RATT Vs. VATT for Early-stage TETs

Inclusion Criteria: * Thymoma was diagnosed by chest enhanced CT or MRI (clinical stage: Masaoka Koga I-II) with AJCC/UICC TNM grade system (9th edition). The patients whose tumor diameter was not larger than 8 cm; The patients with the estimated survival time should be over 12 months; ASA grade：1-2; The patients should have no functional disorders in main organs; The patients should be able to understand our research and sign the informed consent. Exclusion Criteria: * Imaging examination showed that the tumor had invasion of surrounding organs, pleural or pericardial dissemination, lymphatic or hematogenous metastasis; Patients with myasthenia gravis; Patients had undergone a sternotomy; The patients have proved history of congestive heart failure, angina without good control with medicine; ECG-proved penetrating myocardial infarction; hypertension with bad control; valvulopathy with clinical significance; arrhythmia with high risk and out of control; The patients have severe systematic intercurrent disease, such as active infection or poorly controlled diabetes; coagulation disorders; hemorrhagic tendency or under treatment of thrombolysis or anticoagulant therapy; Female who is positive for serum pregnancy test or during lactation period; The patients have history of organ transplantation (including autologous bone marrow transplantation and peripheral stem cell transplantation; The patients have history of peripheral nerve system disorders, obvious mental disorders or central nerve system disorders; The patients attend other clinical trials.