Pathology And Histology Of Fibroids

Leiomyomas grossly appear as round, well circumscribed (but not encapsulated), solid nodules that are white, or tan whorled. The size varies, from microscopic to lesions of considerable size. Typically lesions the size of a grapefruit or bigger are felt by the patient herself through the abdominal wall. Microscopically, tumor cells resemble normal cells (elongated, spindle-shaped, with a cigar-shaped nucleus) and form bundles with different directions (whirled). These cells are uniform in size and shape, with scarce mitoses. There are three benign variants: bizarre (atypical); cellular; and mitotically active.

Leiomyomas arise from the smooth muscle (myometrium) and of the components of the Extracellular Matrix (ECM).

Leiomyomas are estrogen sensitive and have estrogen receptors. They may enlarge rapidly during pregnancy due to increased estrogen levels. As estrogen levels decline with menopause, fibroids tend to regress after menopause. Hormonal therapy is based on these facts.

More recent studies have revealed a possible role of progesterone and progestins to fibroid growth as well, and applicability of progestin agonists as part of treatment are currently being considered.