What is the likely diagnosis for a 47-year-old female with prolonged heavy menses and an enlarged uterus with firm masses?

In this scenario, the diagnosis of leiomyoma, or uterine fibroids, is indicated due to the combination of prolonged heavy menstrual bleeding (menorrhagia) and the presence of an enlarged uterus with firm masses on examination.

Leiomyomas are benign tumors composed of smooth muscle and fibrous tissue, and they are one of the most common causes of abnormal uterine bleeding in women of reproductive age and perimenopause. The heavy menstrual bleeding occurs as the fibroids can cause distortion of the uterine cavity or increase uterine contractions. The enlargement of the uterus is often palpated as a firm, irregular mass due to the fibroids' growth, which can be multiple and vary in size.

The presence of firm masses is particularly indicative of leiomyomas because they have a palpable consistency that is distinct compared to soft or cystic masses that might be associated with other conditions.

Adenomyosis, while it can also cause menorrhagia and enlarged uterine size, typically presents with a softer, somewhat less defined uterus, and the diagnosis is often made with imaging rather than palpation of distinct masses. Endometriosis primarily involves the presence of endometrial-like tissue outside the uterus and may cause painful menstruation but