Guidelines for medical therapy before and after surgery for endometriosis as given in published guidelines are evidence based and thus based on the published evidence. However these existing guidelines are highly biased and not very useful neither for patients nor for gynecologists. Indeed the do not take into account observational surgical knowledge.

The randomised controlled trial is poorly suited for endometriosis surgery because the variability in the disease and in the  skill of the surgeons requires prohibitively large series. In addition rare events require very large series.

Important aspects of endometriosis surgery are practically impossible to demonstrate. It is impossible to demonstrate that endometriosis lesions were missed during surgery, unless a repeat laparoscopy is performed which is not possible for ethical reasons. it is impossible to judge incomplete surgery unless video-registration of the entire surgery is available  to review the surgery. It is close to impossible to organise blinding in severe surgery

Therefore guidelines by surgeons with a large expertise in laparoscopic surgery for endometriosis are needed. Today we start with guidelines by, a group of deep endometriosis surgeons with a cumulative experience of over 10.000 interventions as we did for the review on diagnosis and treatment of deep endometriosis (Fertil Steril 2013) and for the article on epidemiology of endometriosis (Gynaecological Surgery 2017).

Medical therapy Before surgery

Facts

Medical therapy for endometriosis suppresses ovarian function. The lack of estrogens will inactivate endometriosis lesions (as during menopause)  or the high doses of progestogens will decidualise (as during pregnancy) these lesions .
Subtle and possibly typical lesions thus risk to become invisible. Cystic ovarian endometriosis will sometimes decrease slightly in volume. Deep endometriosis will shrink and probably becomes less vascularized.

Potential Benefits

The absence of ovulation and of a corpus luteum can be a surgical advantage.  A corpus luteum indeed bleeds easily during ovarian surgery  with subsequent risks of adhesion formation.
The absence of a corpus luteum will prevent the occurrence of a cystic corpus luteum and thus the eventual confusion with a  cystic ovarian endometriosis.
Practically however, a cystic corpus luteum van persist for more than 6 months under oral contraception.

Risks

Subtle and typical lesions risk to be missed during surgery. Thus the diagnosis is not made and so is the excision.
Surgical excision of cystic ovarian endometriosis is not facilitated by medical therapy. Smaller lesions however might be missed.
Deep endometriosis grows irregularly and common sense suggest that excision could be incomplete since extensions are missed.
Appendicular endometriosis could be missed.

Conclusions

Solid evidence for the risks as defined does not exist. It should be clear that it is also virtually impossible to demonstrate this in a surgical trial. The risks however are logical and all surgeons agree about this.
Medical treatment before surgery for endometriosis; therefore should not be given since it does not facilitate surgery while carrying the risk of incomplete surgery.

Medical therapy after surgery

Facts

Medical therapy after endometriosis surgery to prevent recurrences. The only available evidence is that medical treatment given for six months after surgical excision of cystic ovarian endometriosis will decrease the recurrence rate during this period
Medical therapy to prevent progression. The arguments are the same as those before surgery. Only for typical lesions there is scanty evidence that the prevalence is less after years of oral contraception. It is unclear whether this is not an artefact by missing lesions.

Potential Benefits

Abolishing menstruation in order to reduce recurrences of endometriosis is a myth based on the Sampson theory.
After complete surgery there are no demonstrated advantages, only speculation.
After incomplete surgery, for whatever reason medical treatment can be given to reduce pain similar to medical treatment in women before surgery.

Risks

Medical therapy therapy risks to be given after incomplete surgery when this was caused by the lack of skills by the surgeon.

Conclusions

If surgery is too difficult for the experience of the surgeon,

the best option for the patient is that no surgery should be done and that the patient should be send for complete surgery elsewhere. This is the model we developed in Oxford UK
A worse option is incomplete surgery with medical therapy after surgery.  Examples of this are an hysterectomy or a bowel resection while leaving the endometriosis in the lateral wall or in the douglas.

Following complete surgery

there is no hard evidence that medical therapy is an advantageit seems prudent, and widely accepted to give medical therapy as oral contraception until the woman wants to become pregnant.
there are no arguments not to give hormone replacement therapy after menopause. It seems wise however not give sequential hormone replacement therapy.
There are no arguments to fear the development of an adenocarcinoma in endometriosis when given estrogens only.

Which medical therapy should be given before or after surgery?

The available medical therapies  comprise those that suppress ovarian function as  Gn-RH and oral contraception and progestagens only in high dose

There is no solid evidence to claim superiority of any of these treatments before or after surgery for endometriosis.

 Content approved and/or updated by

Philippe R. Koninckx , Prof em OBGYN  KULeuven Belgium,  Univ of Oxford-Hon Consultant, UK, Univ Cattolica, Roma, Moscow State Univ. ;  Gruppo Italo Belga, Villa del Rosario Rome Italy ;  Anastasia Ussia Gruppo Italo Belga, Villa del Rosario Rome Italy, Consultant Università Cattolica, Rome, Italy

Pending approvement/update :  Jörg Keckstein,  Landeskrankenhaus Villach, Austria. APL Professor University Ulm, Germany   Arnaud Wattiez,  Prof OBGYN, University of Strassbourg, France and  Dubai  Leila Adamyan, Moscow state University,  Moscow, Russia, Jacques Donnez, Prof em Catholic University of Louvain