The thyroid may occasionally have diffusely increased uptake on FDG-PET scans obtained for malignancy elsewhere. Between 1%-3% of patients undergoing a PET scan will have such uptake. This finding can be seen as a normal variant or associated with chronic lymphocytic (Hashimoto) thyroiditis, with or without the presence of hypothyroidism and can be seen even in patients receiving thyroid hormone replacement therapy.
Focal uptake in the thyroid should raise concern for carcinoma or metastasis.
References
- Chen YK, Chen YL, Cheng RH, Yeh CL, Lee CC, Hsu CH. The significance of FDG uptake in bilateral thyroid glands. Nucl Med Commun. 2007 Feb;28(2):117-22.
- Karantanis D, Bogsrud TV, Wiseman GA, Mullan BP, Subramaniam RM, Nathan MA, Peller PJ, Bahn RS, Lowe VJ. Clinical significance of diffusely increased 18F-FDG uptake in the thyroid gland. J Nucl Med. 2007 Jun;48(6):896-901.
- Shreve PD, Anzai Y, Wahl RL. Pitfalls in oncologic diagnosis with FDG PET imaging: physiologic and benign variants. Radiographics. 1999 Jan-Feb;19(1):61-77; quiz 150-1.
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