Analysis of the Characteristics of Intestinal Endometriosis Lesions with Rectal Involvement Using Three-Dimensional Endorectal Ultrasound

► bowel endometriosis ► deep endometriosis ► 3D endorectal ultrasound

Objective To evaluate the characteristics of endometriosis lesions affecting the rectum, using three-dimensional (3D) endorectal ultrasound.

Retrospective, observational, cross-sectional study, with data obtained through the evaluation of elec tronic medical records of patients treated at the Coloproctology Service of the Unive rsity Hospital of Universidade Federal do Maranhão (HU-UFMA). All patients assessed w ere referred for ultrasound evaluation of the rectum due to suspected lesions in another previous imaging study. Patients underwent 3D endorectal ultrasound examination from May 2017 to May 2024. The evaluated data included lesion location, degree of lesion depth in the rectal wall, longitudinal and axial length of the lesion, and its distance from the anal margin.

The sample consisted of 69 patients with a total of 72 foci. All lesions found were in the anterior hemicircumference of the rectum. The most common location of the foci was the middle (25) and upper (27) recta, with 8 foci also found in the lower rectum. Six patients had foci in more than one segment. Of the 72 foci found, the majority (39) involved the muscularis pro pria of the rectum. Regarding the length of the longest axis of the lesion, in the longitudinal plane the average was 1.84 cm and in the axial plane the average was 1.86 cm. The lesions were on average 9.0 cm from the anal margin.

Intestinal endometriosis lesions predominate in the middle and upper recta, approximately 9.0 cm from the anal margin, and mostly involve the muscularis propria of the rectum. /C3 Study developed at the Coloproctology Service, Hospital Universi- tário da Universidade Federal do Maranhão (HU-UFMA) São Luís, MA, Brazil, and presented in the 72nd Brazilian Congress of Coloproctology, in 2024. received April 9, 2025 accepted after revision November 10, 2025 DOI https://doi.org/ 10.1055/s-0046-1817784. ISSN 2237-9363. Editor-in-Chief :H e n r i q u e Fillmann. © 2026. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution 4.0 International License, permitting copying and reproduction so long as the original work is given appropriate credit (https://creativecommons.org/licenses/by/4.0/) Thieme Revinter Publicações Ltda., Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil THIEME Original Article 1 Article published online: 2026-05-05

Endometriosis is a gynecological disease, characterized by the presence and growth of endometrial tissue outside the uterine cavity, affecting approximately 10 to 15% of women of reproductive age. Intestinal involvement occurs in 3 to 37% of cases of deep endometriosis, representing one of the most complex and challenging forms of this condition. 1,2 Intesti- nal involvement presents a characteristic anatomical distri- bution, with a prevalence of 85% in the rectum and sigmoid, followed by the terminal ileum (7%), appendix (5%), and cecum (3%). This distribution has important clinical signi fi- cance, as it directly in fluences the symptomatologic presen- tation and therapeutic approach. 2 The pathophysiology of intestinal endometriosis involves a chronic inflammatory process that can result in progressive fibrosis and structural changes in the intestinal wall. Lesions typically progress from the serosa toward the mucosa, with a characteristic in filtration pattern that respects the layered architecture of the organ. This biological behavior results in different degrees of tissue invasion, ranging from super ficial involvement to complete transmural invasion. 3 The clinical presentation is heterogeneous and frequent- ly overlaps with other functional gastrointestinal condi- tions. The most prevalent symptoms include dysmenorrhea (79%), chronic pelvic pain (69%), dyspareunia (45%), and cyclical intestinal changes such as pain during defecation (29%), constipation (28%), and rectal bleeding (15%). The non-specific nature of these symptoms contributes to an average diagnostic delay of 7 years from the onset of symptoms. 2,4,5 Accurate diagnosis and detailed characterization of lesions are fundamental for adequate therapeutic planning. Recent advances in prepared transvaginal ultrasound (TVUS) and prepared magnetic resonance imaging (MRI) protocols have signi ficantly improved diagnostic accuracy, although

remain for rectal wall characterization. In this context, three-dimensional endorectal ultrasound 3D (ERUS) emerges as a complementary tool. It allows detailed visualization of rectal wall layers, the extent of invasion, lesion size, and distance from the anal margin. These findings support surgical planning, including decisions between segmental resection and more conservative options such as discoid resection or shaving. 2,6 The diagnostic accuracy of 3D ERUS has been consistently demonstrated in the literature, with a sensitivity of 97% and specificity of 96% for detecting rectal lesions, surpassing other imaging methods in assessing the depth of invasion in the rectal wall. Additionally, the method offers practical advantages such as good tolerability and absence of exposure to ionizing radiation. 4 The precise characterization of rectal endometriotic lesions also has important prognostic implications. Lesions with deep in filtration of the rectal wall (beyond the muscu- laris propria) are associated with a higher risk of surgical complications and a greater likelihood of requiring segmen- tal resection. On the other hand, super ficial lesions may be candidates for more conservative techniques such as discoid resection, highlighting the importance of precise preopera- tive staging. 2 The objective of the present study was to evaluate the characteristics of endometriosis lesions affecting the rectum, using 3D ERUS.

The present is a retrospective, observational cross-sectional study, with data obtained through the evaluation of elec - tronic medical records, using the University Hospitals Man- agement Application (Aplicativo de Gestão para Hospitais Universitários, AGHU, in Portuguese), of patients treated at the Coloproctology Service of Hospital Universitário da Uni- versidade Federal do Maranhão (HU-UFMA). The study was conducted in accordance with the required ethical standards and approved by the Research Ethics Committee of HU- UFMA, in accordance with the attributions de fined in Reso- lution nr. 466/2012 of the Brazilian National Health Council (Conselho Nacional de Saúde, CNS, in Portuguese) and CNS Operational Standard nr. 001 of 2013, under CAAE: 86250825.1.0000.5086. Patients underwent 3D ERUS examination from May 2017 to May 2024. The inclusion criteria were women aged 18 to 49 years with suspected intestinal endometriosis based on clinical symptoms (dysmenorrhea, pelvic pain, dyspareunia, painful defecation, rectal bleeding, constipation) and con- firmed by previous imaging (TVUS and/or MRI). The BK Medical Flex-Focus (GE HealthCare) equipment was used. Patients were examined in the left lateral decubi- tus position and underwent one rectal enema 2 hours before the examination. After digital rectal examination, the probe was introduced up to 14 cm from the anal margin, and subsequently, scans were performed from proximal to distal. Procedures were performed without anesthetic sedation, as tolerance was good with only rectal preparation. To ensure homogeneity in the study population and reduce bias, patients with associated anorectal conditions such as in flammatory bowel disease, anorectal cancer, and patients who had undergone previous pelvic radiation were excluded. The evaluated data included lesion location (lower, rec - tum, or upper rectum), degree of lesion depth in the rectal wall, longitudinal length of the lesion, axial length of the lesion, and distance of the lesion from the anal margin. All evaluations were made on multiplanar images. Two planes were used simultaneously to minimize errors. The final sample consisted of 69 patients with intestinal endometri- osis. Three patients were excluded because rectal involve- ment was not visualized on endorectal ultrasound, leaving 66 patients in the study. The anal canal was systematically evaluated during probe insertion and withdrawal; no endometriotic foci were iden- tified in this region. The creation of the database and spreadsheets for statis- tical analysis, tables, and graphs was carried out with the help of GraphPadPrism (GraphPad Software) and Microsoft Excel (Microsoft Corp.) applications. J Coloproctol Vol. 46 No. 1/2026 © 2026. The Author(s). 3D Endorectal Ultrasound for Intestinal Endometriosis Lesions Fernandes et al.2

The current study evaluated 69 patients diagnosed with intestinal endometriosis, with 3 of them being excluded for not presenting visible focus on 3D ERUS, thus resulting in a final sample of 66 patients. The mean age of the patients was 37.4 (range: 18 –49) years. A total of 72 foci were found. Regarding the location of the foci, all lesions found were in the anterior hemicircumfer- ence of the rectum ( ►Fig. 1). As for height, the most common locations of the foci were the middle (30) and upper (32) recta, with 10 foci also being found in the lower rectum ( ►Fig. 2 ). Six patients had foci in more than one segment (one with foci in the lower and middle recta; one in the lower and upper recta, and four in the middle and upper recta). Regarding the depth of infiltration in the rectal wall, of the 72 foci found, the majority (39) involved the muscularis propria of the rectum ( ►Fig. 3 ). Twenty-four affected the perirectal fat, 6 reached the submucosa, and 3 reached the muscularis mucosa ( ►Fig. 4 ). In the evaluation, the average length of the longest axis of the lesion, in the longitudinal plane, was 1.84 cm (0.37 – 3.5 cm), and in the axial plane the average was 1.86 cm (1.12–4.25 cm). In terms of distance from the anal margin, the lesions were on average 9.0 cm from it ( ►Fig. 5 ).

Deep endometriosis with intestinal involvement represents a signi ficant challenge both in diagnosis and therapeutic management. Studies show that intestinal involvement occurs in up to 37% of cases of deep endometriosis, with the rectum and rectosigmoid junction being the most fre- quently affected segments. 1,3 The mean age of patients in the current study was 37.4 years. Of the studies evaluated on the topic, 8 reported the mean age of patients, resulting in a general average ranging Fig. 1 Endometriosis focus evaluated by three-dimensional endor- ectal ultrasound (axial view) affecting the anterior circumference of the rectum. Fig. 2 Distribution by rectal segment. Fig. 3 Endometriosis focus evaluated by three-dimensional endor- ectal ultrasound (axial view) involving the muscular layer of the rectum. Fig. 4 Depth of lesion invasion. J Coloproctol Vol. 46 No. 1/2026 © 2026. The Author(s). 3D Endorectal Ultrasound for Intestinal Endometriosis Lesions Fernandes et al. 3 from 27.8 to 36.8 years. These data are consistent with the epidemiology of the disease, which has incidence and prev- alence concentrated in women of reproductive age. 1 Diagnostic precision is fundamental for adequate therapeu- tic planning. In this context, 3D ERUS has emerged as a promising tool, demonstrating high sensitivity and specificity in the detection and characterization of rectal lesions. Recent studies, such as that by Broch et al., 7 involving 120 patients with suspected deep endometriosis, of whom 60 underwent 3D ERUS, showed a signi ficant correlation between the find- ings of 3D ERUS and videolaparoscopic surgical findings. The work of Lunardelli et al., 8 which compared the histo- pathological findings of 40 patients with deep endometriosis previously subjected to 3D ERUS, concluded that 72.5% of patients had concordance between the examination findings and the anatomopathological report. Grif fiths et al., 9 in a similar study, evaluated 32 women who underwent 3D ERUS showing endometriotic focus in the rectovaginal septum, who were subsequently subjected to therapeutic laparosco- py. The results showed a sensitivity and specificity of 78% and 93%, respectively, concluding that the method is a particu- larly important preoperative test, with high concordance between ultrasound and histopathological findings. In the present study, of the 66 patients evaluated, 6 (9.09%) had foci in more than 1 rectal segment. Other studies have also observed patients with multiple foci in the rectal wall. Bahr et al., 10 for example, evaluated 37 patients using 3D ERUS, of whom 25 presented only 1 focus, 4 patients presented 4 foci, and one presented 3 foci. The work of Mezzi et al., 11 which evaluated 63 patients diagnosed with pelvic endometriosis using 3D ERUS, also showed that the method may be able to evidence endometriotic lesions in other pelvic organs, not just the rectum. The locations found were: uterus (33.3%), pouch of Douglas (31.7%), rectosigmoid junction (42.8%), rectovaginal septum (9.5%), ovary (9.5%), and others (1.6% had bladder involvement). Of the 63 patients, 4 pre- sented multiple focus of endometriosis in the pelvic region. The multifocal involvement pattern of endometriosis is observed in most studies on the topic. Broch et al. 7 mention patients with lesions in the ileum and right colon seen during videolaparoscopy, in addition to nine patients requiring appendectomy. Sagae et al., 12 in their 2007 study, during the cavity inventory, also identified lesions in other locations such as ileum, right colon, sigmoid, and appendix. Cazalis et al., 13 in their analysis involving MRI, 3D ERUS, and TVUS evaluation, showed foci distributed in different pelvic struc - tures such as the pouch of Douglas, bladder, and uterosacral ligaments. In the present study, all lesions found were located in the anterior hemicircumference of the rectum, corroborating the findings of authors such as Bahr et al., 10 who also identi fied 100% of lesions in this location, with 63% in an anteromedial location and 37% anterolateral. Since there is a scarcity of studies on the use of 3D ERUS to assess rectal wall involvement, we compared the depth of the lesion with those of other modalities. It is important to note that some studies cited in the literature use endoscopic ultrasonography, which, although similar, has a distinct methodology from 3D ERUS. 13 Regarding the in filtration of focus, Rossi et al. 14 analyzed the ability of endoscopic sonography to predict the depth of involvement of endometriosis focus in the rectal wall in 38 patients who underwent the examination and were subse- quently subjected to laparoscopic surgery. Their results showed that for the detection of in filtration of the muscular layer by endometriosis, the positive predictive value (PPV) of 3D ERUS was 100%, while for the detection of submucosa/mucosa layer involvement, the sensitivity was 89%, the speci ficity was 26%, the PPV was 55%, the negative predictive value (NPV) was 71%, with test accuracy of 58%. Thus, the analysis concluded that, in 3D ERUS, endometriotic infiltration of the muscular layer can be predicted with precision. However, it is less accurate in detecting submuco- sa layer involvement. The present study identi fied greater involvement of the muscularis propria (54.2% of cases), similar to the findings of Broch et al., 7 who in their work also found a greater number of lesions that affected up to the muscularis propria layer of the rectum (24 of the 41 patients with intestinal endometri- osis evaluated). Tomiyoshi et al. 15 corroborate these data, showing, in their analysis, that 44.44% of patients had focus affecting the muscular layer of the rectum, followed by 31.4% of patients with focus restricted to the perirectal fat, and other patients excluded due to lack of data. In contrast, the Fig. 5 Endometriosis focus (arrows) evaluated by three-dimensional endorectal ultrasound (sagittal view) approximately 10 cm from the anal margin. J Coloproctol Vol. 46 No. 1/2026 © 2026. The Author(s). 3D Endorectal Ultrasound for Intestinal Endometriosis Lesions Fernandes et al.4 study by Sagae et al., 16 published in 2009, shows a more heterogeneous distribution of this involvement, evidencing that 75% of patients studied by 3D ERUS had focus restricted to the perirectal fat, only 15% with focus involving the muscularis propria, and 10% with focus involving all layers of the rectum. Tomiyoshi et al., 15 in their analysis of 63 patients with suspected deep endometriosis, compared the findings of 3D ERUS with MRI. The authors found almost perfect concor- dance for lesions that invaded the muscularis propria of the rectum, findings that highlight the similar speci ficity be- tween 3D ERUS and the method traditionally considered the gold standard (MRI). In accordance with the cited data, a literature review conducted by Roseau et al. 17 concluded that when compared to other imaging examinations appropriate for diagnosing deep pelvic endometriosis, 3D ERUS is better at diagnosing infiltrations of the rectal wall and the rectovaginal septum, while MRI and TVUS seem more appropriate for diagnosing ovarian endometriomas and infiltrations of the uterine torus, uterosacral ligaments, or bladder. Piketty et al., 18 comparing the performance of 3D ERUS in relation to TVUS in diagnosing involvement by endometriotic focus in the intestinal wall, noted that the former presented sensitivity of 96% and speci ficity of 100% (PPV ¼ 100% and NPV ¼ 95.2%), while the latter showed sensitivity of 90.7% and speci ficity of 96.5% (PPV ¼ 97.1% and NPV ¼ 88.9%), concluding that both methods present similar degrees of precision for diagnosis. This work also evaluated the size of lesions found in the rectum, by measuring the largest axis in the longitudinal plane and in the axial plane, finding an average of 1.84 cm and 1.86 cm, respectively. When comparing with other stud- ies, it is noted that there is no signi ficant difference in this average. The study by Lunardelli et al., 8 for example, showed a general average of 2.1 cm. The authors also evaluated the distance of the focus from the sphincter apparatus, finding an average of 4.2 cm. The present study evaluated the distance between the focus and the anal margin, resulting in an average of 9 cm. When considering that the female anal canal can vary from 2.5 to 4 cm in length, associating with the findings of Lunardelli’s study, 8 we note that the focus tends to predominate in the middle and upper rectum. Technical Aspects and Clinical Implications The comparative analysis of these studies reveals some important points: 1. Diagnostic accuracy: 3D ERUS consistently demonstrates high sensitivity and specificity for detecting rectal lesions, especially when there is invasion of the muscularis prop- ria, a finding con firmed in all analyzed series. 2. Pattern of involvement: There is a clear predominance of lesions in the anterior hemicircumference of the rectum and in the middle and upper portions, a pattern observed in different studies. 3. Multimodal validation: The strong concordance between different diagnostic methods (3D ERUS, MRI, and video- laparoscopy) reinforces the reliability of 3D ERUS as a diagnostic tool.

Three-dimensional endorectal ultrasound proved to be an effective diagnostic tool in characterizing endometriosis lesions with rectal involvement. Intestinal endometriosis lesions predominate in the anterior hemicircumference of the middle and upper recta, at an average distance of 9.0 cm from the anal margin, affecting the muscularis propria layer and are less than 2.0 cm in length per plane. The precise characterization of lesions through 3D ERUS provides impor- tant information for de fining the surgical strategy, contrib- uting to a more individualized and potentially more effective approach in the treatment of intestinal endometriosis. Data Availability Data will be available upon request to the corresponding author. Funding The authors declare that they did not receive funding from agencies in the public, private or non-pro fit sectors to conduct the present study. Conflict of Interests The authors have no con flict of interests to declare.

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