A nomogram integrating a novel uterine isthmus ratio (APTUIR), sonographic signs and clinical symptoms for predicting posterior deep endometriosis

Objective This study aims to propose a novel, reproducible transvaginal ultrasound (TVUS) measurement—anterior–posterior wall thickness of the uterine isthmus ratio (APTUIR)—and to construct a nomogram model integrating this parameter with other ultrasound assessments and clinical symptoms for predicting the risk of posterior pelvic deep endometriosis (DE).

This retrospective study included 362 patients with endometriosis (153 with posterior pelvic DE; 209 without) who underwent TVUS and surgery between 2021 and 2024. APTUIR, uterine white sliding lines (WSL), and clinical symptoms were assessed. LASSO regression was used to identify independent predictors and construct a nomogram. Model performance was evaluated by area under the curve (AUC), calibration curves and decision curve analysis (DCA) with internal validation (500 bootstrap samples).

Results showed statistically significant differences between groups in dyspareunia, menstrual defecation abnormalities, CA125, uterine anteroposterior diameter, concomitant endometrial polyps (EPs), uterine posterior isthmus echo, uterine anterior WSL, uterine posterior WSL, ovarian kiss sign and APTUIR (p < 0.05). Four key predictors were identified: APTUIR, posterior uterine wall WSL, EPs, and menstrual bowel dysfunction. The nomogram demonstrated excellent predictive performance: AUC 0.933 (95% CI: 0.901–0.957), sensitivity of 85.0%, specificity of 88.0% and accuracy of 86.7%. The calibration curve of the nomogram demonstrated good consistency, whilst the decision curve indicated favourable clinical utility.

The APTUIR-based nomogram provides a non-invasive, highly accurate tool for identifying high-risk posterior pelvic DE. It facilitates objective risk stratification and timely specialist referral, particularly in non-specialised settings. Similar content being viewed by others

The posterior pelvic cavity is the most common site for deep endometriosis (DE), primarily involving the posterior cervical region, uterosacral ligaments, rectovaginal septum and anterior rectal wall [1]. Posterior pelvic DE typical clinical symptoms include chronic pelvic pain, dyspareunia, defecation abnormalities and infertility [2, 3]. Moreover, the complex anatomical structure of the posterior pelvic cavity significantly increases the endometriosis surgical complexity and the risk of organ dysfunction [4, 5]. Accurate preoperative identification and assessment of lesions are crucial for surgical planning, risk evaluation and patient consultation [6, 7]. Although transvaginal ultrasound (TVUS) is the first-line diagnostic tool [8, 9], its diagnostic efficacy is constrained by a relatively high “experience threshold”, leading to diagnostic delays and unequal distribution of healthcare resources in non-specialist centres [10, 11]. Consequently, developing an objective and widely applicable screening tool is crucial for optimising resource allocation. Recent studies have shown the potential of simplified uterine morphological parameters in evaluating endometriosis-related lesions. The anteroposterior diameter [12] and the myometrial–cervical ratio [13] have emerged as effective quantitative tools for evaluating endometriosis-related pathologies. The uterine “torsion sign” [14] and white sliding lines (WSL) [11] are primarily employed to predict posterior pelvic displacement. However, the clinical application of these indicators is limited by their restricted sensitivity or high operator dependency. Over one-third of posterior pelvic DE cases lack the “torsion sign”, whilst WSL assessment remains a qualitative technique, posing significant challenges for clinicians in non-specialist centres. From a pathological mechanism perspective, the development of DE involves complex processes including chronic inflammation, fibrotic deposition, and tissue remodelling [15, 16]. Fibrosis, as one of the central features of DE, can lead to pelvic organ adhesions and distortion of anatomical structures [17]. Within this inflammatory microenvironment, endometrial polyps (EPs) may serve as systemic markers reflecting overall pathological activity [18]. As the anterior boundary of the posterior pelvic space, the myometrial structure of the uterine isthmus is more directly affected by the fibrotic infiltration of adjacent lesions. Bernigaud [19] assessed the impact of endometriosis surgery by measuring the thickness of the uterine isthmus by MRI, indirectly confirming the association between the posterior pelvic DE and isthmic morphology. However, no studies to date have systematically investigated the association between the APTUIR—a readily obtainable quantitative parameter by routine TVUS—and posterior pelvic DE. A nomogram is a statistical model for individualised risk assessment that is easily applied, reproducible and relatively objective, providing clinicians with a tool for quantitatively predicting disease occurrence [20]. Given the complex manifestations of posterior pelvic DE, this study aims to propose a novel, reproducible TVUS measurement—APTUIR—and to establish a predictive model for the risk of posterior pelvic DE by integrating clinical baseline data and other ultrasound assessment parameters. This model enables the early identification of high-risk individuals through simple ultrasound screening, optimises referral pathways, reduces diagnostic delays and facilitates individualised treatment decisions.

Study subjects A retrospective cohort study was conducted involving patients diagnosed with endometriosis by transvaginal ultrasound examination and laparoscopic surgery at Shenzhen Second People’s Hospital between January 2021 and December 2024. Participants were categorised into two groups based on surgical and pathological findings: the group with posterior pelvic DE and the group without posterior pelvic DE. Exclusion criteria: (1) pregnancy; (2) multiple fibroids exceeding 5 cm in size or isthmic-cervical fibroids; (3) history of prior pelvic surgery; (4) incomplete clinical data or poor ultrasound image quality; (5) concurrent uterine malformations; (6) perimenopausal or postmenopausal status; (7) concurrent caesarean scar diverticulum (Fig. 1). This study received approval from the Ethics Committee of Shenzhen Second People’s Hospital (Ethics Approval Number: 2025–391-01PJ). Informed consent was not required for this retrospective review. Archives were examined for the temporal sequence and outcomes, and patient care was not altered in any manner during the audit process. Furthermore, all information was de-identified. Clinical and laboratory data The clinical data collected included: age, body mass index (BMI), history of infertility, EPs, menstrual characteristics including cycle length and flow volume, severity of dysmenorrhea (VAS score), abnormal defecation during menstruation and dyspareunia. The laboratory data collected included CA125 levels. The visual analogue scale (VAS) is a 10-cm line marked at its ends with ‘no pain’ and ‘the worst pain imaginable’. Patients can quantify their pain on a scale of 0–10 cm based on the distance from either end of the scale. When the VAS score is ≥ 7 cm, many researchers classify endometriosis pain symptoms as severe [21, 22]. Ultrasonic data Utilise GE Volusion E6, E8, and E10 ultrasound diagnostic systems (GE Healthcare, USA) with transvaginal probes operating at 5–9 MHz. Routine transvaginal ultrasound examinations (TVUS) are performed on patients. For those unable to undergo TVUS, transrectal examinations may be conducted. Preoperative ultrasound examinations were performed and reported by physicians with 7 to 15 years’ experience in gynaecological ultrasound. At a minimum, standard images retained include the uterine midline sagittal view, transverse section and bilateral ovarian views. The standard mid-sagittal plane is defined as simultaneously displaying the uterine fundus, uterine body and the entire length of the cervical canal. Ultrasound image measurement and analysis were performed by the same primary doctor Y (5 years of experience) following training by a specialist (C.QX.) in endometriosis ultrasound, who remained unaware of surgical and pathological outcomes. Measurement and assessment parameters include: uterine longitudinal diameter, transverse diameter, anteroposterior diameter, anterior and posterior uterine WSL, anterior isthmic thickness, posterior isthmic wall thickness, uterine isthmic-cervical level myometrial echogenicity, bilateral ovarian kiss sign. Measurement of the isthmic thickness, assessment of the anterior and posterior uterine WSL, and evaluation of the myometrial echogenicity at the isthmic-cervical junction are all performed on a single standard sagittal plane encompassing both the uterine body and cervix. The uterine isthmus is defined as the junction between the endometrium and the cervical mucosa. To improve measurement agreement, the point of peritoneal reflection is uniformly used as the measurement reference. The measuring line is perpendicular to the endometrium (Fig. 2). WSL assessment: The uterine surface displays a curved, fine white line. An interruption or disappearance of this white line indicates an abnormal WSL (Fig. 2). The uterine isthmus-cervical level echoes are primarily assessed for uniformity. To ensure the reliability of the newly proposed APTUIR method, we implemented an expert quality control process. Initial measurements were performed by Dr Y.S. Subsequently, a senior ultrasound specialist Dr B.YL with over 15 years’ experience reviewed all mid-sagittal images to confirm anatomical landmarks of the uterine isthmus. Both physicians were blinded to clinical histories and surgical outcomes. To assess reproducibility, 30 cases were randomly selected for independent re-measurement by the senior sonographer. The intra-class correlation coefficients (ICC) for the thickness of the anterior and posterior of the uterine isthmus were 0.914 (95% CI: 0.827–0.958) and 0.934 (95% CI: 0.867–0.968), respectively, indicating that the APTUIR assessment indicators have excellent reliability. The formula for calculating APTUIR is: APTUIR = anterior uterine isthmus thickness/posterior uterine isthmus thickness. Surgical and pathological data To record the presence of adenomyosis in the posterior uterine wall, ovarian chocolate cysts, and the location of endometriotic lesions during laparoscopic surgery. To record whether endometrial tissue is present within the lesions as determined by histopathological examination. Statistical analysis All statistical analyses were performed using Empower® (X&Y Solutions, Inc., Boston, MA, USA) and R software version 3.4.3 (http://www.r-project.org). Comparisons of clinical, laboratory characteristics and ultrasound parameters between the group with posterior pelvic DE and the group without posterior pelvic DE were performed using the Mann–Whitney U test, X2test or Fisher’s exact test. Continuous variables with a normal distribution are presented as mean ± standard deviation, whilst those with a skewed distribution are presented as median (interquartile range). Categorical variables are expressed as frequency (percentage). A nomogram was constructed, and ROC curves were plotted to assess its efficacy. The model was internally validated using 500 bootstrap samples. Calibration curves were plotted to verify the model’s predictive ability, and decision curve analysis was used to assess the model’s clinical utility. p < 0.05 was considered statistically significant.

Clinical baseline data for patients This study included a total of 362 patients, of whom 153 (42.3%) had posterior pelvic DE, whilst 209 (57.7%) had no posterior pelvic DE. Both patient groups showed statistically significant differences (p < 0.05) in dyspareunia, abnormal defecation during menstruation, CA125. There were no statistically significant differences in the remaining parameters (Table 1). Ultrasound characteristics of the uterus in the two patient groups Table 2 demonstrates statistically significant differences between the two patient groups in uterine anteroposterior diameter, combined EPs, uterine posterior wall isthmus echoes, uterine posterior wall WSL, the anterior uterine wall WSL, ovarian kiss sign, and APTUIR. There were no statistically significant differences in the remaining parameters. Construction and validation of nomogram Based on the LASSO regression lambda.min, four predictors associated with posterior pelvic DE were selected: APTUIR, the posterior uterine WSL, endometrial polyp and abnormal defecation during menstruation as shown in Fig. 3. The formula was as follows: 4.36531- 0.01446*Menstrual defecation abnormalities - 0.18749*endometrial polyp - 2.12754*the posterior uterine WSL- 3.84995*APTUIR. A nomogram was constructed based on the aforementioned four predictors of posterior pelvic DE (Fig. 4). Figure 5 shows that the AUC, sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) were 0.933 (95% CI: 0.901–0.957), 85.0%, 88.0%, 86.7%, 83.9% and 88.9%, respectively. Additionally, the sensitivities and specificities of the four indicators are shown in Supplementary Fig. 1. Validation of the nomogram The nomogram underwent internal validation using 500 bootstrap samples to mitigate overfitting bias. The AUC, sensitivity, specificity, accuracy, positive predictive value and negative predictive value for internal validation were 0.932, 85.0%, 88.0%, 89.0%, 88.4% and 89.0%, respectively. The blue shading in Fig. 6a shows the 95% confidence interval for the area under the curve estimated by bootstrap. The calibration curve of the model shows good agreement between the predicted and actual probabilities (Fig. 6b). The DCA suggests that patients with posterior pelvic DE can benefit from the constructed model over a considerable range of thresholds (Fig. 6c). Comparison of the diagnostic performance of nomograms and APTUIR The ROC curve analysis of APTUIR indicates that the optimal risk threshold for APTUIR is logit = −0.4089, corresponding to a clinical APTUIR value of approximately 0.793, as determined by maximising the sum of sensitivity and specificity (Youden’s Index) (Supplementary Fig. 2a). Below this threshold, the AUC, sensitivity and specificity of APTUIR for predicting posterior pelvic DE were 0.887 (95% CI, 0.849–0.924), 90.9% and 83.3%, respectively. The AUC, sensitivity and specificity of the nomogram for predicting posterior pelvic DE were 0.933 (95% CI: 0.901–0.957), 85.0% and 88.0%, respectively. Supplementary Fig. 2b shows that the nomogram has a higher net benefit than APTUIR. It is suggested that the nomogram demonstrates a higher AUC and net benefit in predicting the risk of posterior pelvic DE.

This study proposes a novel reproducible TVUS measurement metric—the APTUIR—and combines it with other ultrasound assessment parameters and clinical history to establish a model capable of predicting the risk of posterior pelvic DE. Through LASSO regression, four independent predictors were identified: APTUIR, posterior uterine wall WSL, EPs, and abnormal defecation. A nomogram model was constructed, demonstrating excellent efficacy in predicting the risk of posterior pelvic DE. This study was the first to propose APTUIR as a repeatable measurement on routine TVUS, as an indirect indicator for predicting posterior pelvic DE. In this study, it was observed that patients with posterior pelvic DE had reduced anterior–posterior wall ratios of the uterine isthmus. This may be due to the infiltration of endometriotic lesions into the posterior uterine wall and paracervical tissues, leading to local fibrosis and contracture, thereby causing an imbalance in the isthmus wall proportions. This was consistent with the pathological features of ‘adenomyosis externa’, a hallmark of deep endometriosis [23, 24], whereby lesions frequently involve the uterine sacral ligaments, rectovaginal septum and posterior cervical regions [4], subsequently tractioning or compressing the posterior wall of the uterine isthmus to induce structural alterations. Concurrently, our research indicates that APTUIR constitutes a significant proportion within the nomogram model, suggesting it plays a crucial role in diagnosing posterior pelvic DE. When APTUIR is 0.79 (sensitivity: 90.9%, specificity: 88.2%), it can predict the presence or absence of posterior pelvic DE by TVUS. Measuring APTUIR enhances diagnostic accuracy and confidence, offering high sensitivity and simple accessibility. Although its specificity may be affected by localised fibroids or adenomyomas at the isthmic junction, its primary value is to provide non-endometriosis specialists with an objective, reproducible and simple measurement method. Posterior uterine wall WSL was a significant predictor in the findings of this study. WSL is an indicator proposed by the Swiss Society for Ultrasound in Medicine for assessing adhesions in the mid-sagittal plane [11]. Physiologically, the WSL freely glides between the uterus and the surrounding environment. At the posterior fornix, this white line directly merges with the equally echogenic rectovaginal septum (RVS). Pelvic DE typically causes adhesions that result in abnormalities in adjacent WSL, presenting as disruptions or ambiguities. The widely employed ‘sliding sign’ in TVS can indicate adhesions between the uterus and ovaries, pelvic walls and rectum [25]. However, the diagnostic accuracy of the sliding sign is highly dependent on the operator’s experience [26, 27]. WSL appears to be an indirect indicator of simplifying this operation. In this study, it was found that 103 cases (67.3%) of patients with posterior pelvic DE exhibited abnormalities in posterior wall WSL, with a sensitivity of 67.3% and a specificity of 95.2%. This indicates that in clinical practice, abnormal uterine posterior wall WSL shows high specificity in predicting posterior pelvic DE. The lower sensitivity is mainly attributed to adenomyosis externa or early cases in which the WSL sign may not yet show obvious disruption or marginal blurring. However, APTUIR can sensitively detect asymmetric thickening of the uterine isthmus. Compared with purely qualitative observation, this quantitative metric provides a more sensitive diagnostic clue, highlighting its clinical utility in detecting early anatomical changes—details that are often easily overlooked in non-specialised centres. EPs were also identified as an independent predictive factor in this study. Results showed that patients with posterior pelvic DE exhibited a significantly higher incidence of EPs compared to those without posterior pelvic DE (p < 0.05). Several studies suggest that endometriosis may be associated with an increased incidence of EPs [28, 29]. Despite differing clinical presentations, their core pathological mechanisms are highly similar, primarily manifesting as hormonal imbalance [30], chronic inflammation [31] and uncontrolled cell proliferation [32]. The findings of this study not only further confirm the clinical association between EPs and DE in the posterior pelvis, but also suggest that patients with EPs, especially those with typical symptoms (such as bowel dysfunction during menstruation or dyspareunia), should be highly vigilant for the presence of posterior pelvic DE. This provides a crucial “early warning signal” for clinical practice—incorporating EPs into the risk assessment framework for DE can enhance the ability to identify occult cases, thereby preventing missed diagnoses. Abnormal defecation during menstruation also was a significant predictor in this study. It is well known that DE not only causes anatomical and functional lesions but also significantly impacts patients’ quality of life, particularly through chronic pelvic pain and its associated symptoms such as dysmenorrhoea, dyspareunia and abnormal defecation [33]. Sacroiliac ligament dysfunction is highly correlated with dyspareunia [34], whilst defecation abnormalities are frequently associated with bowel DE [35, 36]. Recent evidence from a prospective cohort study by Szabó et al. [36] further confirms that the systematic application of the IDEA protocol yields high diagnostic accuracy for rectosigmoid DE. However, the assessment of specific signs remains largely qualitative. Our findings suggest that the APTUIR metric provides a valuable quantitative supplement to the IDEA framework, potentially facilitating more objective decision-making in the preoperative evaluation of posterior DE. Our study also demonstrated a significantly increased prevalence of defecation abnormalities and dyspareunia in patients with posterior pelvic DE, although dyspareunia was not included in the predictor selection process. This is in agreement with the IDEA consensus [25], emphasising the importance of medical history taking during endometriosis ultrasound examinations. Our findings suggest that the overall pain index may lack the precision required for diagnosing specific regions, although studies recommend using the VAS as an indicator of disease severity [22]. Nikolaos et al. also suggested that pain–lesion correlation in endometriosis is inconsistent [37]. In our LASSO selection, symptom-specific “menstrual bowel dysfunction” outperformed VAS scores. This indicates that symptom-specific inquiries predict posterior DE more effectively than general pain intensity. Consequently, the possibility of DE should not be ruled out solely on the basis of low or negative VAS scores when objective ultrasound markers such as APTUIR or WSL are present. By including the above predictive factors, this study constructed a nomogram to predict the risk of posterior pelvic structure DE involvement. The area under the curve (AUC) for this model is 0.933, with an AUC of 0.930 for internal validation. This model demonstrates comparable performance to that of Perelló [38] (AUC: 0.91), yet we have higher sensitivity and specificity (sensitivity: 80% vs 83.0%, specificity: 84% vs 91.9%). Compared with the nomogram model established only by clinical history characteristics by Wang et al. [39] (AUC = 0.858), this model, incorporating both clinical and imaging features simultaneously, provided superior predictive performance. The variables incorporated into the model established in this study (APTUIR, uterine posterior WSL, EPs and abnormal defecation during menstruation) were derived from routine gynaecological history taking and TVUS, ensuring clinical feasibility and reproducibility. Consequently, this model not only provides a quantitative tool for individualised risk stratification, thereby facilitating patient referral to specialised endometriosis treatment centres; it also assists surgeons in optimising surgical planning and patient consultations, ultimately enhancing the efficiency of endometriosis diagnosis and treatment alongside improving patient outcomes. Our study has several limitations. First, this retrospective study exclusively included patients who underwent surgery, thereby excluding any individuals who may have had posterior pelvic DE but did not undergo surgical intervention, resulting in unavoidable selection bias. Second, whilst internal validation via 500 bootstrap samples demonstrated high diagnostic accuracy (AUC 0.932) and robust consistency, the current study lacks an independent external validation cohort. The high performance of the APTUIR-based model may partially reflect the specific patient population and the high level of expertise in our centre. Finally, as this is a single-centre study, our findings should be interpreted as a preliminary step towards quantifying DE diagnosis. Future prospective, multicentre studies with larger cohorts are essential to confirm the generalisability and reliability of this model across different clinical settings and experience levels before its widespread clinical implementation. The nomogram model constructed based on APTUIR in this study shows high predictive efficacy, excellent calibration, and clinical utility. It can assist in further stratifying diagnostic and therapeutic decisions for patients outside specialised endometriosis centres, enabling endometriosis patients to receive early, individualised and precise treatment. Data availability No datasets were generated or analysed during the current study. Abbreviations - APTUIR: - Anterior–posterior wall thickness of the uterine isthmus ratio - DE: - Deep endometriosis - TVUS: - Transvaginal ultrasound - WSL: - White sliding lines - AUC: - Area under the curve - DCA: - Decision curve analysis - CI: - Confidence interval - VAS: - Visual analogue scale

Chapron C, Chopin N, Borghese B et al (2006) Deeply infiltrating endometriosis: pathogenetic implications of the anatomical distribution. Hum Reprod 21:1839–1845 Saunders PTK, Horne AW (2021) Endometriosis: etiology, pathobiology, and therapeutic prospects. Cell 184:2807–2824 Rolla E (2019) Endometriosis: advances and controversies in classification, pathogenesis, diagnosis, and treatment. F1000Res 8:- Koninckx PR, Ussia A, Adamyan L, Wattiez A, Donnez J (2012) Deep endometriosis: definition, diagnosis, and treatment. Fertil Steril 98:564–571 Mijatovic V, Vercellini P (2024) Towards comprehensive management of symptomatic endometriosis: beyond the dichotomy of medical versus surgical treatment. Hum Reprod 39:464–477 Guerriero S, Condous G, Rolla M et al (2024) Addendum to consensus opinion from International Deep Endometriosis Analysis (IDEA) group: sonographic evaluation of the parametrium. Ultrasound Obstet Gynecol 64:275–280 Ballester M, Santulli P, Bazot M, Coutant C, Rouzier R, Daraï E (2011) Preoperative evaluation of posterior deep-infiltrating endometriosis demonstrates a relationship with urinary dysfunction and parametrial involvement. J Minim Invasive Gynecol 18:36–42 Melnyk A, Rindos NB, El Khoudary SR, Lee TTM (2020) Comparison of laparoscopic hysterectomy in patients with endometriosis with and without an obliterated cul-de-sac. J Minim Invasive Gynecol 27:892–900 Scioscia M, Scardapane A, Virgilio BA, Libera M, Lorusso F, Noventa M (2021) Ultrasound of the uterosacral ligament, parametrium, and paracervix: disagreement in terminology between imaging anatomy and modern gynecologic surgery. J Clin Med 10:- Leonardi M, Ong J, Espada M et al (2020) One-size-fits-all approach does not work for gynecology trainees learning endometriosis ultrasound skills. J Ultrasound Med 39:2295–2303 Metzler JM, Finger L, Burkhardt T et al (2024) Systematic, noninvasive endometriosis diagnosis in transvaginal sonography by the Swiss Society of Ultrasound in Medicine. Ultraschall Med 45:367–388 Che J, Gao Y, Sun M, Zhou S, Lu P, Zhao T (2023) Uterine anteroposterior diameter measured by transvaginal sonography is a predictor for dysmenorrhea in patients with and without endometriosis: a pilot study. J Ultrasound Med 42:1647–1660 Sewell M, Mooney S, Cvejic E, Stone K (2024) The myometrial-cervical ratio: can a simple sonographic measurement improve diagnosis of adenomyosis in a regional setting? Ultrasound 32:19–26 Barra F, Ferrero S, Perrone U et al (2025) Uterine “twisting sign”: a new potential ultrasonographic soft marker for deep endometriosis. Int J Gynaecol Obstet 171:1355–1363 Antar SA, Ashour NA, Marawan ME, Al-Karmalawy AA (2023) Fibrosis: types, effects, markers, mechanisms for disease progression, and its relation with oxidative stress, immunity, and inflammation. Int J Mol Sci 24:- Park W, Lim W, Kim M et al (2025) Female reproductive disease, endometriosis: from inflammation to infertility. Mol Cells 48:100164 Maddern J, Grundy L, Castro J, Brierley SM (2020) Pain in endometriosis. Front Cell Neurosci 14:590823 Inagaki N, Ung L, Otani T, Wilkinson D, Lopata A (2003) Uterine cavity matrix metalloproteinases and cytokines in patients with leiomyoma, adenomyosis or endometrial polyp. Eur J Obstet Gynecol Reprod Biol 111:197–203 Bernigaud O, Dubernard G, Maissiat E et al (2025) Assessment of postoperative uterine isthmus thickness on MRI after surgical resection of retrocervical deep infiltrating endometriosis. Abdom Radiol. 51(2):916–923 Zhou P, Jin C, Lu J et al (2021) The value of nomograms in pre-operative prediction of lymphovascular invasion in primary breast cancer undergoing modified radical surgery: based on multiparametric ultrasound and clinicopathologic indicators. Ultrasound Med Biol 47:517–526 Bourdel N, Alves J, Pickering G, Ramilo I, Roman H, Canis M (2015) Systematic review of endometriosis pain assessment: how to choose a scale? Hum Reprod Update 21:136–152 Andres MP, Riccio LGC, Abrao HM, Manzini MS, Braga L, Abrao MS (2024) Visual analogue scale cut-off point of seven represents poor quality of life in patients with endometriosis. Reprod Sci 31:1146–1150 Arnold LL, Ascher SM, Schruefer JJ, Simon JA (1995) The nonsurgical diagnosis of adenomyosis. Obstet Gynecol 86:461–465 Kishi Y, Suginami H, Kuramori R, Yabuta M, Suginami R, Taniguchi F (2012) Four subtypes of adenomyosis assessed by magnetic resonance imaging and their specification. Am J Obstet Gynecol 207:114.e111-117 Guerriero S, Condous G, van den Bosch T et al (2016) Systematic approach to sonographic evaluation of the pelvis in women with suspected endometriosis, including terms, definitions and measurements: a consensus opinion from the International Deep Endometriosis Analysis (IDEA) group. Ultrasound Obstet Gynecol 48:318–332 Young SW, Jha P, Chamié L et al (2024) Society of Radiologists in Ultrasound consensus on routine pelvic US for endometriosis. Radiology 311:e232191 Menakaya U, Infante F, Lu C et al (2016) Interpreting the real-time dynamic “sliding sign” and predicting pouch of Douglas obliteration: an interobserver, intraobserver, diagnostic-accuracy and learning-curve study. Ultrasound Obstet Gynecol 48:113–120 Kontoravdis A, Augoulea A, Lambrinoudaki I et al (2007) Ovarian endometriosis associated with ovarian cancer and endometrial-endocervical polyps. J Obstet Gynaecol Res 33:294–298 Fiore A, Casalechi M, Somigliana E, Viganò P, Salmeri N (2025) Association between endometriosis and endometrial polyps: a systematic review and meta-analysis. Reprod Biomed Online 52:105106 Yan C, Xing C, Wei T et al (2023) Impact of estrogen and progesterone receptor expression on the incidence of endometrial polyps. Biomark Med 17:881–887 Cicinelli E, Trojano G, Mastromauro M et al (2017) Higher prevalence of chronic endometritis in women with endometriosis: a possible etiopathogenetic link. Fertil Steril 108:289-295.e281 Park JS, Lee JH, Kim M, Chang HJ, Hwang KJ, Chang KH (2009) Endometrium from women with endometriosis shows increased proliferation activity. Fertil Steril 92:1246–1249 Krug RS (2003) Metal framework modifications to accommodate wrought wire clasps in distal extension removable partial dentures. J Prosthet Dent 89:79–81 Zondervan KT, Becker CM, Koga K, Missmer SA, Taylor RN, Viganò P (2018) Endometriosis. Nat Rev Dis Primers 4:9 Doglioli M, Raffone A, Maletta M et al (2025) Different ultrasound morphologies of rectosigmoid endometriosis nodules: an exploratory analysis of their prevalence and associated clinical characteristics. Fertil steril 125(2):308–315 Szabó G, Hudelist G, Madár I et al (2024) Diagnostic accuracy of the IDEA protocol for non invasive diagnosis of rectosigmoid DE - a prospective cohort study. Ultraschall Med 45:61–68 Apostolopoulos NV, Alexandraki KI, Gorry A, Coker A (2016) Association between chronic pelvic pain symptoms and the presence of endometriosis. Arch Gynecol Obstet 293:439–445 Perelló M, Martínez-Zamora MA, Torres X et al (2017) Markers of deep infiltrating endometriosis in patients with ovarian endometrioma: a predictive model. Eur j obstet gyn r b 209:55–60 Wang C, Li Y, Zhu W, Li X, Wang M, Liu H (2025) Predicting the risk of endometriosis in Chinese infertile women: development and assessment of a predictive nomogram. Front Surg 12:1541667 Funding This study was supported by grants from the Shenzhen Key Medical Discipline Construction Fund (grant no. SZXK052). Author information Authors and Affiliations Contributions SY was the major contributor in writing the manuscript. YTH measured the data. CCJ analysed the data. MFD, YYZ, KJL and LHQ collected the data. YLB captured the images. QXC projected development. Corresponding author Ethics declarations Conflict of interest The authors declare no competing interests. Additional information Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Supplementary Information Below is the link to the electronic supplementary material. Rights and permissions Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/. About this article Cite this article Yang, S., He, Y., Jin, C. et al. A nomogram integrating a novel uterine isthmus ratio (APTUIR), sonographic signs and clinical symptoms for predicting posterior deep endometriosis. Arch Gynecol Obstet 313, 221 (2026). https://doi.org/10.1007/s00404-026-08466-4 Received: Accepted: Published: Version of record: DOI: https://doi.org/10.1007/s00404-026-08466-4