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BackgroundEpidermal cysts (ECs) are the most common type of epithelial cyst. On ultrasound, ECs typically exhibit peripheral shadowing and posterior acoustic enhancement. However, their internal echogenicity varies, and the factors influencing these sonographic features remain largely unknown. Objectives: To identify factors associated with each ultrasound feature of ECs based on review of medical records and ultrasound findings of histologically confirmed EC patients.Materials & MethodsWe reviewed ultrasound findings from 55 histologically confirmed EC cases. The cohort included 34 male patients, the mean age for all patients was 52.8 years, and the median EC diameter was 2.0 cm.ResultsLogistic regression analyses revealed that associated redness and pain tended to correlate with a lower frequency of peripheral shadowing, consistent with previous reports. In contrast, EC diameter was the only factor significantly associated with a smaller proportion of anechoic areas. Consistent with this, the Mann-Whitney test showed that the proportion of anechoic areas was significantly smaller in larger ECs. Additionally, logistic regression analyses demonstrated that EC diameter was significantly associated with the presence of filiform low echoic areas and hyperechoic areas.ConclusionThis study is the first to demonstrate a significant correlation between EC size and sonographic features. Larger ECs exhibited a smaller proportion of anechoic areas and a higher likelihood of containing hyperechoic areas. These findings suggest that EC size plays a key role in determining internal echogenicity, and recognition of these patterns may enhance the diagnostic accuracy of ECs on ultrasound.