/coagulative necrosis 1, 5
• Frozen section cannot reliably diagnose malignancy; permanent sections are required 1

Common Pitfalls

• Do not assume rapid growth always indicates malignancy—this can occur in benign fibroids during pregnancy 1, 5
• Recognize that the incidence of leiomyomata far exceeds the frequency of clinical problems they cause 1
• Be aware of the 50% recurrence rate after surgical removal, reflecting the multifocal nature of this condition 1