What is the most likely diagnosis for a 49-year-old female with an enlarged uterus and left adnexal mass?

Uterine fibroids, also known as leiomyomas, are the most common benign tumors of the uterus, particularly in women of reproductive age and can persist into the perimenopausal period, which is relevant for a 49-year-old female. The presence of an enlarged uterus is frequently associated with uterine fibroids, as these growths can significantly increase the size of the uterus due to their growth within the uterine wall. Additionally, fibroids can sometimes lead to the development of a mass in the adnexa, which may be perceived as an adnexal mass during clinical evaluation.

In this case, the combination of an enlarged uterus and a left adnexal mass aligns with the likely diagnosis of uterine fibroids. While other conditions may also present with similar symptoms, such as adnexal masses being more commonly associated with ovarian neoplasms, the specific context of an enlarged uterus strongly points to fibroids as the underlying cause. Adenomyosis typically presents with uterine enlargement and can sometimes simulate fibroids, but it lacks the distinct physical mass effect that is often characterized by fibroids. Diverticular disease primarily affects the colon and would not typically present with findings in the uterus or adnexa.

Therefore, in the context