Abstract: Objective Despite the high incidence of lateral neck lymph node metastasis in papillary thyroid carcinoma(PTC), its management has remained controversial. The accuracy of ultrasound and computed tomography(CT)in lateral neck evaluation for PTC is unsatisfactory. An unnecessary neck dissection may lead to increased complications, while undetected lymph node metastasis may facilitate recurrences and necessitate resurgery. We aimed to map the draining lymph nodes in the lateral neck using carbon nanoparticles and explore its potential in neck assessment. Methods We conducted a multicenter, prospective study from August 2016 to April 2019 in PTC patients who had unpalpable lateral lymph nodes that appeared suspicious on ultrasound and/or CT. Carbon nanoparticles were injected peritumorally into the thyroid gland, and modified lateral neck dissection(compartment Ⅱ-Ⅴ)was performed. The lateral lymph nodes were classified into dyed and undyed and sent for pathological analysis. Thyroidectomy and central neck compartment dissection were performed. Results A total of 125 neck dissections were performed in 122 patients. Of the dissections, 117 were for lateral neck metastases, 7 were for central metastases, and metastasis was absent in the remaining 1. A total of 4302 lateral lymph nodes were removed, 952 of them were dyed. The median number of dyed nodes was 6 per case(range: 1-33). The distribution of dyed nodes in the neck compartments was Ⅳ> Ⅲ> Ⅱ> Ⅴ, independent of tumor size, location, or extra-thyroidal extension. The percentages of dyed lymph node metastasis in Ⅱ-Ⅴ compartments were 33.3%, 60.0%, 68.8%, and 40.0%, respectively, on a per-case basis and 10.2%, 31.4%, 27.5%, and 20.8%, respectively, on a per-node basis. Compared to undyed nodes, the risk of metastasis in dyed nodes was significantly higher in all neck compartments(compartment Ⅱ: 19.9% vs. 5.6%, P<0.001; compartment Ⅲ 35.0% vs. 18.3%, P<0.001; compartment Ⅳ: 37.1% vs. 15.2%, P<0.001; compartment Ⅴ: 14.8% vs 3.7%, P<0.05). A lateral sentinel lymph node biopsy was performed in 51 patients. The sensitivity of the lateral neck sentinel lymph node biopsy was 89.5%, the false-negative rate was 26.7%, and the overall accuracy rate was 91.8%. Conclusion Using carbon nanoparticles, we successively mapped the lateral neck lymph nodes. We found that dyed nodes had a significantly higher risk of metastasis than that of undyed nodes. This method may be useful for lateral neck sentinel lymph node biopsies in PTC.

Key words: Papillary thyroid carcinoma, Lateral cervical lymph node, Lymph node mapping, Neck dissection, Sentinel lymph node biopsy