The thymus gland is an important immune organ in the body and is part of the lymphatic system whose function is to differentiate some lymphocytes into T-lymphocytes. The thymus, like other organs in the body, can develop benign or malignant tumors, the most common being thymoma. Other tumors or tumor-like diseases include: thymic carcinoma, thymic cyst, thymic lipoma, thymic hyperplasia, etc. The thymus gland is located in the anterior mediastinum and is generally divided into two asymmetrical lobes connected by an isthmus in an “H” shape. The thyroid gland is connected to the left and right lobes of the thyroid gland by the thyroid ligament. The lower pole is flat at the level of the 4th to 6th intercostal space and is covered by the pericardium and the great vessels at the base of the heart.
The thymus is covered by a fibrous envelope that extends to the interior of the thymus, forming fibrous tissue intervals that divide the thymus into lobules 0.5-2 mm in size, each lobule consisting of a cortex and a medulla, with the peripheral part of the lobule being the cortex and dense with lymphocytes; the medulla is located in the center of the lobule and is pale with few lymphocytes, and the medullary area is connected to the medulla of the adjacent lobule.
Although the thymus is an important immune organ, it has largely degenerated by adulthood, and no changes in immune function have been observed in adults and children after thymectomy. Although there may be a reduction in lymphocyte counts and experiments in immunity, there is no specific clinical disease as a result. Clinical manifestations Multiple populations Thymoma occurs mainly in adults and is very rare in children. The average age of diagnosis is 45 to 52 years (5 to 80 years), slightly more common in women, and more often associated with myasthenia gravis.
Symptoms of thymoma
1. 50% to 60% of patients are asymptomatic and are found incidentally during physical examination.
2.More than 25% of patients have local chest symptoms caused by tumor invasion or compression of adjacent mediastinal structures, including: cough, chest pain, dyspnea, dysphagia, recurrent respiratory infections, etc.. Hoarseness and diaphragmatic paralysis are not common, but they mostly suggest the possibility of malignant spread.
3.Malignant thymoma metastases are mostly confined to the chest cavity, which may be accompanied by pleural fluid, causing symptoms such as dyspnea, chest pain and chest discomfort. Only about 3% of malignant thymoma eventually metastasize outside the chest, and the metastatic site is most common in the skeletal system, causing related metastatic symptoms.
4. Systemic symptoms: 18% of patients with thymoma have general systemic symptoms, such as weight loss, fatigue, fever, night sweats and other non-specific symptoms. The concomitant symptoms of thymus disease are a complex group of systemic diseases, which may be complicated with thymoma by more than 30 diseases, the four most common ones being: myasthenia gravis, simple red blood cell aplastic anemia, hypogammaglobulinemia, and extrathymic malignancy. These diseases may occur at the same time as the thymoma, after its removal, or many years before.
Complications of thymoma
1. Myasthenia gravis: It is the most common complication of thymoma. About 1/3 of thymomas are complicated by myasthenia gravis, and conversely, 10% to 15% of patients with myasthenia gravis are accompanied by thymoma. It is believed that thymoma without MG tends to be more malignant than thymoma with MG and has a worse prognosis than the latter, which may be related to the fact that thymoma with MG is often detected early.
2, simple red blood cell aplastic anemia: the exact relationship between thymoma and simple red blood cell aplastic anemia is not very clear, but about 30% of patients can get complete remission of anemia after a long time after thymoma removal. Patients with thymoma may also have other hematologic disorders including leukopenia and thrombocytopenia, T-lymphocytosis, lymphocytic leukemia, and multiple myeloma.
3. Hypo-Υglobulinemia: 4% to 12% of thymoma patients have combined hypo-Υglobulinemia, usually with recurrent bacterial infections, viral infections, and mycobacterial infections. Thymoma resection does not effectively raise immunoglobulin levels
Diagnosis and differentiation of thymoma
1.Radiological examination: Chest plain film and chest CT are the most commonly used examinations to detect and determine thymic tumors (see Figure 4, Figure 4 chest plain film and chest CT (2 pictures). 80% of thymomas are located in the anterior mediastinum at the heart base, and 80% of their tumors can cover the hilum. The vast majority are located in the anterosuperior or superior mediastinum, and the rest are located in the neck, hilum, intrapulmonary, and posterior mediastinum.
2.Biopsy: It is generally believed that invasive biopsy is not recommended for anterior mediastinal tumors because: imaging combined with tumor markers can basically confirm the diagnosis of anterior mediastinal tumors; biopsy destroys the envelope of non-invasive thymoma and turns it into invasive thymoma; needle aspiration biopsy often cannot collect enough specimens for immunohistochemical examination. However, it is also believed that needle aspiration or VATS biopsy can be considered when it cannot be differentiated from other malignant tumors or when there are symptoms.
3. Other tests: All patients suspected of thymoma should be examined for acetylcholine antibodies, blood tests, AFP, β-hCG and LDH to exclude anemia, myasthenia gravis and germ cell tumors. Other diseases to be differentiated include: lymphoma, aortic aneurysm, teratoma, etc.
Most thymomas are slow-growing tumors with an intact envelope and can be cured by resection. The proportion of aggressive (malignant) thymomas reported in the literature varies widely, from 5% to 50%. The average time from diagnosis to recurrence after treatment for malignant thymomas is generally 6 years, so it is believed that thymomas should be followed up for a long time.
Treatment options for thymoma
1.Stage IV thymoma: Chemotherapy is preferred. If the initial chemotherapy is effective, surgery can be considered for stage IVA thymoma. A trial of thoracic radiotherapy as combined treatment can also be considered. Relapsed thymoma that is resistant to chemotherapy can be treated with palliative radiotherapy as appropriate.
Local recurrence and distant metastasis: Stage I and II thymoma can also recur locally, up to 12% of non-invasive thymoma recurrence, but 0% to 5% are also reported. 13% of stage II, 29% of which have no adjuvant therapy after surgery. Stage II recurrence rates of 28% to 33% have also been reported. If possible, all of them should be resected twice. Most of the patients with satisfactory results of secondary surgery can still survive for a long time and need to add radiotherapy after surgery. Chemotherapy is preferred for distant metastases.