Previous literatures[2-4] have shown that lymph node involvement is relevant to local recurrence, in fact. This is controversial according to the current American Thyroid Association (ATA) guidelines for a routine prophylactic or therapeutic CLND in patients with PTC[7-8].
The anatomic boundaries of a CLND include the carotid arteries from the hyoid bone superiorly to the innominate artery inferiorly. An appropriate range of CLND should both reduce the local recurrence rate and the incidence of post-operative complications. Paratracheal LNs are the most commonly involved central LNs. For PTC, a precise range of paratracheal LN dissection is still controversial. There have been none articles written on the significance of the LN-epRLN, as part of paratracheal LNs. In the current study[9-10], therefore, LN-epRLN did not fall under the normal subdivisions of the central compartment.
The LN-epRLN was defined as the lymph node located within the distance from outer edge of the lymph node to the RLN entrance point less than 5 mm (Fig.1). In our study, there were inconstant nodes, 1 to 4 (1 in average), in diameter between 6 mm and 10 mm. In the present study, LN-epRLN was found in 73 of 878 patients and the metastasis rate was 3.76% (33/878). Thinking only about involved thyroid lobes, the positive LN-epRLN rate was 46.84% (37/79), and the incidence of the right side was slightly higher than that on the left side. The univariate analysis showed that the factors affecting LN-epRLN involvement were the other central cervical lymph node metastasis, the upper third tumor location and tumor multifocality.
The LN-epRLN receives afferent lymphatic drainage from the thyroid gland. Considering the anatomical location of the LN-epRLN, it may be expected that tumors located in the upper third will spread to the LN-epRLN more frequently than other.
In our study, the rate of other central neck node metastasis in the presence of LN-epRLN metastasis was 93.9%. Supporting our results, the positive LN-epRLN was highly predictive of other central nodal metastasis. However, this tendency merits further investigation. On the other hand, the exploration and removal of LN-epRLN should be included in CLND for clinically node positive PTC.
Usually, most patients with PTC obtain a 10-year survival rate of 80–90%, but the regional recurrence rate after surgery is 5-20%. Therefore, it’s important to improve the thoroughness of CLND. In our study, two PTC patients suffered second operation as a consequence of the presence of metastatic LN-epRLN, which may mistake for a parathyroid gland or give consideration to recurrent laryngeal nerve injury, and be reserved during the primary operation. After the second operation, the two patients both had transient hoarseness. Our results mirror the data from literature: Reoperative CLND has been shown to have rates of RLN injury 21% transiently and postoperative hypocalcemia with a large range of 0-24%[13-20]. PTC patients with clinically involved lymph nodes in the central compartment should be managed with a LN-epRLN dissection procedure as the time of CLND, taking into consideration RLN and parathyroid glands which are closely related to the nodal basins.
Our prospective study was limited by small samples, which means our results may not be as powerful as a randomized clinical trial with a large population. Moreover, patients with lateral neck lymph node matastases were excluded due to inclusion criteria. These patients may have experienced worse outcomes than patients enrolled in our study. However, to our knowledge, this is the first article in English to progress our understanding of LN-epRLN metastases in PTC patients.