A 32-year-old woman presents with heavy menstrual bleeding for the past 6 months. Pelvic examination reveals an irregularly enlarged uterus with multiple nodular masses. Transvaginal ultrasound confirms multiple intramural lesions with preserved endometrial-myometrial interface. Which single feature best distinguishes uterine fibroids from adenomyosis in this clinical context?

Explanation

## Distinguishing Fibroids from Adenomyosis ### Structural Hallmark **Key Point:** The defining difference lies in the anatomical relationship to the endometrial-myometrial interface (junctional zone). ### Comparative Features | Feature | Uterine Fibroids | Adenomyosis | |---------|------------------|-------------| | **Junctional Zone** | Preserved, normal | Disrupted, thickened (>12 mm) | | **Margins** | Discrete, well-demarcated | Diffuse, poorly demarcated | | **Echogenicity** | Hypoechoic/heterogeneous with pseudocapsule | Heterogeneous, no capsule | | **Distribution** | Localized (intramural, submucosal, subserosal) | Diffuse myometrial involvement | | **MRI Appearance** | Low T2 signal, preserved junctional zone | Abnormal junctional zone, high T2 signal | | **Infertility** | Variable (depends on location/size) | Common but not universal | **High-Yield:** On MRI, fibroids show a **normal junctional zone**, while adenomyosis shows **junctional zone thickening (>12 mm) and disruption**. This is the gold-standard discriminator. ### Clinical Pearl **Clinical Pearl:** A woman with multiple discrete, well-defined masses and an intact junctional zone has fibroids. If the myometrium is diffusely infiltrated with loss of the normal junctional zone architecture, adenomyosis is the diagnosis. ### Why This Matters - **Fibroids** are benign smooth muscle tumors with a pseudocapsule; they displace but do not invade the myometrium. - **Adenomyosis** is ectopic endometrial glands and stroma invading the myometrium, causing diffuse thickening and junctional zone disruption. [cite:Park 26e Ch 9]