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This chapter should be cited as follows:
Kuan KKW, Leonardi M, Glob. libr. women's med.,
ISSN: 1756-2228; DOI 10.3843/GLOWM.417653

The Continuous Textbook of Women’s Medicine SeriesGynecology Module

Volume 3


Volume Editors: Professsor Andrew Horne, University of Edinburgh, UK
Dr Lucy Whitaker, University of Edinburgh, UK


Diagnosing Endometriosis

First published: September 2022

Study Assessment Option

By completing 4 multiple-choice questions (randomly selected) after studying this chapter readers can qualify for Continuing Professional Development awards from FIGO plus a Study Completion Certificate from GLOWM
See end of chapter for details


Diagnosing endometriosis can be challenging for clinicians due to its complex nature. Endometriosis most commonly presents with pelvic pain but can also manifest itself in various ways such as dysmenorrhea, dyspareunia, and infertility.1 The three most common subtypes of endometriosis are superficial endometriosis (SE), deep endometriosis (DE), and ovarian endometriomas (OE).2  According to the 2021 international working group of American Association of Gynecologic Laparoscopists (AAGL), European Society of Gynaecological Endoscopy (ESGE), European Society of Human Reproduction and Embryology (ESHRE), and World Endometriosis Society (WES), SE consists of endometrium-like tissue lesions involving the peritoneal surface lining the pelvis and pelvic organs.3 Meanwhile, DE is defined as endometrium-like tissue lesions in the abdomen, extending on or under the peritoneal surface, which are usually nodular, able to invade adjacent structures, and associated with fibrosis and disruption of normal anatomy. Historically, DE was defined as endometriosis infiltrating a peritoneal surface by more than 5 mm.4 DE often affects the posterior compartment such as the uterosacral ligaments (USL) and bowel.5 OE are filled with dark endometrial fluid (hence, known as "chocolate cysts") that can develop anywhere in the pelvis, but most commonly in the ovaries. Less common sites of endometriosis can exist, such as diaphragmatic, thoracic, and abdominal wall, which will be discussed here as well.

Apart from the wide range of symptoms, diagnostic barriers such as delayed referrals to gynecologists, patient uncertainty between “normal” versus “abnormal” menstrual cycles, and stigmatization related to menstrual problems all contribute to the average diagnostic delay of 6.7 years, which can negatively impact the patient’s quality of life and work productivity.6,7 Currently, laparoscopic visualization and histological confirmation remains as the standard for making a definitive diagnosis but may not always be available or attainable for all patients for a variety of reasons. Furthermore, surgery as a diagnostic tool imparts many disadvantages including surgical complications and cost.8 Advancements in non-invasive (i.e. non-surgical) diagnostic tools have been made, including imaging tests such as ultrasound and magnetic resonance imaging (MRI), yielding improvements in diagnostic performance of OE and DE reliably.9 Non-invasive tests for biomarkers are also being studied but a reliable marker has not yet been identified.10,11,12 Others argue for a clinical diagnosis based on signs and symptoms rather than visualization of endometriosis itself or identification of abnormal testing.13 While research and adoption of novel diagnostic methods into clinical practice is ongoing, there does not appear to be one right answer for everyone. As such, we may consider categorizing diagnostic methods for endometriosis into five main pillars: clinical diagnosis, radiological diagnosis, biomarkers, surgery, and histopathology (Figure 1). It is important to recognize and understand the value of all possible diagnostic modalities, which can help patients achieve a timelier diagnosis and earlier initiative management strategies.13


The five pillars of endometriosis diagnosis. Created with


Clinical History

Making a clinical diagnosis starts with taking a comprehensive history. Listening to a patient’s symptoms may point in the correct diagnostic direction and ascertain unique forms of endometriosis (Table 1). As mentioned earlier, pelvic endometriosis is commonly associated with pelvic pain, dysmenorrhea, and dyspareunia, but these symptoms are non-specific and can be caused by other gynecological/non-gynecological pathologies. Asking about other characteristics such as chronic, cyclical, progressive, or intermenstrual pelvic pain can increase the accuracy of diagnosing endometriosis in the clinical setting.13 Certain menstrual history characteristics can also increase the risk of developing endometriosis such as early menarche before the age of 12 and short menstrual cycles (<26 days).14 Although rare, symptoms like focal abdominal pain, chest pain, or catamenial pneumothorax can be caused by extra-pelvic endometriosis and further investigations may be required.15 Previous cesarean section/abdominal surgical scars with focal abdominal pain further increases the likelihood for abdominal wall endometriosis (AWE).16


Common signs/symptoms depending on location of endometriosis.

Location of Endometriosis


Pelvic endometriosis

  • Dysmenorrhea
  • Cyclical/chronic pelvic pain
  • Deep dyspareunia
  • Infertility
  • Changes in bowel habits

Abdominal wall endometriosis

  • Abdominal pain associated with menses
  • History of abdominal surgery

Thoracic endometriosis

  • Catamenial (cyclical) pneumothorax
  • Referred shoulder pain
  • Shortness of breath

Red flags

  • Buttocks/leg pain (sacral roots' involvement)

Another possible sign of endometriosis is subfertility. Approximately 15–30% of women undergoing assisted reproductive techniques are diagnosed with "unexplained infertility" with normal results following the standard infertility evaluation leaving endometriosis possibly undiagnosed.17 If endometriosis is diagnosed beforehand and surgically removed, around 41.9% of women may be able to achieve spontaneous pregnancy.18 The current American Society for Reproductive Medicine (ASRM) committee's opinion for the diagnostic evaluation of infertile females recommends laparoscopic investigation for women with a clear indication for peritoneal disease or advanced stages of endometriosis.19 However, other non-invasive and readily available imaging techniques such as transvaginal ultrasound (TVS) can easily be incorporated into routine infertility (guidance for performing the scan can be found under the "Ultrasound" section).

Beyond developing an understanding of a patient’s “endometriosis symptoms”, one must grasp the broader experience of the patient including co-existing symptom profiles, which may indicate co-morbidities and central sensitization (Table 2). For example, if a patient with an altered bowel habit is diagnosed with bowel endometriosis and managed accordingly, their symptoms may prevail due to unrecognized conditions such as irritable bowel syndrome. When preparing for laparoscopy, awareness of other underlying causes can allow clinicians to request other relevant specialists who can assist during surgery to treat existing co-morbidities minimizing the number of procedures required for the patient. Recently, a study by Orr and colleagues found that a Central Sensitization Inventory questionnaire score ≥40 can be a useful tool to identify those with endometriosis complicated by central sensitization,20 implying that treatments focused exclusively on endometriosis may not be as effective. An accurate and comprehensive appreciation of the patient’s constellation of symptoms and various diagnoses is vital to the ideal and specific management strategies that are implemented.


Symptoms between central sensitization syndromes and endometriosis.

Central Sensitization Syndromes

Possible Overlapping Symptoms with Endometriosis

Irritable bowel syndrome

  • Abdominal pain/bloating
  • Altered bowel habits
  • Dyschezia


  • Abdominal pain
  • Back pain
  • Dyspareunia

Myofascial pelvic pain

  • Chronic pelvic pain
  • Back pain
  • Vaginal tenderness
  • Dyspareunia

Painful bladder syndrome

  • Dysuria
  • Abnormal urine frequency

Physical Examination

A physical examination for endometriosis includes general inspection of the external genitalia and bimanual pelvic examination. On speculum examination, red, blue, or hemorrhagic nodules may be seen on the external genitalia, vagina (Figure 2), and cervix.21 During a bimanual pelvic exam, the USL, vagina, rectovaginal space, pouch of Douglas (POD), rectosigmoid space, and posterior wall of the urinary bladder should be assessed for any adnexal masses, reduced cervical/uterine mobility, tenderness on palpation/movement, and nodularity in the posterior compartment structures.22 The 2022 ESHRE guideline for managing endometriosis also provides recommendations for localizing lesions based on findings.23 The presence of adnexal masses may suggest the presence of ovarian endometriomas. Furthermore, painful nodules in the rectovaginal wall or vaginal nodules in the posterior fornix may suggest DE.22 Some studies have suggested a link between endometriosis and a retroverted uterus, although the association is often non-significant.24,25 The specificity for localizing endometriosis using the bimanual technique is relatively high ranging from 86–99% while the sensitivity can range between 23–88% depending on the lesion location. The use of adjunct imaging techniques such as TVS can increase the sensitivity of localizing lesions to 67–99% allowing for a more accurate diagnosis and will be discussed in the next section.22 Physical examination for AWE should involve an abdominal examination where focal nodularity and tenderness may be appreciated. In rare circumstances (e.g. umbilical endometriosis) bleeding from an area of focus can be noted (Figure 3).


Vaginal endometriosis on speculum examination (white arrows). Courtesy of Dr Mathew Leonardi.


Umbilical endometriosis with bleeding (white arrows). Courtesy of Dr Mathew Leonardi.


Regardless of whether the clinical examination is normal, imaging should be sought if endometriosis is suspected.23 Ultrasound and MRI are two common non-invasive techniques for diagnosing endometriosis with a high diagnostic accuracy (especially when used in combination) for detecting ovarian endometriomas, DE, and POD obliteration when performed systematically and with appropriate training.26 However, these imaging modalities are underappreciated and underutilized by gynecologists worldwide.27 In an international cross-sectional online survey, only 28.8% and 16.6% of the respondents believed that USS and MRI could diagnose endometriosis, respectively.27 When imaging is used pre-operatively, it can better prepare surgeons (e.g. requesting for a colorectal surgeon in the case of bowel DE) and avoid intra/post-operative surprises for both patients and clinicians.28 Computerized tomography (CT) and chest x-rays can also be used but is mainly indicated for thoracic endometriosis and excluding pulmonary diseases.29 Therefore, this section will mainly focus on ultrasound and MRI. Table 3 outlines the main imaging tests used for specific subtypes or locations of endometriosis.


Summary of radiological imaging techniques for endometriosis depending on disease location.

Location of Endometriosis

Imaging Techniques

Pelvic endometriosis

  • Transvaginal ultrasound using the IDEA protocol
  • Transrectal ultrasound using the IDEA protocol
  • Transabdominal ultrasound for evaluation of ovarian endometriomas
  • SonoPODography for SE
  • MRI

Appendix and ileocecal

  • Transabdominal ultrasound
  • MRI

Abdominal wall endometriosis

  • Abdominal ultrasound (linear probe)
  • MRI

Thoracic endometriosis

  • CT
  • MRI

Abbreviations: IDEA, International Deep Endometriosis Analysis group; MRI, magnetic resonance imaging; CT, computerized tomography; SE, superficial endometriosis.


Ultrasound is an affordable, non-invasive, first-line imaging modality that can be performed quickly by an experienced clinician. It is also commonly used for diagnosing endometriosis at "atypical" sites such as the abdominal wall and scar endometriosis due to its convenience and accuracy when performed by a trained professional.30 Apart from the benefits of pre-operative mapping, identifying the etiology of symptoms can provide a therapeutic benefit for patients as seeing tangible evidence of their clinical problem holds potential validation power and can impact psychological symptom experience.31 Moreover, non-invasive diagnosis and staging enables informed decisions to be made regarding the patient’s following management.

Previously, TVS has been used by gynecologists to perform a “basic pelvic ultrasound” (Table 4) to visually assess the uterus, ovaries, and cul-de-sac. This technique has a high sensitivity for detecting ovarian endometriomas but is limited to only one form of endometriosis as the locations that are affected by SE and DE are not evaluated. In simple terms, if one does not look at a location, one cannot find the pathology that may be there. A major limitation with ultrasound at present is the skill to perform ultrasound at a level that can accurately diagnose endometriosis is not widely distributed.27 This is multifactorial but differences in healthcare systems geographically may be contributing to this, including the variations in how ultrasound is performed by sonographers versus sonologists.


Comparison of the basic pelvic ultrasound versus the advanced pelvic ultrasound.

Focus of Assessment

Basic Pelvic Ultrasound

Advanced Pelvic Ultrasound



Rectouterine pouch

Ovarian mobility

Rectouterine pouch adhesions (i.e. obliteration)





Uterosacral ligaments

Rectovaginal septum

Site-specific tenderness

The International Deep Endometriosis Analysis (IDEA) group, created and agreed upon by an international panel of endometriosis specialists, has inspired the adoption of the “advanced pelvic ultrasound”, which looks beyond the basic pelvic ultrasound and incorporates the assessment of the bowel, anterior (bladder, ureters, uterovesical junction) and posterior (posterior vaginal fornix, rectovaginal septum, USL) compartments.32 High diagnostic sensitivity and specificity has been reported when using TVS for diagnosing DE in the rectal/rectosigmoid region (sensitivity 89% and specificity 97%),33 USL (60% and 95%), rectovaginal septum (57% and 100%), vaginal (52%, 98%),34 and bladder (62% and 100%).35 Furthermore, Leonardi and colleagues found that ultrasound can accurately predict rASRM staging scores, allowing clinicians to devise management plans for patients earlier (more information on rASRM can be found in the Laparoscopy section).36 Similarly, ultrasound has been found to accurately predict the #Enzian surgical stage of endometriosis.37 The ultrasound-based endometriosis staging system (UBESS) is also being developed to triage patients to appropriately trained surgeons according to endometriosis complexity improving surgical planning.38,39

The IDEA ultrasound protocol comprises four main steps, which can be performed in any order:32

  • Evaluating the uterus and adnexa (including a high-level inspection for signs of adenomyosis/presence or absence of endometrioma).
  • Evaluation of transvaginal sonographic "soft markers" (i.e. site-specific tenderness (SST) and ovarian mobility).
  • Assessment of status of POD using real-time ultrasound-based "sliding sign".40
  • Assessment for DE nodules in anterior and posterior compartments.

When the uterus is visualized, the Morphological Uterus Sonographic Assessment (MUSA) consensus statement provides a useful framework for documenting findings and presence of adenomyosis.41,42 A uterus may exhibit an appearance like a question mark, known as the "question mark sign", when it is anteverted and retroflexed.43 Generally, this is secondary to the fundus adhering posteriorly to DE and/or adenomyosis with a disproportionately thickened posterior myometrium. While evaluating the adnexa, ovarian endometriomas or other ovarian abnormalities should be recorded according to the International Ovarian Tumor Analysis (IOTA) Group consensus.44 The most "common" endometrioma appearance is described as a homogenous, hypoechogenic unilocular cyst with fluid45 (ovarian endometrioma ultrasound video Furthermore, color Doppler energy may be used to increase diagnostic accuracy,46 primarily of non-endometrioma type ovarian cysts. Ovarian motility is another useful "soft marker", and reduced motility may indicate SE and/or DE.47,48 When ovaries appear fixed together, it is known as "kissing ovaries" and is associated with intra-abdominal adhesions and/or fallopian tube obstruction (especially in infertile patients).49

While SST falls under the second point in the IDEA approach, Leonardi and Condous recommend performing this test last to avoid early disruption or termination to the scan and patients should be warned that pain or discomfort may be elicited. Feedback from the patient is key to record SST properly.50

When assessing the bowel, hypoechoic nodules may be found in the upper (intraperitoneal) and lower (retroperitoneal) rectum. Since the lower rectum is outside the peritoneal cavity, and thus not accessible during laparoscopy, detection of nodules in this area can be valuable for pre-operative planning. On the other hand, it is extremely rare for lesions to exclusively affect the retroperitoneal rectum or rectovaginal septum. In the cases of severe endometriosis and POD obliteration, anatomical planes can be distorted, giving the impression that the nodules are retroperitoneal when in fact, they were formally intraperitoneal and have simply become invisible (i.e. beneath the surface) laparoscopically due to severe adhesions. The "sliding sign" to evaluate the POD obliteration state can be elicited with one hand holding the probe and the other on the patient’s lower abdomen. A "positive sign" is characterized by the rectum sliding against the uterus (exemplar video can be found at, whereas movement of the rectum and uterus in unison ("negative sign") suggests POD obliteration (exemplar video

The other main areas of the posterior compartment are the USLs, the most common site of DE and SE, and the posterior vaginal fornix (PVF).51 The USL is around 12–14 cm long and extends caudally from the posterior cervix and vaginal dome to the sacrum.52 USL DE can be difficult to visualize laparoscopically as POD obliteration may obstruct the view highlighting the role of pre-operative imaging.53 If lesions are found, the extent of parametrial and/or torus uterinus (posterior insertion of USLs to the posterior cervix) should be assessed as well (detailed guide for ultrasound USL endometriosis diagnosis can be found at Compared to bowel endometriosis, TVS has lower sensitivity and other contrast mediums should be explored.33,34 The poorer diagnostic test performance for USL DE warrants adoption of new approaches to visualize these important structures. PVF endometriosis is suspected if the PVF is thickened or if a discrete nodule is found in the hypoechoic layer of the vaginal wall. Diagnostic potential of imaging for PVF is important but physical examination must also be used. The rectovaginal septum, while often thought of as a common place for DE, is indeed an unusual location. In addition to anatomical distortion that propagates confusion, nomenclature differences around the world may lead to some confusion. In some regions, posterior compartment DE is referred to as “rectovaginal” DE. The similarity of rectovaginal DE and rectovaginal septal DE permits this misunderstanding. While the use of the term rectovaginal DE made some sense in a world before imaging could better localize nodules in the distorted posterior compartment anatomical locations, it is a term that should now retire. Rectovaginal DE does not actually need to directly involve the rectum or vagina for the term to be used. In these cases, it is misleading what type of surgery is exactly needed to treat the disease.

When scanning the anterior compartment (bladder, ureters, uterovesical region), a relatively empty bladder enables visualization of lesions.55 DE most commonly infiltrates the muscular layer of the bladder wall especially near the base.50 Lesions appear spherical or comma-shaped and hyperechoic.55,56,57 Although rare, it is important to recognize ureteral endometriosis by routinely assessing the ureters on TVS.58,59,60 Dilation of the ureters can signify ureteral stenosis from DE and a transabdominal scan of the kidneys is needed to exclude hydroureteronephrosis.61 While not part of the IDEA statement, parametrial DE, often extended from the USLs,58,59,60 can be responsible for ureteral obstruction and should be assessed for as well.62,63

Diagnosing SE using ultrasound has been challenging due to its non-infiltrative (i.e. small) nature.48,64 However, a novel technique called "saline-infusion sonoPODography (SPG)" has been piloted with promising results (in those without DE, OE, or POD obliteration: accuracy 80.0%, sensitivity 77.7%, specificity 100.0%, positive predictive value 100.0%, negative predictive value 33.3%). This technique can be combined with hysterosalpingography in the infertility clinic to assess for uterine cavity abnormalities and tubal patency. In the study, a median of 60 ml of saline was infused into the POD through patent tubes but this amount should be validated in an outpatient setting. This provides an acoustic window enhancing contrast in the POD peritoneum improving visualization of superficial irregularities (i.e. SE) and superior RVS border (not possible without SPG) (video demonstration at

Abdominal wall endometriosis can be scanned using a high-frequency linear probe along with Doppler examination. Lesions appear like DE of the posterior compartment (hypoechoic), but the majority of the nodules appear solid in nature with irregular/unclear borders surrounded by adipose tissue. Furthermore, when nodules are pressed with the probe, it may elicit SST.66

Transrectal ultrasound may also be used for assessing the pelvis for endometriosis and has the highest diagnostic accuracy for rectal DE compared to TVS and MRI, but TVS remains as the more common ultrasound approach because it is perceived as less invasive and it is more familiar.33,67 It is a reasonable approach to consider in those who cannot undergo a TVS. Like TVS, informed consent should be obtained for transrectal ultrasound.

Stand-Off Techniques and Image Optimization

Stand-off techniques involve the use of biological (e.g. filled bladder) or mechanical (e.g. saline or ultrasound gel) methods, introducing an acoustic window between the ultrasound probe and surrounding structures resulting in a clearer image. One example is sonovaginography, which involves the injection of ultrasound gel into the PVF.50 In an observational study with 28 patients, sonovaginography had a high sensitivity, specificity, and positive-predictive value (100%, 91.7%, 100%, respectively) for the detection of POD obliteration and DE.68 It also helps to identify how many layers of the posterior compartment (vagina, rectovaginal septum, anterior rectal wall) are affected for a more accurate diagnosis.

Bowel preparation may also be done prior to ultrasounds. Bowel preparation regimes differ, but may involve as much as a three-day low-residue diet and rectal enemas to clear the rectum to decrease potential artifacts caused by bowel loops, with some groups claiming it improves diagnostic performance.69 However, this requires more work from the patient, may not be well-tolerated, and other groups have not noted it to improve the diagnostic performance of TVS in detecting rectal endometriosis.70


Magnetic resonance imaging (MRI) is a radiology technique that does not require ionizing radiation and provides clear images for analyzing soft tissue morphology. MRI is commonly utilized to evaluate for DE.71 In 2017, the European Society of Urogenital Radiology (ESUR), comprised of radiologists, gynecologists, and gynecological imaging experts from eight institutions, developed a clinical guideline for evaluating pelvic endometriosis with MRI.72 In a recent study by Indrielle-Kelly and colleagues, we have seen the adaptation of the IDEA consensus for MRI reporting.26 However, a review of 32 centers in 2020 found many inconsistencies in MRI protocols for endometriosis evaluation.73

The T1- and T2-weighted two-dimensional fast spin-echo (FSE) are the most used sequences. The ESUR guidelines state that two-dimensional T2-weighted sequences taken in >2 orthogonal planes (sagittal, axial, oblique) from renal hila to pubic bone without fat-suppression is the best method for detecting pelvic endometriosis.74 When analyzing T2-weighted sequences, hypointense nodules with irregular borders suggest the presence of DE lesions, which contain fibrous tissue and dense smooth muscle (Figure 4 Case 1). Depending on the glandular tissue makeup of endometriosis implants, dilated endometrial glands may appear with hyperintense foci.75 A preliminary study by Bazot et al. suggests that three-dimensional (3D) sequences may also be considered since it can shorten the time required for imaging. Although 3D images of the pelvis are of poorer quality, it had similar diagnostic accuracy to multiplanar T2-weighted sequences in one study.76




CASE 1. This is a patient who had endometriosis surgery 5 years prior and is currently presenting with pelvic pain and pain in the right extremity suspicious for neurological/sciatic nerve involvement. While the sciatic nerve trunk itself was not involved, MRI confirmed involvement of one of the sciatic nerve roots. (A) Axial T2-weighted MR image shows low-signal intensity stellate mass along the right pelvic wall (white arrow). When followed, the S3 nerve root is noted passing through this mass. (B) Corresponding sagittal T1-weighted MR images with fat suppression shows hyperintense foci indicating hemorrhage (white arrow), confirming that this is an endometriotic deposit as opposed to post-operative fibrosis. Courtesy of Dr Basma Al-Arnawoot.

On the other hand, T1-weighted images can be used for diagnosing endometriotic cysts since blood products from recurrent bleeding displays hyperintense foci (Figure 5 Case 2).71 Additionally, fat suppression such as the Dixon technique or spectrally adiabatic inversion recovery increases tissue contrast facilitating the detection of cystic lesions.77,78




CASE 2. 32 year old with infertility and cystic lesions on ultrasound. (A) Axial T1-weighted MR image with fat suppression revealing a 7.2 cm T1 bright mass (white arrow) in the middle in keeping with a left ovarian endometrioma. (B) Sagittal T2-weighted MR image demonstrates the same endometrioma with the expected T2 intermediate signal intensity (white arrow) and reveals that it is adherent to the posterior serosal surface of the uterus (black arrow). Review of the remainder of the exam also revealed medialization of both ovaries and extensive Deep infiltrative endometriosis resulting in obliteration of the cul-de-sac (not visible on this image). Courtesy of Dr Basma Al-Arnawoot.

One of the main benefits of MRI is diagnosing endometriosis in areas difficult to access using other imaging modalities such as sciatic nerve involvement and extra-pelvic sites such as AWE (Figure 6 Case 3).79 For example, diaphragmatic lesions can have varying hyperintense appearances (deep nodules, punctate, spots, plaques) and are best visualized using the fat-suppressed T1-weighted sequences with an 83% sensitivity.80 A systematic review and meta-analysis by Guerriero and colleagues compared the diagnostic accuracy of TVS and MRI, and found similar performances in detecting endometriosis lesions in the posterior compartment.81 This has been recently confirmed in a series of diagnostic test accuracy meta-analyses by Gerges and colleagues.33,34 Of note, the same group of investigators found that MRI had a higher sensitivity for detecting USL and PVF DE (81% and 70%, respectively) compared to TVS (61% and 58%, respectively).34 However, MRI also has several limitations such as higher healthcare costs compared to ultrasound, limited availability, and possible patient discomfort, especially if certain image optimization strategies are used such as bowel preparation, stand-off techniques, and anti-peristaltic agents. Balancing all factors, the authors advocate for ultrasound to remain as the first-line imaging technique with advanced principles implemented while MRI would be beneficial for cases that extend beyond the potential of ultrasound, including cases of potentially extra-pelvic endometriosis or bulky, obscuring pelvic pathology making ultrasound more challenging.33,34




CASE 3. 28-year-old patient with enlarging left lower quadrant mass at the edge of a Pfannensteil incision from prior Cesarean section. MRI revealed that the mass corresponds to endometriotic deposits. (A) Axial T2-weighted MR image reveals a stellate nodule within the subcutaneous fat at the edge of the prior incision displaying increased T2 signal intensity (white arrow). It also has a very subtle T2 dark rim in keeping with hemosiderin deposition. (B) Axial T1-weighted MR image with fat suppression reveals T1 bright foci (white arrows) in keeping with hemorrhage. Courtesy of Dr Basma Al-Arnawoot.

Image Optimization

The timing of imaging in relation to the patient’s menstrual period remains inconclusive. Since endometriosis implants may bleed during menses, Fiaschetti et al. does not recommend performing T1-weighted sequences during the first 8 days of the menstrual cycle to avoid spontaneous hyperintensity.82 However, other studies found no significant difference in image quality regardless of the menstrual cycle phase and possible beneficial effects of pelvic free fluid facilitating image interpretation.83,84 The efficacy of rectal and/or vaginal opacification to identify DE using sonographic gel has also been debated as studies have shown variable results. If these techniques are used, bowel preparation is recommended to accurately identify lesions especially in the rectum.71 Lastly, administration of anti-peristaltic agents like butyl-scopolamine or hyoscine butylbromide can limit bowel motion artifacts to improve diagnostic accuracy.85


Surgery and pathology work hand in hand since samples must be collected first before they can be analyzed. Since the appearance of endometriotic lesions (discussed below) have high variability between patients, surgeons often "over-biopsy". A recent validation study by Gratton and colleagues found that laparoscopic visualization had a high sensitivity (90%) while the specificity was 40%.86 Low specificity when diagnostic laparoscopy is performed alone had also been reported by previous studies highlighting the importance of a histological diagnosis.87 However, a negative diagnostic laparoscopy is helpful in excluding endometriosis.88 Hence, surgery and pathology will be discussed together within this section.


Laparoscopy is a minimally invasive procedure often alongside histopathological confirmation for diagnosing all types of pelvic endometriosis (ovarian endometriomas, DE, SE) since surgeons can directly visualize the pelvic and abdominal cavity. In 2022, ESHRE no longer considered laparoscopy as the "gold standard" and recommends its use if initial imaging results are negative and/or patients are not suitable/unresponsive to empirical treatment.23 Depending on the goal, during the same operation, surgeons could also aim for complete treatment of endometriotic lesions to provide symptomatic control and reduce the number of laparoscopies (which carries its own risks). Herein lies the issue with surgery as the diagnostic test of choice – many patients exhibit endometriosis that cannot be appropriately managed at a surgery that is simultaneously diagnostic. Either the surgery is not planned for long enough, the surgical skill of the surgeon is insufficient for the complexity of the endometriosis identified, or the patient has not fully consented to what could/should happen based on what is found.28 As such, the concept of laparoscopy being the gold standard is increasingly being challenged.39,89

Laparoscopy for endometriosis should always involve a comprehensive exploration of the abdominal and pelvic contents. The traditional contents of the pelvis including ovarian, uterine surface, fallopian tubes and peritoneum need to be adequately surveyed. In order to identify subtle lesions, the laparoscope must be brought right up to the surfaces being inspected. In addition, the gastrointestinal and genitourinary systems need to be assessed as well, including the appendix. The diaphragm should routinely be inspected, especially if the patient describes right upper quadrant symptoms. If the patient underwent pre-operative ultrasound/MRI where endometriosis was visualized, these areas should be closely inspected surgically. In some situations, endometriosis may not be obviously visible at laparoscopy despite clear identification with imaging.90

SE has been described to have a black (“powder burn”) or dark bluish appearance from the accumulation of blood pigments.91 However, subtle forms can appear as white opacifications, red flamelike lesions, or yellow-brown patches in earlier, active stages of disease.92 Ovarian endometriomas have a distinct morphology classically described as a "chocolate cyst" containing old menstrual blood giving it a dark brown appearance. Adhesions are often found in association with endometriomas and consists of fibrous scar tissue because of chronic inflammation. In many cases, there is endometriosis at the site of ovarian fixation.47,48 Like an imaging-based assessment following the IDEA protocol, the posterior and anterior compartments should be assessed carefully for DE. Often times, DE appears as multifocal nodules and may infiltrate the surrounding viscera and peritoneal tissue.93 As mentioned earlier, depending on the extent of POD obliteration, posterior compartment (USL, bowel, PVF) DE may be difficult to assess and diagnose surgically, with evidence supporting a better diagnostic test performance using non-invasive imaging-based assessment for this specific type of DE.53 An atlas of endometriosis appearances can be at

When combining diagnostic laparoscopy with operative laparoscopy, the surgeon must consider the importance of a biopsy to ensure their visual diagnosis is indeed correct. There is ample evidence that surgeons overcall endometriosis at surgery.86,87,88 In the cases where surgeons perform excision of endometriosis, all specimens should be sent to pathology for analysis. In some cases, it is inappropriate to use biopsy as a diagnostic test. For example, in a patient who undergoes diagnostic laparoscopy and the surgeon suspects bowel DE, this area should only be biopsied/excised if the patient explicitly provided informed consent following a discussion about the benefits and risks of a “bowel surgery” component and the patient was adequately prepared with bowel preparation and antibiotic prophylaxis. Surgeons should also consider concurrent appendectomy during excision of endometriosis since women with DE have a high risk of appendiceal endometriosis.94 Often, appendectomy is not within the skill set of gynecologists, which again creates a unique challenge with surgery being used as a combined diagnostic test and treatment modality.

Surgical Diagnosis for Extra-pelvic Endometriosis

Although non-invasive imaging techniques (i.e. chest x-ray, CT, MRI) exist, they have low sensitivity. Hence, video-assisted thoracoscopic surgery (VATS) is the "gold standard" for diagnosing thoracic endometriosis. In a systematic review of women with catamenial pneumothorax, thoracic endometriosis and diaphragmatic lesions were detected in 52.1% and 38.8% of women, respectively, following VATS.95 Like laparoscopy, excision of endometriosis lesions can be considered if found for both diagnostic and therapeutic value, and the previously used exploratory thoracotomy should be reserved if minimally invasive techniques are inadequate. VATS will not be able to diagnose endometriosis affecting the abdominal side of the diaphragm. This requires laparoscopy, occasionally with manipulation of the liver to adequately inspect the diaphragm, especially when clinical symptoms exist. It is unclear if there is any clinical utility in diagnosing and surgically treating diaphragmatic endometriosis in patients who are asymptomatic (in the RUQ/chest region). It is essential to recall that in both VATS and laparoscopy, diagnosis is operating dependent, with individuals more familiar with extra-pelvic endometriosis better equipped to recognize (sometimes) subtle abnormalities and when needed, surgically biopsy/treat them as well.

Enhanced Intra-Operative Techniques

Conventional laparoscopy uses white light when exploring the pelvic cavity. However, three novel intra-operative methods have been explored to improve detection of peritoneal endometriosis: narrow-band imaging (NBI), autofluorescence (AFI), and 5-aminolevulinic acid induced fluorescence (5-ALA).96 Both NBI and AFI work by detecting increased neovascularization, which is associated with endometriotic tissue while 5-ALA accentuates damaged tissue.97,98,99 However, their benefits are limited to a few studies and more research is being done to better understand their use.96

Surgical Staging Methods

In 2017, the World Endometriosis Society consensus for diagnosis endometriosis recommended the use of the rASRM classification tool during surgery to classify endometriosis based on the size, extent, and location of lesions found (Figure 7).100 There are four stages ranging from minimal (Stage 1), mild (Stage 2), moderate (Stage 3), and severe (Stage 4).100,101 However, a prospective analysis found considerable inter-variability among surgeons reducing its diagnostic accuracy. In 2021, the AAGL Special Interest Group in Endometriosis published the AAGL Classification Tool solely based on intraoperative findings to better quantify the surgical complexity of endometriosis cases (Figure 8). Like the rASRM system, there are four AAGL endometriosis stages. However, the recent validation study found higher reproducibility with the AAGL score (kappa = 0.621) compared to rASRM (kappa = 0.317) when discriminating surgical complexity.102 The rASRM system fails to properly incorporate DE, which often equates to surgical complexity, leading to this deficiency in the system. The Enzian classification tool has been introduced in recent years to better describe DE, and has recently introduced the updated system, #Enzian, which also incorporates SE and tubal pathology (Figure 9).100,103 A recent study by Montanari and colleagues demonstrates that the #Enzian system score can be accurately predicted with ultrasound, increasing the utility of this model significantly.37 The Endometriosis Fertility Index (EFI), reliant on the rASRM staging system, was also recommended after surgical staging/treatment for women considering pregnancy in the future (Figure 10).100,104 Although several staging tools exist, they mainly focus on the physical extent of disease and do not correlate well with the pain symptoms and impact on quality of life for patients.105 Beyond accurately representing the experience of the patient, there should be functionality to prognosticate clinical outcomes, which currently only the EFI attempts to do. The utility of the newest system, the AAGL Classification Tool, remains to be seen but it must be validated.106


The revised American Society for Reproductive Medicine classification tool is the most commonly used staging system and categorizes endometriosis into four stages: minimal (Stage 1), mild (Stage 2), moderate (Stage 3), and severe (Stage 4). Reproduced with permission.101


The new AAGL tool utilizes intra-operative anatomical findings to differentiate endometriosis by surgical complexity. Reproduced with permission.102


The #Enzian classification tool aims to better describe deep endometriosis, although more external validation is required. Reproduced with permission.103


The Endometriosis Fertililty Index (EFI) is an externally validated tool used to predict spontaneous pregnancy without assisted reproductive techniques following surgical treatment. Reproduced with permission.104


During laparoscopy, several biopsies of lesions suggestive of endometriosis should be taken and submitted to pathology. In extra-pelvic endometriosis like AWE, imaging techniques used (i.e. USS, MRI, CT) may detail the extent of disease, but are sometimes unable to differentiate abdominal masses from neoplasms, abscesses, or hematomas.16 Furthermore, AWE cannot be visualized laparoscopically and specimens can be retrieved using ultrasound-guided fine-needle aspiration or core needle biopsy (Figure 11).107 Depending on the context, histopathological confirmation should be ascertained to reach a definitive diagnosis and decide the appropriate management plan. Again, this can sometimes be challenged by the desire to simultaneously diagnose and treat. The American College of Obstetricians and Gynecologists (ACOG) suggests, in general, that the presence of two or more of the following features must be detected in specimens in order to confirm endometriosis: endometrial epithelium, endometrial glands, endometrial stroma, hemosiderin-laden macrophages (Figure 12).108 However, the standard pathological protocol may also contribute to the underdiagnosis of endometriosis, especially for appendiceal endometriosis (Figure 13). A modified pathological analysis with serial sectioning and evaluation of the appendix and mesoappendix can significantly improve the detection of more abnormal pathology.109 One may extrapolate the results of this study to other specimens where 'in toto' assessment (submitting the entire specimen for microscopic analysis) will improve the diagnostic potential of histolopathology. Histological diagnosis of endometriosis is mainly limited by the surgeon’s ability to correctly identify endometriotic lesions due to more subtle/atypical appearances and submitting suspicious lesions to histology may help reduce this risk.86 On the other hand, a more liberal biopsy/excision approach may reduce the specificity of surgical visualization and may institute unnecessary surgical risk.


Abdominal wall endometriosis on histology. Courtesy of Dr Shangguo Tang.


Histology of endometriosis biopsy with endometrial epithelium, endometrial glands, endometrial stroma, and hemosiderin-laden macrophages. Courtesy of Dr Shangguo Tang.


Appendiceal endometriosis on histology. Courtesy of Dr Shangguo Tang.

Compared to pelvic endometriosis, thoracic/diaphragm endometriosis does not commonly contain endometrial glands on histology adding to the diagnostic challenge.110,111 Furthermore, only a small focus of endometriotic tissue may be found for biopsy. The fewer samples available and less obvious features of endometriosis on histology can make this diagnosis overlooked by pathologists unfamiliar to thoracic endometriosis.110 Immunohistochemical analysis can be used concurrently to improve the diagnostic accuracy of thoracic endometriosis. Several studies have found improved detection of thoracic endometrial cells when tissue stained positive for estrogen receptor (88%), progesterone receptor (100%), and CD10 (88%) on immunohistochemical staining.110,111,112


Many research studies and Cochrane reviews have investigated potential biomarkers that can be used to detect endometriosis,10,11,12 with an appropriate goal of reducing the diagnostic delay that exists in diagnosing endometriosis. Unfortunately, all of these are often non-specific/unreliable making them inappropriate for routine clinical use. In this section, the main biomarkers used in clinic will be discussed as well as a brief overview of biomarkers currently being studied academically.

Clinical Use of CA-125

The Cancer Antigen 125 (CA-125) biomarker has been the most researched biomarker for endometriosis. Most laboratory tests have set a CA-125 cut-off at 35 units/ml to suggest the possibility of endometriosis.113 Although serological CA-125 levels may be raised in some cases of endometriosis, the 2016 Cochrane review by Nisenblat and colleagues found that CA-125 had a poor specificity and sensitivity for detecting endometriosis.10 Another limitation of CA-125 is that raised levels are associated with many other physiological and pathological conditions including menstruation, pregnancy, fibroids, and most notably, ovarian cancer.114,115,116 Given its several limitations, the National Institute for Health and Care Excellence (NICE), The Society of Obstetricians and Gynecologists of Canada (SOGC), ESHRE, and ACOG guidelines currently do not recommend the use of CA-125 as a diagnostic tool for endometriosis.4,117,118,119 When used clinically, an elevated CA-125 may lead patients down a path of unnecessary, risky, and anxiety-provoking investigations and procedures. Unless there are suspicious features for ovarian malignancy in the context of endometriomas diagnosed on imaging (based on IOTA nomenclature), CA-125 is not of additional value since the diagnosis is already made by the imaging test, leaving the CA-125 as only a potential harm-causing test.

Academic Use

As mentioned earlier, many research articles have investigated the use of biomarkers from blood, urine, menstrual effluent, and peritoneal fluid as alternative diagnostic techniques for endometriosis.10,11,12 Some of the more popular biomarkers include inflammatory cytokines, angiogenic factors, reactive oxygen species, microRNA, and matrix metalloproteinases.120,121,122 However, the heterogeneity and overall low quality of studies limits the applicability of findings in clinical practice, and higher quality research is warranted.11


Clinical Diagnosis
  • A comprehensive history and thorough physical examination can aid clinicians in making a presumptive clinical diagnosis
  • Endometriosis can present with a wide range of symptoms depending on the site of lesions
  • Co-existing pain-generating mechanisms and/or central sensitization with endometriosis should be managed; the Central Sensitization Inventory questionnaire score can be used
  • Clinical assessment is subject to operator skill and knowledge in the history taking/physical examination
  • If clinical examination is normal but endometriosis is suspected, imaging techniques should be sought
  • Ultrasound and MRI can be used pre-operatively to accurately diagnose ovarian and deep endometriosis pre-operatively; these imaging modalities may be complementary
  • Ultrasound and MRI have similar diagnostic accuracy for pelvic endometriosis
  • The International Deep Endometriosis Analysis (IDEA) ultrasound protocol goes beyond the basic pelvic ultrasound and is highly sensitive and specific for diagnosing ovarian endometrioma(s) and deep endometriosis
  • Saline-infusion sonoPODography is a novel technique that can diagnose SE on ultrasound, but requires validation
  • The ultrasound-based endometriosis staging system (UBESS) has been developed to triage patients using ultrasound based on disease complexity
  • According to ESUR guidelines, the two-dimensional T2-weighted sequences without fat suppression is the best method for diagnosing endometriosis on MRI
  • MRI can be used for more complex cases involving extra-pelvic/difficult to access sites
  • Imaging tests are subject to operator skill in performance of imaging test and interpretation
Surgery and Pathology
  • Laparoscopy is a minimally invasive procedure, which can diagnose all types of endometriosis alongside histopathological confirmation
  • Peritoneal endometriosis classically appears as black or "powder-burn" appearances although more subtle forms (white, red, yellow-brown) can exist
  • Ovarian endometriomas appear as "chocolate cysts" containing old menstrual blood
  • Depending on patient goals, surgeons should aim for complete treatment of endometriosis if found during laparoscopy but biopsy must be obtained to utilize histopathology as the final diagnostic test method since surgeons do not have perfect diagnostic accuracy
  • The revised American Society of Reproductive Medicine (rASRM) staging system is the most used, but newer tools (Enzian tool, AAGL tool) have been developed and should be validated
  • The Endometriosis Fertility Index (EFI), based on the rASRM system, can be used to predict spontaneous pregnancy post-operatively
  • Current endometriosis staging systems poorly represent the severity of symptoms or impact on quality of life for the patient
  • Video-assisted thoracoscopic surgery (VATS) is the "gold standard" for diagnosing thoracic endometriosis
  • Histopathological confirmation of endometriosis is achieved in the presence of two or more features: endometrial epithelium, endometrial glands, endometrial stroma, hemosiderin-laden macrophages
  • Histopathology is subject to variability in operator diagnostic performance
  • CA-125 is not recommended for diagnosing endometriosis
  • Reliable biomarkers for endometriosis have not yet been discovered and is not recommended for use outside of the academic research settings
  • Future research may explore serum, menstrual effluent, urine, or peritoneal fluid for potential biomarkers


We would like to thank Dr Basma Al-Arnawoot and Dr Shangguo Tang at McMaster University in the Departments of Radiology and Pathology, respectively, for providing case images.


Kevin Kuan declares that they have no interests that conflict with the contents of this chapter. Mathew Leonardi reports personal fees from GE Healthcare, TerSera, Bayer, AbbVie, grants from Australian Women and Children’s Research Foundation, Endometriosis Australia, CanSAGE, Hamilton Health Sciences, HyIvy Health, all outside of the work of this chapter.



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