Although there have been many studies identifying clinical and pathologic factors that may predict central lymph node metastases (CLNM) in papillary thyroid microcarcinoma (PTMC) patients without clinically cervical lymph node metastasis (cN0), the results were inconsistent. And whether prophylactic central lymph node dissection (pCLND) should be performed in cN0 PTMC remains controversial. The EMBASE, PubMed, MEDLINE and the Cochrane Library were searched until Oct 2015 to identify relevant studies. Primary outcomes were clinical and pathologic factors for CLNM. Secondary outcomes included CLNM rate, surgical complications of hypocalcaemia and recurrent laryngeal nerve(RLN) injury and neck recurrences. Statistical analysis was performed using Stata 12.0. Fourteen eligible studies enrolling 4573 patients were included in this meta-analysis. The overall incidence of CLNM was 33 % (95 % CI 29-37). An elevated risk of CLNM was significantly associated with male gender (OR 2.33, 95 % CI 1.71-3.17), age <45 years (OR 1.27, 95 % CI 1.08-1.48), tumor size >5 mm (OR 2.16, 95 % CI 1.87-2.50), multifocality (OR 1.73, 95 % CI 1.45-2.05), extrathyroidal extension (OR 1.99, 95 % CI 1.66-2.37) and lymphovascular invasion (OR 3.87, 95 % CI 1.64-9.10), but not with thyroid bilaterality (OR 1.41, 95 % CI 0.89-2.22) and chronic lymphocytic thyroiditis (OR 0.98, 95 % CI 0.66-1.47). The pooled frequency of permanent hypocalcaemia, permanent RLN injury and neck recurrences was 1.1, 0.5 and 2.8 %, respectively. cN0 PTMC patients have a considerable CLNM rate and have a low pooled incident of surgical complications and neck recurrences with pCLND. Six unfavorable clinical and pathologic factors, which were significantly associated with CLNM, were identified. These findings may help guide the application of pCLND or subsequent treatment in cN0 PTMC.
Keywords: Central lymph node metastasis; Meta-analysis; Papillary thyroid microcarcinoma; Risk factors.