**1. Introduction**

Differentiated thyroid carcinoma (DTC) is traditionally considered as a tumor with good prognosis, with an overall survival nearly comparable to the general population. Nevertheless, a certain number of patients experience a poor clinical outcome, with local recurrence requiring further medical or surgical treatment, with a considerable worsening of the quality of life.

The incidence of local recurrence is widely variable; the American Thyroid Association (ATA) guidelines for patients with differentiated thyroid cancers, published in 2015, report an incidence of local recurrence in 3–13% of patients with low-risk tumors, 21–36% in cases of intermediate-risk tumors, and in 68% of high risk tumors [1]; similar findings have been extensively reported in literature [2–7].

The most important risk factors for local recurrence have been reported in the literature and are the presence of lymph node metastases, the extrathyroidal extension of the tumor with invasion

of perithyroidal tissues, the presence of BRAF V600E mutation, and the incomplete resection of the tumor [1,2,8,9].

In fact, one of the outstanding issues is the role of lymphectomy of the central compartment in cases of clinically uninvolved lymph nodes. In fact, the incidence of occult node metastases is high, with a reported incidence up to 90% [2,10–14]. Furthermore, the real prognostic value of lymph node metastases in DTC is still uncertain, with some authors suggesting that lymph node metastases do not decrease the survival rate [3,15–18], while others have reported a worsening in both overall and in disease-free survival [8,19–23].

For these reasons, a prophylactic central lymph node dissection (pCLND) has been proposed for tumors with clinically uninvolved lymph nodes, but suspected of having aggressive behavior at preoperative and intraoperative evaluation. Nevertheless, this suggestion is met with considerable resistance due to the higher incidence of postoperative complications including hypoparathyroidism and recurrent laryngeal nerve (RLN) injury, and to the doubtful role of lymph node metastases on prognosis [24–26]. Consequently, the most important guidelines on DTC are discordant on this topic, with the ATA guidelines and National Comprehensive Cancer Network (NCCN) guidelines suggesting a prudent approach [1,27], while the Japanese Association of Endocrine Surgeon and the Japanese Society of Thyroid Surgeons recommend routine pCLND [28].

The aim of this study was to assess whether prophylactic CLND is effective in reducing the incidence of recurrent disease, to evaluate the incidence of postoperative complications in patients who underwent pCLND, and the influence of occult node metastases on the prognosis.
