Background: To assess the accuracy of ultrasound in differentiating endometrioma from ovarian cancer andto describe pattern recognition for atypical endometriomas mimicking ovarian cancers. Materials and Methods:Patients scheduled for elective surgery for adnexal masses were sonographically evaluated for endometriomawithin 24 hours of surgery. All examinations were performed by the same experienced sonographer, who hadno any information of the patients, to differentiate between endometriomas and non-endometriomas using asimple rule (classic ground-glass appearance) and subjective impression (pattern recognition). The final diagnosisas a gold standard relied on either pathological or post-operative findings. Results: Of 638 patients availablefor analysis, 146 were proven to be endometriomas. Of them, the simple rule and subjective impression couldsonographically detect endometriomas with sensitivities of 64.4% (94/146) and 89.7% (131/146), respectively. Of52 endometriomas with false negative tests by the simple rule, 13 were predicted as benign masses and 39 weremistaken for malignancy. Solid masses and papillary projections were the most common forms mimicking ovariancancer, consisting of 38.5% of the missed diagnoses. However, with pattern recognition (subjective impression),32 from 39 cases mimicking ovarian cancer were correctly predicted for endometriomas. All endometriomassubjectively predicted for ovarian malignancy were associated with high vascularization in the solid masses. Conclusions: Pattern recognition of endometriomas by subjective assessment had a higher sensitivity than thesimple rule in characterization of endometriomas. Most endometriomas mimicking ovarian malignancy couldbe correctly predicted by subjective impression based on familiarity of pattern recognition.
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