What is a primary characteristic of uterine leiomyomas?

Uterine leiomyomas, commonly known as fibroids, are primarily characterized by being composed of smooth muscle tissue. This is fundamental to their structure, as they arise from the myometrium, which is the smooth muscle layer of the uterus. The smooth muscle tissue gives leiomyomas their characteristic appearance and behavior, which contributes to their ability to grow in response to hormonal stimulation, particularly estrogen and progesterone.

While leiomyomas can be asymptomatic and are more commonly diagnosed in women of reproductive age, those features do not define their basic biological composition. They can occur in a range of ages but are not exclusive to older women, nor are they malignant; in fact, they are benign tumors. Understanding that they are made of smooth muscle tissue is key to recognizing how they develop and their potential effects on the uterus and surrounding structures.