The typical ovarian endometrioma has a surface origin.

9 07 2010

To the Editor:

While the complexity of the ovarian endometrioma is well appreciated, reconstructive surgery may differ according to the pathogenesis. Resected cysts are useful for confirmation of the diagnosis, but fail to demonstrate the structure and pathogenesis of the endometrioma.

Few authors, however, have studied the ovarian endometrioma in situ. In a detailed study of 29 ovary specimens with the endometrioma in situ, Hughesdon (1) found that in all, except 3 cases, the endometrioma was a pseudocyst with an essentially similar structure: the ovary is adherent to the posterior side of the parametrium, the inside of the cyst is constituted by invaginated ovarian cortex, endometriosis is found at the site of adhesion and a thin layer of superficial endometrial-like tissue extends to cover partially or fully the invaginated cortex.

Hughesdon described further four characteristic features of ovarian endometriomas. First, primordial and ripening follicles are found in the wall of the cyst. Second, the ovary does not invaginate uniformly, but remains on one side more or less normal. Third, on the extended side the wall is relatively thin and the attenuation of layers on this side is usually too great to reveal the original structure. Fourth, the identity of the cortex on the inner side is frequently obscured by smooth muscle cell metaplasia. Hughesdon concluded that ectopic endometrium does not simply erode its way into the ovary: the ovary is actively invaginated, thus, providing a pseudo-uterus.

Using a cystoscopic technique Brosens et al. (2) investigated a series of 51 patients with uni- or bilateral endometriomas in situ and confirmed that in most cases the ovarian endometrioma is formed by invagination of cortex. The fact that the majority of endometriomas have cortex as their wall also explains the frequent combination of endometrial cysts with cystic corpora lutea and lutein cysts. In such cases, endometrial-like tissue can colonize the luteal cyst through the ovulatory stigma showing that under such circumstances endometriosis can “invade” the ovary (3).

We would agree with the conclusion of Hughesdon that the findings are in favor of a surface origin by implantation or metaplasia. The findings support the view that in most, but not all endometriomas the combined approach of excisional and ablative surgery as proposed by Donnez et al. (4) is likely to be in agreement with the pathogenesis.

Ivo Brosens M.D., Ph.D.
Emeritus Professor
Catholic University of Leuven
Leuven, Belgium

References
1. Hughesdon P.E. The structure of endometrial cysts of the ovary J Obstet Gynaecol Br Emp 1957; 44: 481-7.

2. Brosens I.A., Puttemans PJ, Deprest J The endoscopic localization of endometrial implants in the ovarian chocolate cyst. Fertil Steril 1994; 61:1034-8.

3. Sampson J.A. Perforating hemorrhagic (chocolate) cysts of the ovary . Arch Surg. 1921;3: 245-323.

4. Donnez J, Lousse J_C, Jadoul P, Donnez O, Squifflet J.
Laparoscopic management of endometriomas using a combined technique of excisional (cystectomy) and ablative surgery. Fertil Steril 2010; 64: 28-32.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2010.07.1056

The Authors Respond:

We were interested to read the letter of Ivo Brosens and agree that the typical ovarian endometrioma has a surface origin. However, we disagree with Hughesdon’s theory (1). Indeed, we strongly believe that ovarian endometriomas are caused by metaplasia of invaginated coelomic epithelium that covers the ovarian surface.

Our arguments are as follows:

1. In our series, we found 12% of endometriomas not fixed to the broad ligament, and Hughesdon’s theory cannot explain the formation of endometriomas free of adhesions (2).

2. It was not unusual to find multilocular endometriomas.

3. The epithelium covering the ovary, which is the mesothelium, can invaginate into the ovarian cortex. Invaginations of this mesothelial layer covering the ovarian tissue were described in both animal and human fetal ovaries (3).

4. Primordial follicles were found surrounding the endometriotic cyst, corroborating our hypothesis further. When the mesothelium invaginates deep into the ovary, follicles located at the site of invagination are pushed concomitantly with the mesothelium.

5. Importantly, we identified epithelial invaginations in continuum with endometrial tissue, proving the metaplasia theory (2).

6. Common epithelial tumors of the ovary are considered to be derived from the surface epithelium covering the ovary and from the underlying stroma. Why not ovarian endometriomas?

Arguments to support our hypothesis can also be found in the literature. Indeed, endometriomas have been described in patients with Rokitansky- Küster-Hauser syndrome, who do not have a uterus and, consequently, do not experience retrograde menstruation.

Our theory therefore differs from the conclusions of Hughesdon and Brosens et al. In our opinion, endometriomas should be considered as invaginations, but not the result of bleeding of superficial implants. Metaplasia of coelomic epithelium invaginated into the ovarian cortex has been proved and explains endometrioma formation. Even if our hypotheses differ, they are nevertheless both based on the invagination theory and, as stated by Brosens (4), the combined excisional and ablative surgical approach is consistent with the pathogenesis (5).

Jacques Donnez, M.D., Ph.D.
Université Catholique de Louvain
Cliniques Universitaires Saint-Luc
Brussels, Belgium

References
1. Hughesdon P.E. The structure of endometrial cysts of the ovary. J Obstet Gynaecol Br Emp 1957;44:481-7.

2. Nisolle M. and Donnez J. Peritoneal endometriosis, ovarian endometriosis, and adenomyotic nodules of the rectovaginal septum are three different entities. Fertil Steril 1997;68:585-96.

3. Motta PM, Van Blerkom J, Mekabe S. Changes in the surface morphology of ovarian germinal epithelium during the reproductive life and in some pathological conditions. Submicroscy Cytology 1992;99:664-7.

4. Brosens IA, Puttemans PJ, Deprest J. The endoscopic localization of endometrial implants in the ovarian chocolate cyst. Fertil Steril 1994;61:1034-38.

5. Donnez J, Lousse JC, Jadoul P, Donnez O. Squifflet J. Laparoscopic management of endometriomas using a combined technique of excisional (cystectomy) and ablative surgery. Fertil Steril 2010;64:28-32.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2010.07.1057

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