Connecting the dots: Exploring appendiceal endometriosis in women with diaphragmatic endometriosis

•Appendiceal endometriosis as a predictive marker for diaphragmatic endometriosis.•Patients with concurrent diaphragmatic and appendiceal endometriosis presented more often dyspareunia, dyschezia, diaphragm-specific pain.•Presence of both diaphragmatic and appendiceal endometriosis is associated with severe endometriosis.•When the appendix and diaphragm are involved simultaneously, we identified a specific distribution pattern of endometriotic lesions involving diaphragm, left ovary, right ureter, and appendix.•Peritoneal flow seems to follow a transversal direction from the left pelvis up to the right side. This study aims to ascertain the prevalence of appendiceal endometriosis (AppE) in patients diagnosed with diaphragmatic endometriosis (DiaE), compare it with the prevalence in patients without DiaE, and delineate the anatomical distribution of endometriotic lesions within these cohorts. Comparison of the characteristics of patients with AppE and DiaE with the characteristics of patients with abdominal endometriosis without diaphragmatic involvement, in a prospective cohort study. Tertiary referral center; endometriosis center. A cohort of 1765 patients with histologically confirmed endometriosis Evaluation of correlations between demographic, clinical, and surgical variables of AppE patients with DiaE and without DiaE. We performed appendectomies selectively, in the presence of gross abnormalities of the appendix, such as endometriotic implants, edema, tortuosity, and discoloration of the organ. Patients’ characteristics were evaluated using basic descriptive statistics (chi-square test or Fisher’s exact test). A logistic regression analysis was performed to evaluate the relationship (hazard ratio) between patient characteristics and the presence of DiaE and AppE. Within a cohort of 1765 patients with histologically confirmed endometriosis, 31 were identified with AppE (1.8 %), and 83 with DiaE (4.7 %). The prevalence of DiaE was significantly elevated at 30.1 % (25/83), among patients with AppE compared to those without AppE, who showed a DiaE prevalence of 7.2 % (6/83). The calculated odds ratio for DiaE given the presence of AppE was 5.5, 95 % CI 2.1–14.4, p = 0.0004, and risk ratio was 4.2, 95 % CI 1.8–9.6, p = 0.0008, indicating a profound association. Surgical interventions did not lead to significant perioperative or postoperative complications. In the group with DiaE, the left ovary was affected in 96 % of cases (24/25), p