{"paper_id":"d0c31327-643c-486c-af63-a73b4827252d","body_text":"Ruaux et al. Insights into Imaging           (2024) 15:19  \nhttps://doi.org/10.1186/s13244-023-01587-3\nEDUCATIONAL REVIEW Open Access\n© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which \npermits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the \noriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or \nother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line \nto the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory \nregulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this \nlicence, visit http://creativecommons.org/licenses/by/4.0/.\nEndometriosis MR mimickers: \nT1-hyperintense lesions\nEdouard Ruaux1, Stéphanie Nougaret2, Marie Gavrel3, Mathilde Charlot3, Mojgan Devouassoux‑Shisheboran4, \nFrançois Golfier5, Isabelle Thomassin‑Naggara6 and Pascal Rousset1*   \nAbstract \nEndometriosis is a chronic and disabling gynecological disease that affects women of reproductive age. Magnetic res‑\nonance imaging (MRI) is considered the cornerstone radiological technique for both the diagnosis and management \nof endometriosis. While MRI offers higher sensitivity compared to ultrasonography, it is prone to false‑positive results, \nleading to decreased specificity. False‑positive findings can arise from various T1‑hyperintense conditions on fat‑sup‑\npressed T1‑weighted images, resembling endometriotic cystic lesions in different anatomical compartments. These \nconditions include hemorrhage, hyperproteic content, MRI artifacts, feces, or melanin. Such false positives can have \nsignificant implications for patient care, ranging from incorrect diagnoses to unnecessary medical or surgical inter‑\nventions and subsequent follow‑up. To address these challenges, this educational review aims to provide radiologists \nwith comprehensive knowledge about MRI criteria, potential pitfalls, and differential diagnoses, ultimately reducing \nfalse‑positive results related to T1‑hyperintense abnormalities.\nCritical relevance statement\nMRI has a 10% false‑positive rate, leading to misdiagnosis. T1‑hyperintense lesions, observed in the three phenotypes \nof pelvic endometriosis, can also be seen in various other causes, mainly caused by hemorrhages, high protein con‑\ncentrations, and artifacts.\nKey points\n• MRI in endometriosis has a 10% false‑positive rate, leading to potential misdiagnosis.\n• Pelvic endometriosis lesions can exhibit T1‑hyperintensity across their three phenotypes.\n• A definitive diagnosis of a T1‑hyperintense endometriotic lesion is crucial for patient management.\n• Hemorrhages, high protein concentrations, lipids, and artifacts are the main sources of T1‑hyperintense mimickers.\nKeywords Endometriosis, Deep infiltrative endometriosis, Ovarian cysts, Functional hemorrhagic cysts, Magnetic \nresonance imaging\n*Correspondence:\nPascal Rousset\npascal.rousset@chu‑lyon.fr\nFull list of author information is available at the end of the article\n\nPage 2 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \nGraphical Abstract\nBackground\nPelvic endometriosis is a chronic inflammatory disease \ndefined by the presence of endometrial-like tissue out -\nside the uterine cavity. It is estimated to affect 5 to 10% \nof women of reproductive age [1]. Common symptoms \nexperienced by patients with endometriosis include \nchronic pelvic pain, dysmenorrhea, dyspareunia, dysche -\nzia, dysuria, and infertility, depending on the anatomic \nlocation and degree of infiltration, which can greatly \naffect quality of life [2]. Endometriosis is divided into \nthree clinical phenotypes that can coexist: ovarian cysts \nthat known as endometriomas, superficial peritoneal \nendometriotic implants, and deep infiltrative endome -\ntriosis (DIE) [3]. Hemorrhagic changes are commonly \nobserved in all these phenotypes. Endometriomas occur \nwhen ectopic endometrial-like tissue implants invaginate \ninto the ovarian parenchyma, leading to cyclical bleed -\ning in response to hormonal stimulation and resulting \nin hemorrhagic ovarian cysts. This is the most prevalent \nform of endometriosis observed in magnetic resonance \nimaging (MRI) [4]. Superficial endometriotic implants \nare rarely visible on imaging. Therefore, they can be iden-\ntified based on their microcystic and/or hemorrhagic \nnature. DIE is defined as the extension of endometrial-\nlike tissue beneath the peritoneal surface, with the ability \nto invade surrounding structures. It is associated with \nfibrosis, hemorrhagic changes, and disruption of normal \nanatomical structures.\nThis disease represents a public health issue [5], \nimpacting patients’ quality of life. Thus, the importance \nof accurate and early diagnosis must be emphasized. \nTransvaginal ultrasound is the first-line imaging modality \nfor initial evaluation and management [6]. However, MRI \nhas the highest accuracy, which aids in accurate diagno -\nsis, and provides a detailed mapping of the extent and \nseverity of the disease. The more detailed information \nobtained from MRI results improves the quality of care \ngynecologists can provide when considering medical and \nsurgical management with patients [7]. The overall sen -\nsitivity of MRI in diagnosing endometriosis is estimated \nat 94% [8]; however, the specificity is slightly lower, lead -\ning to a 10% false-positive rate [9]. This limitation under -\nscores the importance of educating radiologists about \npotential causes of inaccurate MRI results. In the dedi -\ncated recommended MRI protocol [10], fat-suppressed \nT1-weighted images (WI) is a pivotal sequence that \nallows for the detection of cystic endometriotic hemor -\nrhagic component, whatever the phenotype of lesion \n[10]. However, various degrees of T1-hyperintense cystic \nlesions may be observed within the pelvis due to other \n\nPage 3 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \nphysical entities, such as hemorrhage from other causes, \nhigh concentrations of proteins, lipids, melanin, feces, or \nartifacts. These sources of false positives can significantly \nimpact patient management. Misdiagnosing endome -\ntriosis during the initial diagnosis, or even in the event \nof incidental discovery on pelvic MRI can lead to inap -\npropriate medical treatment up to unnecessary surgery \nand severe psychological consequences for the patient. In \ncases of confirmed pelvic endometriosis, mistaking other \nT1-hyperintense findings for endometriosis may overes -\ntimate the extent and the severity of the disease leading \nto inappropriate decision-making choice between medi -\ncal and surgical treatments.\nThus, the aim of this review is to provide guidance \nto radiologists so that they may better differentiate \nT1-hyperintense endometriotic lesions from other pel -\nvic lesions and imaging artifacts. We will highlight the \nimportance of multi-sequence reading, morphological \nanalysis, and accurate anatomical localization, as these \nfactors can enhance diagnostic accuracy and improve \npatient care.\nT1‑hyperintense typical features of pelvic \nendometriosis\nEndometriomas appear as cystic ovarian structures (> \n10 mm) containing degenerated blood from repeated \ncyclic hemorrhage, resulting in T1-hyperintensity due \nto methemoglobin, that markedly shorten the T1 of flu -\nids [11]. Further, low T2 signal intensity, also known as \nshading, is observed due to iron overload, high protein \nconcentrations, and high viscosity due repeated bleed -\ning and degradation of old blood products [12]. Both a \nhypointense peripheral ring from hemosiderin stain -\ning and a clot-induced T2-dark spot adjacent to the \ncyst can be seen [13]. In rare cases (< 5%), endometrio -\nmas may appear T2-hyperintense, depending on protein \nand hemosiderin concentrations as well as the patient’s \nage [14]. Endometriomas typically have thin walls with \ninconsistent, absent, or low wall enhancement [15]. The \novarian-adnexal reporting and data system on magnetic \nresonance imaging (O-RADS MRI) score has entered \nclinical practice in terms of reporting ovarian lesions \nand indicating the possibility of malignancy [16]. Endo -\nmetriomas are rated O-RADS MRI 2 (almost certainly \nbenign) [17]. Adhesions to the surrounding anatomical \nstructures, additional ovarian endometriotic implants \n(≤ 5 mm) or micro-ovarian endometriomas (< 10 mm), \nand bilateral endometriomas with multiplicity are also \nstrongly suggestive of endometriosis, sometimes leading \nto a “kissing-ovaries” sign (Supplemental - Figure 1) [18]. \nDIE can affect almost any organ or structure, although \nmost lesions are found in the pelvic cavity, particularly \nin the posterior compartment. DIE consists of lesions \ncomprised of glandular, stromal, and fibrotic tissue [19], \nreadily identifiable on MRI as T2-hypointense fibrotic \nlesions. Such lesions often contain microcystic changes, \nwith variations in the number of T2-hyperintense and \nT1-hyperintense hemorrhagic foci dependent on ectopic \nglandular tissue activity. Superficial endometriotic \nimplants are histologically defined as peritoneal implants \nand commonly described at surgery as bluish or clear red \nlesions during surgery due to hemosiderin deposition or \nacute hemorrhage [20]. However, due to their small size \nand/or low thickness, they may not be identifiable on \nMRI, resulting in false negatives. Despite the above, when \nlarge enough, they are well depicted as T1-hyperintense \nfoci along the peritoneal layer or pelvic organ surface, \nand they may sometimes be the sole finding for the radi -\nologist to suspect endometriosis [21].\nT1‑hyperintense differential diagnosis and pitfalls \nfor pelvic endometriosis\nVarious physical entities can lead to different degrees \nof T1-hyperintense cystic lesions in the pelvis (Table  1). \nHemorrhages, high protein concentrations, lipids, and \nartifacts are the four primary causes of high T1-weighted \n(T1-W) signal intensity in various disease conditions. Of \nnote, the systematic use of a fat-suppressed T1-weighted \nimaging (T1-WI) in pelvic MRI protocols is crucial to \nrule out differential diagnosis of fat-containing lesions \n[10].\nHemorrhagic T1‑hyperintense cyst\nThe MRI signal characteristics of a hemorrhagic lesion \nlargely depend on the age of the hemorrhage. The pres -\nence of intracellular and extracellular methemoglobin \nwithin the lesion creates a paramagnetic effect that \naffects T1 relaxation times. This effect leads to a shorten-\ning of T1 relaxation times, resulting in high signal inten -\nsity on MRI. The degree of T1-shortening is influenced \nby the duration of the hemorrhage, ranging from 3 days \nto several months.\nAdnexa\nFunctional hemorrhagic cysts Differentiating endo -\nmetriomas from hemorrhagic cysts (O-RADS MRI 1) \ncan be challenging. Both can appear as solitary, uni -\nlocular T1-hyperintense cysts with smooth linings. \nHowever, hemorrhagic cysts often show a T1-hyper -\nintense rim due to peripheral oxidation of an acute \nhematoma (deoxyhemoglobin) [22]. Hemorrhagic \ncysts also exhibit heterogeneous and mild signal loss \non T2-WI, with possible shading but lacking a T2-dark \nspot [13]. Contrast-enhanced imaging reveals enhance -\nment of the cyst wall, forming a “ring sign” (better seen \n\nPage 4 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \non post-contrast-enhanced subtracted T1-W images) \n[22]. Additionally, analyzing internal enhancement after \ncontrast administration can help differentiate a clot \n(non-enhanced solid component) from a mural nod -\nule (enhanced solid tissue) (Fig.  1). While diffusion-\nWI (DWI) is not recommended but optional in ESUR \nguidelines, some studies suggest that endometriomas \nhave lower apparent diffusion coefficient values on DWI \n(around 1 ± 0.1 ×  10−3  mm2) compared to other cystic \novarian lesions, including functional hemorrhagic cysts \n[23, 24]. In our experience, DWI can show a hyperintense \nrim, known as the “DWI-ring sign” favoring a hemor -\nrhagic cyst. Lastly, ultrasound follow-up after a few men -\nstrual cycles allows for definitive diagnosis, as hemor -\nrhagic cysts tend to completely or partially resolve, while \nendometriomas persist [25].\nA diagnostic dilemma may arise in the case of a single \nand isolated micro-endometrioma (< 10 mm) or ovarian \nendometriotic implant (≤ 5 mm), in which differentiation \nTable 1 T1‑hyperintense mimickers: MRI key features\nNature of the \nT1‑hyperintensity\nStructure involved\nType of condition\nMRI key features\nHemorrhagic Adnexa\nFunctional hemorrhagic cyst T1‑hyperintense rim, « ring sign » enhancement, variable signal intensity on T2‑WI, resolution \non 8–12 weeks imaging follow‑up on ultrasonography\nOvarian ischemic necrosis Enlarged medially displaced ovary in case of adnexal torsion, T1‑hyperintense rim, T2 hetero‑\ngeneous signal intensity, no enhancement of the ovary +/− fallopian tube\nEctopic pregnancy Unilateral hematosalpinx, T2‑hypointense tubal debris or fetal pole , hemoperitoneum, con‑\ntrast enhancement of the adnexa\nACUM Extra‑ovarian topography within the uterus or the broad ligament, thick peripheral ring \nof muscular tissue in low signal intensity on T2‑WI and with low enhancement, central \nround cavity with hematometra (+/− T2‑ shading)\nHyperproteic Adnexa\nEpithelial cystic tumors Unilateral and unilocular thin‑walled fluid‑filled cyst, no shading T2‑WI, papillary projections\nParatubal serous cyst Extra‑ovarian with negative beak sign, no shading T2‑WI, papillary projections\nHydrosalpinx (chronic) Serpentine structure, low to mild wall enhancement\nTubo-ovarian abscess (chronic) Thickened wall, hyperintense rim on T1 FS ‑WI, heterogeneous signal intensity on T2‑WI, \nmoderate to sustained wall enhancement\nVulva and vagina\nEpithelial inclusion cyst Location within the wall or vaginal cuff depending on prior surgery or vaginal procedure, \nsingle cystic lesion, hypointense perilesional scar tissue on T2‑WI in case of episiotomy\nGartner’s duct cyst Preferential location within the anterolateral wall, single thin‑walled and well‑defined cystic \nlesion, possible association with renal abnormalities\nBartholin’s gland cyst Posterolateral surface of the vestibule, can be bilateral with symmetric location\nSkene’s gland cyst Along the posterior course of distal urethra, small unilocular cyst\nUrachus\nUrachal insertion cyst Small to middle‑sized single cyst at the exact insertion of urachus, thin wall, mostly hyperin‑\ntense on T2‑WI, no fibromuscular component\nPeritoneum\nMulticystic peritoneal mesothelioma Multicystic grape‑like lesions with some loculi in high signal intensity on T1 FS ‑WI, \nwith no fibrous tissue, often with multi‑focal peritoneal involvement\nRetroperitoneal\nTailgut cyst Uni‑ or multilocular retrorectal cyst, variable size (mostly small) along anococcygeal raphe\nArtifacts Vessels\nVascular Flow-Related Enhancement Any highcirculating vessels, linear or serpiginous structures on other sequences or MPR 3D \nT2‑WI, flow‑voids on T2‑WI, disappearance using spatial saturation bands\nVascular ghosts Illiac vessels with ghosting in the direction of phase‑encoding, not seen on other sequences\nCalcification (phlebolith) Endoveinous location (mostly parametrium and paravagina), tiny round low  signal intensity \non T2‑WI, calcium hyperdensity on CT\nFeces Appendix / Sigmoid diverticula Endoluminal digestive connection or location on other sequences or MPR 3D T2‑WI\nMelanin Vulva and vagina Variable signal intensity on T2‑WI, solid component enhancement on contrast‑enhanced \nsubtracted MR images\n\nPage 5 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \nwith an involuting functional cyst on MRI is limited, and \nits visualization or characterization on ultrasound almost \nimpossible. The use of gadolinium injection could be lim-\nited as peripheral ring enhancement may not be visible in \nsmall hemorrhagic cysts due to their small size or resolu -\ntion. Therefore, uncertain diagnosis should be considered \nto avoid systematic false-positive diagnosis of endome -\ntriosis. Depending on the level of clinical suspicion and \navailable treatment options, follow-up with MRI may aid \nin obtaining a definitive diagnosis.\nAnother pitfall is the presence of bilateral hemorrhagic \ncysts after controlled ovarian stimulation and follicular \npuncture, as many patients undergoing in vitro fertiliza -\ntion procedures are diagnosed with pelvic endometriosis, \nincluding endometriomas [26]. In this scenario, the clini -\ncal context and surgical report specifying the side of and \nthe timeframe since the surgical puncture are relevant for \naccurate diagnosis. Post-procedure hematomas usually \npresent as bilateral and multiple hemorrhagic ovarian \ncysts, with moderate to high signal intensity on T1-WI, \ngenerally not exceeding 1 cm in diameter (Supplemen -\ntal - Figure  2). Distinguishing between prior bilateral \nmicro-endometriomas and post-procedure hematomas \ncan be challenging. Depending on clinical impact, follow-\nup MRI performed after 8–12 weeks remains the optimal \napproach, as complete or partial resolution of hemor -\nrhagic cysts can assist in the differential diagnosis.\nOvarian ischemic necrosis Adnexal torsion is defined \nby the twisting of the ovary and fallopian tube, caus -\ning vascular compromise and tissue damage, with vary -\ning degrees of ischemia, hemorrhagic infarction, and/or \nnecrosis. It is commonly associated with a benign lesion \nin 80% of cases [27], but spontaneous torsion can occur \nwithout a predisposing mass, resembling endometrio -\nmas. The clinical manifestation of adnexal torsion can \nbe variable, with acute lower abdominal pain associated \nwith nausea, and vomiting. Chronic pelvic pain due to \nan unnoticed permanent torsion (Fig.  2) may also occur \nand be misleading. In this context, MRI is less often the \nfirst-line imaging technique since adnexal torsion diag -\nnosis is rarely problematic, as the condition is usually \nevident based on clinical and other imaging findings \nsuch as massive ovarian enlargement, thickened twisted \nFig. 1 Functional hemorrhagic ovarian cyst in a 28‑year‑old woman with dysmenorrhea and acute pelvic pain at the time of MRI, and no medical \nhistory. a Axial T1‑W fat‑suppressed MR image shows a T1‑hyperintense left hemorrhagic ovarian cyst (arrow). b Axial T2‑W MR image shows \na heterogeneous cyst (arrow) with upper hypointense lace‑like reticular areas (arrowhead) and lower fluid‑fluid level (star) with T2 shading. c Axial \nT1‑W contrast‑enhanced subtracted MR image shows homogeneous hyperintense rim wall enhancement (arrow). d Axial diffusion‑weighted MR \nimage shows an equivalent hyperintense “DWI‑ring sign” (arrowheads) compared to c \n\nPage 6 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \npedicle, hemorrhage in the stroma, abnormal displace -\nment of the involved ovary and the uterus, and pelvic \nascites [28]. Severe ischemic necrosis of the ovary may \nresult in minimal or absent enhancement. However, the \npresence of T1-hyperintense signal after fat suppres -\nsion is predictive of hemorrhagic infarction, which typi -\ncally appears as a T1-hyperintense rim and may appear \nsimilar to a hemorrhagic cyst. Lastly, in rare cases of iso -\nlated tubal torsion, a thickened and dilated T1-hyperin -\ntense fallopian tube may show hemorrhage and lack of \npost-contrast enhancement [29]. It is worth highlight -\ning that the O-RADS MRI score may not be applicable \nin certain acute scenarios where the signal is modified \nindependently of the nature of the mass, like cases involv-\ning adnexal torsion or ectopic pregnancy.\nEctopic pregnancy Tubal ectopic pregnancy (with or \nwithout a viable gestational sac) can cause nonspecific \nsubacute pelvic pain, leading to diagnostic challenges if \na pregnancy test is not performed prior to MRI. Differ -\nentiating between endometriosis with a single hematosal-\npinx presentation and ectopic pregnancy is important, \ngiven that tubal ectopic pregnancies frequently appear as \na unilateral hematosalpinx (Fig.  3) [30]. A saclike cystic \ntubal structure with a thick wall may be absent; how -\never, its presence should be checked [31]. Hemoperito -\nneum suggests rupture, supporting the possibility of an \nFig. 2 Ovarian severe ischemic necrosis, explored 1 month after presumed acute pelvic infection, in a 47‑year‑old woman. a Axial T1‑W \nfat‑suppressed MR image shows a T1‑hyperintense left ovary (star) with a peripheral hyperintense rim (arrowheads), consistent with hemorrhage. \nA hemorrhagic follicle of the external cortex of the left ovary is identified (arrow). b Axial T2‑W MR image shows enlarged centrally migrated left \novary (star) with peripheral hypointense rim (arrowheads). c Coronal T2‑W MR image shows a pedicle twist (arrow). d Axial T1‑W contrast‑enhanced \nsubtracted MR image shows complete absence of enhancement in the left ischemic ovary\n\nPage 7 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \nectopic pregnancy. A T2-hyperintense solid component \nindicates the presence of trophoblastic tissue in ectopic \npregnancy, aiding in differential diagnosis. Contrast-\nenhanced T1-WI can help detect the gestational sac and \na strong wall enhancement encountered in tubal ectopic \npregnancy. Of note, caution should be exercised when \nadministering contrast agents if pregnancy is suspected. \nThe absence of other MRI pelvic endometriotic features \nshould also be in favor of an ectopic pregnancy. However, \na recent metanalysis of 15 studies found that endome -\ntriosis is a possible risk factor for ectopic pregnancies, \nand therefore could be present in the case of an ectopic \npregnancy [32]. In these cases, clinical context and a \nbeta-HCG blood test should be performed to aid in the \ndiagnosis.\nAccessory cavitated uterine mass\nAccessory cavitated uterine mass (ACUM) is a rare but \nunderdiagnosed condition, mostly seen in young patients \n(< 30 years) presenting severe dysmenorrhea and chronic \npelvic pain [33]. This congenital anomaly of the female \ngenital tract, most likely due to gubernaculum dys -\nfunction, consists of an isolated cavitated round mass, \nsituated in close proximity to the insertion point of the \nuterine round ligament, and lined by a functional endo -\nmetrium [34]. ACUM could be defined on MRI as a func-\ntioning and non-communicating accessory horn located \nin the external myometrium or the broad ligament of an \notherwise normal uterus [35]. The broad ligament pres -\nentation is less common but can be misdiagnosed as an \nendometrioma when it is close to the ovary. ACUM dif -\nfers from endometrioma by its extra-ovarian location, \nand its specific MRI features, including a central round \ncavitated mass filled with hematometra (high signal \nintensity on T1-WI and shading effect or fluid-fluid level \non T2-WI), and a well-defined thick T1- and T2-hypoin -\ntense peripheral ring of muscular tissue resembling the \njunctional zone (inner myometrium) with low enhance -\nment if contrasts agents are used (Supplemental - Fig -\nure 3) [35]. Laparoscopic surgery is the primary option, \naiming to preserve fertility and relieve symptoms, allow -\ning for histological diagnosis [35]. Hormone-suppressive \ntherapy may also be considered, often leading to the reso-\nlution of central hemorrhagic hypersignal on follow-up \nMRI.\nHyperproteic T1‑hyperintense cyst\nProtein-containing lesions may exhibit a T1-hyperin -\ntense signal on fat-suppressed T1-WI, depending on \nthe amount of free water and viscosity within the lesion, \nresulting in shortening of T1 relaxation times [36]. The \nT2 signal is typically sensitive to variations in tissue water \ncontent but may be less sensitive and require significant \ndehydration for the signal to decrease [37]. Small lesions \nwith protein content tend to dehydrate faster, resulting in \nan increase in their T1 signal and a relative decrease in \ntheir T2 signal.\nAdnexal lesions\nChronic pelvic inflammatory disease Pelvic inflamma -\ntory disease is the most common cause of tubal occlu -\nsion and hydrosalpinx [38]. It is one of the most frequent \ngynecologic causes of emergency department visits. Pel -\nvic inflammatory disease is usually caused by an infec -\ntion ascending from the lower genital tract [39]. In acute \ncases, an MRI is not necessary for symptomatic women. \nHowever, the symptoms are often mild and nonspe -\ncific (fever and increased white blood cell count may be \nabsent) [40], making it challenging for clinicians to reach \nthe correct diagnosis, particularly in chronic cases. In \nFig. 3 Ectopic tubal pregnancy with early tubo‑ovarian abortion in a 39‑year‑old woman with subacute abdominal pain, and no medical history. \na Axial T1‑W fat‑suppressed and (b) axial T2‑W MR images show a left hemorrhagic cyst (thick arrows) corresponding to a hemorrhagic corpus \nluteum cyst of pregnancy, and an associated hematosalpinx (thin arrows). c Axial T1‑weighted fat‑suppressed contrast‑enhanced subtracted MR \nimage shows a significant enhancement of the fallopian tube wall (thin arrows), as well as the hemorrhagic corpus luteum cyst (thick arrow). Tubal \npregnancy was confirmed after MRI exam with a positive HCG blood test\n\nPage 8 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \nsuch situations, a hydrosalpinx develops as a result of \nadhesions and scarring, and it may appear as a dilated \nfallopian tube folding upon itself, forming a sausage-like \nC- or S-shaped cystic mass [41]. The signal intensity of \nthe fluid in the fallopian tube depends on the cause of the \nblockage [42]. The tubal content in chronic salpingitis \ncan exhibit a T1-hyperintense signal due to the retention \nof mucus secreted by the mucosal epithelium (Fig.  4), \nrated O-RADS MRI 3. It is often unilateral, isolated, \nand lacks other suggestive signs of pelvic endometriosis. \nContrast-enhanced T1-WI can also aid in the differential \ndiagnosis of subacute episodes by demonstrating either \nno enhancement or low enhancement in cases of chronic \ninfection (excluding concurrent infectious episodes).\nLess commonly, a persistent remnant ovarian abscess can \nbe observed in subacute or chronic tubo-ovarian presen -\ntations [43]. The signal intensity of the abscess can vary \ndepending on its viscosity or protein concentration, dis -\nplaying T1-hyperintense content and high signal intensity \nFig. 4 Chronic hydrosalpinx in a 58‑year‑old woman with pelvic pain and history of PID. a Axial T1‑W fat‑suppressed, (b) axial T2‑W, and (c) \naxial T1‑W fat‑suppressed contrast‑enhanced MR images show a fluid‑filled fallopian tube (arrows) with high T1‑ and T2‑signal intensity. Note \nthe absence of fat stranding, peritonitis, or significant adnexal enhancement\nFig. 5 Subacute tubo‑ovarian abscess in a 30‑year‑old woman with subacute pelvic pain (3 weeks ago) and persistent left pelvic pain. a \nAxial T1‑W fat‑suppressed MR image shows a T1‑hyperintense cystic ovarian lesion (thick arrow), corresponding to proteic and hemorrhagic \ncontent. b Sagittal and (c) axial T2‑W MR images show an ovarian well‑defined cystic cavity with intermediate T2‑signal intensity, surrounded \nby a hypointense peripheral rim (thick arrows). Note the presence of an adjacent hydrosalpinx with heterogeneous signal intensity (thin arrows). \nOf note, the presence of a homolateral T2‑hyperintense functional ovarian cyst (arrowheads). d Axial T1‑W fat‑suppressed contrast‑enhanced \nMR image shows enhancement of the collapsed walls of the remnant ovarian abscess (thick arrow) as well as the walls of the hydrosalpinx (thin \narrows), with obliteration of the fat planes around the left ovary. Of note, the presence of a homolateral functional ovarian cyst showing a peripheral \nenhancement (arrowheads)\n\nPage 9 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \non T2-WI (Fig.  5) and DWI. A DWI-hyperintense rim \nalong the inner layer of the thickened wall indicates gran-\nulation tissue with microscopic bleeding, accompanied \nby moderate to sustained post-contrast enhancement \n[29]. In contrast, endometriomas do not exhibit post-\ncontrast enhancement and typically display homogene -\nous high signal intensity on DWI [25]. It is important \nto note that both endometriomas and the abscess cavity \nmay exhibit restricted diffusion, but the signal heteroge -\nneity on DWI is suggestive of an abscess process.\nTubo-ovarian infection must be distinguished from \nsuperinfection of an endometrioma, a rare condition \noccurring in around 2% of cases [44]. Fever is present in \nonly 30% of cases, and about 60% show signs of biologi -\ncal inflammatory response [45]. Endometriomas create a \nconducive environment for bacterial growth due to aged \nblood (acting as an effective culture medium for bacterial \ngrowth) [46], increasing the risk of infection. Infections \ncan occur through bacterial ascent from the vaginal ori -\nfice to the fallopian tube, direct inoculation (e.g., during \nhysterosalpingography), or digestive translocation, espe -\ncially in cases involving the rectosigmoid. Superinfection \nprimarily affects the endometrioma rather than the fal -\nlopian tube, distinguishing it from typical tubo-ovarian \ninfections. Infected endometriomas tend to be large and \nmay exhibit changes in signal intensity on MRI, such as \nloss of high signal intensity on T1-WI and/or loss of shad-\ning on T2-WI due to liquefaction. Contrast agents do not \naid in distinguishing between these entities, as both show \nsignificant wall enhancement with adjacent fatty infiltra -\ntion in intermediate signal intensity on T2-WI. In such \ncases, the diagnosis is often based on monitoring the \ninfectious episode, particularly when other suggestive \npelvic endometriosis lesions are absent.\nEpithelial cystic tumors Serous cystadenomas are the \nmost common benign epithelial neoplasms in women of \nreproductive age [47], and overall, in ovarian neoplasms \n[48]. Unilateral lesions are more common, but bilateral \ncases can occur in up to 20% of cases [49]. They typically \nappear as fluid-filled cystic lesions that are T2-hyperin -\ntense and T1-hypointense, rated O-RADS MRI 2. In rare \ncases, they may show moderate to high signal intensity \non T1-WI due to proteinaceous secretions, cell desqua -\nmation, and microbleeding, and should suggest a serous \nborderline cystadenoma [50]. However, the signal inten -\nsity on T1-WI remains lower than that of blood, and the \nshading effect on T2-WI is usually absent. Moreover, sus-\npicion of malignancy should be raised by the presence \nof enhancing solid (nonfatty, nonfibrous) components, \nthickened irregular septa (> 3 mm), papillary projec -\ntions, or a mural nodule, encountered in borderline or \ninvasive tumors, rated O-RADS MRI 4 or 5 [48]. Differ -\nentiating a T1-hyperintense malignant epithelial cystic \ntumor from a malignant transformation of an endome -\ntrioma can indeed be challenging. Malignant transfor -\nmations of endometriomas are relatively rare, occurring \nin approximately 1–2% of cases [51]. These transforma -\ntions involve the development of malignancies within \npre-existing endometriomas. In the context of imaging, \nseveral features can help differentiate between the two \nconditions. Signs suggestive of malignant transformation \nof an endometrioma include an increase in size, presence \nof solid tissue, loss of shading (seen as an increased signal \non T2-WI), and wall enhancement [52]. Lastly, border -\nline seromucinous cystadenomas should be considered in \nthe differential diagnosis of malignant transformations of \nendometriomas. Such ovarian borderline tumors are rel -\natively uncommon but not rare neoplasms, and they can \ninvolve both ovaries in up to 40% of patients [53], often \nbeing associated with endometriosis in 30–50% of cases \n[54]. On imaging, a key finding of borderline seromuci -\nnous cystadenomas is the presence of T2-hyperintense \npapillary projections, reflecting their mucinous nature. \nIn contrast, malignant endometriomas typically exhibit \ncontrast-enhanced mural nodules instead [55].\nParatubal cysts Paratubal cysts, also known as para-\novarian cysts, originate from vestigial tissue of the Wolf -\nfian mesonephric ducts [56]. They are located in the \nbroad ligament at the fimbriae end of the fallopian tube \nand account for approximately 10% of all adnexal masses \n[57]. On MRI, paratubal cysts appear as well-defined, \nround cystic structures that are separate from the ovary \n(negative beak sign) and located on the surface of the \ntube, rated O-RADS MRI 2. It is important to check for \nadjacent or contralateral paratubal cysts, as bilateral cysts \nare frequently observed. Occasionally, they may exhibit \nT1-hyperintense content due to viscosity or high pro -\ntein content but do not show a shading effect on T2-WI \n(Fig. 6).\nVagina, vulva, and urethra\nA vaginal cyst may be secondary to an embryologic deriv-\native, ectopic tissue, or represent a urologic abnormality; \nvulvar cysts are most often related to dilated glands. Epi -\nthelial inclusion cyst, Gartner’s duct cyst, and Bartho -\nlin’s gland cyst represent common vulvovaginal cystic \nabnormalities not to be confused with endometriosis. It \nis important to note that endometriosis in this region is \nexceptionally rare, especially in the absence of prior vagi -\nnal surgeries or a history of childbirth complications.\n\nPage 10 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \nGartner’s duct cysts Gartner’s duct cysts are mesone -\nphric remnants within the vagina. They are often asymp -\ntomatic, especially in the absence of complications, but \nlarge cysts can cause urinary symptoms by pressing on \nthe urethra [58]. They are usually located in the antero -\nlateral vaginal wall but can be mistaken for cystic vaginal \nendometriosis when found in the posterosuperior wall \n[59]. High signal intensity on T1-WI is typically caused \nby high proteinaceous content, resulting in heterogene -\nous signal intensity. Additionally, there may be a potential \nfor low signal intensity on T2-WI (Supplemental - Fig -\nure 4). Gartner’s duct cysts are usually single, more rarely \nmultiple, and may be associated with renal abnormalities \nsuch as agenesis, dysplasia, or cross ectopy [60]. Adding \nT2 large-field-of-view sequences is helpful in this context \nto complete imaging evaluation.\nEpithelial inclusion cysts Epithelial inclusion cysts are \nthe most prevalent type of vaginal cysts, comprising \napproximately 23% of all cases [60]. These cysts occur \nwhen epithelial tissue becomes focally trapped due to \ntrauma or prior surgeries like episiotomy. They are com -\nmonly found on the lower posterior vaginal wall or the \nvaginal cuff (Fig. 7). Distinguishing between a typical scar \nand an endometriotic episiotomy scar involves examin -\ning the patient’s surgical history, such as hysterectomy \nor episiotomy (either mediolateral or midline), assessing \nthe nature of perineal pain (whether it is cyclic or non-\ncyclic), and conducting thorough physical examinations. \nFurthermore, specific imaging features, like differentiat -\ning between single or very few versus multiple T1-hyper -\nintense hemorrhagic microcysts and thin linear versus \nthick fibromuscular T2-hypointense scars enclosing \nhemorrhagic implants (Fig.  7), offer valuable clues, pre -\nventing premature assumptions of an endometriotic scar.\nFig. 6 Right‑sided paratubal serous papillary cystadenofibroma in a 29‑year‑old woman with right pelvic pain during first trimester pregnancy. \na Axial T1‑W fat‑suppressed and (b) axial T2‑W MR images show a bilocular paratubal cystic lesion (star) with a T1‑ and T2‑hyperintense posterior \nloculus (star). The wall is irregular with endocystic tiny papillary projections (arrowheads). Note the gravid uterus (arrows)\nFig. 7 Vaginal epithelial inclusion cyst in a 35‑year‑old woman with non‑cyclic perineal pain and palpable vaginal induration, 1 year after childbirth \nwith episiotomy. a Axial T1‑W fat‑suppressed MR image shows a single small T1‑hyperintense cyst (arrow) in the posterior vaginal wall. b Axial \nT2‑W MR image shows a T2‑hypointense cyst and T2‑hypointense thin linear fibrous scar tissue within the puborectalis muscle (arrows), consistent \nwith an episiotomy scar\n\nPage 11 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \nBartholin’s gland cysts Bartholin’s glands, or greater \nvestibular glands, arise in the superficial perineal pouch \nof the urogenital triangle. When the ducts of these glands \nbecome obstructed, it leads to retention of secretions and \nthe formation of cysts [61]. Bartholin’s gland cysts are \nthe most common type of vulvar cysts, mostly ranging in \nsize from 1 to 4 cm. While many patients with Bartholin’s \ngland cysts are asymptomatic, some may experience mild \ndyspareunia during vaginal penetration, which needs to \nbe differentiated from deep dyspareunia associated with \nendometriosis. It is important to note that the specific \nanatomical location of these cysts on the posterolat -\neral surface of the vestibule, often occurring bilaterally, \nshould not be mistaken for cystic endometriotic implants \nin patients with a history of vaginal delivery (with or \nwithout episiotomy) or prior transvaginal surgeries. On \nimaging, Bartholin’s gland cysts with high proteinaceous \ncontent exhibit high signal intensity on T1-WI, along \nwith heterogeneous and low signal intensity on T2-WI \n(Supplemental - Figure 5).\nSkene’s gland cysts Skene’s glands, or periurethral \nglands, are tubule-alveolar structures located at the 3 \nand 9 o’clock positions along the distal two-thirds of the \nurethra, providing lubrication [62]. These are typically \nround and unilocular fluid-filled cysts. Homogeneous \nT1-hyperintensity, suggesting high proteinaceous con -\ntent, can help in their detection and physical examination \nidentification [61] (Supplemental - Figure  6). It is essen -\ntial to differentiate these cysts from urethral diverticu -\nlum considering a mutlicystic or circular appearance, the \npresence of a connection with the urethra (Supplemental \n- Figure 7) and the patient’s medical history.\nPeritoneum\nMulticystic peritoneal mesothelioma Multicystic peri -\ntoneal mesothelioma is a rare benign neoplasm arising \nfrom the peritoneum [63]. It is often found in women \nof reproductive age, with a preferential location in the \npelvis, and can be discovered incidentally or present \nwith symptoms such as heaviness, distension, or pain \n[64]. These mesotheliomas appear as well-defined cystic \nlesions, typically over 10 cm in size, with grape-like \nclusters and possible mild septal enhancement. In some \ncases, the cystic nature of the lesions and debris within \nthem may cause a mildly elevated signal on T1-WI \n(Fig.  8). This can occasionally lead to confusion with \nendometriotic lesions, particularly in cases of severe \nperitoneal involvement with combined cystic peritoneal \nendometriotic lesions and pelvic adhesions with perito -\nneal hemorrhagic inclusion cysts. However, the absence \nof deep endometriotic lesions and normal ovaries helps \ndifferentiate multicystic peritoneal mesothelioma. In \naddition to the grape-like appearance which argues for \na full-fledged lesion (versus adhesions), the presence of \nmulti-focal peritoneal involvement further supports the \ndiagnosis. Therefore, a dedicated peritoneal MRI in addi -\ntion to pelvic MRI is necessary [65]. Patients suspected \nof having multicystic peritoneal mesothelioma should be \nreferred to a specialized center for a comprehensive eval -\nuation, which includes obtaining an accurate pathological \ndiagnosis. Treatment options, such as complete cytore -\nduction with or without hyperthermic intraperitoneal \nchemotherapy, can be discussed to minimize recurrence \nor potential malignant transformation [64].\nRetrorectal space\nRetrorectal cystic lesions in adults are rare and most \ncases are congenital. Developmental cysts are the most \ncommon congenital entities found in the retrorectal \nspace and include tailgut cysts (also known as retrorectal \nhamartomas), epidermoid cysts, and dermoid cysts [66].\nTailgut cysts Tailgut cysts are rare congenital cysts \nthought to arise from the embryonic postanal gut tissue \n[67]. They are the most common asymptomatic retrorec -\ntal developmental cysts, often incidentally found in adult \nwomen [68]. Despite not aligning with the pathogenic \ntheories of endometriosis dissemination, tailgut cysts \nmay routinely be misdiagnosed as cystic endometriosis \nlesions. Indeed, while deep extra or retroperitoneal endo-\nmetriosis mainly consist of an extension from DIE, tailgut \ncysts appear on MRI as isolated thin-walled uni- or mul -\ntilocular cystic masses [69], with low signal intensity on \nT1-WI, although they can be T1-hyperintense depend -\ning on their mucoid content, and exhibit variable signal \nintensity on T2-WI ranging from T2-hyperintense to \nT2-hypointense (Fig.  9) [70]. Contrast-enhanced T1-WI \ncan reveal thick and regular septa and vegetations, which \nare indicative of possible malignant transformation to \nadenocarcinoma [71]. Despite often being discovered \nincidentally, recent retrospective evidence highlights \nthat surgical intervention, accompanied by preoperative \nMRI, is the recommended approach for cystic and solid \nretrorectal tumors due to the potential risk of malignant \ntransformation, even in incidental cases, and ensures a \ndefinitive histological diagnosis [72].\nOther retrorectal cysts Other retrorectal developmental \ncysts, such as teratomas and epidermoid cysts, are even \nrarer [66]. Teratomas are uniloculated cysts that contain \nfat tissue and other components, while epidermoid cysts \nare large cysts with heterogeneous dense content. These \ncysts are less likely to mimic endometriotic cysts.\n\nPage 12 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \nFig. 8 Multicystic peritoneal mesothelioma in a 38‑year‑old woman with chronic pelvic pain addressed for suspicion of endometriosis. a, b Axial \nT1‑W fat‑suppressed MR images show an anterior and posterior pelvic multicystic lesion with some loculi showing hyperintense content (arrows). \nc, d Axial and (e) sagittal T2‑W MR images show a thin‑walled multiple grape‑like clusters lesion, with intermediate signal intensity in thick‑content \nloculi (arrows), gently molding to the polymyomatous uterus and normal ovaries, as well as the pelvic wall. f Axial fat‑suppressed contrast‑enhanced \nsubtracted T1‑W image shows no thick or irregular wall enhancement of the multicytic lesion, nor tissular portion\n\nPage 13 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \nUrachus\nUrachal cysts The urachus is a ductal remnant that \nforms during early embryological development, connect -\ning the bladder dome to the umbilicus [73]. Normally, \nthe urachus undergoes involution and its lumen is oblit -\nerated. However, in some cases, remnants of the urachus \ncan persist and result in various abnormalities such as \nurachal fistula, umbilical-urachal sinus, urachal cyst, and \nvesico-urachal diverticulum [74]. These abnormalities are \noften discovered incidentally during MR imaging per -\nformed for unrelated reasons. Urachal cysts occur when a \nsegment of the urachus fails to close, most commonly in \nthe lower third of the urachal tract. These cysts are typi -\ncally small and asymptomatic. On imaging, the presence \nof a fluid-filled structure along the midline of the urachal \ncourse indicates an uncomplicated cyst. The signal inten-\nsity within the cyst can vary, ranging from low to high \nsignal intensity on T1-WI depending on the presence of \nmucoid material and proteinaceous content (Supplemen-\ntal - Figure 8).\nArtifacts\nHaving a thorough understanding of MRI artifacts is cru-\ncial when conducting pelvic imaging. Their presence can \nmask, distort, or mimic pathological lesions, potentially \nleading to misinterpretation of the images.\nVascular artifacts\nFlow‑related enhancement Flow-related enhancement \nartifact, also known as the “entry slice phenomenon, ” \nrefers to the bright signal of blood within the initial slices \nof an imaging acquisition. It is commonly seen with gra -\ndient-echo sequences and, to a lesser extent, spin-echo \nsequences [75]. This artifact occurs because flowing \nblood entering a slice is unsaturated, leading to increased \nsignal on MR images [75]. To address this artifact, spatial \nsaturation bands can be used to remove the undesired \nsignal enhancement. However, in the pelvic region, arter-\nies and large-caliber fast-flowing veins oriented in the \nphase-encoding direction may still show increased signal \nintensity on T1-WI, resulting in paradoxical enhance -\nment (Fig.  10). It is crucial to distinguish this artifact \nfrom endometriotic implants, especially in the parame -\ntrium or adnexal region (Supplemental - Figure  9). Fac-\ntors such as anatomical location, linear or serpiginous \nappearance, presence of flow-voids on T2-WI, and gado -\nlinium-enhanced sequences can help confirm suspicions \nof vascular origin. The artifact typically spans multiple \nconsecutive slices but fades with distance. In challeng -\ning cases, inversion recovery sequences or fat-saturated \nblack-blood double inversion recovery sequences can \naid in detecting and differentiating this artifact from true \npathology.\nVascular ghosts Vascular ghost artifacts in the pelvis \nresult from phase variations caused by pulsatile arte -\nrial flow, typically originating from the iliac vessels [75]. \nPulsatile flow can lead to ghosting in the phase-encod -\ning direction, resulting in one or more T1-hyperintense \nghost images. Vascular ghost artifacts can overlap with \ngynecologic structures, particularly the ovaries, which \nare situated in the path of the iliac vessels (Supplemental \nFig. 9 Retrorectal hamartoma (tailgut cyst) in a 46‑year‑old patient with gradually worsening dysmenorrhea and menometrorrhagia. a Axial \nfat‑suppressed T1‑W MR image shows a small‑sized, well‑defined and thin‑walled T1‑hyperintense cyst (thick arrow) isolated in the retrorectal \nspace, along the right side of the anococcygeal raphe. b Sagittal and (c) axial T2‑W MR images show a distinct T2‑hypointense retrorectal cyst (thick \narrows). Note the absence of posterior deep infiltrating endometriosis lesions but the presence of internal adenomyosis (thin arrows) consistent \nwith the symptomatology\n\nPage 14 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \n- Figure  10) [76]. The repeating pattern of this artifact \nin the phase direction, along with the absence of corre -\nsponding findings on other sequences, usually facilitates \nits identification. However, in challenging cases, addi -\ntional sequences with a reversal of the phase-encoding \ndirection can be used to help rule out this artifact.\nCalcification artifacts\nIn specific circumstances, calcium can appear T1-hyper -\nintense, despite being a diamagnetic substance [77]. The \nT1 signal intensity increases until a certain calcium con -\ncentration is reached (30% by weight), primarily due to \nT1 shortening. However, for high calcium concentra -\ntions, the T1-weighted signal intensity decreases due to \nthe dominant effect of low proton density. Nevertheless, \nan increase in the surface area of calcifications leads to an \nelevated T1-weighted relaxivity [76]. Phleboliths, which \nare calcium concretions found within the endoluminal \nvessels, can exhibit a bright T1-hyperintense signal after \nfat suppression, especially in the parametrium veins of \nthe pelvic cavity. Their round shape, endovascular loca -\ntion, and T2-hypointense appearance help in their recog-\nnition (Fig.  11). Computed tomography scan, if already \nperformed for another reason and available at the time of \ndiagnosis, can also assist in identifying phleboliths.\nLack of fat suppression\nFat suppression techniques are commonly used in MR \nimaging to either detect or suppress the signal from \nadipose tissue. Three main methods are used: fat satu -\nration, inversion recovery, and opposed-phase imag -\ning, each with their own advantages, disadvantages, and \npotential pitfalls [78]. Short Inversion Time Inversion \nRecovery (STIR) sequences, frequently used in muscu -\nloskeletal MR imaging, may not completely suppress the \nsignal from tumors containing fat. This is due to varia -\ntions in T1 relaxation time between tissues containing fat \nFig. 10 Flow‑related enhancement artifact, also known as “the entry slice phenomenon” , in a 36‑year‑old woman with chronic pelvis pain \nand dysmenorrhea. a Axial and (b) sagittal reconstruction T1‑W fat‑suppressed MR image show a bright spot (arrows) in close proximity \nwith the right USL insertion, also present on contiguous slices (not shown). c Axial and (d) sagittal T2‑W MR images show a sub‑serous vein (arrows) \nin place of the T1 bright spot, near the right USL insertion\n\nPage 15 of 18\nRuaux et al. Insights into Imaging           (2024) 15:19 \n \nand pure fat itself. Consequently, failure in fat suppres -\nsion can lead to misleading high signal intensity, making \nit challenging to differentiate between endometriomas \nand mature cystic teratomas, or, less commonly, sequelae \nof epiploic appendagitis. Opposed-phase imaging relies \non the fact that the lipid signal and water signal are addi -\ntive on in-phase images, but on opposed-phase images, \nthe signal represents the difference between the lipid and \nwater signals. As a result, opposed-phase imaging helps \nto reduce the signal from fatty tissue. The Dixon method \nacquires both in-phase and opposed-phase images, ena -\nbling the production of pure water and pure lipid images, \nwhich can aid in the differential diagnosis process.\nFeces\nProteinaceous concretions or fecal matter within the \nintestinal lumen exhibit increased signal on T1-WI [79] \nand should not be mistaken for endometriosis, especially \nwhen dealing with coproliths (Supplemental - Figure  11) \nor appendicoliths in the pelvic area. Confirmation of \nan appendicolith can be achieved through multiplanar \nreconstruction on 3D T2-WI, along with the presence \nof an intraluminal increased signal on T1-WI (Fig.  12). \nEndometriosis of the appendix typically involves the \nouter wall layers with extrinsic involvement, resulting \nin stenosis and possible appendicular distension, also \nknown as mucocele.\nFig. 11 Parametrial left‑sided phlebolith in an 18‑year‑old woman. a Axial T1‑W and (b) axial T2‑W MR images show a punctiform T1‑hyperintense \n“spot” matching a T2 “dark spot” within the lumen of a parametrial vein (arrows)\nFig. 12 Normal appendix filled with feces in a 34‑year‑old woman with chronic pelvic pain and medical history of endometriosis referred \nfor infertility issues. a Axial T1‑W fat‑suppressed MR image shows a T1‑hyperintense “spot” in the right lateral pelvic side (thick arrow). b Axial and (c) \nsagittal T2‑W MR images show that the T1‑hyperintense “spot” is located in a tubular structure (thin arrows) referring to the appendix running \nover the right ovary (black star), consistent with endoluminal feces concretion (white star). Note the presence of a left endometrioma with T2 \nshading (thick arrows in a and b)\n\nPage 16 of 18Ruaux et al. Insights into Imaging           (2024) 15:19 \nMelanin\nVulvar or vaginal melanomas are very rare tissular malig -\nnancies that exhibit T1-hyperintense signal intensity, \nattributed to the paramagnetic properties of melanin and \nmethemoglobin, with corresponding low to intermediate \nsignal intensity on T2-WI [80]. Contrast-enhanced sub -\ntracted MR images can be helpful in confirming the pres-\nence of tissue malignancies (Supplemental - Figure 12).\nConclusion\nIn summary, many pitfalls and differential diagnoses \nshould be known to the radiologist specializing in pel -\nvic endometriosis. T1-hyperintense signal abnormalities \nmay mimic lesions and condition-like mimickers that \nare radiologically similar to endometriosis, but different \nin every respect. Acknowledging key MR findings for \nthe differential diagnosis of endometriosis is therefore \nessential in the diagnostic accuracy and proper treatment \napproach for such entities to improve clinical and surgi -\ncal workflows.\nAbbreviations\nACUM  Accessory and cavitated uterine mass\nDIE  Deep infiltrative endometriosis\nDWI  Diffusion‑ weighted images\nFS T1‑WI  Fat‑suppressed T1‑weighted images\nMRI  Magnetic resonance imaging\nO‑RADS MRI  Ovarian‑Adnexal Reporting and Data System on Magnetic \nResonance Imaging\nT1 T2‑WI  T1 T2‑weighted images\nUSL  Uterosacral ligament\nSupplementary Information\nThe online version contains supplementary material available at https:// doi. \norg/ 10. 1186/ s13244‑ 023‑ 01587‑3.\nAdditional file 1. \nAuthors’ contributions\nER: writing—original draft, conceptualization, data curation. SN: conceptu‑\nalization—review and editing. MG: data curation. MC: data curation. MDS: \nreview—data curation. FG: data curation. ITN: writing—review and edition. \nPR: conceptualization, writing—review and editing, project administration, \nsupervision. All authors read and approved the final manuscript.\nFunding\nNot applicable.\nAvailability of data and materials\n The data of cases in the manuscript are available from the corresponding \nauthor on reasonable request.\nDeclarations\nEthics approval and consent to participate\nAll procedures performed in studies involving human participants were in \naccordance with the ethical standards of the institutional and/or national \nresearch committee and with the 1964 Helsinki Declaration and its later \namendments or comparable ethical standards. The Institutional Review Board \nwaived the need to obtain informed consent.\nConsent for publication\nThe authors of this manuscript consent for publication.\nCompeting interests\nPascal Rousset reported consultant fees from Ziwig and EDAP TMS (France), \nreported receiving lecture fees from Bracco, compensation for serving on the \nboard from Guerbet.\nFrançois Golfier reported consultant fees from ZIWIG.\nIsabelle Thomassin‑Naggara reported receiving lecture fees from General \nElectric, Siemens, Canon, and GSK; lecture fees and compensation for serving \non the board from Guerbet; compensation for serving on the board from \nBayer; lecture fees from Incepto, ICAD, Fujifilm, and Hologic; and lecture fees \nand compensation for serving on the board from Bracco.\nAuthor details\n1 Department of Radiology, Hospices Civils de Lyon, Lyon Sud University \nHospital, Lyon 1 Claude Bernard University, 165 Chemin du Grand Revoyet, \nEMR 3738, 69495 Pierre Bénite, France. 2 Department of Radiology, Montpel‑\nlier Cancer Institute, U1194, Montpellier University, 34295 Montpellier, France. \n3 Department of Radiology, Hospices Civils de Lyon, Lyon Sud University \nHospital, Lyon 1 Claude Bernard University, EMR 3738, Pierre Bénite, France. \n4 Department of Pathology, Hospices Civils de Lyon, Lyon Sud University \nHospital, Lyon 1 Claude Bernard University, 69495 Pierre Bénite, France. \n5 Department of Gynecology and Obstetrics, Hospices Civils de Lyon, Lyon Sud \nUniversity Hospital, Lyon 1 Claude Bernard University, EMR 3738, 69495 Pierre \nBénite, France. 6 Department of Radiology, Service Imageries Radiologiques et \nInterventionnelles Spécialisées, Hôpital Tenon, Assistance Publique Hôpitaux \nde Paris, Sorbonne Université, 75020 Paris, France. \nReceived: 27 June 2023   Accepted: 25 November 2023\nReferences\n 1. 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Eur Radiol 18:1269–1280. https:// doi. org/ 10. 1007/ \ns00330‑ 008‑ 0865‑5\nPublisher’s Note\nSpringer Nature remains neutral with regard to jurisdictional claims in pub‑\nlished maps and institutional affiliations.","source_license":"CC0","license_restricted":false}