Beyond the Mass Effect: Decoupling Endometrioma Size and Bilaterality from Ovarian Reserve Depletion

Ovarian endometriomas are commonly assessed according to cyst size and laterality, anatomical features that have long been regarded as indicators of disease severity and potential ovarian compromise. Consequently, these characteristics have influenced decisions regarding surveillance, fertility preservation, and surgical management. The traditional "mass effect" concept proposes that increasing cyst size and bilaterality are associated with progressively greater ovarian damage and depletion of ovarian reserve. However, accumulating clinical evidence suggests this relationship is more complex than previously appreciated. Recent studies and meta-analyses have failed to demonstrate consistent dose-response relationships between cyst diameter, bilaterality, and baseline ovarian reserve markers, indicating that these anatomical characteristics may not reliably reflect the biological extent of ovarian injury. By comparison, the association between surgical treatment and postoperative reduction in ovarian reserve has been more consistently demonstrated, highlighting the importance of distinguishing disease-related from treatment-related effects. These observations raise important questions regarding the mechanisms responsible for ovarian dysfunction in women with endometriomas. Experimental and histopathological studies implicate inflammation, oxidative stress, fibrosis, altered vascularization, iron-mediated toxicity, and micro-environmental remodeling as potential contributors to ovarian injury. Nevertheless, the available mechanistic evidence remains heterogeneous and is largely based on surrogate biological markers whose clinical relevance has yet to be established. We propose an integrated conceptual framework that interprets anatomical characteristics alongside the biological processes underlying ovarian injury to improve understanding of endometrioma-associated ovarian dysfunction and to support more individualized clinical decision-making. Future research should focus on identifying clinically meaningful biomarkers of ovarian micro-environmental damage and establishing their relationship with ovarian reserve, reproductive outcomes, and response to treatment. Until these mechanisms are better defined, management should integrate symptoms, reproductive goals, ovarian reserve assessment, and the anticipated benefits and risks of intervention rather than relying on cyst morphology alone.