DIFFERENTIAL DIAGNOSIS OF BORDERLINE OVARIAN TUMOURS, OVARIAN ENDOMETRIOMAS, AND WELL-DIFFERENTIATED OVARIAN CARCINOMA: AN IMAGING-PATHOLOGY NARRATIVE REVIEW

Borderline ovarian tumours (BOTs), ovarian endometriomas, and well-differentiated ovarian carcinoma may present with overlapping clinical and imaging features, yet their prognostic implications and surgical planning differ markedly. Diagnostic errors commonly arise when haemorrhagic or fibrous benign lesions mimic solid tumour, or when early malignant transformation within endometriosis manifests as subtle mural change. Aim of this work was to provide a pragmatic, stepwise, imaging-pathology differential diagnosis framework for distinguishing BOTs, endometriomas, and well-differentiated ovarian carcinoma, emphasising reproducible discriminators and common pitfalls. Material and Methods. A narrative review was conducted in PubMed/MEDLINE and supplemented by reference-chaining. Search terms included "borderline ovarian tumour", "serous borderline tumour", "mucinous borderline tumour", "endometrioma", "endometriosis-associated ovarian cancer", "low-grade serous carcinoma", "endometrioid ovarian carcinoma", "ultrasound", "MRI", "diffusion-weighted imaging", "dynamic contrast enhancement", and "O-RADS". Priority was given to consensus systems and comparative imaging literature from 2019-2025, supplemented by seminal earlier studies defining enduring diagnostic signs. Results and Discussion. A practical differential diagnosis requires integration of 1) clinical risk context (age, menopausal status, endometriosis history), 2) first-line ultrasound morphology and vascularity, and 3) MRI problem-solving with diffusion and post-contrast assessment. O-RADS MRI provides a reproducible framework centred on enhancing solid tissue, diffusion restriction and enhancement characteristics. Typical endometriomas show T1 hyperintensity and T2 shading without enhancing solid tissue; malignant transformation is suggested by new enhancing mural nodules and diffusion-restricted solid components. BOTs often demonstrate papillary projections; well-differentiated carcinoma more often shows more convincing solid tissue and restricted diffusion, although overlap persists and histology remains definitive. Conclusions. Standardised reporting (O-RADS) combined with MRI confirmation of true enhancement and multidisciplinary imaging-pathology correlation reduces misclassification. Key pitfalls include clot-related "pseudo-nodules", decidualised endometrioma and fibrous benign tumours such as cystadenofibroma.