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A leiomyoma (aka fibroid) is a benign smooth muscle neoplasm that is not pre-malignant. It is the most common neoplasm in females, with 25% of all reproductive females having it. Leiomyomas are estrogen-responsive, which causes rapid growth during pregnancy in some, and for them to often regress or shrink after menopause or removal of the ovaries. Usually, patients are asymptomatic. Important symptoms include abnormal genital tract bleeding, pain, infertility, urinary frequency, abortion, pregnancy-related bleeding, or interference with the position of the fetus.
The gross pathological appearance has leiomyomas as round, well circumscribed, solid nodules that are white, or tan whorled. There are usually multiple leiomyomas in three sites - intramurally (most common), submucosal, and subserosal. Other changes that may be detected grossly are hemorrhage, necrosis, or cystic changes. Less frequently, leiomyomas may occur at the lower uterine segment, cervix, or uterine ligaments.
Microscopically, bundles of smooth muscle cells can be seen. These cells are uniform in size and shape, with scarce mitoses. There are three benign variants: bizarre (atypical); cellular; and mitotically active.