{"paper_id":"9d6f98d4-07ce-4547-b26a-4b91a6c6d20c","body_text":"138\nImaging diagnosis of endometriosis\nLuciana P . Chamiea*\nChamie Imagem da Mulher and Fleury Medicina e Saúde, São Paulo, SP , Brazil\nORCID: a0000-0002-8975-1075\nIN-DEPTH REVIEW\nCorresponding author:  \n*Luciana P . Chamie  \nE-mail: luciana@chamie.com.br\n2696-8444 / © 2022 Federación Mexicana de Radiología e Imagen, A.C. Published by Permanyer. This is an open access article under the \nCC BY-NC-ND ( https://creativecommons.org/licenses/by-nc-nd/4.0/ ).\nAvailable online: 19-09-2022\nJ Mex Fed Radiol Imaging. 2022;1(3):138-150\nwww.JMeXFRI.com\nFEDERACIÓN MEXICANADE RADIOLOGÍA E IMAGEN, A.C\nJournal of the Mexican Federation of Radiology and Imaging\nOfficial Journal of the \nJournal of the Mexican Federation \nof Radiology and Imaging\nReceived for publication: 10-05-2022\nApproved for publication: 16-05-2022\nDOI: 10.24875/JMEXFRI.M22000019\nABSTRACT\nEndometrosis is a common gynecologic disease that affects women of reproductive age and commonly causes pelvic pain \nand infertility. The most common types are superficial peritoneal implants, ovarian endometriotic cysts (endometriomas), and \ndeep-infiltrating subperitoneal lesions. Diagnosis is often delayed, and up to 65% of women are initially misdiagnosed. Imaging \nmethods play a pivotal role in patient counseling and clinical management of the disease, and have been replacing diagnostic \nlaparoscopy in specialized centers worldwide. Comprehensive imaging mapping is required for adequate surgical planning \nand to assist fertility doctors in determining the appropriate treatment options. T ransvaginal ultrasound (TVU) is the first-line \nimaging modality and is a widely available tool that enables accurate diagnosis of endometriosis when a dedicated protocol \nis used. TVU is the best imaging method to investigate multiple bowel lesions and small peritoneal implants. Magnetic \nresonance imaging (MRI) is an excellent multiplanar method for evaluating the pelvic cavity and extrapelvic sites in \nendometriosis. It is the method of choice to differentiate ovarian cysts and investigate endometriosis affecting the ureters, \npelvic nerves, pelvic floor, and diaphragm. This In-Depth Review describes the imaging protocol and findings of TVU and \nMRI to investigate endometriosis. \nKeywords: Endometriosis. Endometrioma. Deep endometriosis. Magnetic resonance imaging. T ransvaginal sonography.  \nImaging protocol.\nINTRODUCTION\nEndometriosis is a chronic and progressive gyneco -\nlogical disease characterized by the presence of  \nendometrium-like tissue outside the uterus and is \nassociated with fibrosis and inflammatory reactions 1. \nThe establishment and growth of endometriotic lesions \ndepends on estradiol stimulation, followed by an \nincrease in prostaglandin production, resulting in a \nfeed-forward mechanism of prostaglandin-mediated \nestradiol production 2. It is mostly found in women of \nreproductive age, affecting up to 10% of the female \npopulation and 60% of patients with infertility 3,4. \nClinically, endometriosis can exhibit different \n phenotypes, varying from being asymptomatic to \nmanifesting with excruciating pelvic pain; the most \nintriguing characteristic is the lack of correlation \nbetween advanced stages and the associated level of \npain5,6.\nMultifocal pelvic endometriosis is the most common \npresentation, and three types of lesions may be \nobserved: superficial implants on the peritonial surface, \novarian cysts (endometriomas), and deep-infiltrating \nlesions beneath the peritoneal surface and into the \nmuscularis propria of the hollow viscera 7. Although  \nhistologically benign, deep lesions can exhibit  malignant \nbehavior not only in terms of the depth of infiltration in \na localized area, but also metastasize to regional lymph \nnodes. Endometriosis has been extensively defined as \na pelvic disease; however, recent research has \n\nL.P . Chamie: Imaging diagnosis of endometriosis\n139\ndemonstrated multiple effects throughout the body, \naffecting cardiovascular, neurological, and metabolic \nsystems, as well as immune function 2.\nDiagnosis of endometriosis remains clinically chal -\nlenging, and despite the high prevalence of the \n disease, it can take between 4 to 12 years between \nthe onset of symptoms and a reliable diagnosis 8. \nAccording to the new guidelines of the European \nSociety of Human Reproduction and Embriology, lap -\naroscopy is no longer the diagnostic gold standard \nand has been replaced by imaging methods, such as \ntransvaginal ultrasound (TVU) and magnetic reso -\nnance imaging (MRI) 9. TVU is the first-line imaging \nmodality when endometriosis is suspected, and when \nperformed by an expert in the field, it can provide \naccurate mapping of the affected sites 10. It yields  \nbetter performance for multible bowel lesions and \nsmall peritoneal implants 11,12. MRI is an excellent \nimaging method for the diagnosis of ovarian endome -\ntriomas and multiple deeply infiltrating implants. \nUreteral, diaphragmatic, and pelvic floor infiltrations \nare also important indications for MRI 13.\nThe impact of non-invasive diagnosis and staging of \nendometriosis based on imaging methods is tremen -\ndous and extends beyond preoperative evaluation. It \nplays a pivotal role in clinical counseling and treatment \nplanning throughout a woman’s life, from adolescence \nto menopause 9. This In-Depth Review describes the \nimaging protocol used to investigate endometriosis \nusing TVU and MRI, discusses its advantages and \nlimitations, and reviews the most common imaging  \nfindings of endometriosis using both methods.\nTransvaginal ultrasound (TVU)\nTVU is the first-line imaging modality to investigate \npatients with suspected endometriosis 10. It is widely \navailable, cost-effective, and achieves excellent results \nwhen performed by an experienced radiologist. For \nstudies assessing ovarian endometriomas, TVU has \ndemonstrated high sensitivity (95%) and specificity \n(96%). For deep infiltrative endometriosis (DIE), studies \nare heterogeneous, reporting an overall sensitivity and \nspecificity of 79% and 94%, respectively 14–16. TVU  \nperformed after bowel preparation is a powerful tool to \nevaluate pelvic endometriosis enabling detection of the \ndisease with high accuracy. It also allows a compre -\nhensive roadmap detailing all the structures affected \nand the degree of infiltration to be obtained, which is \ncrucial for appropriate clinical counseling and multidis -\nciplinary surgical planning.\nPatient preparation and imaging \ntechnique\nAlthough routine TVU does not require specific \npreparation, an endometriosis search using ultrasound \n(US) can be optimized when simple bowel preparation \nis performed 17. Advantages of such protocol include \nbetter detection of multiple bowel lesions, and identifi -\ncation of the layers and the circumference of the \naffected bowel. In addition, bowel cleaning improves \nthe overall view of the pelvic cavity and pelvic organs \nby eliminating or minimizing artifacts such as gas  \nand bowel content 18. Bowel preparation is performed \nthe day before and on the day of the examination  \n(Table 1). The adverse effects are minimal and may \ninclude abdominal cramps and mild hypotension.\nMild bladder filling is another important issue in  \nanterior compartment evaluation. Patients are instructed \nto empty bladder imediately before the procedure and \ndrink aproximately 300 mL of water just before the \nexam. The latter is useful for ureteral evaluations. In \naddition to bowel and bladder preparations, patient \npositioning requires special attention. The pelvis should \nbe elevated to facilitate free angulation of the probe  \ninto the posterior compartment, thereby enhancing  \nthe diagnostic capability while minimizing patient dis -\ncomfort. The application of 60 mL of US gel to the \nupper third of the vagina is optional and can facilitate \nthe search for DIE lesions in the posterior vaginal  \nfornix. At the author’s institution, TVU is performed after \nbowel preparation and interpreted in real time by the \nradiologist using a US equipment with a 5–9 MHz  \nfrequency transducer (Voluson E8, GE Healthcare, \nMilwaukee, WI USA). \nThe imaging algorithm should be standardized and \nshould include evaluation of the anterior, medium, and \nposterior compartments of the pelvis 19,20. The bladder \nwall, vesicouterine peritoneum, anterior uterine wall, \nand round ligaments were evaluated in the anterior \ncompartment. The ovaries, fallopian tubes, ovarian \nfossa, broad ligaments, parametrium, and ureters were \nassessed in the middle compartment. In the posterior \ncompartment, evaluation of the retrocervical space \nplays a pivotal role in the diagnosis of endometriosis \nbecause of a high prevalence of the disease in the \nuterosacral ligaments. The retrovaginal space, vagina, \nrectosigmoid colon, pararectal fossa, posterior uterine \nwall, and rectovaginal septum were also examined. \nIt is noteworthy that when performing routine TVU, \nthe probe is primarily located in the anterior vaginal \nfornix. To properly evaluate the posterior compartment, \n\nJ Mex  Fed  Radiol  iMaging . 2022;1(3):138-150\n140\nthe vaginal probe must be displaced posteriorly into the \nposterior vaginal fornix in association with downward \nangulation. The posterior location of the probe allows \naccurate assessment of the right and left uterosacral \nligaments, the superior third of the vagina and the  \nrectosigmoid colon, from the anal border to the \ndescending-sigmoid colon transition. Supplemental \nVideo 1 shows the dynamic assessment of the retro -\ncervical space with TVU and demonstrates the normal \naspect of the pelvic peritoneum, which is homoge -\nneously hyperechoic. Supplemental Video 2 shows the \ndynamic assessment of the rectosigmoid colon using \nTVU after bowel preparation. The transducer is pressed \nagainst the posterior vaginal wall while following the \nbowel from the anal border to the descending – sigmoid \ncolon transition.\nAs a dynamic method, the search for adhesions is \nmandatory during the TVU examination by applying the \nsliding sign maneuver in all three compartments. The \nmaneuver comprises gentle pushing of the probe \n combined with abdominal palpation with the free hand. \nWhen the target structures do not slide freely against \neach other, the test is negative, with a high probability \nof adhesion and underlying DIE. In the anterior com -\npartment, the test was used to determine if the poste -\nrior bladder wall was sliding against the anterior uterine \nwall; in the middle compartment if the ovaries were \nsliding easily against the pelvic side walls. In the pos -\nterior compartment, the test evaluates the mobility \nbetween the posterior uterine wall and the rectosigmoid \ncolon. Site-specific tenderness and pain during the \nmaneuvers can provide invaluable information during \nthe examination, which can be a warning sign for  \nDIE. Examiners should pay careful attention to painful \nareas, particularly in the posterior compartment of the \npelvis20,21. The average duration of the exam is  \n20–30 minutes and depends on the complexity of  \neach case. \nThree-dimensional TVU (3D TVU) can be an  \nadditional tool to investigate endometriosis. The 3D \nreconstruction makes the retractile pattern of bowel and \nbladder lesions more evident 22. Moreover, other tools \nsuch as volume contrast image (VCI) with thin slices \nimproves spacial resolution and orientation by providing \nthe observer with a range of different displays of the \nimages in the three orthogonal planes 23.\nMagnetic resonance imaging\nMRI is a multiplanar imaging modality that allows \nexcellent evaluation of multifocal DIE with a larger field \nof view than that of TVU, providing additional informa -\ntion regarding extrapelvic disease. It is particularly use -\nful for characterization of ovarian cysts, ureteral and \nneural infiltration, pelvic floor extension and diaphrag -\nmatic disease 13,16. MRI is more reproducible and  \nmultiple sequences acquired can be evaluated \nindependently. \nPatient preparation and imaging \ntechnique\nPatient preparation is very important and includes  \n(a) bowel cleansing, (b) a fasting period of at least 4 h, \n(c) medium bladder filling, (d) intravenous administra -\ntion of an antiperistaltic agent (Buscopan: Boehringer \nIngelheim, Germany), (e) vaginal distension with 60 mL \nof gel, and (f) infusion of 150 mL of saline solution into \nthe rectum to obtain a mild distension of the rectosig -\nmoid colon 24. From the author’s experience, bowel \npreparation and rectal distension are two indispensable \ntools to improve imaging. MRI was performed using a \n1.5- or 3.0-T MRI imaging system (Signa, GE Healthcare, \nMiwaukee, WI, USA) and a high-resolution phased \narray coils (8–16 channels). The overall examination \nwas completed in approximately 25–30 min and was \nwell tolerated.\nThe imaging protocol included acquisition of axial, \nsagittal, and coronal T2-weighted fast-spin-echo \nimages; axial T1-weighted gradient-echo images with \nfat suppression; and axial T1-weighted gradient-echo \nimages in and out of phase. Post-contrast images are \nnot mandatory for DIE evaluation but can be used in \ncases of complex ovarian or adnexial cysts, or when \nthe possibility of malignant transformation must be \nruled out 25. Recently, we demonstrated that an abrevi -\nated protocol including a volumetric coronal T2-weighted \nfast-spin-echo sequence and axial T1-weighted  \ngradient-echo sequence with fat suppression had  \nsimilar performance for diagnosing multiple sites of DIE \nwhen compared with the full protocol 26. \nImaging interpretation and description should follow \na standardized approach to enable accurate mapping \nTable 1. Preparation of the intestine for TVU\nPrevious day Examination day\nOral laxative bisacodyl  \n(2 tablets): \n8 am and 2 pm\nMaintenance of a low-residue diet\nLow-residue diet all day Administration of a rectal enema up \nto 1 hour before the examination\nTVU: Transvaginal ultrasound.\n\nL.P . Chamie: Imaging diagnosis of endometriosis\n141\nof the disease. The Society of Abdominal Radiology \n(SAR) Disease Focused Panel (DFP) on endometriosis \nrecently published a consensus lexicon statement for \nreporting MRI findings 27. Similar to the TVU recommen-\ndation, findings should be reported according to the \ncompartments being analyzed (anterior, medium, and \nposterior). With a more comprehensive view compared \nto ultrasound (US), refined anatomical structures are \nincluded in each compartment, such as the entire path \nof the round ligaments, Retzius’ space, and vesicovag -\ninal space in the anterior compartment, the obturator \nfossa and parametrial ureteral path in the middle com -\npartment, and the hypogastric plexus, presacral nerves, \nand lumbosacral plexus in the posterior compartment. \nPelvic floor structures, sciatic nerves, and the abdom -\ninal wall can also be evaluated using MRI. \nImaging findings of endometriosis \nThe imaging findings of endometriosis reflect the  \nhistological components of the lesions characterized by \nthe presence of endometrial-like tissue, smooth muscle \nproliferation, and fibrosis. Lesions can vary from small \nsubperitoneal plaques to large nodules, with irregular \nmargins and infiltrative patterns. On TVU, DIE lesions \nare predominantly hypoechoic compared with the  \nmyometrium19. On MRI, they present markedly low \n signal intensity on T2-weighted images, similar to the \nsmooth muscle, intermediate signal intensity on \nT1-weighted images, and late contrast enhancement on \npost-contrast sequences. Cystic components are com -\nmon, varying from small to large cavities with or without \nhemorrhagic content 28. Bowel lesions demonstrate a \nmarked hypoechoic pattern on TVS and a very low \nsignal intensity on T2-weighted images, reflecting the \npredominance of stromal tissue and fibrosis. \nANTERIOR COMPARTMENT\nBladder\nBladder endometriosis is uncommon and is fre -\nquently preceded by DIE in the vesicouterine space \nand round ligaments. Clinically, patients can present \nwith dysuria, urgency, hematuria, and suprapubic \npain29. It is defined by full-thickness infiltration of the \ndetrusor muscle by a solid nodule of endometriotic tis -\nsue, frequently located in the bladder dome and above \nthe trigonal zone at the midline. On TVU, they are typ -\nically hypoechoic and heterogeneous owing to small \ncystic spaces and hyperechogenic foci ( Figure 1). On \nA\nB\nFigure 1. Bladder endometriosis in 32-year-old woman. A: axial oblique \nand B: sagittal TVU images demonstrating a hypoechoic nodule (arrows) \ncontaining small echogenic foci attached to the posterior bladder dome \ndeeply infiltrating the detrusor muscle. \nB: bladder; TVU: transvaginal ultrasound.\nMRI, they exhibit low signal intensity on T2-weighted \nimages and are associated with hyperintense spots on \nT1-weighted images, with fat saturation representing \nhemorrhagic content ( Figure 2 ). Post-contrast images \ndemonstrated minimal enhancement of solid compo -\nnents. When located in the anterior bladder dome, the \nmain differential diagnoses include a urachal remnant \nand mesenchymal tumors 28. \n\nJ Mex  Fed  Radiol  iMaging . 2022;1(3):138-150\n142\nFigure 2.  Bladder endometriosis in a 33-year-old woman with dysuria and chronic pelvic pain. A: coronal and B: sagittal  \nT2-weighted MRI demonstrating a nodule with low signal intensity and small cystic areas (black arrows) attached to the posterior bladder wall, \ndeeply infiltrating the detrusor muscle. A nodular thickening of the left round ligament is also seen (white arrows), adhered to the bladder nodule.\nMRI: magnetic resonance imaging.\nA B\nTVU performs better than MRI in detecting small \nbladder lesions, usually <1.5 cm, especially because of \nthe dynamic nature of the method, allowing detailed \nevaluation of the bladder wall 17. The corrugated aspect \nof the bladder wall, when partially filled, may impair \nadequate assessment using MRI. Imaging plays a  \ncrucial role in bladder infiltration confirmation and  \nstaging, because the laparoscopic view is restricted to \nthe peritoneal component of the lesions. In addition,  \nit can provide reliable information regarding the  \ninvolvement of the trigonal area and the distance to the \nuretovesical junction.\nVesicouterine peritoneum and  \nround ligaments\nThe vesicouterine space and proximal thirds of the \nround ligaments are the most common locations of DIE \nin the anterior compartment 19. Lesions can vary from \nsmall plaques to large masses that obliterate the  \nanterior cul-the-sac. They frequently display a mixed pat-\ntern due to cystic spaces and small hemorrhagic foci. On \nTVU, they are hypoechoic with anechoic or hypoechoic \ncystic spaces (representing thick content), and frequently \nexhibit small echogenic foci (Figure 3). TVU is the most \nFigure 3.  Endometriosis of the anterior compartment of the pelvis in a 28-year-old woman.  A: sagittal TVU image showing heterogeneous \nhypoechoic tissue (white arrows), with ill-defined margins attached to the uterine wall. B: axial TVU image demonstrating a nodular thickening \n(black arrows) of the proximal third of the right round ligament.\nTVU: transvaginal ultrasound.\nAB\n\nL.P . Chamie: Imaging diagnosis of endometriosis\n143\nAB C\nFigure 4. Ovarian endometrioma in a 25-year-old woman with dysmenorrhea A: TVU image shows an endometrioma with thick content, ground \nglass echogenicity and fluid-fluid level (arrow). B: three-dimensional image from TVU better demonstrating the fluid–fluid level within the cyst \n(arrow). C: TVU with power Doppler US image demonstrating a hyperechoic peripheral nodule (arrow) without internal flow.\nTVU: transvaginal ultrasound; US: ultrasound.\nappropriate choice for detecting tiny plaques attached to \nthe anterior uterine wall and the round ligaments.\nOn MRI, they demonstrate low signal intensity on \nT2-weighted images, intermediate spinal intensity on \nT1-weighted images, and hemorrhagic content within \nthe cystic spaces28. When present, adherence between \nthese lesions and a bladder nodule is common and \nmay be associated with obliteration of the anterior  \ncompartment. Differential diagnosis includes uterine \nleiomyoma, particularly when lesions have a nodular \nconfiguration instead of a plaque. Regular contours, \nnodular shape, and a lack of cystic components favor \nthe possibility of leiomyoma. \nSometimes, these lesions can grow into the myome -\ntrium, deeply infiltrating the muscle in an imaging pat -\ntern that resembles adenomyosis. These patterns are \nconsidered markers for severe endometriosis, with an \nincreased risk of bladder and intestinal lesions 30. \nComplete resection of these lesions can result in uter -\nine wall thinning, which increases the risk of uterine \nrupture during pregnancy 31.\nMIDDLE COMPARTMENT\nOvaries \nOvarian endometriosis primarily manifests as chronic \nretention cysts with cyclical bleeding, called endometrio-\nmas. Although they have been frequently cited as one of \nthe most common sites of endometriosis, prolonged use \nof oral contraceptives among young women has contrib-\nuted to changes in the clinical scenario as they may \nprevent the development and growth of these cysts17. In \ncontrast, the presence of an ovarian endometrioma is \nconsidered a marker of severe endometriosis with an \nincreased risk of intestinal, ureteral, and vaginal lesions32.\nTVU demonstrates high sensitivity (84–100%) and \nspecificity (90–100%) in the diagnosis of endometriomas, \neven for less experienced examiners. They present as \nuni- or multiloculated thick-walled cysts with hypoecho -\ngenic content. Echogenic mural nodules, bright internal \nfoci, and fluid-fluid levels are commonly associated \nfindings33. Color Doppler can be used to demonstrate the \nhypovascular pattern without internal flow and could help \nto identify nodular areas within the cysts ( Figure 4). As \npart of the algorithm, the search for adhesions is man -\ndatory when evaluating ovaries 17. The maneuver con -\nsisted of gentle pushing of the probe combined with \nabdominal palpation with the free hand. When the ova -\nries are medially located and fixed (kissing ovaries), there \nis a high probability of underlying endometriosis 34. \nMRI is the best imaging modality for diagnosing \nendometriomas and differentiating them from functional \nand other cysts, with high specificity (98%) 14. They \nexhibited high signal intensity on T1-weighted images \nand low signal intensity on T2-weighted images (shading \nsign) (Figure 5 ). Shading can vary from a faint signal \nto a complete signal void, representing the old  \nhemorrhagic content of the cysts (due to the high iron \ncontent). Similar to TVU, fluid levels, mural nodules, \nand thick septa were observed. \nWhen reporting endometriomas, important issues \nshould be addressed, such as (a) location within the \novary, peripheral or central, (b) maximum diameter,  \n(c) laterality, (d) distance to the ureteral path, and  \n(e) antral follicle count. \n\nJ Mex  Fed  Radiol  iMaging . 2022;1(3):138-150\n144\nOvarian fossa\nThe peritonium of the ovarian fossa is a common site \nof DIE, especially when there is an endometrioma in the \nperiphery of the ovary. Lesions manifest as plaques or \nnodules with ill-defined margins attached to the ovarian \ncapsule; they appear hypoechoic on TVU, with low signal \nintensity on T2-weighted MRI images. The distance \nbetween the ureteral path and the endo metriotic tissue is \ncrucial for surgical planning and should be provided17. \nUreters\nUreteral endometriosis is uncommon and frequently \npresents as extrinsic involvement of the distal ureters \nby direct extension of a large paracervical lesion  \n(80% of cases) 35. Intrinsic endometriosis, when the \nmuscularis of the ureter is infiltrated, is rare and is \nresponsible for the silent loss of renal function 36. \nThe comprehensive TVU protocol should include \nevaluation of both ureters. In our experience, it is better \nwhen performed at the end of the examination, when \nrenal excretion of the ingested water is ongoing 17. \nSupplemental Video 3 shows the dynamic assessment \nof the left ureteral path with TVU and demonstrates \nureteral peristalsis, distal ureter, and ureterovesical \njunction. US allows evaluation of the ureter from the \nsegment below the iliac vessels to the ureterovesical \njunction. Renal evaluation using a convex transducer \nthrough the abdominal wall can be useful in detecting \nhydronephrosis.\nMRI is considered the best imaging method for \nureteral and pelvic evaluation as a one-stop shot \nprocedure, combining MR-Urography with the con -\nventional pelvic protocol 28. Lesions appear as solid \nnodules with irregular contours that enclose the ure -\nteral path, are hypoechoic on TVU, and have low \nsignal intensity on T2-weighted images. The ureters \ncan be partially or completely involved by the endo -\nmetriotic tissue, which is later associated with \nupstream dilatation. \nPOSTERIOR COMPARTMENT\nRetrocervical and rectovaginal space\nThe retrocervical space is the most common location \nof DIE, and is the site at which endometriosis usually \nbegins5. In decreasing order of frequency, the most \ncommon locations are the proximal third of the utero -\nsacral ligaments and torus uterinus, rectovaginal space, \nposterior vaginal wall, and rectosigmoid colon. The rel -\nevant clinical manifestations include chronic pelvic \npain, dysmenorrhea, and deep dyspareunia. Physical \nexamination can show a thickened uterosacral ligament \nor nodularity in the posterior cul-the-sac; however, in \nmost cases, this is insufficient for adequate diagnosis \nand staging of the multiple sites affected 37.\nRetrocervical lesions can vary from small subperito -\nneal plaques to large nodules with irregular contours \n(Figure 6). They can be uni- or bilateral, display a mixed \ntexture due to cystic areas, and show an inferior exten -\nsion to the rectovaginal space, below the peritoneal \nreflection, and into the posterior vaginal fornix 28. \nSupplemental Video 4 shows the dynamic assessment \nof the retrocervical space with TVU and demonstrates a \nA B\nFigure 5.  Endometrioma in a 29-year-old infertile woman. A: axial T2-weighted MRI demonstrating a cyst (arrows) with the shading sign \nrepresenting old hemorrhagic content. B: axial T1-weighted fat-saturated MRI demonstrates hyperintense signal intensity (light bulb bright \nsign) characteristic of endometriomas (arrows).\nMRI: magnetic resonance imaging.\n\nL.P . Chamie: Imaging diagnosis of endometriosis\n145\nA\n B\n C\nFigure 6. Different examples of retrocervical endometriosis. A: axial TVU after bowel preparation of a 33-year-old woman with deep dyspa -\nreunia demonstrating hypoechoic subperitoneal plaque affecting the retrocervical space (arrows). B: axial oblique TVU after bowel prepa -\nration in a 36-year-old infertile woman reveals a hypoechoic nodule compromising the ligament insertion (arrow). C: axial oblique TVU after \nbowel preparation of a 38-year-old woman with dysmenorrhea and deep dyspareunia, demonstrating a hypoechoic nodule with irregular \nmargins located in the right insertion of the USL (dotted circle). \nTVU: transvaginal ultrasound. USL: uterosacral ligament.\nhypoechoic nodule in the proximal third of the right utero-\nsacral ligament. Another common presentation is lateral \nextension of the parametrium. A comprehensive descrip-\ntion of these lesions is mandatory, including the two \nlargest dimensions of a nodule and the thickness of an \nabnormal uterosacral ligament in the oblique axial plane. \nIn large retrocervical nodules, proximity to the hypogas -\ntric plexus and ureteral path should be addressed, as well \nas extension to the pelvic floor and presacral nerves 20. \nIn TVU, they are fundamentally hypoechoic and may \ncontain small cystic areas and punctate hyperechoic \nfoci. On MRI, they show a low signal intensity on \nT2-weighted images. Cystic areas can contain simple \nfluid or hemorrhagic content with a high signal intensity \non T1-weighted fat-saturated images. Another possible \npattern of presentation is when the endometriotic tissue \ndeeply infiltrates the posterior uterine wall from the \noutside-in, which is frequently associated with uterine \nretractile retroflexion. It is considered a marker for \nsevere endometriosis with an increased risk of intesti -\nnal and vaginal lesions and severe adhesions 38. \nVagina\nIsolated vaginal lesions are rare. Vaginal endometri -\nosis is almost always an inferior extension of a retro -\ncervical lesion, with the posterior vaginal wall being the \nmost affected area. They show a mixed pattern owing \nto the presence of rich glandular components that fre -\nquently contain hemorrhagic content 28. Large nodules \ncan protrude into the posterior fornix as polypoid \nmasses. Deep dyspareunia is the most common clini -\ncal presentation.\nOn TVU, careful examination of the posterior vaginal \nwall may reveal asymmetric homogeneous or \nheterogeneous thickening and extension to the retro -\ncervical tissue. MRI is highly specific for vaginal endo -\nmetriosis, particularly when hemorrhagic cysts are \npresent. Vaginal distension with US gel is useful for \ndisplaying fornix obliteration of asymmetric thickening \nof the vaginal wall ( Figure 7).\nRectosigmoid colon\nIntestinal endometriosis is among the most aggres -\nsive of diseases and is present when the endometriotic \ntissue deeply infiltrates the bowel wall beyond the mus -\ncular layer from outside-in 39. The mucosa is rarely \naffected. The rectosigmoid colon is the most affected \nsite, followed by the appendix, ileum and cecum. \nSymptoms are nonspecific and can include abdominal \ndistension, chronic constipation, diarrhea, and, rarely, \nhematochezia. Bowel endometriosis can be multifocal \nwhen multiple lesions are detected in the same seg -\nment or multicentric when different bowel segments are \ncompromised40. \nTVU after bowel preparation is an excellent tool for \ninvestigating bowel endometriosis, allowing compre -\nhensive evaluation of the rectosigmoid colon from the \nanal verge to the descending colon 18. Other bowel \nloops, such as the ileocecal region and appendix, can \nbe accurately evaluated using transvaginal and trans -\nabdominal approaches. The main advantage of US \nover MRI is the dynamic nature of the method, enabling \ncareful examination of the bowel loops in both the \naxial and sagittal planes. Supplementary video 5 \nshows the dynamic assessment of the rectosigmoid \ncolon by TVU after bowel preparation and shows two \nadjacent bowel lesions at the level of the peritoneal \nreflexion. Bimanual examination is mandatory during \n\nJ Mex  Fed  Radiol  iMaging . 2022;1(3):138-150\n146\nbowel inspection to stretch the bowel loops and avoid \nfolds and peristaltic artifacts. The sliding sign maneu -\nver is also crucial to identify obliteration in the pouch \nof Douglas and must be included in the algorithm 18. \nMRI can also accurately detect bowel lesions, but \nthis method is certainly more susceptible to artifacts. \nIn our experience, the combination of bowel prepara -\ntion, fasting, antiperistaltic agent, and saline distension \nof the rectosigmoid colon can improve the sensitivity \nof the method, particularly for small lesions (< 1.5 cm). \nImaging should provide the size of the lesions in three \ndimensions: circumference of the bowel involved, \naffected bowel layers, distance to the anal border, \nand distance between different nodules. Surgical \nmanagement differs among shaving (tiny to small \nnodules), discoid resection (nodules < 3 cm), and \nsegmental resection (nodules > 3 cm). \nBowel lesions appeared as homogeneous hypoechoic \nnodules on TVU, with markedly low signal intensity on \nT2-weighted images, attached to the bowel wall, and \ndeeply infiltrating the bowel from outside-in ( Figures 8 \nand 9). They rarely contained cystic areas or invaded \nmucosal layers. When the submucosa is infiltrated, a \nstriated aspect can be observed ( Figure 10)28. \nRight iliac fossa\nThe right iliac fossa (cecum, ileum, and appendix) \ncan be compromised by endometriosis in \napproximately 28% of cases in which rectosigmoid dis -\nease is present. Appendiceal endometriosis is uncom -\nmon and is an incidental finding in patients with \nmultifocal DIE. It can be associated with mucocele or \nintussusception of the cecal base 28. US is better than \nMRI in detecting small ileal nodules or subtle lesions \naffecting the tip of the appendix. The transabdominal \napproach with a linear transducer is recommended as \nan additional component of the TVU algorithm. Lesions \ndemonstrate the same aspect as the rectosigmoid nod -\nules, hypoechoic on TVU, and with low signal intensity \non T2-weighted images ( Figure 11). The main differen -\ntial diagnosis for appendiceal endometriosis is carci -\nnoid tumor, and histopathological analysis is required \nbecause the image cannot rule out malignancy 41. \nDiaphragm\nThe diaphragm is the most common location of \nthoracic endometriosis and clinically manifests as \ncatamenial shoulder pain and right-sided sponta -\nneous pneumothorax. Approximately 91.7% affect \nthe right chest, and up to 85% of the cases are asso -\nciated with severe pelvic endometriosis. MRI is the \nmethod of choice for demonstrating plaques or nod -\nules with high signal intensity on fat-suppressed \nT1-weighted sequences, representing hemorrhagic \ncontent 42.\nA B C\nC\nFigure 7.  Endometriosis of the posterior compartment of the pelvis in a 41-year-old-woman with severe dyspareunia. A: axial T2-weighted \nMRI showing mixed thickening compromising the posterior vaginal wall associated with partial obliteration of the posterior vaginal fornix \n(white arrows). B and C: there is also thickening of the right uterosacral ligament insertion (thin black arrow) and anterior rectal wall (thin \nwhite arrow). Note that vaginal distension with US gel (asterisk) in sagittal and coronal T2-weighted MRI better demonstrates the vaginal \nlumen and the nodular vaginal thickening (arrows). \nMRI: magnetic resonance imaging; US: ultrasound.\n\nL.P . Chamie: Imaging diagnosis of endometriosis\n147\nA B\nFigure 9. Rectal endometriosis in a 37-year-old woman with pelvic pain and dyschesia.  A: sagittal. B: coronal. T2-weighted MRI demonstrating \na nodule with low signal intensity attached to the anterior rectal wall and deeply infiltrating the muscularis propria from outside-in (arrows). \nMRI: magnetic resonance imaging.\nA\n B\nFigure 8. Intestinal endometriosis. A: sagittal and B: axial TVU after bowel preparation of a 31-year-old woman demonstrating a hypoechoic \nnodule attached to the bowel wall and deeply infiltrating the muscularis propria from outside-in (arrows). The submucosa (asterisk) is \npreserved. \nTVU: transvaginal ultrasound.\nIn our experience, transabdominal US evaluation \nusing a convex transducer through the right subcostal \narea may demonstrate findings suggestive of endome -\ntriotic implants. The findings can range from \nheterogeneous hyperechoic plaques associated with \ncystic areas to multiple cystic areas with predominant \nanechoic content attached to the right diaphragmatic \nsurface ( Figure 12). \n\nJ Mex  Fed  Radiol  iMaging . 2022;1(3):138-150\n148\nAB\nFigure 11. Endometriosis of the right iliac fossa in an asymptomatic 43-year-old woman. A: axial TVU image after bowel preparation demons -\ntrating a large hypoechoic nodule deeply infiltrating the cecal base (arrows). B: sagittal TVU image after bowel preparation demonstrating a \nnodular hypoechoic thickening of the distal third of the appendix (arrow).\nTVU: transvaginal ultrasound.\nFigure 10.  Sigmoid colon endometriosis in a 39-year-old woman. Sagittal TVU image after bowel preparation shows a hypoechoic nodule \ninfiltrating the muscularis propria and the submucosa, the latter demonstrated by the striated pattern (arrows).\nTVU: transvaginal ultrasound.\nStructured report\nImaging diagnosis of endometriosis should include \na standardized report to improve communication with \nreferring physicians and patients, as well as to ensure \nuniform interpretation and documentation among \nradiologists. It must follow the appropriate anatomical \nterminology and updated lexicon for endometriosis \nreports, including all potential sites affected. Schematic \ndrawings or sketches pointing to the exact location of \nDIE implants can add value to the report, providing a \nroadmap for surgeons during the procedure 43. \n\nL.P . Chamie: Imaging diagnosis of endometriosis\n149\nCONCLUSION\nThe diagnosis of endometriosis remains a clinical \nchallenge and may take up to 12 years until definitive \ndetection. Imaging has altered the clinical scenario, \nreplacing diagnostic laparoscopy and acting as an \ninvaluable tool for patient counseling and surgical plan -\nning. A dedicated TVU protocol is the first-line imaging \nmodality for diagnosis and staging of DIE. US is the most \nappropriate method for evaluating bowel endometriosis \nand small peritoneal implants. MRI is very useful for \nmultiple-site evaluation and has an advantage for ovar -\nian, ureter, diaphragm, pelvic floor, and pelvic nerve \nevaluation. Early diagnosis can avoid long-term sequelae, \nand accurate preoperative staging can optimize surgical \nmanagement and complete eradication of DIE implants. \nFunding \nThe research received no funding from agencies in \nthe public, commercial, or not-for-profit sectors are \navailable in this article.\nConflicts of interest\nThere are no conflicts of interest to declare.\nEthical disclosures\nProtection of individuals.  This study was con -\nducted in compliance with the Declaration of Helsinki \n(1964) and its subsequent amendments.\nConfidentiality of data.  The author declare that no \npatient data are available in this article. \nRight to privacy and informed consent. The author \ndeclares that there are no ethical responsibilities, since \nhandling human beings’ confidential information was \nnot necessary.\nREFERENCES\n 1. Giudice LC, Kao LC. Endometriosis. Lancet. 2004:13-19;364(9447):  \n1789-1799. doi: 10.1016/S0140-6736(04)17403-5.\n 2. Taylor HS, Kotlyar AM, Flores VA. Endometriosis is a chronic systemic  \ndisease: clinical challenges and novel innovations. Lancet. \n2021:27;397(10276):839-852. doi: 10.1016/S0140-6736(21)00389-5.\n 3. Bulun SE. Endometriosis. N Engl J Med. 2009:15;360(3):268-279. doi: \n10.1056/NEJMra0804690.\n 4. Fauconnier A, Fritel X, Chapron C. Relations entre endométriose et  \nalgie pelvienne chronique: quel est le niveau de preuve? 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