No prior studies have stratified the difficulty of transoral and submental thyroidectomy (TOaST). The investigators aimed to investigate preoperative factors as indicators of difficult TOaSTs and to develop a predictive model accordingly.

Thyroid cancer is the most common endocrine malignancy, with a female predominance. Thyroidectomy is the main treatment for thyroid cancer, and considering the good prognosis of thyroid cancer, endoscopic thyroid surgery, which avoids neck incision, is being widely used in the clinic in order to improve the life treatment of patients. Among them, endoscopic thyroidectomy with transoral approach has a shorter learning curve because of the short surgical path. However, due to the complex structure of the neck, small space, and rich blood supply of the thyroid gland, surrounded by parathyroid glands and important nerves, endoscopic thyroid is difficult and has a long learning curve. In addition, a series of complications such as haemorrhage, hypoparathyroidism and laryngeal reentrant nerve injury can seriously affect the quality of patient survival. Difficult thyroidectomy is usually characterized by a long operative time, high intraoperative bleeding and a high incidence of postoperative complications. According to the literature, in open thyroid surgery, the degree of difficulty is associated with factors such as goiter, inflammation, and hyperthyroidism. However, the degree of difficulty of thyroidectomy due to various factors varies and is difficult to predict. Surgical difficulty is closely related to the outcome and safety of thyroidectomy, which is an urgent concern for surgeons. And there is no study on the degree of difficulty of transoral and submental endoscopic thyroidectomy, therefore, there is an urgent need for an effective and objective method to determine the preoperative factors affecting the degree of surgical difficulty and to establish a model for validation, so that it can be subsequently replicated in other hospitals.

Inclusion Criteria:

• Clinical diagnosis of differentiated thyroid cancer with a maximum diameter not exceeding 4 cm
• Absence of suspicious lateral lymph nodes or distant metastases
• Participants with high cosmetic expectations
• Participants who underwent total thyroidectomy and central lymph node dissection.

Exclusion Criteria:

• Participants with fusion or fixation of lymph nodes in the neck
• Participants with history of neck surgery or radiation
• Participants with vocal fold fixation by preoperative fibrolaryngoscope
• Participants with preoperative examination suggestive of extrathyroidal invasion
• Participants with a significantly restricted neck

Patients with FNA proven differentiated thyroid cancer, were willing to undergo total thyroidectomy and central lymph node dissection via transoral and submental approach. Patients were well informed about the transoral and submental approach and were aware of the potential benefits and risks. Patient consented for us to use perioperative data.

Data are available on request due to privacy or other restrictions. The data that support the findings of this study are available on request from Ling Zhan. The data are not publicly available due to them containing information that could compromise research participant privacy.