What is a myomatous uterus?

What is a Myomatous Uterus?

A myomatous uterus is a uterus containing leiomyomata (fibroids)—benign smooth muscle tumors that are the most common pelvic tumors in women of reproductive age, affecting up to 70% of women by menopause. 1

Definition and Pathophysiology

• Leiomyomata are benign, sex steroid-responsive, clonal expansions of individual smooth muscle cells originating from the myometrium. 1
• The histology is virtually indistinguishable from normal myometrium, with highly variable cellularity and areas of fibrosis and calcification, especially after degeneration. 1
• These tumors grow in a spherical nodular fashion with distinct demarcation from surrounding normal myometrium, reflecting their clonal origin. 1

Epidemiology and Clinical Significance

• Approximately 200,000 hysterectomies and 20,000 myomectomies are performed annually in the United States for symptomatic leiomyomata. 1
• The incidence of leiomyomata far exceeds the frequency of clinical problems they cause—estimates suggest up to 70% of women have identifiable leiomyomata at menopause, though most remain asymptomatic. 1
• Leiomyomata are more common in African-American women and have a non-Mendelian inheritance pattern with up to 50% recurrence rate after surgical removal. 1

Clinical Presentation Spectrum

Symptoms vary dramatically based on size, location, and number of fibroids: 1

• Heavy or prolonged menstrual bleeding (menometrorrhagia) leading to anemia 1
• Pelvic pain and dysmenorrhea 1
• Bulk symptoms from compression of adjacent pelvic organs (bladder, rectum) 1
• Reproductive dysfunction including infertility and pregnancy complications 1
• Many remain completely asymptomatic despite large size 1

Anatomic Classification

Location determines symptoms and treatment approach: 1

• Subserosal (SS): Project outward from the uterine surface; typically cause bulk symptoms but not bleeding 1
• Intramural (IM): Within the myometrial wall; most common type, can cause both bleeding and bulk symptoms 1
• Submucosal (SM): Project into the uterine cavity; most likely to cause heavy bleeding and impact fertility even when small 1

Critical Distinction: Benign vs. Malignant

Leiomyosarcoma is rare but must be considered, particularly in specific populations: 1, 2

• Leiomyosarcomas comprise only 0.1% of all uterine tumors. 1, 3
• Risk increases dramatically with age: 1.7% of women undergoing hysterectomy for presumed leiomyomata in their seventh decade actually have leiomyosarcoma. 1, 3, 2
• For practical purposes, these tumors should be considered benign in premenopausal women, but all specimens require careful pathologic examination. 1
• Histologic criteria for malignancy include increased mitoses, cellular pleomorphism, and thrombotic degeneration within the tumor. 1, 2
• Frozen section cannot reliably diagnose leiomyosarcoma; permanent sections are required. 1

Natural History

• Many leiomyomata have limited growth potential and remain static until sex steroid levels decline at menopause. 1
• Rapid growth can occur during pregnancy due to hormonal stimulation, with central necrosis and hyalinized degeneration possible. 1
• Fibroids typically stabilize or regress after menopause. 4

Common Pitfall

Do not assume rapid growth indicates malignancy—the prevalence of sarcoma in rapidly growing myomas (0.27%) is essentially identical to that in all myomas (0.26%). 4 However, any new or growing uterine mass in a postmenopausal woman requires thorough evaluation. 2, 4