Gender differences in superior hypogastric plexus block via the sacral notch approach for chronic pelvic pain: A retrospective CT-based observational study.

The sacral notch approach showed no significant sex‑related differences in either the angle between the needle trajectory and the sagittal plane or the distance from the needle entry point to the target, indicating that these technical parameters are relatively stable and provide a reliable basis for standardized clinical practice. In contrast, the SHGPB index differed significantly between sexes and may serve as an important reference parameter for individualized selection of puncture approaches, which may help guide approach selection and potentially improve procedural planning and safety. Based on the findings of this study, we propose the following recommendations: For patients with a lower SHGPB index (more commonly observed in men), the sacral notch or transintervertebral disc approach may be preferentially considered to enhance puncture success and reduce the risk of complications. A standardized preprocedural imaging assessment protocol should be established, incorporating the SHGPB index as an objective tool for approach selection. In interventional management of CPP, sex‑related anatomical differences should be fully considered to facilitate more precise and individualized treatment strategies. Future studies should further validate the clinical efficacy of the sacral notch approach in large‑scale prospective cohorts, with particular attention to sex‑specific differences in key outcome measures, including the magnitude of pain relief, duration of therapeutic effect, and incidence of complications. Such investigations will help provide more robust and individualized guidance for precision interventional treatment of CPP.

Chronic pelvic pain (CPP) is a common clinical syndrome characterized by continuous or intermittent pain in the lower abdomen or pelvis lasting for more than 6 months. [ 1 , 2 ] The European Association of Urology defines chronic pelvic pain syndrome (CPPS) as pain perceived in pelvic structures in men or women in the absence of identifiable pathology after appropriate evaluation. [ 2 , 3 ] CPP not only markedly reduces quality of life but also imposes a substantial psychological burden on affected individuals. Epidemiological studies indicate that the prevalence of CPP among women worldwide is approximately 26%. [ 1 ] A 2019 survey reported that the lifetime risk of CPPS among Chinese men aged 40 to 81 years was 25.3%. [ 4 ] The etiology of CPP is complex and multifactorial. In women, common causes include endometriosis, chronic pelvic inflammatory disease, uterine fibroids, ovarian cysts, irritable bowel syndrome, and interstitial cystitis. [ 5 ] In men, CPP is frequently associated with prostatitis, chronic prostatitis/CPPS, varicocele, and bladder pain syndrome. [ 6 ] In addition, CPP may involve neuromusculoskeletal and psychosocial factors regardless of sex. [ 7 ] Significant sex-related differences exist in pelvic anatomy. The female pelvis is generally wider and shallower, with a larger inter–posterior superior iliac spine distance and an oval pelvic inlet, whereas the male pelvis is narrower and deeper, with a smaller interspinous distance and a heart-shaped pelvic inlet. [ 8 , 9 ] These bony anatomical differences may influence the spatial distribution of pelvic organs and neural structures and directly affect the safety, accessibility, and technical difficulty of interventional puncture pathways. Previous studies have also demonstrated sex differences in pain perception and modulation. Women typically exhibit greater pain sensitivity and stronger pain responses, whereas men may have more effective descending pain inhibitory mechanisms. [ 10 ] These differences suggest the importance of individualized interventional strategies in the treatment of CPP. The superior hypogastric plexus is a critical neural pathway connecting the sympathetic nervous system to pelvic organs and has become an important target for CPP management. Superior hypogastric plexus block (SHGPB) interrupts pelvic pain signal transmission and has been shown to be a safe and effective minimally invasive treatment. [ 7 ] Previous studies have confirmed its efficacy in pelvic cancer pain, endometriosis-related pain, and nonspecific pelvic pain, with durable analgesic effects and a low complication rate. [ 11 , 12 ] In the development of SHGPB techniques, the selection of puncture approaches has always been a focus of clinical practice. Commonly used puncture approaches mainly include the classic approach, the transdiscal approach, and the anterior approach. [ 13 ] However, there is no consensus on the optimal choice among different puncture approaches, and relevant clinical controlled trials are limited. Previous studies have reported superior hypogastric plexus neurolysis via transdiscal approach under X-ray fluoroscopy and computed tomography (CT) guidance. [ 14 - 16 ] The transsacral notch approach, as an improved version of the transdiscal approach, has attracted clinical attention in recent years. The sacral notch is described as the depression between the medial aspect of the sacral wing and the lateral aspect of the superior articular process. This approach utilizes direct access to the target area through the intervertebral disc. Compared with the classic approach, the transsacral notch approach may have advantages such as a more direct path and simpler technique. [ 17 , 18 ] Currently, there is a lack of systematic studies analyzing the gender differences in technical parameters of the transsacral notch approach from an imaging perspective. This study aims to systematically analyze gender differences in key technical parameters such as puncture angle and path distance of the transsacral notch approach through CT imaging data, and explore the influence of the SHGPB index on puncture parameters. The results of this study are expected to provide scientific basis for the optimization and individualized application of SHGPB technology, further improving the therapeutic effect of CPP.

Conceptualization: Meixiang Yu, Qingyu Zhang. Data curation: Meixiang Yu, Qingyu Zhang, Meige Li, Shuaichen Jin. Investigation: Meixiang Yu, Qingyu Zhang, Meige Li. Methodology: Meixiang Yu, Qingyu Zhang. Project administration: Wenzhe Jin. Resources: Wenzhe Jin. Software: Meige Li. Validation: Meige Li, Shuaichen Jin, Wenzhe Jin. Visualization: Shuaichen Jin. Writing – original draft: Meixiang Yu, Qingyu Zhang. Writing – review & editing: Meixiang Yu, Qingyu Zhang, Wenzhe Jin.

We retrospectively analyzed 200 randomly selected eligible patients who underwent abdominal CT examination in our hospital’s outpatient and inpatient departments from September 2024 to March 2025. Among them, 100 cases (50%) were male and 100 cases (50%) were female, aged 50 to 80 years (mean ± standard deviation [SD], 67.32 ± 8.46 years). Inclusion criteria were: age ≥ 18 years; good quality abdominal CT scan clearly showing lumbosacral structures. Exclusion criteria were: history of lumbosacral surgery; lumbosacral fracture or tumor; severe osteoporosis; sacral congenital malformation; and severe lumbar intervertebral disc endplate lesions. This study protocol was approved by the hospital ethics committee (approval number: 2025283), and the ethics committee agreed to waive patient informed consent since the study was a retrospective imaging analysis without actual intervention. All CT examinations were performed for clinical diagnostic purposes rather than specifically for this study. All CT examinations were performed with patients in the supine position. Although this differs from the prone position commonly used during SHGPB procedures, the effect on bony anatomical measurements is considered minimal. CT scan results of all patients meeting the inclusion criteria were retrieved. Two senior radiologists (both with> 10 years of work experience), blinded to the study objectives, conducted independent measurements. Based on a predefined sacral notch approach via the transintervertebral disc pathway, bilateral simulated puncture trajectories were analyzed on CT images at the sacral notch level (see Figs. 1 and 2 ). The following parameters were measured: marking the puncture target point; marking the skin puncture entry point; measuring and recording the distance of the puncture path (from the skin entry point to the target point) and the entry angle (the angle between the simulated puncture needle and the sagittal plane); and measuring and recording the distance between the posterior superior iliac spines and the transverse diameter of the L5 vertebra. To reduce measurement error, each parameter was independently measured 3 times by 2 senior radiologists, and the average value was taken. CT measurement diagram of the transsacral notch approach. T is the puncture target point; angle a is the angle between the puncture needle and the sagittal plane, AB is the distance from the puncture entry point to the target point. CT = computed tomography. Measurements for the SHGPB index. AB is the transverse diameter of the L5 vertebral body; CD is the distance between the posterior superior iliac spines. SHGPB = superior hypogastric plexus block. The above data were measured using the CT’s built-in software tool, with angles accurate to 0.1° and distances accurate to 0.1 cm. All data were statistically analyzed using Statistical Package for the Social Sciences (SPSS) 26.0 software (Chicago). After normality testing, measurement data were expressed as mean ± SD, with minimum and maximum range provided. Comparisons between sexes were performed using independent-samples t tests. P  < .05 was considered statistically significant. Sample size estimation was based on preliminary data, with α = 0.05, β = 0.10, expected effect size d  = 0.5, the calculated minimum sample size required was 172 cases, and considering possible data loss, 200 patients were eventually included.

This study analyzed gender differences in key technical parameters of the sacral notch approach through CT imaging, including the angle between the puncture needle path and the sagittal plane, the distance between the puncture entry point and the target point, and the SHGPB index (the ratio of the distance between the posterior superior iliac spines to the transverse diameter of the L5 vertebral body). The results are summarized in Table 1 . Gender comparison of key technical parameters of the transsacral notch approach [mean ± SD (min–max)], cm. SD = standard deviation, SHGPB = superior hypogastric plexus block. P  < .05, statistically significant difference. For the puncture parameters of the sacral notch approach, the angles between the puncture needle path and the sagittal plane were 25.33 ± 7.26° and 27.18 ± 8.44° for male and female patients, respectively, with no statistically significant difference ( P  = .099). The distances between the puncture entry point and the target point were 13.43 ± 1.53 cm and 13.29 ± 2.39 cm for male and female patients, respectively, also with no significant difference ( P  = .615). These 2 parameters indicate that the puncture angle and distance of the sacral notch approach remain relatively stable between different genders, providing reliable reference benchmarks for clinical operations. However, the SHGPB index showed a significant difference between males and females, with values of 1.75 ± 0.23 and 1.96 ± 0.24, respectively ( P  < .001). This result indicates that females have a wider distance between posterior superior iliac spines relative to the L5 vertebral body transverse diameter, possibly reflecting the basic differences in pelvic anatomical structure between males and females. This index can serve as an important reference basis for individualized selection of the sacral notch approach.

SHGPB is an effective minimally invasive interventional technique for the treatment of CPP. However, there is currently no consensus regarding the optimal puncture approach. In this study, CT‑based imaging parameters were used to analyze the anatomical characteristics and technical parameters of the sacral notch approach, with the aim of providing imaging evidence to support the clinical selection of the most appropriate puncture pathway. This study found that there was no significant difference between males and females in the angle between the simulated needle trajectory and the sagittal plane (25.33 ± 7.26° vs 27.18 ± 8.44°, P  > .05). This indicates that the puncture angle of this approach is relatively stable and not affected by gender factors. This finding is consistent with the research results of Erdine et al, [ 15 ] who believed that the transdiscal approach (including the transsacral notch approach) has advantages such as ease of use, minimal risk of organ puncture, low risk of intravascular injection, and the ability to complete the procedure with a single needle. Yanaizumi et al [ 19 ] also pointed out when comparing different puncture approaches for splanchnic nerve block that the paravertebral approach requires the widest insertion angle of the needle with the sagittal plane, with a high risk of the needle hitting surrounding important organs, and usually requires bilateral puncture, while the transdiscal approach has fewer important organs in the needle path, making it simpler and safer. Similarly, there was no significant difference between genders in the distance from the puncture entry point to the target point (13.43 ± 1.53 cm vs 13.29 ± 2.39 cm, P  > .05), indicating that this parameter is relatively stable and can be used for preoperative planning. It should be noted that the distance from the entry point to the target point of the transsacral notch approach is relatively long (average about 13.36 cm), which may increase the difficulty of puncture technique, requiring operators to have more precise puncture skills. This study measured and analyzed the SHGPB index (distance between posterior superior iliac spines/L5 vertebral body transverse diameter) and found that the male SHGPB index was significantly smaller than that of females (1.75 ± 0.23 vs 1.96 ± 0.24, P  < .05). This finding is consistent with the research results of Choi et al, [ 20 ] who developed the SHGPB index, defined as the ratio of the posterior iliac border, and found that when the bony pelvis is relatively narrow compared to the target vertebra (SHGPB index < 1.5), the transdiscal approach may be superior to the classic posterior approach. The SHGPB index represents the relative transverse diameter of the bony pelvis and can show the differences between male and female pelvises. This index may have advantages in evaluating the choice between the 2 approaches. The lower SHGPB index in males indicates a relatively narrower pelvis, which may limit the operation of the classic approach, so the transsacral notch approach may be more suitable for male patients. In the present study, male patients exhibited a lower SHGPB index (mean, 1.75), indicating a relatively narrower pelvis. Accordingly, the sacral notch approach may be preferentially considered in this population, as it may theoretically contribute to improved procedural safety and indirectly enhance clinical efficacy. In contrast, female patients demonstrated a higher SHGPB index (mean, 1.96), suggesting a greater range of available anatomical space; therefore, the choice of puncture approach may be tailored based on individual clinical conditions and operator experience. For patients with SHGPB index values approaching the threshold, a detailed preprocedural imaging evaluation is recommended to facilitate the development of an individualized puncture strategy that accounts for patient‑specific anatomical characteristics. Future studies should further investigate how these anatomical differences translate into actual clinical outcomes, including sex‑related differences in pain relief magnitude, duration of analgesia, complication rates, and patient satisfaction. Although the present study did not directly evaluate the degree of pain relief or the incidence of complications, previous studies have demonstrated that approaches with a more direct puncture trajectory and fewer osseous obstructions are generally associated with shorter procedural times and a reduced risk of inadvertent vascular or visceral injury. [ 21 , 22 ] Therefore, from a theoretical perspective, for patients with a lower SHGPB index and a relatively narrow pelvis (more commonly observed in men), selecting the sacral notch or transintervertebral disc approach may contribute to improved procedural safety and indirectly enhance clinical outcomes. The transsacral notch approach, as a modified approach, has the following advantages: the angle between the puncture needle and the sagittal plane is smaller, with good operational stability; the puncture path is single and intuitive, easy to locate and operate; bone structures can be accurately identified and anatomical variations can be discovered under CT guidance; in most cases, neurolysis can be completed with a single needle puncture, reducing the number of punctures. However, the sacral notch approach has limitations. Because the needle traverses the intervertebral disc, discitis is a potential complication, although rare. Therefore, strict aseptic technique, minimizing needle passes, and prophylactic antibiotics when appropriate are recommended. [ 21 ] In addition, the needle path is relatively long, which increases technical demands; preprocedural lumbar imaging is recommended to exclude anatomical variations and degenerative changes. [ 20 , 22 ] This study has several limitations. First, the analysis was based solely on CT imaging measurements, and the clinical efficacy across different sexes was not validated in actual patients. Consequently, correlations with real‑world treatment outcomes, such as the degree and duration of pain relief, complication rates, and other clinical endpoints were not assessed, nor were anatomical (cadaveric) studies performed. Second, all CT measurements were obtained with patients in the supine position, whereas SHGPB is typically performed in the prone position. Differences in patient positioning may have influenced the measurements, particularly due to changes in soft‑tissue anatomy. Third, all participants were of Asian ethnicity; therefore, racial and individual anatomical variations may limit the generalizability of the findings. Fourth, although the sample size was determined based on statistical calculations, larger multicenter studies are still required to validate and extend these conclusions.