Clinical and histologic classification of endometriomas. Implications for a mechanism of pathogenesis

One hundred eighty-seven consecutive patients with persistent ovarian cysts and endometriosis underwent laparoscopic evaluation and ovarian cystectomy. All patients had been followed for a minimum of 6 weeks prior to surgery. The cysts were identified initially to be endometriomas based on their gross appearance and the presence of endometriosis at other pelvic sites. Presumed endometriomas were classified into three types based on size, cyst contents, ease of removal of the capsule, adhesions of the cyst to other structures and location of superficial endometrial implants relative to the cyst wall. After clinical laparoscopic classification, the cysts were evaluated histologically without knowledge of the clinical assessment. Histologically small (< 2 cm), superficial ovarian cysts were always endometriomas, and the cyst wall was very difficult to remove (type I). Large cysts with easily removed walls were usually luteal cysts (type II). Large cysts with walls adherent in multiple areas adjacent to superficial endometriosis were generally endometriomas but some also had histologic characteristics of functional (luteal or follicular) cysts (types IIIa and IIIb). These findings led to the conclusion that superficial ovarian endometriosis is similar to endometriosis in extra-ovarian sites in that the formation of superficial cysts is limited in size by fibrosis and scarring. In contrast, large endometriomas may develop as a result of secondary involvement of functional ovarian cysts by the endometriotic process.