1.When combined with hyperthyroidism, thyroid function tests can be done, and there will be elevated serum T3 and T4 and reduced TSH. 2. Chest X-ray (1) When the retrosternal goiter is small, the mediastinal shadow is not widened, and the density of the upper mediastinum is slightly increased, which can often compress the trachea, and the presence of tumor can be inferred by the curved tracheal pressure. After tumor enlargement, the shadow of upper mediastinum may widen to one or both sides. If the tumor occurs in the right lobe, the mediastinal shadow will protrude in an arc to the right side, and the larger one may also protrude slightly to the left side; if the tumor occurs in the left lobe, when the tumor is small, the shadow will only protrude to the left side, but when it is large, the shadow may protrude to the right side at the same time. If the tumor occurs in both sides or in the isthmus, the mediastinal shadow protrudes in an arc to both sides. Since the aortic arch is more fixed and resists more to the pressure of tumor, the mediastinal shadow mainly protrudes to the right side, while the enlarged thyroid gland can press the aortic arch and shift to the lower left side. (2) When the size of goiter is large, it can compress the trachea and make it shift to the contralateral and posterior sides; if it is located in the posterior side of trachea, it can compress the trachea and shift to the anterior and contralateral sides; when both sides of trachea are compressed, it is deformed in the shape of scabbard. The curvature of the trachea is large and often extends all the way to the neck, ending at the larynx, a phenomenon that is strong evidence of goiter. (3) The shadow of retrosternal goiter is connected with the soft tissue of the neck. On fluoroscopy or X-ray, the tumor shadow of the upper mediastinum is seen to extend toward the neck, according to which it can be distinguished from other mediastinal tumors. Since the mass is often closely connected with trachea, there is upward movement during swallowing action. If there is no such movement, the possibility of this disease cannot be completely excluded. (4) The esophagus may be displaced to the left or right by pressure, and the tumor may occasionally be embedded between the esophagus and trachea, widening the distance between them. (5) The edge of benign thyroid tumor can be slightly lobulated, while malignant tumor is wavy. The density of tumor shadow is uniform, sometimes there may be calcification in the form of block or dot, and in the edge may be arc-shaped, but the benignity or malignancy of tumor cannot be identified by the presence or absence of calcification, and malignant tumor may metastasize to the lung or bone. (6) Mediastinal inflatable imaging can show thyroid tumor clearly, and the application of transverse tomography can show that the mass is located above the anterior part of the aorta. 3.CT examination Typical manifestations are as follows: ① connected with the thyroid gland in the neck, located in the anterior tracheal space, and may also extend into the trachea and esophagus posteriorly; ② clear boundary; ③ accompanied by punctate and annular calcification; ④ the mass is mostly substantial shadow, with non-uniform density, accompanied by non-enhanced low density area; ⑤ accompanied by tracheal displacement, compression, esophageal compression, etc.; ⑥ CT value is higher than the surrounding muscle tissue. It is often 50～70HU, sometimes up to 110～300HU, and the CT value of cystic area is 15～35HU. 4.B ultrasound, MRI and DSA B ultrasound can clarify whether the mass is cystic or solid. MRI can understand the relationship between the mass and the surrounding large blood vessels and exclude the possibility of hemangioma. DSA understands the source of blood supply to the mass and the blood circulation of the mass itself. 5.Radionuclide 131I examination can determine whether the mass is thyroid tissue, and also its size, location or the presence of hot nodules secondary to hyperthyroidism.