Endometriosis and Chronic Endometritis: Shared Mechanisms, Diagnostic Challenges, and Clinical Implications in Infertility.

Endometriosis (EM) and chronic endometritis (CE) are both implicated in female infertility, yet the relationship between them remains incompletely understood. In this narrative review, we synthesize non-systematically selected clinical and mechanistic evidence on EM-CE coexistence, with emphasis on infertility-related settings and diagnostic uncertainty. Available studies, largely from selected infertility cohorts, suggest that CE is identified more often in women with EM, raising the possibility that their coexistence reflects a biologically meaningful association rather than incidental overlap. The two conditions share several abnormalities that may impair reproduction, including persistent inflammation, immune dysregulation, altered cytokine and chemokine signaling, impaired macrophage and natural killer cell function, progesterone resistance, and reduced endometrial receptivity. In addition to the pelvic anatomical distortion and ovarian dysfunction associated with EM, CE may further compromise implantation by impairing decidualization, displacing the window of implantation, and disrupting the local endometrial microenvironment. Both conditions also remain diagnostically challenging. EM is most reliably confirmed by laparoscopy with histologic verification, whereas CE is generally diagnosed by hysteroscopy and endometrial biopsy demonstrating plasma cells. For CE in particular, the lack of standardized diagnostic criteria and uniform CD138 thresholds continues to limit diagnostic consistency. Emerging imaging techniques, molecular biomarkers, microbiota-based approaches, and artificial intelligence-assisted models remain investigational or adjunctive rather than established tools for routine integrated assessment. Taken together, the current evidence is hypothesis-generating and supports selective, phenotype-driven consideration of coexisting EM and CE in infertility care rather than routine dual invasive evaluation. Further studies are required to clarify the mechanisms linking these conditions, define their combined reproductive impact, and determine whether integrated diagnostic and therapeutic strategies can improve fertility outcomes.