Clinical Impact of Multifocality and Bilaterality on Lymph Node Metastasis in Papillary Thyroid Microcarcinoma

<b>Objective:</b> Papillary thyroid microcarcinoma (PTMC) often presents with multifocality and bilaterality, but the clinical significance of these features and their association with cervical lymph node metastases (LNMs) remain debated. The aim of this study was to investigate the patterns of multifocality and bilaterality in PTMC and their association with central and lateral neck lymph node metastases. <b>Methods:</b> This retrospective study analyzed 254 patients with histologically confirmed PTMC treated at the Institute for Oncology and Radiology of Serbia between 2004 and 2016. All patients underwent total thyroidectomy with central and, when indicated, lateral neck dissection. Associations between multifocality, bilaterality, and cervical LNM were evaluated using appropriate statistical tests. A <i>p</i>-value < 0.05 was considered statistically significant. <b>Results:</b> Multifocal tumors were present in 40.55% of patients, with bilateral involvement in 27.17%. Cervical LNM occurred in 33.07% of patients, with 26.77% showing central and 20.08% lateral metastases. Patients with multifocal tumors were associated with significantly higher proportions of male patients (<i>p</i> = 0.0283), higher rates of capsular invasion (<i>p</i> = 0.0002), larger tumor size (<i>p</i> = 0.0134), and increased incidence of LNM (<i>p</i> = 0.0152). Bilateral tumors were associated with larger tumor size (<i>p</i> = 0.0004) and more frequent capsular invasion (<i>p</i> = 0.0248), but not with a statistically significant increase in LNM. The number of tumor foci was strongly associated with both central and lateral LNM (<i>p</i> < 0.001). <b>Conclusions:</b> Multifocality, particularly with a higher number of tumor foci, is significantly associated with more aggressive tumor features and higher rates of cervical lymph node metastases in PTMC. While bilaterality also reflects a more aggressive phenotype, it was not independently predictive of LNM. These findings underscore the importance of careful risk stratification in PTMC and suggest that multifocality should inform surgical and follow-up strategies.