A multicenter prospective study of lateral neck lymph node mapping in papillary thyroid cancer

Background: Despite the high incidence of lateral neck lymph node (LN) metastasis in papillary thyroid cancer (PTC), the management of the lateral neck remains controversial. We aimed to map the draining LNs in the lateral neck using carbon nanoparticles and explore its potential in neck evaluation. Methods: We conducted a multicenter, prospective study in PTC patients who had non -palpable yet suspicious metastatic lateral LNs on ultrasound and/or computed tomography (CT) but could not be confirmed by fine needle aspiration. Carbon nanoparticle suspension was injected peritumorally into the thyroid and modified lateral neck dissection was subsequently performed. Results: A total of 154 patients were enrolled for analysis. And 5,070 lateral LNs were removed, of which 1,079 (21.3%) were dyed. The median of dyed LNs was 6 per case (range, 1-33). The distribution of dyed LNs in neck compartments was IV > III > IIA > IIB/V, independent of tumor size, location, multifocality or microscopic extra -thyroidal extension (ETE). Compared with undyed LNs, the probabilities of metastasis in dyed LNs were significantly increased in compartment III, IV, V, and II-V (III: 29.3% vs. 15.4%, P<0.001; IV: 26.3% vs. 14.5%, P<0.001; V: 16.7% vs. 3.3%, P=0.005; II-V: 26.3% vs. 10.0%, P<0.001). The relative risks of metastasis in dyed LNs compared with undyed LNs were 1.90, 1.82, 5.04 and 2.62 in compartment III, IV, V, and II-V, respectively. Conclusions: It was the first prospective multicenter study to map the lateral neck LNs with carbon nanoparticles, which could help surgeons visualize the suspicious LNs during surgery. Instead of unguided LN biopsy, this method has a potential role in lateral neck assessment for indeterminate lateral LNs in PTC.