Papillary Thyroid Microcarcinomas Detected by Nuclear Medicine Imaging: Distinct Clinicopathological Features Compared with Conventional Modalities

Objectives: Papillary thyroid carcinomas detected by nuclear medicine imaging techniques may have a worse prognosis than those identified by conventional methods. However, it remains unclear whether this applies to papillary thyroid microcarcinomas (PTMCs). Methods: Patients diagnosed with PTMC at Hacettepe University Faculty of Medicine between 2008 and 2020 were categorized into three groups: (1) incidental PTMCs (Inc-PTMC; n=249), (2) non-incidental PTMCs (NonInc-PTMC; n=134), and (3) PTMCs detected by nuclear medicine imaging methods (NM-PTMC; n=24). Tumor pathological characteristics, including multifocality, extrathyroidal extension, vascular invasion, and lymph node involvement, were analyzed. Logistic regression analysis was performed to assess the association between detection method and tumor aggressiveness while adjusting for potential confounders. Results: Patients in NM-PTMC group were significantly older at diagnosis (54.7±11.2 years) than those in Inc-PTMC (51.1±11.3 years) and NonInc-PTMC (46.9±11.7 years, p=0.001) groups. Tumor size was larger in NM-PTMCs (4.8±2.5 mm) and NonInc-PTMCs (5.3±2.2 mm) compared to Inc-PTMCs (3.4±2.4 mm, p<0.0001). Multiple logistic regression analysis revealed that NM-PTMCs had a markedly higher risk of cervical lymph node metastasis compared with both Inc-PTMCs [odds ratio (OR): 36.04; 95% confidence interval (CI): 6.02-215.59, p=0.001) and NonInc-PTMCs (OR: 8.68; 95% CI: 1.15-65.22, p=0.036). NM-PTMC also had an increased risk of positive surgical margins compared with Inc-PTMC (OR: 5.08; 95% CI: 1.57-16.39, p=0.006), whereas only NonInc-PTMC had a higher risk of extrathyroidal extension (OR: 3.19; 95% CI: 1.48-8.84, p=0.003). The detection method was not associated with multifocality. Conclusion: Nuclear medicine-detected PTMCs may differ in their clinicopathological profile from other PTMC subgroups and may represent an intermediate phenotype between Inc-PTMC and NonInc-PTMC.