Endpoints (Outcome measures)：

1. Primary endpoint: Incidence of conversion rate during surgery

   - The primary performance endpoint will be assessed as the ability to successfully complete the planned mediastinal procedure with da Vinci SP System, with no conversion to open surgery, video-assisted thoracoscopic surgery (VATS), multi-port robotic surgery or approach requiring undocking of the da Vinci SP Surgical System in order to complete the planned procedure using the alternate approach. Use of additional assistant port(s) is not considered a conversion

2. Secondary endpoints: Incidence of treatment related adverse events - The safety endpoint will be assessed as the incidence of all intra-operative and post-operative adverse events that occur through the 30-day follow up period

During the past several years, minimally invasive thoracic surgery has evolved from thoracoscopic approaches using 3 -4 ports to a single incision video-assisted thoracoscopic surgery (VATS) techniques. Recently, the experience acquired with the uniportal VATS technique through the intercostal space has allowed the development of a uniportal VATS subxiphoid or subcostal approach for anterior mediastinal tumor resections. The advantage of using a subxiphoid or subcostal entry is to reduce pain by avoiding possible trauma of intercostal nerves caused by thoracic incisions. However, the longer distance from the subxiphoid or subcostal incision to the anterior mediastinal area makes this approach more difficult to perform extended thymothymectomy. During this same period of evolution into uniportal VATS surgery, robotic thoracic surgery has gained popularity as an alternative to traditional VATS. The advantages of robotics are the ability to perform surgery more precisely with articulated or wristed instruments, motion scaling, and tremor filtration, as well as improved visualization thanks to 3D high-definition video. However, currently 4 -5 incisions are still necessary to perform anatomic robotic resections.Recently, there has been a convergence of these two trends-uniportal surgery and robotic-assisted surgery-and has resulted in a single port robotic system, the da Vinci SP by Intuitive Surgical Cooperation. For this new platform, investigators plan to practice in extended thymothymectomy

Inclusion criteria

1. Age >20 and <75 years-old

2. Willing and able to provide informed consent

3. ASA≤ 3

4. The subject fulfills one or both of the following criteria:

   • Diagnosis of myasthenia gravis
   • Masaoka stage I or II thymoma; thymic mass ≤ 5 cm diameter

5. Class I-IV Myasthenia gravis according to the Myasthenia Gravis Foundation of America Scientific Session (MGFA)

Exclusion criteria. Myasthenia gravis or thymoma patients with

1. Congestive heart failure (NHYA > II)
2. Arrhythmia required medication control
3. Subjects with a known bleeding or clotting disorder
4. Subjects actively receiving therapeutic dose anticoagulation or anti-platelet medications at the time of operation
5. Subjects under immunomodulatory within 30 days prior to the planned surgery
6. Previous ipsilateral thoracic surgery or sternotomy
7. Uncontrolled illness 6 months prior to planned surgical procedure including, but not limited to ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
8. Previous neoadjuvant medical and/or radiation therapy
9. Subject has a contraindication for general anesthesia or surgery
10. Uncontrolled myasthenia gravis symptoms at the time of scheduled surgery
11. Confirmed thymic carcinoma
12. Patients who are not suitable for performing endoscopic surgery.
13. Myasthenia gravis patients with positive serum MuSK antibody. -