Patterns of Lateral Lymph Node Involvement by Neck Level in cNIb Differentiated Thyroid Carcinoma: A Systematic Review and Meta-Analysis.

Background/Objectives: The optimal extent of lateral lymph node dissection in cN1b differentiated thyroid cancer remains controversial. This systematic review aimed to assess the frequency of lymph node involvement across neck levels I to V. Materials and Methods: A systematic review was conducted following PRISMA guidelines. PubMed was searched for studies on lateral neck dissection in differentiated thyroid cancer. Included studies reported level-specified metastatic rates. Data on patient numbers and metastatic events were extracted. A random-effects meta-analysis with Freeman-Tukey double arcsine transformation was performed for each neck level to calculate pooled prevalence proportions and 95% confidence intervals. Heterogeneity was assessed using the I2 statistic. Results: Meta-analysis of 57 studies revealed that level III (68%, 95% CI: 63-73) and level IV (66%, 95% CI: 61-70) had the highest metastatic prevalence, followed by level IIA (46%, 95% CI: 37-56). Level V demonstrated an overall prevalence of 22% (95% CI: 18-26), with sublevel VB (19%, 95% CI: 11-28) significantly higher than VA (4%, 95% CI: 1-9). Level I (6%, 95% CI: 2-11) and sublevel IIB (14%, 95% CI: 9-20) showed the lowest risk. Significant heterogeneity (I2 71-94%) was observed across all levels. Conclusions: Our findings support sparing level I, and sublevels IIB and VA during lateral neck dissection. Current guidelines recommend systematic dissection of IIA, III, IV, and VB, although VB involvement was found to be only 19% in our study. Future personalization of the extent of neck dissection, based on individual risk factors, may be key to optimizing oncologic and functional outcomes.