{"paper_id":"c25e265b-ae53-4bd7-951a-363659451852","body_text":"1\nV olume 11; Issue 01\nAnn Case Rep, an open access journal\nISSN: 2574-7754\nExtra-Pelvic Endometriosis: A Pictorial Essay\nCaroline Chabot1*, Bruno Vande Berg2\n1Department of Radiology, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Brussels, Belgium\n2Department of Radiology, Clinique CHC MontLégia, Liège, Belgium\nAnnals of Case Reports\nChabot C, et al. Ann Case Rep: 11: 102531\nwww.doi.org/10.29011/2574-7754.102531\nwww.gavinpublishers.com\nReview Article\n*Corresponding author: Dr. Caroline Chabot, Department of Radiology, Cliniques Universitaires Saint Luc, Université Catholique de \nLouvain, Avenue Hippocrate, 10 ; B-1200 Brussels, Belgium \nCitation: Chabot C, Vande Berg B. (2026). Extra-Pelvic Endometriosis: A Pictorial Essay. Ann Case Report. 11: 2531. DOI: \n10.29011/2574-7754.102531\nReceived: 08 February 2026; Accepted: 12 February 2026; Published: 16 February 2026\nAbstract\nExtra-pelvic endometriosis is an uncommon manifestation that may involve the abdominal wall, skeletal muscles, or peripheral \nnerves, presenting with painful masses or neuropathic symptoms. Magnetic resonance imaging (MRI) plays a pivotal role in lesion \ndetection by enabling detailed assessment of tissue composition, localization, and extent, as well as evaluation of associated pelvic \ndisease.\nThis pictorial essay illustrates the spectrum of MRI appearances of extra-pelvic endometriosis and emphasizes imaging features that \nfacilitate accurate diagnosis and guide optimal patient management.\nKeywords: Abdominal wall; Extra-pelvic endometriosis; MRI; \nUltrasound\nIntroduction\nEndometriosis is defined by the presence of endometrial glands \nand stroma outside the uterine cavity and affects approximately \n5-10% of women of reproductive age. [1] Although pelvic \ninvolvement is most common, extra-pelvic manifestations can \noccur in the abdominal wall, skeletal muscles, peripheral nerves, or \neven distant sites such as the lungs and diaphragm. These atypical \npresentations often pose diagnostic challenges, as symptoms \nmay not follow a cyclical pattern and may mimic other benign or \nmalignant conditions.\nPatients with extra-pelvic endometriosis may present with a \npainful mass, focal discomfort, or unusual neuropathic symptoms. \nImaging is therefore critical for lesion identification and \ndifferentiation from desmoid tumors, granulomas, hernias, or \nsoft tissue malignancies. [2,3]\n Among imaging modalities, MRI \noffers superior tissue characterization, enabling precise mapping \nof lesion composition, extent, and relation to adjacent structures, \nwhich is particularly valuable for surgical planning.\nAbdominal Wall Endometriosis\nAbdominal wall endometriosis is the most frequent form of extra-\npelvic endometriosis and is predominantly associated with prior \nsurgical scars, most commonly following cesarean sections or \nlaparotomies, with a reported incidence ranging from 0.03% to \n1%. [2,4]\n The prevailing mechanism is iatrogenic implantation of \nendometrial cells during surgery. Nevertheless, up to 20% of cases \noccur in patients without prior abdominal surgery, often located \nin inguinal or periumbilical regions, suggesting alternative routes \nsuch as lymphatic or hematogenous dissemination. [1]\nClinical symptoms typically appear several years after surgery, \nwith a mean delay of 3-4 years. Pain is present in the majority of \npatients and is cyclic in roughly half of cases. [2,5] Associated \npelvic endometriosis has been reported in 13-46% of patients [4,5].\nUltrasound is often the first-line imaging modality but remains \nnonspecific. Lesions usually appear as ill-defined hypo- to isoechoic \nmasses with variable vascularity on color Doppler imaging. Cystic \ncomponents may be present, and lesion appearance can fluctuate \nthroughout the menstrual cycle. Fine-needle aspiration often yields \ninsufficient or non-diagnostic material due to the fibrotic content \n\nCitation: Chabot C, Vande Berg B. (2026). Extra-Pelvic Endometriosis: A Pictorial Essay. Ann Case Report. 11: 2531. DOI: \n10.29011/2574-7754.102531\n2\nV olume 11; Issue 01\nAnn Case Rep, an open access journal\nISSN: 2574-7754\nof the lesions. Core biopsy may be considered, but puncture tracts \nshould be excised during subsequent surgery to prevent recurrence \n[3].\nMRI is the reference standard for evaluating abdominal wall and \nintramuscular endometriosis. Imaging features vary according to \nlesion composition. Predominantly fibrous lesions exhibit low \nto intermediate signal intensity on T2-weighted images, often \nwith ill-defined margins and infiltrative growth patterns (Figure \n1). Intramuscular cystic lesions may be well-circumscribed, \noccasionally resembling ectopic ovarian endometriomas (Figure \n2). Infiltrative intramuscular lesions with hemorrhagic microcysts \npresent as punctate or confluent hyperintense foci on fat-\nsuppressed T1-weighted images (Figure 3). Overall, lesions can \nbe iso- to hyperintense relative to muscle on T2-weighted images, \nwith focal T1 hyperintensity reflecting hemorrhagic components, a \nfeature highly suggestive of endometriosis. [3,5]\n After gadolinium \nadministration, lesions usually demonstrate moderate to marked, \noften heterogeneous, enhancement. Lesions may appear nodular, \nspiculated, or retractile and can infiltrate adjacent muscular layers, \nincluding the rectus abdominis or oblique muscles. Diffusion-\nweighted imaging often demonstrates intermediate diffusion \nrestriction, with reported apparent diffusion coefficient (ADC) \nvalues around 0.93 × 10⁻³ mm²/s. [5]\n MRI also permits accurate \ndelineation of lesion extent through the abdominal wall layers and \nfacilitates detection of concurrent pelvic disease, which is essential \nfor comprehensive surgical planning [3,5].\nFigure 1: 33-year-old woman with predominantly fibrous hypodermic abdominal wall endometriosis on the left side. (a) B-mode \nultrasound image shows an ill-defined hypodermic lesion of the left abdominal wall. (b) Color Doppler ultrasound image shows minimal \nvascularity. (c) Axial T1-weighted MRI image demonstrates low signal intensity. (d) Axial fat-suppressed T1-weighted MRI image \nshows foci of hyperintensity. (e) Axial and (f) coronal T2-weighted MRI images demonstrate low to intermediate signal intensity \n(arrow), consistent with a predominantly fibrous infiltrative lesion. (g) Axial contrast-enhanced 3D T1-weighted GRE MRI image shows \nmoderate heterogeneous enhancement.\n\nCitation: Chabot C, Vande Berg B. (2026). Extra-Pelvic Endometriosis: A Pictorial Essay. Ann Case Report. 11: 2531. DOI: \n10.29011/2574-7754.102531\n3\nV olume 11; Issue 01\nAnn Case Rep, an open access journal\nISSN: 2574-7754\nFigure 2: 25-year-old woman with intramuscular cystic abdominal wall endometriosis involving the left rectus abdominis muscle. (a) \nSagittal T1-weighted MRI image shows a well-circumscribed predominantly cystic lesion with high signal intensity (arrow). (b) Fat-\nsuppressed T1-weighted MRI image demonstrates marked hyperintensity, consistent with hemorrhagic content (arrow). (c) Sagittal T2-\nweighted MRI image shows heterogeneous signal intensity with a well-defined fluid component (arrow), resembling an ectopic ovarian \nendometrioma.\nFigure 3: 51-year-old woman with infiltrative intramuscular abdominal wall endometriosis involving the right rectus abdominis muscle. \n(a) B-mode ultrasound image shows a parietal intramuscular lesion. (b) Color Doppler ultrasound image demonstrates mild hyperemia. \n(c) Sagittal T1-weighted MRI image shows slight hyperintensity (arrow). (d) Fat-suppressed T1-weighted MRI image demonstrates \npunctate and confluent foci of marked hyperintensity, reflecting hemorrhagic microcysts (arrow). (e) Sagittal T2-weighted MRI image \nshows iso- to moderately hyperintense signal relative to muscle (arrow), consistent with infiltrative endometriosis.\n\nCitation: Chabot C, Vande Berg B. (2026). Extra-Pelvic Endometriosis: A Pictorial Essay. Ann Case Report. 11: 2531. DOI: \n10.29011/2574-7754.102531\n4\nV olume 11; Issue 01\nAnn Case Rep, an open access journal\nISSN: 2574-7754\nNerve Endometriosis\nEndometriotic involvement of peripheral nerves is rare but can lead to severe neuropathic pain, which may be cyclic or continuous. \nFrequently affected nerves include the sciatic nerve, lumbosacral plexus, genitofemoral nerve, ilioinguinal nerve, iliohypogastric nerve, \nand branches of the abdominal wall nerves. Pathophysiology typically involves perineural or endoneural infiltration, sometimes tracking \nalong the round ligament [1].\nTwo main MRI phenotypes are recognized. Fibrous infiltrative lesions appear hypointense on both T1- and T2-weighted sequences and \nare often associated with deep endometriosis (Figure 4), whereas cystic or hemorrhagic lesions demonstrate hyperintensity on T1- and \nT2-weighted sequences. Advanced MRI sequences, such as high-resolution 3D T2 and diffusion tensor imaging (DTI), enhance lesion \ndetection and allow visualization of the relationship between endometriotic tissue and nerve fascicles. Accurate imaging is crucial, as \nnerve-sparing surgery or targeted medical therapy may be required to prevent irreversible neurological deficits [6].\nFigure 4: Woman with fibrous infiltrative right sciatic nerve endometriosis. (a) T1-weighted MRI image shows a low-signal-intensity \nfocus along the right sciatic nerve (arrow), consistent with perineural fibrous infiltration. (b) Coronal and (c) axial T2-weighted MRI \nimages demonstrate hypointense infiltrative tissue along the right sciatic nerve (arrows), characteristic of deep endometriosis. No \nabnormality is observed on the left side.\nConclusion\nExtra-pelvic endometriosis, though uncommon, should be \nconsidered in women of reproductive age presenting with painful \nabdominal wall masses, groin pain, or atypical neuropathic \nsymptoms. MRI provides comprehensive assessment of lesion \ncomposition, location, and extent, and enables detection of \nassociated pelvic disease. Recognition of characteristic imaging \npatterns facilitates accurate diagnosis, reduces misdiagnosis, and \nguides appropriate management strategies, including surgical \nplanning and medical therapy. Early identification and precise \nmapping of lesions can significantly improve patient outcomes and \nquality of life.\nFunding: None.\nAcknowledgment: None.\nReferences\n1. Hirata T, Koga K, Osuga Y. (2020). Extra-pelvic endometriosis: a \nreview. Reprod Med Biol. 19: 323-333.\n\nCitation: Chabot C, Vande Berg B. (2026). Extra-Pelvic Endometriosis: A Pictorial Essay. Ann Case Report. 11: 2531. DOI: \n10.29011/2574-7754.102531\n5\nV olume 11; Issue 01\nAnn Case Rep, an open access journal\nISSN: 2574-7754\n2. Hensen JH, Van Breda Vriesman AC, Puylaert JB. (2006). Abdominal \nwall endometriosis: clinical presentation and imaging features with \nemphasis on sonography. Am J Roentgenol. 186: 616-620.\n3. Gidwaney R, Badler RL, Yam BL, Hines JJ, Alexeeva V, et al. (2012). \nEndometriosis of abdominal and pelvic wall scars: multimodality \nimaging findings, pathologic correlation, and radiologic mimics. \nRadiographics. 32: 2031-2043.\n4. Carsote M, Terzea DC, Valea A, Gheorghisan-Galateanu AA. (2020). \nAbdominal wall endometriosis (a narrative review). Int J Med Sci. 17: \n536-542.\n5. Busard MP, Mijatovic V, van Kuijk C, Hompes PG, van Waesberghe \nJH. (2010). Appearance of abdominal wall endometriosis on MR \nimaging. Eur Radiol. 20: 1267-1276.\n6. Colak C, Chamie LP, Youngner J, Forney MC, Luna Russo MA, \nGubbels A, et al. (2024). MRI features of pelvic nerve involvement in \nendometriosis. Radiographics. 44: e230106.","source_license":"CC0","license_restricted":false}