Nerve Fiber Density in DIE Nodules & Pelvic Pain

Deep infiltrating endometriosis (DIE) is a highly symptomatic phenotype of endometriosis that invades retrocervical, parametrial, rectovaginal, bowel, and other pelvic structures, and is frequently associated with severe dysmenorrhea, dyspareunia, dyschezia, dysuria, and chronic pelvic pain. Emerging evidence suggests that DIE nodules harbor abundant nerve fibers and may show perineural involvement, yet the relationship between intranodular nerve fiber density and patient-reported pelvic pain has not been defined with sufficient clinical granularity.

This retrospective, cross-sectional study with prospective pathology re-review investigates whether nerve fiber density within surgically excised DIE nodules correlates with the intensity and localization of pelvic pain. Eligible participants are women (18-55 years) operated for DIE after inadequate response to medical therapy (e.g., nodule excision, nerve-sparing hysterectomy ± salpingo-oophorectomy, ovarian surgery, and/or bowel resection when indicated). Demographic characteristics, obstetric/gynecologic history, prior surgeries and medical treatments, and standardized pain assessments (visual analogue scale [VAS] scores for dysmenorrhea, dyspareunia, dyschezia, dysuria, and chronic pelvic pain) are abstracted from the hospital information system.

All resected specimens are routinely fixed in buffered formalin and processed for histopathology. For this study, archived blocks from endometriotic foci are recut (3-µm sections) and stained with hematoxylin-eosin and immunohistochemically labeled with SOX-10 to visualize neural elements. Under ×200 magnification, the number of SOX-10-positive neural profiles within endometriotic foci is quantified, and mean nerve fiber counts (per evaluated field/area) are calculated to derive a nerve fiber density metric for each nodule. The primary endpoint is the association between nodule-level nerve fiber density and pain severity/localization. Secondary endpoints include associations with clinicopathologic variables (lesion site and depth, parametrial/rectovaginal/bowel involvement), and exploratory analyses of indices that may discriminate patients with severe pain.

Statistics will be performed with SPSS (v23). Categorical variables are summarized as n (%) and compared with χ² or Fisher's exact tests; continuous variables as mean ± SD (or median [min-max]) and compared with Student's t-test or Mann-Whitney U test as appropriate; within-group paired comparisons may use the Wilcoxon test. Two-sided p < 0.05 denotes statistical significance. Because this is a retrospective audit with predefined time frame and all-comer surgical inclusions, no formal sample size calculation is planned.

Risks/Benefits: This is minimal-risk research using archived pathology and existing clinical records; no additional procedures or changes to care are required. Results may clarify whether tissue-level neural metrics in DIE nodules reflect the patient's pain phenotype, potentially informing counseling, surgical planning (e.g., nerve-sparing strategies), and the development of response biomarkers for future prospective studies.

Inclusion criteria

Female, 18-55 years of age at time of surgery

Surgically treated for deep infiltrating endometriosis (DIE) with curative intent within the study period

Histopathologic confirmation of DIE on resected specimen (e.g., rectovaginal septum, uterosacral/cardinal ligaments, parametria, bowel, ureter, bladder, retrocervical/cervicovaginal sites)

Availability of archived FFPE tissue blocks adequate for H&E and immunohistochemistry (e.g., SOX10) to quantify nerve fiber density

Documented preoperative pain assessment (e.g., VAS 0-10 for dysmenorrhea, dyspareunia, dyschezia, dysuria, and/or chronic pelvic pain) obtained within ≤3 months prior to index surgery

Accessible clinical data in the medical record (demographics, gynecologic history, prior medical/surgical therapies) sufficient for planned analyses

IRB approval in place; inclusion under written informed consent or IRB waiver applicable to retrospective data/tissue use -

Exclusion criteria

No surgical resection of DIE (e.g., diagnostic laparoscopy only) or no histopathologic confirmation of DIE

Insufficient biospecimen (no/poor-quality FFPE tissue for H&E/IHC)

Missing preoperative pain assessment (no VAS data within ≤3 months before index surgery)

Concomitant malignancy of the pelvis/abdominopelvic organs or malignancy treated within the past 5 years

Prior pelvic radiotherapy or major pelvic/nerve ablative surgery that precludes meaningful pain attribution

Acute pelvic infection at time of assessment or surgery (e.g., PID, tubo-ovarian abscess)

Primary pain disorders likely to confound attribution (e.g., interstitial cystitis/bladder pain syndrome, IBS with pain as dominant symptom, centrally mediated chronic pain syndromes) without adequate documentation to separate pain sources

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