Background and purpose: The proportion of incidental thyroid cancer in PET imaging was s

ignificantly increased with the wide application of

18

F-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

18

F-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 (G

1

G

2

G

3

and G

4

) 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 G

1

and G

2

groups

G

3

and G

4

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

G

1

and G

2

were 1.51±0.30

4.25±1.70 and 6.34±2.45

respectively. The SUV

max

in the G

1

and G

2

were significantly higher than in the normal thyroid tissue (t=11.0，t=7.10，P0.01). The SUV

max

of G

3

was 4.77±2.15

and the SUV

max

of G

4

group was 4.67±2.02. The differences between G

1

and G

2

groups

G

3

and G

4

groups were not statistically signif

icant (t=3.61

P0.05; 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.