Intrathyroidal thymic carcinoma (ITTC) is a rare epithelial tumor of the thyroid gland. Since ITTC is rare, its imaging findings have not been well defined. In the present study, we studied the US appearance of ITTC by analyzing ten cases retrospectively.Methods: Patients were identified by searching the surgical pathology records at our hospital. There were three male and seven female patients ranging in age from 40 to 79 years. The ultrasound (US) features were evaluated, and the relevant clinical data were combined with the fine needle aspiration (FNA) results from previous publications. Results:The average length of the nodules was 48 mm. Of all ten nodules, half were located in the right lobe of the thyroid, and half were located in the left lobe, either immediately adjacent to the lower lobe or within the lower part of the thyroid lobe. All nodules manifested with a completely solid composition and heterogeneous hypoechoic echogenicity. Three nodules had striped hyperechogenicity within the nodule. All nodules had irregular margins. Seven had a horizontal shape, and three had a vertical shape. Four nodules manifested with mainly peripheral vascularity, two nodules showed mainly central vascularity, and three had mixed vascularity. The vascularity of one remaining nodule was unknown. Cervical lymph node metastasis was detected in two cases by US examination. According to previous literature, FNA cytology revealed atypical type of thyroid cancer, poorly differentiated carcinoma, or a high-grade malignant thyroid neoplasm without further definitive classification. Conclusion:A large cancer-like nodule located within the lower thyroid in middle-aged people, combined with an atypical type of thyroid cancer after FNA, indicated that ITTC should be considered.