Cystic–solid ADC difference on MRI for differentiating seromucinous borderline tumor from endometriosis-associated ovarian cancer

Background Seromucinous borderline tumor (SMBT) and endometriosis-associated ovarian cancer (EAOC) may show overlapping magnetic resonance imaging (MRI) features. Quantitative diffusion-weighted imaging may improve their preoperative differentiation. Purpose To evaluate the diagnostic performance of the cystic–solid apparent diffusion coefficient difference (ΔADC) for differentiating SMBT from EAOC. Material and Methods This retrospective single-center study included 49 patients with pathologically confirmed SMBT (n = 14) or EAOC (n = 35) who underwent preoperative pelvic MRI. Apparent diffusion coefficient (ADC) values were measured in the cystic and solid components, and ΔADC was calculated as cystic ADC minus solid ADC. Receiver operating characteristic (ROC) analysis was performed with EAOC as the positive outcome. Results SMBT showed lower cystic ADC values and higher solid ADC values than EAOC, resulting in a smaller ΔADC. ΔADC and solid ADC yielded areas under the ROC curve of 0.924 (95% confidence interval (CI) 0.817–1.000) and 0.918 (95% CI 0.837–1.000), respectively. The difference was not statistically significant ( P = 0.862). At the internally derived ΔADC cutoff of 0.529 ×10 −3 mm 2 /s, sensitivity was 94.3% (95% CI 80.8–99.3) and specificity was 92.9% (95% CI 66.1–99.8); because the cutoff was derived and evaluated in the same cohort, these performance estimates may be optimistic. Conclusion ΔADC showed high diagnostic performance for differentiating SMBT from EAOC, but incremental diagnostic performance over solid ADC was not demonstrated. The internally derived cutoff and associated performance estimates require independent multicenter validation before clinical application.