Case of right-neck tumor that appears to be ectopic thymus

A 7-year-old female infant presented with an asymptomatic soft tissue mass in the right neck. The tumor was considered to be a benign one because it had a smooth margin and no change in its size was observed. Ultrasonography showed a 4.5-cm-diameter solid tumor with a smooth, well-defined border. Inside the tumor, flow signals were observed on color Doppler and there were numerous echogenic spots. Magnetic resonance imaging (MRI) examination showed findings consistent with an ectopic thymus, i.e., T1- and T2-weighted images showed thymus-like signals. The course of the case is being continuously followed.