A 48-year-old woman comes to the office due to heavy menstrual bleeding for the last several months. The patient has monthly menses with 5-6 days of heavy bleeding and passage of large blood clots and increased abdominal cramping. She has no significant medical history and has had 2 vaginal deliveries. Her family history is significant for endometrial cancer in her mother. BMI is 24 kg/m². Vital signs are normal. Pelvic ultrasound shows a uterine mass. The patient undergoes a total abdominal hysterectomy; gross examination of the uterus is shown below: The abnormal region indicated by the arrow is most likely to display which of the following microscopic findings?

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11ec160b_3926_8687_9249_5fd7503cf310_MD0001_00 This patient with heavy menses and a uterine mass has a uterine leiomyoma, also known as a fibroid. Fibroids are common, benign tumors arising from smooth muscle cells and fibroblasts that can grow in a variety of sizes and locations within the uterine myometrium, resulting in variable clinical presentations. This patient has an intramural fibroid (within the uterine wall), which can increase the endometrial surface area (due to mass effect) and result in heavy menses. Patients with symptomatic uterine fibroids are often treated surgically with a hysterectomy. Grossly, fibroids appear as discrete, yellow-gray tumors with a thin pseudocapsule that separates the fibroid from the normal uterine myometrium. Diagnosis is confirmed with microscopy, which typically reveals monoclonal proliferation of myocytes and fibroblasts because each fibroid arises from a single progenitor smooth muscle cell. Due to their benign nature, fibroid myocytes are uniform in size and shape and have minimal mitotic figures. (Choice A) Patients with cervical cancer are often asymptomatic or have irregular, postcoital spotting rather than heavy menses. Cervical cancer is typically found in the cervical transformation zone (rather than the uterine myometrium) and microscopy shows dysplastic squamocolumnar cells with areas of atypia. (Choice B) Patients with endometriosis typically present with painful menses (ie, dysmenorrhea); however, there are usually endometrial tissue implants outside the uterus rather than an intrauterine mass. Light microscopy typically reveals ectopic endometrial glands and hemosiderin-laden macrophages. (Choice C) Patients with endometrial hyperplasia or cancer typically present with irregular, heavy menses and a thickened endometrium (rather than a mass in the myometrium). Histopathology typically reveals hyperplastic proliferation of irregular endometrial glands. (Choice D) Microscopy of ovarian cancer typically reveals infiltration of the stroma by high-grade serous carcinoma. Ovarian cancer is unlikely in this patient as it typically causes an adnexal mass rather than a solitary intrauterine mass. Educational objective: Uterine leiomyomas (ie, fibroids) are common, benign tumors arising from the uterine myometrium that occur due to monoclonal proliferation of myocytes and fibroblasts. __________ References: Clonality of smooth muscle and fibroblast cell populations isolated from human fibroid and myometrial tissues. (http://www.ncbi.nlm.nih.gov/pubmed/24243625)

A 48-Year-Old Woman Comes to the Office Due to Heavy