A 45-year-old woman presented with a lower abdominal mass and lower abdominal discomfort. On examination, the uterus appears uniformly enlarged and adnexa is free. MRI shows the presence of a myometrial cyst. What is the most probable diagnosis?

Explanation

## Correct Answer: B. Adenomyosis Adenomyosis is characterized by the presence of ectopic endometrial glands and stroma within the myometrium, often forming small cystic spaces (myometrial cysts). The clinical presentation—a 45-year-old woman with a uniformly enlarged uterus, lower abdominal discomfort, and MRI findings of myometrial cysts—is pathognomonic for adenomyosis. The key discriminator is the **uniform enlargement of the uterus** (typically 12–14 weeks size) combined with **myometrial cysts on imaging**. Unlike leiomyomas, which cause focal/nodular enlargement, adenomyosis causes diffuse, symmetric hypertrophy. The myometrial cysts represent areas of ectopic endometrial tissue undergoing cyclical bleeding and degeneration. Adenomyosis is most common in multiparous women in their 40s–50s and is a leading cause of secondary dysmenorrhea and menorrhagia in this age group. The adnexa being free rules out ovarian pathology (endometriosis cysts, ovarian masses). MRI is the gold standard for diagnosis, showing junctional zone thickening (>12 mm) and myometrial cysts, with sensitivity and specificity >80% [cite: DC Dutta Ch. 16]. ## Why the other options are wrong **A. Endometrial hyperplasia** — Endometrial hyperplasia is a proliferative disorder of the endometrium (not myometrium) and does not cause myometrial cysts or uniform uterine enlargement. It presents with abnormal uterine bleeding and is diagnosed by endometrial biopsy/curettage, not MRI imaging of myometrial cysts. This is a common NBE trap—confusing endometrial pathology with myometrial pathology. **C. Leiomyoma** — Leiomyomas (fibroids) cause **focal, nodular uterine enlargement** with well-defined masses on imaging, not diffuse uniform enlargement. While fibroids can undergo cystic degeneration, the clinical picture of uniform uterine enlargement with multiple myometrial cysts is characteristic of adenomyosis, not fibroids. Fibroids typically present with menorrhagia but not the diffuse junctional zone abnormality seen in adenomyosis. **D. Endometriosis** — Endometriosis involves ectopic endometrial tissue in the peritoneum, ovaries, and bowel—not the myometrium. The clinical finding of **free adnexa** specifically excludes ovarian endometriotic cysts. While adenomyosis and endometriosis can coexist, the myometrial cysts on MRI with uniform uterine enlargement and free adnexa point directly to adenomyosis as the primary diagnosis. ## High-Yield Facts - **Adenomyosis** = ectopic endometrial glands/stroma in myometrium forming myometrial cysts; most common in women >40 years, multiparous. - **Uniform uterine enlargement** (typically 12–14 weeks size) is the hallmark clinical sign; differs from focal nodular enlargement in leiomyomas. - **MRI junctional zone thickening >12 mm** and **myometrial cysts** are diagnostic criteria; sensitivity/specificity >80% for adenomyosis. - **Secondary dysmenorrhea and menorrhagia** are cardinal symptoms; adenomyosis is the leading cause in women >40 years in India. - **Free adnexa** on examination rules out ovarian endometriosis and ovarian masses; adenomyosis is purely myometrial. ## Mnemonics **ADENO = Adenomyosis features** **A**dexa free, **D**iffuse/uniform enlargement, **E**ndometrial tissue in myometrium, **N**o nodules (unlike fibroids), **O**lder women (>40 yrs). Use when differentiating adenomyosis from leiomyomas and endometriosis. **Adenomyosis vs Leiomyoma: UNIFORM vs NODULAR** Adenomyosis = **UNIFORM** diffuse enlargement + myometrial cysts. Leiomyoma = **NODULAR** focal masses. Quick bedside rule: if uterus feels uniformly boggy and enlarged, think adenomyosis; if you feel discrete lumps, think fibroids. ## NBE Trap NBE pairs "myometrial cyst" with leiomyoid degeneration to trap students who confuse cystic fibroids with adenomyosis. The discriminator is **uniform vs. focal enlargement**—adenomyosis causes diffuse symmetric hypertrophy, while fibroids cause nodular masses. ## Clinical Pearl In Indian clinical practice, adenomyosis is often underdiagnosed in women >40 years presenting with secondary dysmenorrhea and menorrhagia. MRI has revolutionized diagnosis, replacing the older reliance on hysterectomy specimens. A uniformly enlarged, tender uterus with myometrial cysts on MRI in a perimenopausal woman is adenomyosis until proven otherwise. _Reference: DC Dutta Ch. 16 (Adenomyosis); Harrison Ch. 382 (Uterine Disorders)_