**2. Methods**

In this retrospective observational study, we included patients who underwent thyroidectomy for DTC at our department from January 2011 to December 2016. Ethical approval was obtained from our local ethics committee. Patients were identified from a prospectively maintained institutional database including all patients who underwent thyroidectomy. Inclusion criteria were preoperative diagnosis of DTC and the absence of clinically involved lymph nodes both on Ultrasound (US) and on intraoperative examination (cN0). Exclusion criteria were distant metastases, incidental diagnosis of DTC at pathological evaluation, and surgery performed for recurrent disease.

Patients were divided into two groups: in the first group, we included patients who underwent total thyroidectomy alone (TT group), while in the second group, patients who had undergone thyroidectomy and prophylactic CLND (pCLND group). The design of the study is reported in Figure 1.

**Figure 1.** Design of the study. DTC: differentiated thyroid carcinoma; pCLND: prophylactic central lymph node dissection.
