A 42-year-old woman presents with heavy menstrual bleeding and a 16-week-sized uterus. Imaging reveals multiple intramural fibroids. Which feature would best distinguish intramural fibroids from submucosal fibroids as the primary cause of her menorrhagia?

Explanation

## Intramural vs. Submucosal Fibroids: Key Discriminator ### Anatomical Classification **Key Point:** Fibroids are classified by their location relative to the endometrial cavity: submucosal (projecting into cavity), intramural (within myometrium), and subserosal (projecting outward). The degree of endometrial cavity distortion is the defining anatomical difference. ### Comparison Table | Feature | Submucosal | Intramural | | --- | --- | --- | | **Location** | Bulges into endometrial cavity | Within myometrial wall | | **Cavity distortion** | Marked distortion/compression | Minimal to no distortion | | **HSG/Hysteroscopy finding** | Filling defect, cavity narrowing | Normal or mildly enlarged cavity | | **Menorrhagia severity** | Severe (disproportionate to size) | Moderate (proportionate to size) | | **Mechanism of bleeding** | Increased endometrial surface area, impaired hemostasis | Disrupted vasculature, altered uterine contractions | | **Infertility risk** | High (implantation failure) | Moderate (if large) | | **FIGO classification** | Type 0–2 | Type 3–4 | ### High-Yield Diagnostic Approach **High-Yield:** The **FIGO classification** uses the degree of cavity involvement: - **Type 0:** Entirely submucosal, pedunculated into cavity - **Type 1:** <50% intramural extension - **Type 2:** ≥50% intramural extension - **Type 3:** Intramural, no cavity involvement - **Type 4:** Subserosal ### Clinical Pearl **Clinical Pearl:** Submucosal fibroids cause disproportionately heavy bleeding relative to their size because they increase endometrial surface area and impair local hemostasis. Intramural fibroids cause bleeding proportionate to their size through disruption of myometrial vasculature and altered uterine contractility. ### Imaging Distinction **Key Point:** - **Hysterosalpingography (HSG):** Submucosal fibroids show filling defects and cavity distortion; intramural fibroids show normal or mildly enlarged cavity - **Transvaginal ultrasound:** Submucosal fibroids project into cavity (echogenic mass within endometrial cavity); intramural fibroids are within myometrium with intact overlying endometrium - **MRI:** Submucosal fibroids displace the junctional zone; intramural fibroids are contained within myometrium ### Why Option 0 is Correct The **degree of endometrial cavity distortion** on HSG or hysteroscopy is the single best discriminator. Submucosal fibroids by definition protrude into and distort the cavity, whereas intramural fibroids do not. This anatomical distinction directly explains the pathophysiology of menorrhagia and guides treatment decisions. [cite:Ferenczy A. Pathophysiology of adenomyosis and uterine myomas. Fertil Steril. 2018; Jeffcoate's Principles of Gynaecology Ch 19]