Normalized apparent diffusion coefficient: a novel paradigm for characterization of endometrial and subendometrial lesions

Objectives: To assess the role of normalized apparent diffusion coefficient (ADC) in characterization of endometrial and subendometrial masses, measured as a ratio of the mean ADC of the pathology to mean ADC of two different internal controls, normal myometrium and gluteus maximus muscle, referred to as nADCm and nADCg respectively. Methods: 55 females with pathologically proven endometrial and subendometrial lesions, including 27 cases of endometrial carcinoma, and 28 cases of benign masses were enrolled in this prospective study and assessed with single-shot echoplanar diffusion-weighted imaging. The normalized and absolute ADC of the lesions, measured by two radiologists, were compared in different pathologies and receiver operating characteristics (ROC) performed to distinguish benign and malignant endometrial masses. In the endometrial carcinoma group, the ADC values were further compared with tumor grade and subtype. Results: There was good interobserver agreement (>0.800) for both internal controls, however it was higher for myometrium [intraclass correlation coefficient-0.92; confidence interval (0.86–0.95)] than gluteus maximus muscle [ICC-0.84; CI (0.72–0.90)]. There were statistically significant differences in absolute ADC (p-0.02), nADCm (p-0.02) and nADCg (p < 0.0001) of benign and malignant endometrial masses. Conclusion: Normalized ADC is useful to distinguish benign and malignant masses with comparable accuracy as absolute ADC. Advances in knowledge: Normalized ADC represents an easily measurable quantitative parameter which limits the influence of endogenous and exogenous factors that affect its reproducibility.