Abstract:

Background and purpose: The proportion of incidental thyroid cancer in PET imaging was significantly increased with the wide application of ¹⁸F-FDG PET/CT. The correlation between the glucose metabolism of thyroid incidental thyroid cancer and pathological changes is unclear. The objective of this study is to analyze the relationship between the glucose metabolism by ¹⁸F-FDG PET/CT and tumor differentiation or lymph node metastasis in patients with incidental thyroid cancer. Methods: A total of 195 patients with focal FDG-avid thyroid incidentaloma during cancer evaluation were enrolled. Fifty-three patients were diagnosed as having thyroid cancer by the pathology. The SUV_max of thyroid cancer foci, lesion size, lesion number, and SUV_max of normal thyroid tissue were quantified. The tumor pathological grades and lymph node metastasis were analyzed by the pathology. The patients were broken down into 4 groups (G₁, G₂, G₃ and G₄) according to the tumor pathological grades and lymph node metastasis (differentiated thyroid cancer, non-differentiated thyroid cancer, without lymph node metastasis and with lymph node metastasis). The differences of glucose metabolism between G₁ and G₂ groups, G₃ and G₄ groups were analyzed. Results: Fifty-three foci were found by PET imaging. Sixty-two foci were found by the pathology (37 papillary thyroid carcinoma, 4 follicular thyroid carcinoma, 9 medullary thyroid carcinoma, 3 poorly differentiated thyroid cancer). The SUV _max in the normal thyroid tissue, G₁ and G₂ were 1.51±0.30, 4.25±1.70 and 6.34±2.45, respectively. The SUV_max in the G₁ and G₂ were significantly higher than in the normal thyroid tissue (t=11.0，t=7.10，P<0.01). The SUV_max of G₃ was 4.77±2.15, and the SUV_max of G₄ group was 4.67±2.02. The differences between G₁ and G₂ groups, G₃ and G₄ groups were not statistically significant (t=3.61, P>0.05; t=0.33, P=0.56). Conclusion: The differentiated incidental thyroid carcinoma and non-differentiated incidental thyroid carcinoma had high glucose metabolism, and there was no significant difference in the levels of glucose metabolism in different differentiation degree and metastasis ability cancer.

Key words: Thyroid incidentalomas, Thyroid cancer, ¹⁸F-FDG, PET/CT, Differentiated thyroid cancer, Metastasis