## Most Common Site of Fibroid Origin **Key Point:** Intramural fibroids account for approximately 60–70% of all uterine fibroids and are the most common type encountered clinically. ### Anatomical Classification of Fibroids | Type | Frequency | Clinical Presentation | Symptoms | | --- | --- | --- | --- | | **Intramural** | 60–70% | Within myometrial wall | Menorrhagia, dysmenorrhea, pelvic pain, infertility | | **Submucosal** | 20–25% | Protrudes into uterine cavity | Severe menorrhagia, passage of tissue, anemia | | **Subserosal** | 10–15% | Projects toward peritoneum | Often asymptomatic unless large; may cause mass effect | | **Cervical** | <5% | Arises from cervical stroma | Vaginal bleeding, cervical obstruction | **High-Yield:** Intramural fibroids are the most common because the myometrium is the largest and most vascularized tissue layer of the uterus, providing the optimal microenvironment for smooth muscle proliferation. **Clinical Pearl:** While intramural fibroids are most frequent, **submucosal fibroids**, though less common, are the most **symptomatic** and most likely to cause heavy menstrual bleeding and infertility. This distinction is critical in clinical practice. ### Why Intramural Is Most Common 1. **Largest tissue mass** — the myometrium comprises the bulk of the uterine wall 2. **Rich vascular supply** — supports growth of benign smooth muscle tumors 3. **Estrogen and progesterone receptor expression** — highest in myometrial smooth muscle 4. **Mechanical factors** — intramural location allows gradual expansion without immediate symptoms [cite:Jeffcoate's Principles of Gynaecology Ch 19]
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