A 38-year-old woman presents with menorrhagia for the past 6 months. On examination, the uterus is enlarged and irregular. Transvaginal ultrasound confirms multiple intramural masses. What is the most common structural cause of abnormal uterine bleeding in reproductive-age women?

Explanation

## Most Common Structural Cause of AUB **Key Point:** Uterine fibroids (leiomyomas) are the most common benign pelvic tumor in women and the most frequent structural cause of abnormal uterine bleeding, particularly menorrhagia. **High-Yield:** Fibroids occur in 20–40% of reproductive-age women, though only a minority cause clinically significant bleeding. They are estrogen-dependent tumors that regress after menopause. ### Pathophysiology of Fibroid-Related Bleeding 1. **Submucosal fibroids** — distort the endometrial cavity, increase endometrial surface area, and impair hemostasis 2. **Intramural fibroids** — may thin the overlying endometrium, causing ulceration and bleeding 3. **Increased vascularity** — fibroids have abnormal vascular architecture with dilated vessels 4. **Altered prostaglandin and cytokine expression** — leads to impaired vasoconstriction and increased fibrinolysis ### Comparison of Structural Causes of AUB | Feature | Fibroids | Polyps | Adenomyosis | Endometrial Cancer | |---------|----------|--------|-------------|-------------------| | **Prevalence** | 20–40% of women | 10–40% (varies with age) | 15–30% (increases with age) | 1–2% (postmenopausal) | | **Age of onset** | Reproductive age (peaks 40–50) | Reproductive to perimenopausal | Reproductive to perimenopausal | Postmenopausal (>60 yrs) | | **Bleeding pattern** | Menorrhagia (heavy, prolonged) | Intermenstrual or postcoital | Dysmenorrhea + menorrhagia | Postmenopausal bleeding | | **Ultrasound finding** | Hypoechoic mass, distorts cavity | Echogenic stalk in cavity | Heterogeneous myometrium, thickened | Endometrial thickening || | **Most common type** | Intramural (60%) | Fundal | Diffuse | — | **Clinical Pearl:** Submucosal fibroids (FIGO type 0–2) are most likely to cause heavy menstrual bleeding because they directly distort the endometrial cavity and impair hemostasis. Intramural and subserosal fibroids are often asymptomatic. **Mnemonic:** **SAFE** — Structural causes of AUB: **S**ubmucosal fibroids, **A**denomyosis, **F**ibroids (all types), **E**ndometrial polyps/cancer. Fibroids are the single most common. ### Why Fibroids Are Most Common - Estrogen-dependent smooth muscle tumors arising from myometrial cells - Monoclonal origin (each fibroid is a clone of a single transformed cell) - Risk factors: African descent, nulliparity, obesity, age >40 years - Often multiple (80% of women with fibroids have >1 tumor) **High-Yield:** The FIGO classification (0–8) stratifies fibroids by location relative to the endometrial cavity; types 0–2 (submucosal) cause the most bleeding and are candidates for hysteroscopic resection. [cite:Williams Obstetrics 26e Ch 38]