Patterns of Occult Metastasis to Level Va and Vb in Clinically Lateral Node-Positive Papillary Thyroid Carcinoma

Background The optimal extent of therapeutic lateral neck dissection (ND) in papillary thyroid carcinoma (PTC) continues to be debated. We analyzed the frequency, patterns, and predictive factors of occult level Va and Vb metastasis in clinically lateral node-positive PTC patients. Methods We reviewed the data of PTC patients who underwent thyroidectomy and therapeutic lateral ND from level II to V between May 2008 and August 2020. In our study, 46 patients without clinically positive metastatic lymph nodes (LNs) at level V on the preoperative evaluation were included to analyze occult metastasis at level Va and Vb, respectively. Patient demographics, including age, sex, distribution of pathologic LNs, and characteristics of the primary tumors, were reviewed. In addition, clinicopathologic factors associated with occult level Va and Vb metastasis were analyzed. Results Of the 46 patients, 14 (30.4%) patients had occult metastases at level Vb. No occult metastases were found at level Va. Clinically positive level II metastasis ( p = 0.015) and simultaneous level II, III, and IV metastases ( p = 0.010) in the preoperative evaluation were significantly associated with occult level Vb metastasis. Patients without LN metastasis at level IV or with three or fewer metastatic LNs in the lateral neck never had occult LN metastases at level Vb. Conclusions Occult metastasis at level Va is rare in PTC with lateral LN metastasis. Occult metastasis at level Vb may occur in PTC patients with multilevel involvement, including level II and/or four or more lateral LN metastases.