Can ultrasound distinguish between dermatofibroma and subcutaneous epidermal tumors? - Imaging features and reproducibility.

Abstract Background We evaluated ultrasound (US) features of dermatofibroma and epidermal tumor (ET). We also evaluated the reproducibility of each US findings. Materials and methods We retrospectively assessed US findings of 30 surgically confirmed dermatofibromas and 44 ETs, measuring the lesion (i.e., the depth and the length of the lesion) and calculating the depth to length ratio (DLR). We then determined the sharpness and the shape of the lesion. Finally, we assessed whether the lesion appeared with a “more-than-half sign” (involving more than 50% of the dermal layer) or a “submarine sign” (focal projection to skin). We used Pearson's chi-squared test to analyze the US findings (i.e., presence of more-than-half sign or submarine sign and margin sharpness) between dermatofibroma and ET. Inter-observer agreement of the image findings was assessed using kappa statistics. Results The submarine sign and margin sharpness of ET lesions and the more-than-half sign and submarine sign in dermatofibroma, respectively, showed almost perfect agreement. Also, the more-than-half sign and shape of the lesion in ET and the margin sharpness and shape of the lesion in dermatofibroma showed substantial agreement. The measurements of DLRs showed excellent reproducibility. There were no significant differences of DLRs between two groups (p values = 0.512, 0.671, respectively). The more-than-half sign was observed more frequently in the context of dermatofibroma to a statistically significant degree (p  Conclusions More-than-half signs are common in dermatofibroma while submarine sign and sharp margin are common in ET. Each finding showed high reproducibility and can be useful as a sonographic marker for differentiation between ET and dermatofibroma.