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Etiology
Endometriomas are extensively described in the literature, and their origin is the subject of several theories. In 1921, Sampson noted luteal membrane and ovarian epithelial tissues within endometriomas and was the first to indicate that endometriomas may result from the invasion of functional cysts by endometrial tissue.2,4,5 In 1979, Czernobilsky and Morris6 found endometrial and oviduct-like epithelium in ovarian endometriosis and concluded that ovarian tissue may be a common histologic precursor. Several other authors subsequently have reported finding different types of tissue within ovarian endometriomas, and not all of these chocolate cysts showed histologic evidence of endometriosis.4,7,8