Editor's note: This week brings us the first contribution from Henci Goer. Henci will be a regular contributor to Science & Sensibility, and continues to respond to reader questions on the Ask Henci Forum. - AMR

I was pulling together studies for the chapter on cesarean for Amy's and my new edition ofObstetric Myths Versus Research Realities when I ran across an e-mail in my files from Carol Sakala of Childbirth Connection containing some citations on case reports and series about endometriosis developing in the cesarean wound. When I followed up on them, I discovered that the obstetric literature is peppered with these reports.

This is no trivial problem. Women experienced cyclic pain, which could begi - or at least become severe enough to seek treatment - anywhere from months to years after the delivery. In rare cases, the consequences were catastrophic: there were reports of uterine wound endometriosis that caused intractable hemorrhage leading to hysterectomy and cases where endometriosis devolved into fatal cancers. Authors agreed that endometriosis probably developed from cells from the uterine lining being seeded into the wound during the cesarean surgery, a theory bolstered by most cases occurring in women with no history of endometriosis. They also uniformly agreed that the only effective treatment was wide excision of the affected tissue. Sometimes surgery was so extensive that it required grafting. Doesn't that sound pleasant? Some series authors reported rates in their populations, which ranged from less than 1 to 5 per 1000 women with cesareans, but this is almost surely an undercount, seeing as cesarean wound endometriosis can develop years later, not every woman would seek medical attention, some would not be correctly diagnosed, and some would decide against treatment once they heard the cure. As the authors of one case series wrote, 'Invariably, on discussing the topic with colleagues, each clinician can recall one or more personal cases of his own' (p. 94) (Wolf 1989), and that, of course, wouldn't include the women who were suffering in silence.

So why is this reasonably common serious adverse effect of cesarean surgery something you have never heard of? At least, I hadn't, and keeping up with the med lit on these things is what I do. The answer lies in what 'counts' or doesn't as worthy evidence. Cesarean wound endometriosis would never turn up in a randomized controlled trial (RCT). Even if the problem made it onto the researchers' radar, the trial would have to be extremely large and follow-up impractically long to detect it. Where RCTs are considered the only evidence worth having, outcomes that cannot be picked up on by RCTs functionally don't exist.

'But,' you say, 'we now have some excellent large-scale prospective studies and database analyses of postpartum morbidity according to mode of birth. Why hasn't cesarean wound endometriosis shown up in them?' Prospective studies depend on what outcomes investigators decide ahead of time to look at and databases are limited to the information collected in them. You don't ask the question; you don't get an answer, which, again, renders cesarean wound endometriosis invisible.

The moral of the story is that different study designs are good for different things. Case studies and series may be the humble bottom of the evidence pyramid, but they are the only design that can alert us to serious adverse outcomes that demand more investigation. Now you know about this one. Spread the word. Someone in the research world may be listening.

Click on the extended post for the bibliography.

References 1989 and later (there are earlier ones I didn't retrieve)

Bumpers, H. L., Butler, K. L., & Best, I. M. (2002). Endometrioma of the abdominal wall. Am J Obstet Gynecol, 187(6), 1709-1710.

Eogan, M., & McKenna, P. (2002). Endometriosis in caesarean section scars. Ir Med J, 95(8), 247.

Gajjar, K. B., Mahendru, A. A., & Khaled, M. A. (2008). Caesarean scar endometriosis presenting as an acute abdomen: A case report and review of literature. Arch Gynecol Obstet, 277(2), 167-169.

Gaunt, A., Heard, G., McKain, E. S., & Stephenson, B. M. (2004). Caesarean scar endometrioma.Lancet, 364(9431), 368.

Gunes, M., Kayikcioglu, F., Ozturkoglu, E., & Haberal, A. (2005). Incisional endometriosis after cesarean section, episiotomy and other gynecologic procedures. J Obstet Gynaecol Res, 31(5), 471-475.

Kafkasli, A., Franklin, R. R., & Sauls, D. (1996). Endometriosis in the uterine wall cesarean section scar. Gynecol Obstet Invest, 42(3), 211-213.

Kaloo, P., Reid, G., & Wong, F. (2002). Caesarean section scar endometriosis: Two cases of recurrent disease and a literature review. Aust N Z J Obstet Gynaecol, 42(2), 218-220.

Leng, J., Lang, J., Guo, L., Li, H., & Liu, Z. (2006). Carcinosarcoma arising from atypical endometriosis in a cesarean section scar. Int J Gynecol Cancer, 16(1), 432-435.

Luisi, S., Gabbanini, M., Sollazzi, S., Calonaci, F., Razzi, S., & Petraglia, F. (2006). Surgical scar endometriosis after cesarean section: A case report. Gynecol Endocrinol, 22(5), 284-285.

Minaglia, S., Mishell, D. R., Jr., & Ballard, C. A. (2007). Incisional endometriomas after cesarean section: A case series. J Reprod Med, 52(7), 630-634.

Olufowobi, O., Sorinola, O., Miller, S. J., & Condie, R. G. (2003). Scar endometrioma: A cause for concern in the light of the rising caesarean section rate. J Obstet Gynaecol, 23(1), 86.

Patterson, G. K., & Winburn, G. B. (1999). Abdominal wall endometriomas: Report of eight cases. Am Surg, 65(1), 36-39.
Phupong, V., & Triratanachat, S. (2002). Cesarean section scar endometriosis: A case report and review of the literature. J Med Assoc Thai, 85(6), 733-738.

Sholapurkar, S. L., Sharp, N. C., & Hirschowitz, L. (2005). Life-threatening uterine haemorrhage six weeks after caesarean section due to uterine scar endometriosis: Case report and review of literature. N Z J Obstet Gynaecol, 45(3), 256-258.

Wicherek, L., Klimek, M., Skret-Magierlo, J., Czekierdowski, A., Banas, T., Popiela, T. J., et al. (2007). The obstetrical history in patients with pfannenstiel scar endometriomas - an analysis of 81 patients. Gynecol Obstet Invest, 63(2), 107-113.

Wolf, G. C., & Singh, K. B. (1989). Cesarean scar endometriosis: A review. Obstet Gynecol Surv, 44(2), 89-95.
Zhu, Z., Al-Beiti, M. A., Tang, L., Liu, X., & Lu, X. (2008). Clinical characteristic analysis of 32 patients with abdominal incision endometriosis. J Obstet Gynaecol, 28(7), 742-745.

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