Abstract: Objective To investigate the feasibility of frozen lymph node biopsy with carbon nanoparticles combined with palpation in selective central neck dissection for unifocal cN0 T1-T2 papillary thyroid cancer (PTC) based on the biopsy results. 
Methods A total of 217 patients with unifoal cN0 T1-T2 PTC initially treated in the Fourth Hospital of Hebei Medical University were selected. Lymph nodes with carbon black staining and palpated hard lymph nodes without black staining were sent for frozen pathology, and the remaining dissected tissues were sent for paraffin pathology to analyze lymph node metastasis of the three specimens in the central neck, and matched into two groups for comparison. The lymph nodes with carbon nanoparticles black staining were defined as the control group. The lymph nodes with carbon nanoparticles black staining combined with palpation were defined as the experimental group. The detection rate and false negative rate between the two groups, as well as the influencing factors of lymph node metastasis in the remaining dissected tissues in the experimental group, were compared. 
Results The detection rate, accuracy rate and false negative rate of intraoperative lymph node biopsy were 96.8%, 95.2% and 11.6% in control group, respectively, and 97.7%, 98.6% and 3.4% in the experimental group, respectively. There were significant differences in accuracy rate and false negative rate between two groups (χ2=3.958， 4.250, all P＜0.05). Multivariate analysis of the experimental group showed that intraoperative frozen lymph node metastasis and the number of negative intraoperative frozen lymph nodes were independent factors influencing metastasis of the remaining dissected tissue in the central neck (OR values=14.195， 0.652, all P＜0.01).
Conclusion In the treatment of unifocal cN0 T1-T2 PTC in the central neck, lymph nodes with carbon black staining and palpated hard lymph nodes sent for frozen biopsy can ensure high detection rate and accuracy rate, and low false negative rate. Central neck dissection should be carried out when intraoperative lymph nodes frozen are found to have metastasis. The fewer negative numbers of frozen lymph nodes, the more vigilant doctors should be of lymph node metastasis in the remaining central region.

Key words: thyroid neoplasms, neck lymph node dissection, carbon