Treatment algorithms are dependent on patient symptomatology, location of lesions, and desire to conserve the option for future childbearing. In patients presenting with mild to moderate pain and without the desire for immediate conception, empiric medical therapy is appropriate. First-line regimens include combined oral contraceptives (COCs ) and progestins. There is abundant observational data to support the use of combined oral contraceptives (COCs) for the relief of endometriosis-related pain. COCs act to cause an inactivation of implants through a process of decidualization [36]. Regimens for oral contraceptives may be cyclic but extended cycle and continuous regimens are often used for women with disabling dysmenorrhea. COCs have a good side effect profile and are generally well tolerated by patients. For women on extended cycle and continuous regimens, break through bleeding is the most common side effect [37]. For women who are not candidates for estrogen containing therapy, progestins alone are utilized. These agents inactivate endometrial implants by antagonizing the effects of estrogen. One randomized trial examined the effectiveness of medroxyprogesterone acetate against placebo to cause regression of endometriotic implants. Women who received medroxyprogesterone acetate had significant reduction of lesions after 6 months on second-look laparoscopy when compared to women who received placebo. Symptoms were improved in the medroxyprogesterone actetate group as well [38]. Other progestins have also been shown to improve symptoms related to endometriosis, such as norethindrone acetate and the levonorgestrel intrauterine device [39, 40]. Side effects of progestins can include weight gain, edema, acne, and irregular bleeding which may limit their acceptability by patients.

For women with symptoms refractory to COCs and progestins, second-line agents include gonadotropin releasing hormone (GNRH) agonists , such as leuprolide acetate. There is strong evidence supporting the efficacy of GNRH agonists to reduce pain related to endometriosis. However, GNRH agonists also lead to a hypoestrogenic state simulating menopause and side effects can be poorly tolerated. These include significant loss of bone mineral density and vasomotor symptoms (hot flashes) [41]. Combining GNRH agonists with low dose “add-back” hormone therapy significantly reduces the hypoestrogenic effects and makes the regimen more tolerable for patients. Aromatase inhibitors have been more recently introduced as a potential treatment for endometriosis-related pain. Several studies have shown that these agents reduce pain symptoms in women with endometriosis. When used alone, they share a similar side effect profile to GNRH agonists that make them difficult to tolerate. However, recent study of aromatase inhibitors with combined oral contraceptives showed significant pain relief with an improved acceptability. This option remains promising for otherwise refractory cases but is not yet widely utilized. Androgens, such as danazol, have also been shown to significantly reduce the size of endometriotic lesions and improve pain symptoms, but have significant androgenic effects making them generally not well accepted by patients [2].

When symptoms are refractory to medical therapy, or in circumstances that preclude the use of medical treatments , surgery is the next approach to treatment. For superficial disease, studies comparing surgical treatment through excision or ablation of endometriotic lesions show a significant improvement in pain (63 % versus 23 %) when compared to expectant management. Studies comparing ablative techniques, such as laser ablation versus electrosurgical ablation, have not found a difference in symptom relief [42]. In addition, studies assessing excisional removal versus ablative removal of superficial endometriotic lesions did not show a significant difference in symptoms [42].

In the case of endometrioma, moderate level data supports excisional surgery for the relief of pain symptoms. Women with small endometriomas that are asymptomatic present a challenge, as there is little data to suggest that excisional therapy has benefits over medical management [43].

For the management of deeply infiltrative endometriosis associated with moderate to severe pain, excisional surgery is the current standard of care. However, surgery for DIE is technically challenging and up to 35 % of women need a bowel resection as part of their management [44]. Thus, surgical expertise and a multidisciplinary approach involving colorectal surgery are necessary to safely complete this type of surgery.

A number of studies have demonstrated relief of pain with excisional surgical treatment for DIE. In 2014, Fritzer and colleagues performed a systematic review of three studies that included a total of 128 patients. The authors assessed surgical intervention for the management of refractory pain in women with deeply infiltrative endometriosis. Significant reductions in overall pain and sexual function were seen [45]. The authors noted that though pain was improved and complications were rare, the surgeries required were often radical, thus putting patients at risk for related complications. The most commonly reported complications were hemorrhage requiring transfusion and formation of rectovaginal fistula. A prospective cohort study of 83 patients with rectovaginal endometriosis evaluated long-term outcomes after radical excisional surgery. Though the majority of patients had improvement in symptoms, about 40 % of these patients required bowel resection. In addition, the study showed a 30 % rate of recurrence over time [46]. Complications included bladder denervation with associated atony, and hemorrhage requiring transfusion.

With regards to surgical treatment of endometriosis for infertility , well-designed trials are lacking. A randomized control trial comparing diagnostic laparoscopy with excisional or ablative removal of mild endometriosis showed a statistically significant, but clinically modest, improvement in cumulative pregnancy rates in women with surgical removal. A subsequent smaller trial showed no difference in pregnancy rates in women who had a diagnostic surgery versus a therapeutic surgery [47]. In women with endometrioma, surgical removal of endometriomas increases the likelihood of conception in infertile women but also has the effect of diminishing ovarian reserve. In women with deeply infiltrative disease, one prospective cohort study assessing women with rectovaginal endometriosis evaluated pregnancy rates between those who underwent surgery and those who had expectant management. Pregnancy rates were equivalent in the surgical and expectant management groups [48].

Thus, the general approach to treatment of endometriosis is medical therapy for mild pain symptoms with surgery reserved for moderate to severe symptoms refractory to medical therapy or for circumstances precluding the use of hormonal therapy. The potentially radical nature of surgery and the associated risk of complications necessitates appropriate patient counseling prior to the decision to move forward with surgery. Women should be counseled that surgery may temporarily alleviate pain, but that recurrence is common. Women with infertility and significant pain are not hormonal therapy candidates and thus should be offered surgery. However, these patients should be counseled that pregnancy rates have not been shown to improve substantially after surgery and that assistive reproductive technology should be considered. Women with infertility who plan undergoing in vitro fertilization but significant anatomic distortion may also require surgery for anatomic restoration to facilitate safe oocyte retrieval.

The initial step in assessing a patient with suspected deep infiltrating endometriosis of the rectum involves taking a thorough history. Of particular importance is ascertaining whether or not the patient is experiencing any pain. This includes obtaining a detailed history on multiple components of pain including the location, severity, timing, and whether the pain is associated with any rectal bleeding. Pain associated with rectal bleeding is particularly concerning as it may be due to full thickness erosion of the rectum secondary to the endometriosis. Temporal relationship of pain with menses should be investigated as this may signal endometriosis, particularly DIE [49]. Dyspareunia and dyschezia are other symptoms that are frequently present in rectal endometriosis.

The next step in assessment includes obtaining a thorough surgical history. The purpose of this is twofold. First, it prepares the surgeon for adhesive disease from prior surgery, though DIE often presents as dense adhesions involving the colon, uterus, ovaries, fallopian tubes, and ureters. Second, and more importantly, it determines whether a minimally invasive surgical approach (MIS ) is realistic. The presence of adhesions makes an MIS approach more difficult, and many surgeons will opt for an open approach if there is a significant history of surgeries. However, it should be noted that this practice varies from surgeon to surgeon based on preference and surgical expertise. As with taking any other surgical history, it is important to document the date of the surgery, the primary surgeon, and to note whether there were any complications in the surgery.

As part of the history, it is imperative to inquire about any family inheritance of colorectal conditions including, but not limited to, colon and rectal cancer, inflammatory bowel disease, and hemorrhoids. Any family history of cancer should also be fully explored in depth, whether the cancer is of a colorectal nature or not. Further questioning should also attempt to deduce whether the patient is suffering from any fecal incontinence (FI ). Though FI is not particularly associated with endometriosis, it is an important consideration as low anterior resections (LAR) are associated with exacerbation of FI due to loss of the rectal reservoir.

After a thorough history has been obtained, the next step is an in-depth physical examination. In particular, the presence of any abdominal incisions should be noted, specifically checking around the umbilicus and for the presence of any smaller scars for past incisions. Tenderness to palpation or the presence of any palpable masses increases the suspicion for endometriosis. The most important aspect of the physical exam in these patients, however, is the digital rectal exam (DRE ). This will yield a great deal of information about the patient. On this part of the exam, the surgeon may be able to palpate areas of endometriosis in addition to assessing the strength of the anal sphincter. The strength of the anal sphincter can be determined by having a patient bear down while the surgeon is performing the DRE . A bimanual examination will yield even further information, possibly revealing the presence of endometriosis in the rectovaginal septum or thickened uterosacral ligaments upon palpation. Lastly, a proctoscopy performed outpatient may allow the surgeon to visualize deeply infiltrating endometriosis, and how proximal it is relative to the anal sphincters. This ultimately will allow the surgeon to gage how low any future anastomosis will need to be.

Whether or not endometriosis is suggested based on physical examination, it is important to obtain imaging to further elucidate the extent of disease. As noted in the “Diagnosis” section earlier, transvaginal ultrasound (TVUS ) is still the preferred starting diagnostic imaging study with a relatively high sensitivity [30, 50]. If transrectal ultrasonography is readily available, it should be offered [34], but more than likely MRI is the initial next step if DIE of the rectum is suspected [35]. Additionally, further imaging with the use of a colonoscopy should be obtained prior to any surgical intervention to rule out full thickness erosion or any other colonic pathology such as colon cancer or bowel stenosis.

If surgery is agreed upon, consent is obtained from the patient, and the surgeon should discuss shaving as well as LAR with a possible loop ileostomy [30, 51, 52]. If an ileostomy is considered likely based on the preoperative assessment, the patient should be counseled as such, and preoperative the ostomy site should be determined prior to surgery. Extensive counseling about shaving lesions, discoid resection, low anterior resection, and possible loop ileostomy should be discussed prior to surgery.

The goal of surgical management of endometriosis is to destroy or remove all visible lesions of endometriosis and to restore normal anatomy. For superficial lesions, either ablative or excisional procedures may be utilized. Ablative techniques include electrocautery or Argon Neutral Plasma Energy. Excisional techniques include sharp dissection of lesions and the involved peritoneum as well as respective procedures of the bowel, bladder, vagina, uterosacral ligaments, and ureters when invasive disease is present. Laparoscopic management of endometriomas and superficial endometriosis is considered the standard of care [42]. In addition, there are increasing reports of laparoscopic management of DIE, even in cases where bowel resection is necessary [53]. More recently, the benefits of a robotic surgical approach for the surgical management of endometriosis have been examined. Thus far, limited data suggests comparable outcomes between conventional laparoscopy and robotic-assisted laparoscopy, but a longer operating time [54]. Proponents of robotic surgery suggest that the design advantages of the robotic platform, such as stereoscopic three-dimensional visualization, increased range of movement, and enhanced surgeon comfort, enable surgeons to complete complex dissections necessary for the surgical management of endometriosis. In cases of rectal involvement, robotic assistance has been shown to be feasible and safe with comparable outcomes to laparotomy [55].