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Abstract
Purpose
This study was to investigate the clinical significance of diffusely increased F-18 FDG uptake in the thyroid gland as an incidental finding on F-18 FDG PET/CT imaging in patients with breast carcinoma.
Methods
One hundred four patients with breast carcinoma who had no prior history of thyroid disease were enrolled. All patients underwent F-18 FDG PET/CT, ultrasound and thyroid function test (TFT-TSH, FT4, and T3), anti-TPO antibody test within 2 weeks. Also we checked estrogen (ER) and progesterone receptors (PR). We classified all patients into subgroups according to the existence and degree of F-18 FDG uptake in the thyroid gland, and evaluated the difference between subgroups.
Results
Of the 104 patients, 42 (40.4%) subjects showed diffusely increased thyroid uptakes. There was no significant difference in rate of abnormality in TFT and thyroid US, and existence of anti-TPO antibody and ER/PR between two groups. Of 42 patient who showed diffuse uptake, 12 (28.5%), 13 (31.0%), and 17 (40.5%) subjects demonstrated hypointense, isointense, and hyperintense thyroid uptake compared with activity of mediastinal blood pool. Thirteen (76.4%) of 17 subjects in the hyperintense thyroid uptake group revealed abnormality in various tests (US, TFT, and anti-TPO antibody). The rate of abnormality in this group was significantly different with the other two groups (p=0.002).
Conclusion
Our data suggested that the rate of diffuse thyroid uptakes on F-18 FDG PET/CT imaging of patients with breast carcinoma was higher than healthy subjects. In case of someone who had no prior thyroid disease showed diffuse thyroid uptakes more than activity of mediastinal blood pool on F-18 FDG PET/CT imaging, it should be considered further evaluation about the thyroid gland.
Figures and Tables
 | Figure 1A case of diffusely increased F-18 FDG uptake, but less than activity of mediastinal blood pool, in the thyroid gland of 55-yr-old patient. On ultrasound examination, echogenecity of thyroid gland was homogeneous and blood flow was normal. Serum TSH was 2.61 mIU/L (reference range, 0.17-4.05 mIU/L), free T4 was 10.9 ng/dL (reference range, 9.4-25 ng/dL) and T3 was 2.03 ng/dL (reference range, 0.8-2.2 ng/dL), suggestive of normal state of thyroid function. Shown are 3D MIP image (A), transaxial PET image (B), transaxial fused PET/CT image (C), ultrasound image (D), and doppler ultrasound image (E).
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 | Figure 2A case of diffusely increased F-18 FDG uptake, similar intensity with mediastinal blood pool, in the thyroid gland of 46-yr-old patient. On ultrasound examination, thyroid gland was homogeneous and blood flow was mildly increased. Serum TSH was 2.09 mIU/L, free T4 was 11.3 ng/dL and T3 was 1.22 ng/dL, suggestive of normal state of thyroid function.
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 | Figure 3A case of intensely and diffusely increased F-18 FDG uptake, more than activity of mediastinal blood pool, in the thyroid gland of 58-yr-old patient. On ultrasound examination, thyroid gland was prominent and heterogeneous. Blood flow of thyroid gland was slightly increased. Serum TSH was 2.09 mIU/L, free T4 was 11.3 ng/dL, T3 was 1.22 ng/dL and TPO antibodies were elevated at 100 IU/mL (reference range, 0-0.3 IU/mL), suggestive of diagnosis of Hashimoto's thyroiditis.
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Table 1
Number of patients with abnormal laboratory data, surgical data, and US finding in two groups, classified by diffuse thyroid uptake
Table 2
Number of patients with abnormal laboratory data, surgical data, and US finding in three groups, classified by degree of thyroid uptake
TFT=thyroid function test; anti-TPO Ab=anti-thyroid peroxidase antibody; US=ultrasound; ER/PR=estrogen receptor/progesterone receptor; Group 1=less than blood pool activity of mediastinum; Group 2=equal to blood pool activity of mediastinum; Group 3=higher than blood pool activity of mediastinum.
*Fisher's exact test.
Table 3
Laboratory, surgical data, and US findings in 17 patients who showed diffuse thyroid uptake more than blood pool activity of mediastinum
US=ultrasound; Anti-TPO Ab=anti-thyroid peroxidase antibody; T3=triiodothyronine; FT4=free thyroxine; TSH=thyroid-stimulating hormone; ER/PR=estrogen receptor/progesterone receptor; NS=not significant; P=positive; N=negative.
*Reference values=TSH, 0.17-4.05 mIU/L; T3, 0.8-2.2 ng/dL; FT4, 9.4-25 ng/dL; TPO antibody, 0-0.3 IU/mL.
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