Differential diagnosis of mediastinal teratoma

Most teratomas are located in the anterior mediastinum, and more are located in the middle of the anterior mediastinum, at the junction of the heart and the aortic arch. A few higher masses have their upper edge crossing the top of the aortic arch, or they may be located lower in the lower part of the anterior mediastinum. Occasionally, they may be located in the posterior mediastinum. X-ray and CT examinations show dense round, quasi-round or nodular masses at the level of the heart base in the anterior mediastinum. If bones or teeth are seen, it has diagnostic significance. When the tumor penetrates into the lungs or bronchus, the patient coughs up sebaceous gland secretions or hair, which has characteristic diagnostic value.

Teratoma must be differentiated from the following diseases before final diagnosis.

1. Thymoma is a tumor originating from the thymus. X-ray examination shows that the tumor is often round or oval, with clear and sharp edges, or lobed, located at the heart base of the anterior superior mediastinum, close to the back of the sternum. The density is lighter and the outline is unclear on the lateral chest film, at the level of the sternal angle. Its common location is similar to that of reproductive tumors, but the latter may be located slightly lower than thymoma and is more unilateral. The shadows may contain calcification or osteodontoid hyperplasia, which can be used for identification, while thymoma rarely has the above imaging manifestations. It is easier to identify with myasthenia gravis.

2. Intrathoracic goiter is mostly located in the anterior superior mediastinum. Its source is mostly the cervical goiter that falls into the anterior superior mediastinum through the space behind the sternum, or the residual tissue or ectopic thyroid gland that develops gradually during the embryonic period. Patients are generally asymptomatic. Most of them are over 50 years old when they are discovered, and the number of females is about 4 times that of males. Tumor compression of surrounding tissues may cause corresponding symptoms. The diagnosis method is X-ray examination and CT examination of the neck and chest. Radionuclide scanning should be performed routinely for all suspected patients. In most cases, tumors can be seen on the upper left or right side of the trachea on X-ray films. More than 80% to 90% of them have tracheal displacement. Unlike tracheal displacement caused by other lesions, tracheal displacement caused by intrathoracic thyroid is mostly in the cervical trachea, which is one of its characteristics. The shadow of the mass is mostly round and oval, with clear and sharp edges. Under fluoroscopy, it can be seen that the mass moves up and down with swallowing. Nuclear scanning can determine the location, size and presence of corresponding lesions of the tumor. The function of the thyroid gland can also be determined based on the absorption of 131I. If there is no absorption of 131I in the normal thyroid gland but there is absorption of 131I in the retrosternal mass, it can be diagnosed as retrosternal goiter.

3. Mediastinal malignant lymphoma is the most common disease that is not suitable for surgical treatment. Mediastinal tumors are only the local manifestation of this highly malignant systemic disease. In the early stage, there are severe compression symptoms of the trachea and superior vena cava. Generally, the symptoms of shortness of breath worsen rapidly, and swelling of the face, neck, and upper limbs occurs. Superficial lymphadenopathy and hepatosplenomegaly are also common phenomena. X-rays show huge nodular masses that grow rapidly around the typical trachea and bronchi in one or both sides of the mediastinum. Some cases may have pleural effusion. Small doses of radiotherapy and chemotherapy can quickly improve symptoms, and the tumor shadows seen on X-rays are significantly reduced.

4. Mediastinal cysts are mainly anterior mediastinal cysts, and the more common ones are thymic cysts and cystic lymphangiomas. Most patients are asymptomatic, and the symptoms are mainly caused by increased fluid accumulation in the cyst and enlargement of the mass. The diagnosis is mainly based on radiological examinations. It appears as a low-density space-occupying mass with thin walls, smooth and clear edges, and a semicircular or circular shape. CT can clearly define the relationship between the range of the lesion and the surrounding tissues and can well show that the density of the cyst contents is close to water. But sometimes it is confused with cystic teratoma. It is often impossible to confirm the diagnosis before surgery. The main treatment is surgical removal of the cyst. Surgical treatment is easier when there is no obvious adhesion between the cyst and the surrounding tissues.

5. Thoracic aortic aneurysm Aneurysm patients have typical symptoms and signs such as chest tremor and murmur, tracheal traction, recurrent laryngeal nerve paralysis and pulsating swelling on X-ray, which are easy to identify. Less common is the formation of organized thrombus in the aneurysm sac with neither murmur nor pulsation. The shadow of the aneurysm cannot be separated from the aorta or large brachiocephalic vessels on ordinary X-ray films, which is of great diagnostic significance. Generally, the aneurysm forms an obtuse angle with the large blood vessels. In suspicious cases, cardiac angiography should be performed to confirm the diagnosis.

6. Metastatic tumors Metastatic lesions from tumors of the lung, breast, cervix or other organs are not uncommon. Occasionally, there may be isolated primary lesions of unknown cause, and even after surgical exploration and autopsy, the source of the metastatic lesions cannot be confirmed. Therefore, the diagnosis must be considered comprehensively.