Figure 1A: Ultrasound showed that the left thyroid had a large hypoechoic solid nodule with a clear margin. (B) Enhanced-CT in the axial plane showed an irregular heterogeneous enhanced mass within the left thyroid pushing the trachea to the right. (C) Non-enhanced CT in the axial plane showed multiple solid nodules in the inferior lobe of the right lung. (D) Non-enhanced CT in the sagittal plane showed a mixed ground-glass opacity in the dorsal part of the inferior lobe of the right lung (arrow) and a solid nodule. (E) In the frozen section, the tumor showed a multinodular growth pattern characteristic of the "jigsaw puzzle" pattern. (F) At a higher magnification of (E), tumor cells formed a pseudo-glandular pattern

Figure 2: The postoperative pathological section showed that the tumor involved in the normal thyroid (A) and some intravascular tumor emboli were observed (B). (C) In the lymphocyte-scarce zone, oval-shaped tumor cells formed slit-like or pseudo-glandular structures. (D) In the lymphocyte-rich zone, small and round tumor cells admixed with more lymphocytes. (E) Intrapulmonary solid nodules were well-demarcated and the same histomorphology as the type AB thymoma. (F)Tumor embolus of the inferior thyroid vein was identified as type AB thymoma

Figure 3: (A) Tumor cells in thyroid mass were diffusely positive for CK19. (B) Tumor cells in the thyroid mass and surrounding normal thyroid glands showed nuclear staining for TTF1. (C) Scattered tumor cells in the thyroid mass were positive for PDL1. Tumor infiltrating lymphocytes were positive for CD3 (D) and TDT (E). (F) Scattered tumor infiltrating lymphocytes were positive for PD1