{"paper_id":"73ac1b5f-13e9-443a-ad95-2b00d2bed30d","body_text":"Bourg et al . Insights into Imaging          (2025) 16:131 \nhttps://doi.org/10.1186/s13244-025-02005-6\nEDUCATIONAL REVIEW Open Access\nPelvic nerve endometriosis: MRI features\nand key findings for surgical decision\nJustine Bourg 1, Edouard Ruaux 1, Pierre Adrien Bolze 2, Marie Gavrel 1, Mathilde Charlot 1, François Gol fier2,\nIsabelle Thomassin-Naggara 3 and Pascal Rousset 1*\nAbstract\nEndometriosis is a prevalent gynecological disorder in women of reproductive age. It is the leading cause of chronic\npelvic pain. While the mechanisms underlying this pain remain elusive, rare cases of pelvic nerve involvement can\nresult in severe, debilitating symptoms, adding complexity to the clinical landscape. Nerve involvement typically results\nfrom the direct extension of deep in filtrating endometriosis, though it may also occur in isolation. The nerves most\ncommonly affected include the inferior hypogastric and lumbosacral plexuses, as well as the sciatic, pudendal,\nobturator, and femoral nerves. Early and accurate diagnosis is essential for the effective management of the pain and\nthe prevention of irreversible nerve damage. Given the limitations of transvaginal ultrasonography in visualizing the\nlateral compartment, MRI is considered the gold standard for detecting and evaluating pelvic nerve involvement.\nThrough the use of optimized protocols to enhance the visualization of nerves and their anatomical landmarks,\nradiologists play a key role in the identi fication of endometriotic lesions. A comprehensive and structured radiology\nreport is essential for surgical planning, as nerve involvement often requires precise interventions to alleviate\nsymptoms and restore quality of life.\nCritical relevance statement Accurate identification and a structured reporting of pelvic nerve endometriosis in the\nlateral compartment are pivotal to guide surgical decision-making and optimize patient outcomes.\nKey Points\n●\nPelvic nerve endometriosis is often overlooked, underestimated by clinicians, and underdiagnosed on imaging.\n●\nTimely nerve involvement diagnosis prevents permanent damage in pelvic pain with neurological symptoms.\n●\nDeep endometriosis in the lateral compartment may extend to the pelvic nerves.\n●\nThe inferior hypogastric plexus, sacral plexus, sciatic, and pudendal nerves are commonly affected.\n●\nA dedicated MRI protocol with 3D T2-weighted sequence ensures accurate pelvic nerve assessment.\nKeywords Endometriosis, Magnetic resonance imaging, Pelvic plexus, Pelvic pain\n© The Author(s) 2025. 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\nthe original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The\nimages or other third party material in this article are included in the article ’ s Creative Commons licence, unless indicated otherwise\nin a credit line to the material. If material is not included in the article ’ s Creative Commons licence and your intended use is not\npermitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright\nholder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.\n*Correspondence:\nPascal Rousset\npascal.rousset@chu-lyon.fr\nFull list of author information is available at the end of the article\n1234567890():,;1234567890():,;\n1234567890():,;\n1234567890():,;\n\nGraphical Abstract\nAAccurate identification and a structured reporting of pelvic nerve endometriosis in the \nllateral compartment are pivotal to guide surgical decision making and optimize patient \nooutcomes.\nPPelvic nerve endometriosis: MRI features \naand key findings for surgical decision\nIInsights Imaging (2025) Bourg J, RRuaux EE, BBolze PPA eet aal; \nDDOI: 110.1186/s13244--0025--002005--66\nIntroduction\nEndometriosis is a chronic in flammatory condition char-\nacterized by the presence of endometrial-like tissue out-\nside the uterine cavity. It affects approximately 10% of\nwomen of reproductive age [ 1]. Endometriosis can be\ndivided into three phenotypes: ovarian endometrioma,\nsuperficial endometriosis, and deep in filtrating endome-\ntriosis [ 2]. Deep endometriosis (DE) is de fined by the\ninfiltration of endometrial-like tissue beneath the perito-\nneal surface. It is usually nodular, invasive to adjacent\nstructures, and associated with fibrosis and disruption of\nnormal anatomy [ 3]. It typically involves the uterosacral\nligaments, torus uterinum, vagina, rectosigmoid, recto-\nvaginal septum and urinary tract. In rare cases, endome-\ntriosis may involve pelvic nerves, with the inferior\nhypogastric plexus, sacral plexus, and sciatic nerve being\nmost frequently affected [ 4]. The true incidence of neural\nendometriosis remains uncertain, but is likely under-\nestimated, potentially due to low clinical suspicion or\nlimited familiarity with neural anatomy among abdominal\nor pelvic radiologists. In addition, diagnosis may be dif-\nficult in cases of isolated pelvic endometriosis, without\nconcomitant endometriosis elsewhere in the pelvis [ 5].\nThe clinical presentation of neural endometriosis is\nvariable and often nonspeci fic, including symptoms such\nas pain, weakness, numbness, bladder or rectal dysfunc-\ntion, and lower limb dysfunction in case of severe lesions\n[6]. Symptoms can either be cyclic or constant. When\nendometriosis is not already diagnosed, these symptoms\nare rarely attributed to this disease at first, but rather to\nrheumatologic, osteoarticular, or neurological causes.\nThis misdirection contributes to signi ficant delays in\ndiagnosis, as initial explorations often rely on non-\nspecialized imaging techniques or protocols. Addition-\nally, musculoskeletal radiologists tend to be less familiar\nwith endometriosis imaging.\nEarly diagnosis is crucial to effectively manage the\npatient’s pain and prevent irreversible nerve damage.\nWhile ultrasonography is the first-line imaging modality\nfor assessing deep pelvic endometriosis, it has consistent\nlimitations due to its restricted field of view, particularly\nin lateral compartments —its limited contrast resolution\nin subperitoneal space, and its operator dependence [ 7].\nIn this context, magnetic resonance imaging (MRI) is\nconsidered the imaging modality of choice. It allows\nassessment and detailed mapping of the extent and\nseverity of neural endometriosis, which can alter the\nmedical and surgical management of patients [ 8].\nThe management of these patients is inherently com-\nplex and typically requires a multidisciplinary approach to\nBourg et al . Insights into Imaging          (2025) 16:131 Page 2 of 16\n\ndetermine the optimal treatment strategy. It often\ninvolves a combination of hormonal therapy, surgery, and\npain management. When surgery is decided upon,\nlaparoscopic surgery —frequently assisted by robotic\ntechnology—is preferred for cases involving sacral nerve\nroots and pelvic nerves [ 9].\nThis article provides a comprehensive review of the\npathophysiology of neural endometriosis, proposes an\noptimized MRI protocol tailored for the evaluation of\npelvic nerves, and highlights key anatomical landmarks\ncrucial for the accurate detection and analysis of each\nnerve. Finally, it outlines the key MRI features of endo-\nmetriotic neural involvement that should be reported for\neffective surgical planning.\nPhysiopathology of neural endometriosis\nDE is strongly associated with pelvic pain, severe dys-\nmenorrhea, and deep dyspareunia [ 10]. Among women\nwith chronic pelvic pain, the prevalence of endometriosis\nis estimated at approximately 70% [ 11]. This persistent\npain is often the most debilitating symptom, signi ficantly\nimpacting women ’s quality of life. Depending on the role\nof the nerve fibers, somatic and vegetative symptoms such\nas pain, weakness, numbness, bladder and rectal dys-\nfunction may occur [ 12]. Since pelvic nerve endometriosis\nis a rare clinical presentation, it is often overlooked by\npractitioners. The cyclical nature of catamenial symp-\ntoms, when present, can be a critical diagnostic clue and\nshould alert the practitioner.\nHowever, the mechanisms underlying endometriosis-\nassociated pain remain poorly understood. Nerve fibers\nare believed to play a central role in both the initiation\nand modulation of pelvic pain in women with endome-\ntriosis. Increasing evidence suggests that endometriotic\nlesions exhibit heightened neural density [ 13]. Through\nthis process known as neuroangiogenesis, ectopic endo-\nmetriotic implants establish their own distinct neural\nand vascular networks [ 13]. These lesions engage in\nbidirectional interactions with sensory, sympathetic, and\nparasympathetic fibers, promoting in flammation, angio-\ngenesis, proliferation, and further innervation. This\ncrosswalk may contribute to the development of the dis-\nease. It is thought to affect neuronal activity in the central\nnervous system, increasing pain perception [ 14].\nAdditionally, ectopic endometrial cells may directly\ninvade or irritate peripheral nerves, contributing to pain\n[10]. However, the retroperitoneal course of pelvic nerves\nraises questions about the unclear pathogenesis of endo-\nmetriosis. Sampson ’s theory of retrograde menstruation\nsuggests that menstrual re flux allows endometrial cells to\nimplant on peritoneal surfaces with peritoneal diverticula\nfacilitating their migration into adjacent nerves [ 15, 16].\nPelvic peritoneal pockets —either formed secondarily\nthrough endometriosis-induced in flammation and scar-\nring or existing as primary retraction defects —may serve\nas reservoirs for ectopic tissue. These defects are com-\nmonly found in areas such as the pouch of Douglas or\nposterior ovarian fossa, with a potential extension towards\nretroperitoneal tissues like the sciatic notch [ 17]. A\nnotable right-sided predominance of sciatic nerve invol-\nvement may be attributed to the peritoneal fluid flow and\nthe anatomical location of the sigmoid colon, which limit\ncell re flux into the left posterior hemipelvis pockets, thus\nprotecting the left lumbosacral plexus and the sciatic\nnerve [ 18].\nHowever, this theory does not explain cases of distant\nextrapelvic endometriosis or those without peritoneal\ninvolvement. In such cases, the perineural spread theory,\nproposed by Possover et al and Siquera et al, offers an\nalternative explanation, supported by MRI and surgical\nevidence [19, 20]. This theory suggests that endometriosis\ncan disseminate along pelvic autonomic nerves —similar\nto the perineural spread observed in pelvic malignancies —\nextending from the uterine plexus to the lumbosacral\nplexus. As no single theory can explain all the manifes-\ntations of endometriosis, multiple mechanisms are likely\nat play. Hypotheses such as hematogenous or lymphatic\nspread, coelomic metaplasia, and embryonic cell rest, are\nalso considered [ 4, 21].\nEither way, neural endometriosis can compress, distort,\nor infiltrate the epineural tissue, possibly leading to nerve\nentrapment and fibrosis. In addition, local edema around\nDE lesions may contribute to symptoms even in the\nabsence of direct neural in filtration [ 22].\nTreatment principles\nRegardless of the route of pelvic nerve involvement in\nendometriosis, early diagnosis and treatment of neural\nendometriosis are crucial to prevent irreversible nerve\ndamage caused by chronic in flammation, fibrosis, and\nadhesions. Management is based on a multidisciplinary\napproach, integrating clinical symptoms and MRI fea-\ntures. Medical management is based on GnRH analogs,\nanalgesics, tricyclic antidepressants, and antiepileptics\n[23]. When conservative treatments fail to relieve pain\nsymptoms and impact patients ’ quality of life, surgery\nbecomes the method of choice. The laparoscopic retro-\nperitoneal approach with nerve-sparing technique and\nsomatic nerve decompression is considered the gold\nstandard for appropriate surgical radicality [ 24]. Possover\net al introduced the concept of laparoscopic neuronavi-\ngation, a parasympathetic nerve-sparing technique based\non nerve electrostimulation [ 25].\nFinally, pelvic pain management must be comprehensive,\naddressing the multifactorial and often interrelated factors\nof pain. Endometriosis is particularly associated with\nBourg et al . Insights into Imaging          (2025) 16:131 Page 3 of 16\n\nmyofascial pain, due to active myofascial trigger points,\nwhich can amplify and perpetuate chronic pain [ 26].\nMRI protocol\nStandard optimized MRI protocol\nMRI is the reference technique for diagnosing neural\nendometriosis and offers a comprehensive roadmap for\nassessing DE, which is crucial for preoperative decision\nmaking. The MRI protocol should follow the European\nSociety of Urogenital Radiology and the Society of\nAbdominal Radiology guidelines [ 27, 28]. Imaging can be\nperformed on a 1.5- or 3-Tesla MRI system, though 3T-\nMRI may present limitations such as increased speci fic\nabsorption rate and susceptibility artifacts [ 29]. Both\nsocieties recommend moderate bladder distension and\nthe administration of an anti-peristaltic agent to minimize\nbowel motion artefacts. The core protocol should include\nT2-weighted (T2W) MRI sequences in two or three\nplanes and T1-weighted (T1W) MRI. However, conven-\ntional sequences may be insuf ficient for detecting pelvic\nnerve involvement due to their long course and small\ncaliber. In this context, 3D sequences with multiplanar\nreformats are valuable for their high spatial resolution.\nThe use of 3D-T2W MRI sequences is increasingly\ncommon for the evaluation of deep pelvic endometriosis,\nparticularly for improved assessment of the lateral com-\npartments [ 30]. These sequences also enhance visualiza-\ntion of nerves, which often have an oblique course.\nThe 3D DIXON technique is currently the reference\nstandard for T1W imaging. Non-fat-suppressed T1W MR\nimages allow clear identi fication of nerves surrounded by\nhyperintense perineural fat, and help assess their anato-\nmical relationships. In contrast, fat-suppressed T1W MR\nimages are essential for detecting T1W-hyperintense\nhemorrhagic cystic foci/lesions surrounding or within\nthe nerve.\nAlthough gadolinium injection is not routinely recom-\nmended for the evaluation of pelvic endometriosis, it may\nbe bene ficial when pelvic nerve involvement is suspected\n[22]. Contrast-enhanced T1W fat-suppressed MRI can\nfacilitate the detection of DE surrounding the pelvic\nnerve. However, the extent of the lesion may be over-\nestimated due to perilesional in flammation.\nAdvanced MRI protocol\nIn addition to this optimized MRI protocol, other tech-\nniques may be considered for more advanced analysis.\nMR neurography can be used to identify pelvic nerve\nabnormalities caused by endometriosis [ 31]. It is based on\nhigh T2W imaging with fat suppression and vascular\nsuppression (mainly veins) to enhance nerve signal\nintensity, which is clearly visible due to endoneurial fluid.\nBoth non-contrast techniques and gadolinium-based\ncontrast agents can be used to suppress the vascular\nsignal, with gadolinium reducing the T1 relaxation time of\nblood to match that of fat tissues [ 32]. Multiplanar\nreconstruction and maximum intensity projection tech-\nniques aid in detecting focal nerve abnormalities. This\nsequence, which adds approximately 8 min to the imaging\ntime, can be an optional add-on sequence when neural\nendometriosis is clinically suspected or requires re-\nevaluation [ 22]. It provides a detailed 3D view which\nmay be helpful in procedure planning, but can also help to\nbetter visualize and track the involved nerve, assess its\ndegree of interruption, and help to better see muscle\natrophy, if present. Muscle evaluation should focus on size\nasymmetry—larger, edematous muscles indicate acute\ndenervation, while smaller, fatty muscles indicate chronic\ndenervation atrophy [ 33].\nDiffusion tensor imaging (DTI) is an advanced MRI\ntechnique that assesses microstructural nerve abnormal-\nities. It primarily assesses the integrity of fiber tracts,\nmeasuring fractional anisotropy, an index of the archi-\ntectural organization of tissue [ 34]. Tractography can also\nprovide neural tracts on three-dimensional (3D) images.\nAlthough clinical research is limited, DTI seems to be a\npromising technique to evaluate nerve abnormalities in\nendometriosis; lower fractional anisotropy values have\nbeen found in women with endometriosis compared to\nhealthy controls, suggesting microarchitectural abnorm-\nalities in the affected sacral roots [ 35, 36].\nMRI features and key findings for pelvic nerve\ninvolvement to report in endometriosis\nAccurate identi fication and a structured reporting of\npelvic nerve endometriosis in the lateral compartments\nare crucial for guiding surgical decision making and\noptimizing patient outcomes (Table 1 and Fig. 1)[ 37].\nNeural endometriosis lesions typically appear on MRI\nsimilarly to other DE lesions, presenting as T2-\nhypointense solid nodules or fibrotic thickenings. These\nlesions, may also show microcystic or hemorrhagic foci,\nindicative of active ectopic glandular tissue, and often\ninvolve the pelvic nerve, which may appear thickened,\ninterrupted, or encased.\nInferior hypogastric plexus\nThe inferior hypogastric plexus is the most commonly\naffected structure within the lateral compartments in\nendometriosis [ 38]. This complex neural network pro-\nvides autonomic innervation of the pelvic viscera. It is\nformed by the convergence of the hypogastric nerves\n(which arise from the superior hypogastric plexus), the\npelvic splanchnic nerves (which arise from the anterior\nbranches of the sacral roots S2 –S4) and the sacral\nsplanchnic nerves (which arise from the sacral\nBourg et al . Insights into Imaging          (2025) 16:131 Page 4 of 16\n\nsympathetic trunk at the S2 and S3 ganglia) [ 39]. The\ninferior hypogastric plexus branches into two main\npathways: the anterolateral branch, which innervates the\nuterus and lower bladder, and a posteromedial branch,\nwhich targets the posterolateral aspect of the rectum and\ngives rise to the inferior rectal plexus [ 39].\nThe inferior hypogastric plexus spans from anterior to\nposterior through the later al compartments, within the\nTable 1 Pelvic nerve endometriosis: anatomical landmarks, MRI features, and key points for surgical planning\nKEY ANATOMICAL LANDMARKS MRI FEATURES KEY POINTS FOR SURGICAL\nPLANNING\nINFERIOR\nHYPOGASTRIC\nPLEXUS\nMediolateral parametrium\nPosterolateral parametrium containing the\nsacrorectal septum: lateral to the mesorectal\nfascia and beneath the uterosacral ligament\nand the ureter.\nFibrotic nodular in filtration, more or less\nspiculated, with the loss of the normal aspect\nof the subperitoneal paracervical\ncellulovascular tissue and the pararectal\ncellular layer\nRelationships of the\nendometriosis lesion with:\n- Ureter and uterine artery\n- Sacral roots\n- Levator ani muscle\n- Pelvic fascia, piriformis muscle\n- Gluteal and internal iliac\nvessels\n- Sciatic nerve\nSACRAL ROOTS - Anterior to the piriformis muscle\n- Indentation within the muscle for S2 and S3\nFibrotic thickening of the sacral roots (mostly\nS3 and S4) in continuity with the in filtration of\nthe posterolateral parametrium\n- Extension along the nerve\nroot up to the foramen\n- Relationship with the\npresacral fascia\nSCIATIC NERVE - Anterior to the piriformis muscle\n- Greater sciatic notch, above and outside the\nischial spine\nEndometriotic in filtration extending from the\novarian fossa towards the sciatic notch, or in a\nmore isolated manner, without other pelvic\nidentifiable endometriosis lesion\nThickening with the loss of “spaghetti-like”\nappearance of the sciatic nerve, often with\nhemorrhagic cystic foci\n- Size of the lesion\n- Extrapelvic extension through\nthe greater sciatic foramen\n- Intrinsic or extrinsic\ninvolvement\n- Relationship to the obturator\nnerve and the inferior gluteal\nvessels\n- Muscle denervation\nPUDENDAL NERVE - Origin: anterior to mid-course of the\npiriformis muscle\n- Middle course: ischial spine, between the\nsacrotuberous and sacrospinous ligaments,\nthen entering Alcock ’ s canal\n- Terminal course: ischiorectal fossa at the end\nof Alcock ’ s canal, following the pudendal\nvascular pedicle\nAt three different levels:\n- Proximal nerve involvement in continuity\nwith the in filtration of posterolateral\nparametrium and S3/S4 nerves\n- Fibrotic thickening at the entrance of\nAlcock’ s canal\n- Fibrotic thickening in the perineal region\nadjacent to the episiotomy scar\nRelationships of the\nendometriosis lesion with:\n- Levator ani muscle\n- Obturator internus muscle\n- Vagina and anal canal (in case\nof extensive lesion in the\nperineal region)\nOBTURATOR NERVE\n(Rare)\n- Medial border of the psoas muscle\n- Pelvic brim\n- Obturator foramen\nExtension of a large endometriosis lesion from\nthe ovarian fossa going through the\nmediolateral parametrium up to the obturator\nnerve\nRetractile fibrotic in filtration with possible\nhemorrhagic cystic areas along the pelvic wall,\ntracking the course of the nerve\nRelationships of the\nendometriosis lesion with:\n- Ureter\n- Obturator internus muscle\n- Muscle denervation\nFEMORAL NERVE\n(Rare)\n- Lateral border of the psoas muscle\n- Between the psoas and iliacus muscles\n- Under the inguinal ligament, following the\nround ligament in the canal\nInfiltrating retractile tissue either in the region\niliopsoas muscle or in the inguinal region\n(adjacent to the distal round ligament)\nRelationships of the\nendometriosis lesion with the:\n- Inguinal canal\n- Common femoral artery and\nvein\nBourg et al . Insights into Imaging          (2025) 16:131 Page 5 of 16\n\nmediolateral and posterola teral parametrium (Supple-\nmental Fig. 1) [ 40, 41]. It is located below the ureter and\ndeep uterine vein, both of which serve as important\nlandmarks during surgery [ 39]. It is typically character-\nized by a roughly triangular con figuration with a pos-\nterior base (Supplemental Fig. 2) [ 40]. The sympathetic\ncontingent (from the hypogastric nerves and S2 –S3\nganglia) relaxes the detrusor muscle, contracts the\ninternal urethral and anal sphincters, promoting con-\ntinence. In contrast, the parasympathetic contingent\n(from the pelvic splanchnic nerves) stimulates the\ndetrusor contraction, faci litating bladder emptying,\nand modulates the enteric nervous system of the left\ncolon [ 40].\nThus, inferior hypogastric plexus involvement usually\npresents with vegetative symptoms such as bladder or\nrectal dysfunction (e.g., dysuria, bladder fullness, dysche-\nzia) and vaginal dryness. Sometimes, catamenial sciatica\noccurs due to traction on the sacral roots via connecting\nsplanchnic fibers. The plexus itself is not visible on MRI\ndue to its complex, spiderweb-like structure. Therefore,\nunderstanding its relationship with the pelvic viscera and\nkey anatomical landmarks is crucial. MRI typically shows\ninfiltration from a large retrocervical lesion (torus uter-\ninum and the proximal and/or distal uterosacral liga-\nments) to the sacrorectal septum of the posterolateral\nparametrium, with possible associated involvement of the\nmediolateral parametrium [ 42]. These lesions are often\nsevere, with involvement of the rectal wall [ 43]. On MRI,\nthey present as fibrotic nodular in filtration with low signal\nintensity on T2W, and loss of the normal aspect of the\nsubperitoneal pararectal cellular sheet beneath the uter-\nosacral ligament level and lateral to the mesorectal fascia\n[38]. Spiculated margins, particularly visible in the sagittal\nplane, allow assessment of the posterior extension to the\nsacral roots and deep extension to the iliococcygeus\nmuscle of the levator ani (Fig. 2)[ 38]. Preoperative MRI is\ncrucial for predicting postoperative complications, as\nexcision of these lesions can lead to urinary and rectal\ndysfunctions, often due to damage to the inferior hypo-\ngastric plexus [ 44]. The MRI report should specify the\nFig. 2 DE in a 29-year-old woman with dysmenorrhea, deep dyspareunia, and dyschezia. A Axial and ( B) sagittal T2W MR images show a right\nsubperitoneal in filtrative lesion (dotted lines) involving the anterolateral rectal wall and extending to the mesorectal fascia ( A, white arrowhead) and\nbeyond into the right posterolateral parametrium. The in filtration of the inferior hypogastric plexus shows spiculated margins ( B, black arrows) but no\nextension to the sacral roots or the pelvic wall ( A, dashed arrow). Note the safety fat line between the lesion and the iliococcygeus muscle of the levator\nani muscle ( B, white arrows). Laparoscopic surgery con firms the involvement of the inferior hypogastric plexus and a cleavage plane with the levator ani\nmuscle and sacral roots\nFig. 1 Anatomical illustration of somatic and autonomic pelvic nerves in\na female pelvis (frontal view, adapted from Alkatout et al [ 37]). 1: inferior\nhypogastric plexus, 2: hypogastric nerve, 3: sympathetic trunk with chain\nof ganglia, 4: sacral roots (S1 –S4), 5: sciatic nerve, 6: pudendal nerve, 7:\nobturator nerve, and 8: femoral nerve\nBourg et al . Insights into Imaging          (2025) 16:131 Page 6 of 16\n\ndistance and relationship of the endometriosis lesion to\nthe ureter and uterine artery anterolaterally, to the sacral\nroots posteriorly, to the levator ani muscle inferiorly and\nthe parietal pelvic fascia laterally, extending to the pir-\niformis muscle and the branches of the gluteal and/or\ninternal iliac vessels [ 38]. Extension to the sciatic nerve is\nrare.\nSacral plexus\nThe sacral plexus, formed by the L4 –S4 ventral rami, runs\nalong the anterior surface of the piriformis muscle and\nserves as a significant anatomical landmark [45]. It provides\nmotor and sensory innervation to the pelvis and the lower\nlimbs.\nOn MRI, the sacral roots, although decreasing in caliber\nfrom S1 to S4, are well traced at the level of the foramen and at\nleast in their proximal course (Supplemental Figs. 3 and 4).\nThey extend inferiorly, above, through, or below the piriformis\nmuscle and then towards the greater ischial notch, except for\nS4. The S2 and S3 nerve roots pass through the piriformis\nmuscle in most cases [ 46], with an indentation within the\nmuscle, which facilitates their visualization. However, in the\ndistal course, the S3 and S4 roots are not or barely visible.\nThe symptomatology is polymorphic and depends on\nthe affected sacral roots. It may include pudendal and\ngluteal pain, sciatica, pelvic organ dysfunctions such as\nbladder hyperactivity, urinary urgency, constipation, and\ndyschezia [ 47].\nSacral plexus involvement typically results from direct\ninfiltration by a large retrocervical lesion with posterior\nextension to the inferior hypogastric plexus and then\nthrough the connecting pelvic splanchnic nerves.\nOn MRI, sacral roots may appear thickened with\nfibrotic in filtration, extending continuously with the\nsacrorectal septum in filtration. It mainly affects the roots\nS3 and S4 due to their lower, more posterior course\n(Fig. 3), whereas S1 and S2 are generally located above the\nendometriotic extension (Fig. 4)[ 47]. While surgical\nfindings often reveal endometriotic traction or extrinsic\ninvolvement, accurately assessing the degree of in filtration\non MRI remains challenging due to the small caliber of\nthese sacral roots [ 12].\nFig. 3 DE in a 42-year-old woman, with a history of rectal shaving 10 years ago, who presented with a recurrence of symptoms, in particular deep\ndyspareunia and right sciatica. A, B Axial T2 and ( C) sagittal T2W MR images show right subperitoneal in filtrative lesion involving the anterolateral rectal\nwall ( B, arrowhead), extending to the right posterolateral parametrium with inferior hypogastric plexus involvement (stars), up to the pelvic wall with\nencasement of hypogastric vessels ( A, B, dashed arrows) and contact with the piriformis muscle. The posterior spiculated margins come into contact\nwith the S3 and S4 sacral roots ( C, arrows) and the posterior part of the right sciatic nerve ( B, circle). D Axial fat-suppressed T1W MR image reveals T1-\nhyperintense endometriotic hemorrhagic microcysts (arrows). The surgical procedure con firmed extrinsic involvement and included a shaving of the\nright sacral roots and right sciatic nerve, as well as a section of the hypogastric vessels\nBourg et al . Insights into Imaging          (2025) 16:131 Page 7 of 16\n\nFig. 4 Severe endometriosis in a 31-year-old woman with dysmenorrhea, dyspareunia, and dysesthesia in the right lower extremity. A–C Axial 3D\nT2W images from top to bottom show endometriotic in filtration of the rectal wall ( C, arrowhead) and posterior vaginal fornix ( C,s t a r ) ,w i t hc o m p l e t e\nextension to the right posterolateral parametrium including the inferior hypogastric plexus (black dashed arrows) with posterior attraction of S1 and\ncircumferential involvement of S2, S3 and S4. Note the absence of extension of the ureter ( B, C, white dashed arrow), the piriformis muscle, or\ninternal iliac vessels. D Sagittal 3D reconstruction T2W image at the level of the right posterolateral parametrium showing involvement of the\ninferior hypogastric plexus (star) extending inferiorly to the levator ani muscle (dashed arrow), and posteriorly to sacral roots S2, S3, and S4, and with\nspiculation up to S1 but no involvement. E The robotic laparoscopic view shows a complete adhesion (white arrows) between the anterior rectal\nwall (star), the uterus and vagina, the peritoneal in filtration is being subperitoneal (dotted line). Note the hypogastric nerve (black arrow) passing\nthrough the inferior hypogastric plexus affected by the endometriosis and the course of the ureter (dashed arrows) distant from the endometriotic\nlesion. F The robotic laparoscopic photography view shows, after careful dissection, the upper part of the endometriotic lesion (dotted line)\ninvolving the rectal wall (star), S2, and partially attracting S1. Note the course of the ureter (dashed arrow). G Robotic laparoscopic view showing,\nafter dissection of the endometriotic lesion (dotted line) from the rec tal wall, involvement of the posterior vaginal fornix with a submucous\nhemorrhagic cystic component (arrow) after colpotomy, of S2, S3, and S4 and retraction of S1. Note the absence of involvement of the piriformis\nmuscle (star). A complete nerve-sparing resection was performed, with S1 being retracted but removable from the lesion, and S2 –S4 being\ncircumscribed but without macroscopic intrinsic in filtration\nBourg et al . Insights into Imaging          (2025) 16:131 Page 8 of 16\n\nRarely, neural extension may progress along the sacral\nroots to the foramen, which can be better visualized on\nmultiplanar sagittal plane reconstruction, especially in\ncases of hemorrhagic implants (Supplemental Fig. 5). In\nsuch cases, the lesion ’s relationship with the foramen and\nthe presacral fascia should be reported.\nSciatic nerve\nThe sciatic nerve, the largest peripheral nerve in the body,\narises from the convergence of the ventral roots of L4 –S3,\nanterior to the piriformis muscle. It exits the pelvis\nthrough the greater sciatic foramen, curves posteriorly\nabove and out of the ischial spine, and runs laterally along\nto the common hamstring tendon between the ischial\ntuberosity and the greater trochanter [ 45]. It supplies\nmotor innervation to the posterior thigh muscles and\nsensory innervation to the lower limb, except for the\nmedial part.\nOn MRI, the sciatic nerve is clearly visible on both sides\nof the greater sciatic notch, with a “spaghetti-like”\nappearance. While its course is well traced in the axial\nplane, the coronal plane appears to be more relevant for\ndetailed assessment (Supplemental Fig. 6).\nThe hallmark symptom is a cyclic sciatica associated\nwith menstruation, and progressively shorter pain-free\nintervals. Patients usually report posterior thigh pain\nradiating down to the limb and the foot, sometimes\naccompanied by muscle weakness (foot drop), sensory\nloss, and re flex alterations [ 48].\nSciatic nerve involvement is typically identi fied at the\nsciatic notch [ 22]. It may result from endometriotic\ninfiltration extending from the ovarian fossa towards the\nsciatic notch, or in a more isolated manner, without other\nidentifiable pelvic endometriotic lesions. Isolated cases\ncould be explained by the presence of a peritoneal\ndiverticulum (pocket sign) [ 49] or the theory of perineural\nspread, especially in the absence of other endometriosis\nlesions.\nMRI typically reveals fibrotic in filtration of the sciatic\nnerve, often with hemorrhagic cystic foci, leading to\nthickening and loss of its characteristic “spaghetti-like”\nappearance. In cases of chronic nerve involvement, fatty\nmuscle atrophy may be observed, affecting muscles\ninnervated by the sciatic nerve, such as those of the\nposterior thigh, leg, and foot [ 6, 50]. Atrophy also may\naffect the glutal and piriformis muscles, which are\ninnervated by the posterior branches of the sacral plexus\nand have a close anatomical relationship to the sciatic\nnerve at the level of the greater sciatic notch. Similarly,\nthe internal obturator muscle, innervated by the anterior\nbranches of the sacral plexus, may be involved (Fig. 5).\nMuscle atrophy is mainly non-reversible and has a sig-\nnificant impact on the functional prognosis [ 51].\nAssessing intrinsic or extrinsic nerve involvement\nremains challenging on MRI. However, intraneural\nendometriosis may be suspected when the sciatic nerve\nappears abnormally thickened and hyperintense on\nT2W MR images, with visible interruption and fiber dis-\ncontinuity (Fig. 6)[ 50].\nIn the preoperative assessment, it is crucial to report the\nlesion’s size, its relationship to the obturator nerve and\nthe inferior gluteal vessels, and most importantly, its\nrelationship to the greater sciatic notch and any extra-\npelvic extension through the greater sciatic foramen.\nIndeed such cases, a combined laparoscopic and trans-\ngluteal approach may be necessary to achieve complete\nexcision of the lesion and adequate neurolysis (or\ndecompression) of the sciatic nerve [ 52].\nFig. 5 DE in a 31-year-old woman with right catamenial sciatica. A Axial T2W MR image shows fibrotic thickening in the right sciatic notch involving the\nright sciatic nerve (circle) with loss of its spaghetti aspect compared to the left sciatic nerve (arrow). This lesion is isolated without involvemen t of the\novarian fossa or the sacrorectal septum, and could illustrate the potential existence of a peritoneal diverticulum. Note the hypertrophy of the piri formis\nmuscle (star). B Axial fat-suppressed T1W MR image shows diffuse T1-hyperintense endometriotic hemorrhagic microcysts (dashed arrow). C Axial T2W\nMR image shows fatty atrophy of the right obturator internus muscle (black arrow), indicating a concomitant involvement of the nerve to the obturator\ninternus muscle passing through the sciatic notch. The patient was medically treated with an LHRH analog\nBourg et al . Insights into Imaging          (2025) 16:131 Page 9 of 16\n\nIn most cases, the nerves are embedded but not infiltrated\nwithin the epineurium, and complete release results in sig-\nnificant or complete relief of pain and motor issues [ 53].\nHowever, if the lesion in filtrates the nerves within the epi-\nneurium, excision may involve the nerve itself, thereby\nincreasing the complexity of surgery. Patients are more likely\nto experience neuropathic pain and sensorimotor disorders\nafter surgery. Most patients w ith isolated sciatic nerve\nendometriosis who present motor symptoms, such as foot\ndrop, experience little to no significant improvement [9, 53].\nPudendal nerve\nThe pudendal nerve is formed by the ventral rami of the\nS2-S4 nerve roots. It has a short intrapelvic course and\nexits the pelvis through the greater sciatic foramen,\nbetween the piriformis muscle and the ischio-coccygeal\nligament. It then curves medially along and under the\nischial spine before re-entering the pelvis through the\nlesser sciatic foramen. It joins the internal pudendal ves-\nsels and runs along the lateral ischiorectal fossa within the\npudendal (Alcock ’s) canal, bounded by the obturator\nfascia [ 45]. The pudendal nerve provides motor innerva-\ntion to the levator ani muscle, clitoral muscles, external\nanal and urethral sphincters, as well as sensory innerva-\ntion of the perineum and anus [ 54].\nEven with 3DT2 sequences, the proximal pudendal\nnerve is not easily visualized. It is necessary to identify\nanatomical landmarks of its course in order to accurately\ndiagnose its involvement. Namely, the nerve emerges at\nthe junction of the middle and distal third of the pir-\niformis muscle, then passes through an anatomical win-\ndow between the sacrotuberous and sacrospinous\nligaments. In Alcock ’s canal, the pudendal vascular pedi-\ncle serves as the landmark (Supplemental Fig. 7).\nPudendalgia presents as perineal pain or burning sen-\nsation, often worsened by sitting. Other symptoms, such\nas dyspareunia, dyschezia, or dysuria, are also commonly\nreported.\nThe pudendal nerve is primarily involved at three dif-\nferent levels.\nAt the level of the piriformis muscle, proximal pudendal\nnerve involvement may result from in filtration of the\ninferior hypogastric plexus, with posterior extension to\nthe S3 and/or S4 roots (Fig. 7).\nAt the level of the pelvic wall near the ischial spine, at\nthe entrance of Alcock ’s canal, mid-course of the\nFig. 6 DE in a 31-year-old woman with right sciatica initially cyclical, then became chronic with walking difficulties. A Axial and (B) coronal T2W MR images\nshow an infiltrative endometriotic mass of 5 cm (measure not shown) (dotted line) centered on the right sciatic notch with involvement of the sciatic nerve.\nNote the hypertrophy of the piriformis muscle (A, star). C Axial fat-suppressed T2W MR image shows denervation of the gluteus medius and minimus muscles\n(stars), indicating the involvement of the superior gluteal nerve in the sciatic notch, as well as the piriformis muscle. D Axial fat-suppressed T1W MR image\nshows a right-sided endometrioma (arrow) and hemorrhagic implants of the left ovary (dashed arrow). Surgical intervention was not possible due to th e\nintrinsic involvement of the sciatic nerve, which could risk nerve damage. The patient was treated medically with an LHRH analog\nBourg et al . Insights into Imaging          (2025) 16:131 Page 10 of 16\n\npudendal nerve involvement is often more isolated. This\nmay be associated with a peritoneal diverticulum, similar\nto sciatic nerve involvement (Fig. 8)[ 55]. It is essential to\ndescribe the lesion ’s relationship to the pudendal vascular\npedicle, the sciatic nerve, and the obturator internus\nmuscle sling posterior to the ischial spine.\nAt the level of the perineal region, pudendal nerve\ninvolvement may result from endometriosis of an\nFig. 7 DE in a 29-year-old woman with deep dyspareunia and left pudendalgia. A–C Axial and ( D) sagittal T2W MR images show fibrotic nodular\ninfiltration of the left posterolateral parametrium (stars) extending to the pelvic wall and to the iliococcygeus muscle of the levator ani muscle ( D, black\narrows), involving the left inferior hypogastric plexus, the left sacral nerves courses S3 and S4, and the level of origin of the left proximal pudenda l nerve\n(C, circle). The patient was treated medically with hormone therapy\nFig. 8 DE in a 43-year-old woman with dyspareunia and perineal pain. A Axial and ( B) coronal T2W MR images show an endometriotic lesion (circle) of\nthe right distal mediolateral parametrium extending to the pelvic wall in contact with the pudendal vascular-nerve bundle at the level of arcus tendi neus\nof the levator ani muscle ( B, arrowhead). The right ureter passes quite widely inside this lesion ( A, arrow). This lesion is located in front of the right ischial\nspine mark ( A, dashed arrow) and the sciatic nerve. This lesion is isolated without involvement of the ovarian fossa or the posterolateral parametrium.\nC Axial fat-suppressed T1W MR image showing diffuse T1-hyperintense endometriotic hemorrhagic microcysts (arrows). The patient was treated\nmedically with hormone therapy\nBourg et al . Insights into Imaging          (2025) 16:131 Page 11 of 16\n\nepisiotomy scar extending into the ischiorectal fossa\n(Fig. 9)[ 56]. MRI can assess DE pattern in this region and\nevaluate the lesion ’s relationship to the levator ani muscle,\nobturator internus muscle, vagina and anal canal. How-\never, episiotomy scar endometriosis remains rare and\nMRI is also crucial to exclude differential diagnoses such\nas granuloma, chronic in flammation, or anal fistula.\nPain management in patients with pudendal neuropathy\nincludes medical treatment with drugs (antidepressants or\nneuromodulators) and perineural injection of corticos-\nteroids and lidocaine or bupivacaine [ 55]. In most cases,\nthese injections offer temporary symptom relief. Pudendal\nnerve decompression surgery may be considered for\npatients who do not respond to medical treatment.\nFig. 9 DE in a 34-year-old woman with pudendalgia after vaginal delivery with forceps extraction and bilateral mediolateral episiotomy. A Axial and\n(B) coronal T2W MR images show a bilateral fibrotic in filtration (arrows) of the levator ani muscle at the level of the distal course of bilateral pudendal\nnerves, as well as in filtration of the left part of the vagina (A, arrowhead). C Axial fat-suppressed T1W MR image reveals some T1-hyperintense\nendometriotic hemorrhagic microcysts (arrows). D Axial T1W post-contrast MR image shows a better delineation of the left vaginal (sub) mucosal\ninvolvement (arrow). E Axial T2W and ( F) axial fat-suppressed T1W post-contrast MR images show a right vulvar lesion (arrows) correlating with clinical\nphotographs ( G). The patient was treated medically with hormone therapy\nBourg et al . Insights into Imaging          (2025) 16:131 Page 12 of 16\n\nTreatment of episiotomy scar endometriosis may\nrequire surgical excision to minimize the risk of recur-\nrence. Recently, image-guided percutaneous treatments\nusing cryotherapy have been considered [ 57].\nLumbar plexus\nThe lumbar plexus is formed by the ventral rami of the\nL1–L4 nerve roots. It descends within or posterior to the\npsoas major muscle, anterior to the L2 –L5 transverse\nprocesses, before exiting into the pelvis [ 45]. Key nerves\narising from this plexus include the obturator nerve and\nthe femoral.\nObturator nerve\nThe obturator nerve is formed by the ventral rami of\nL2–L4. It arises from the medial border of the psoas major\nmuscle and descends along the pelvic brim. It joins the\nobturator vessels and passes through the superolateral\naspect of the obturator foramen within the obturator\ncanal [ 45]. The obturator nerve provides motor innerva-\ntion to the adductor muscles of the hip and sensory\ninnervation to the medial thigh and knee.\nAlthough relatively small, this nerve is of suf ficient\ncaliber to be visualized on MRI, particularly using 3D\nT2W sequences. It is well depicted in its proximal course,\nmedial to the psoas major at L5, and then follows a des-\ncending, anterior course to join the obturator vascular\npedicle, which is easily identi fied by its characteristic flow\nvoid appearance (Supplemental Fig. 8).\nSymptomatic obturator nerve endometriosis is rare and\nmanifests with inner thigh pain, thigh adduction weak-\nness, or dif ficulty in walking [ 58].\nEndometriotic involvement of the obturator nerve is\nrare, it is commonly described in the obturator fossa\n[59–62]. It often results from the extension of a large\nendometriotic lesion from the ovarian fossa going through\nthe mediolateral parametrium up to the obturator nerve\n(Fig. 10). MRI features include a retractile fibrotic in fil-\ntration with possible hemorrhagic cystic areas along\nthe pelvic wall, tracking the course of the nerve. The\nMRI report should specify the relationship of the\nendometriosis lesion to the ureter and the obturator\ninternus muscle. In chronic cases, nerve involvement may\nresult in atrophy and fatty degeneration of the adductor\nmuscles [ 59].\nFig. 10 DE in a 29-year-old woman with deep dyspareunia, right sciatica, pain in the right inner thigh, and dif ficulty in walking. A–C Axial and\n(D) coronal T2W MR images show subperitoneal endometriosis lesion along and from the right adnexa ( A, B, white arrows), extending to the right distal\nmediolateral parametrium ( C, D, dashed arrows) and to the right obturator nerve ( B, C, black arrows). The lesion is in contact with the right sciatic nerve\nposteriorly ( B, circle), with an extrinsic traction effect but no involvement. After the failure of the medical treatment, the patient underwent surgery,\nincluding hysterectomy, right adnexectomy, right parametrectomy, ureterolysis, and dissection of the obturator nerve, which was entrapped by the mass\nBourg et al . Insights into Imaging          (2025) 16:131 Page 13 of 16\n\nFemoral nerve\nThe femoral nerve —the largest branch of the lumbar\nplexus—is formed by the L2 –L4 nerve roots. It arises from\nthe lateral border of the psoas major muscle and runs\ninferolaterally between the psoas major and iliacus mus-\ncles (Supplemental Fig. 9), before exiting the pelvis\nbeneath the inguinal ligament [ 45]. Functionally, the\nfemoral nerve is responsible for hip flexion and knee\nextension and provides sensory innervation to the medial\nthigh, anteromedial knee, medial leg, and foot.\nFemoral nerve endometriosis manifests with catamenial\nepisodes of cruralgia and partial sensory and motor loss in\nthe femoral nerve territory [ 23].\nNerve involvement in endometriosis is exceptional and\ngenerally results from a large endometriotic lesion\nextending along the course of the nerve, either in the ilio-\npsoas muscle region (Fig. 11)[ 23] or in the inguinal region\nfollowing the distal third of the round ligament [ 63]. In\nthese cases, the relationship to the inguinal canal and the\ncommon femoral artery and vein should be described.\nConclusion\nPelvic nerve involvement in endometriosis is a condition\noften underestimated by practitioners and underreported\nby radiologists. Early diagnosis is essential to prevent irre-\nversible nerve damage. MRI is the optimal imaging mod-\nality to accurately assess the distribution and the extent of\npelvic nerve involvement in endometriosis. Recognizing the\nkey features of MRI is essential for radiologists to provide\nstructured reports to assist in selecting the best therapeutic\napproach and patient counseling.\nAbbreviations\n3D Three-dimensional\nDE Deep endometriosis\nDTI Diffusion tensor imaging\nMRI Magnetic resonance imaging\nT1W T1-weighted\nT2W T2-weighted\nSupplementary information\nThe online version contains supplementary material available at https://doi.\norg/10.1186/s13244-025-02005-6.\nELECTRONIC SUPPLEMENTARY MATERIAL\nAcknowledgements\nThe authors acknowledge Camille Charpy for her native English speaker\nproofreading.\nAuthor contributions\nJ.B.: writing— original draft, conceptualization, and data curation. E.R.: writing, data\ncuration, and review and edition. P.A.B.: review and edition. M.G.: data curation. M.C.:\ndata curation. F.G.: review and edition. I.T.-N.: conceptualization, and review and\nedition. P.R.: conceptualization, and writing— review and editing, project\nadministration, and supervision.All authors read and approved thefinal manuscript.\nFunding\nThe authors state that this work has not received any funding.\nData availability\nAll patients ’ clinical and radiological data were from Lyon Sud University\nHospital and Tenon University Hospital.\nFig. 11 Femoral nerve endometriosis in a 34-year-old woman. A, B Axial 3D reconstruction T2W MR images show a fibrotic and retractile in filtration\n(circles) in contact with the right iliacus muscle (stars), on the course of the right femoral nerve (arrow). C Axial 3D reconstruction fat-suppressed T1W MR\nimage reveals some T1-hyperintense endometriotic hemorrhagic microcysts (arrow), not to be confused with the external iliac artery (dashed arrow) .\nD Axial T1W post-contrast MR image shows persistent enhancement of the lesion (arrows)\nBourg et al . Insights into Imaging          (2025) 16:131 Page 14 of 16\n\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.\nConsent for publication\nWritten informed consent was not required for this educational review\nbecause of its retrospective design and nature. No patients can be identi fied in\nthe images or clinical information presented in this educational review.\nCompeting interests\nPascal Rousset reported consultant fees from Ziwig and EDAP TMS France,\nreported receiving lecture fees from Bracco, General Electric Health care, and\ncompensation for serving on the board from Guerbet. Isabelle Thomassin-\nNaggara reported receiving lecture fees from General Electric, Siemens, Canon,\nand GSK; lecture fees and compensation for serving on the board from\nGuerbet; compensation for serving on the board from Bayer; lecture fees from\nIncepto, ICAD, Fuji film, and Hologic; and lecture fees and compensation for\nserving on the board from Bracco. François Gol fier reported consultant fees\nfrom ZIWIG.\nAuthor details\n1Department of Radiology, Hospices Civils de Lyon, Lyon Sud University\nHospital, Lyon 1 Claude Bernard University, Pierre Bénite, France. 2Department\nof Gynecology and Obstetrics, Hospices Civils de Lyon, Lyon Sud University\nHospital, Lyon 1 Claude Bernard University, EMR 3738, Pierre Bénite, France.\n3Department of Radiology, Service Imageries Radiologiques et\nInterventionnelles Spécialisées, Hôpital Tenon, Assistance Publique Hôpitaux\nde Paris, Sorbonne Université, Paris, France.\nReceived: 19 February 2025 Accepted: 25 May 2025\nReferences\n1. 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J Obstet Gynaecol\n7:70–71. https://doi.org/10.1080/01443615.1986.11978622\nPublisher’s Note\nSpringer Nature remains neutral with regard to jurisdictional claims in\npublished maps and institutional af filiations.\nBourg et al . Insights into Imaging          (2025) 16:131 Page 16 of 16","source_license":"CC0","license_restricted":false}