To summarize the ultrasonography (US) and magnetic resonance imaging (MRI) findings of lymphoepithelial cysts (LECs) and dermoid cysts (DCs) and to discuss the hyperinternal echo in LECs based on histopathological findings.

Patients who underwent US and MRI before resection and whose lesions were pathologically diagnosed as LECs or DCs were included (January 2010 to December 2023). Internal echo, convective flow, and Doppler signals were evaluated on US, while on MRI, we measured the apparent diffusion coefficient (ADC).

Surprisingly, all lesions (4 LECs and 7 DCs) had hyperinternal echoes. Convective flow and Doppler signals were observed in 2 of the 4 cases of LEC, and the ADC was high in these cases (2.4 × 10–3 and 2.0 × 10–3 mm2/s). In the two cases where they were not, the ADC was low (1.4 × 10–3 and 0.81 × 10–3 mm2/s). Various cells, such as lymphocyte cells, foam cells, erythroid cells, and keratin, have been found in the cystic cavity, which are thought to be the cause of hyperecho. Considering the ADC, the presence or absence of convection and Doppler signals is thought to reflect the ease of movement of the contents. In the DCs, neither internal convection nor obvious Doppler signals were observed. ADCs were quite low for cysts, which was a characteristic finding (1.1 ± 0.13–3 mm2/s).

It is well known that DCs appear hyperechoic on US owing to the presence of keratin; however, it is necessary to recognize that some LECs are depicted as hyperechoic masses and have convective flow and Doppler signals depending on the content.