Diffuse and diffuse-plus-focal uptake in the thyroid gland identified by using fdg-pet: prevalence of thyroid cancer and hashimo

Abstract
Objective  To investigate and evaluate the prevalence of incidental thyroid diffuse and diffuse-plus-focal fluorine-18 fluorodeoxyglucose
(FDG) uptake in healthy subjects who underwent cancer screening on positron emission tomography (PET) scan, and also to evaluate
the prevalence of thyroid cancer and Hashimoto's thyroiditis.

Methods  We carried out a retrospective review of 1626 subjects who underwent PET scanning at our institution. Diffuse uptake was defined
as FDG uptake in the whole thyroid gland, whereas diffuse-plus-focal uptake was defined as a thyroid lesion with both diffuse
uptake and focal FDG uptake. The maximum standardized uptake value of the thyroid lesions was recorded and reviewed. In each
selected subject with positive thyroid FDG uptake, serum thyroid-stimulating hormone, thyroid hormone, and thyroid antibodies
were measured. Fine needle aspiration cytology was performed on patients with a definite nodule using ultrasonography.

Results  Twenty-nine subjects (1.78%) were identified as having either diffuse FDG uptake (n = 25, 1.53%) or diffuse-plus-focal FDG uptake (n = 4, 0.24%). All subjects with diffuse FDG uptake were diagnosed as having Hashimoto's thyroiditis. In 1 of the 25 subjects
with diffuse FDG uptake and two of the four with diffuse-plus-focal FDG uptake, histopathologic diagnosis showed papillary
thyroid carcinoma associated with Hashimoto's thyroiditis. However, PET scan did not detect papillary carcinoma associated
with Hashimoto's thyroiditis in one of the three subjects.

Conclusions  Our results suggest that although diffuse FDG uptake usually indicates Hashimoto's thyroiditis, the risk of thyroid cancer
must be recognized in both diffuse FDG uptake and diffuse-plus-focal FDG uptake on PET scan.

Content TypeJournal Article

JournalAnnals of Nuclear MedicineOnline ISSN 1864-6433Print ISSN 0914-7187

Journal VolumeVolume 21

Journal IssueVolume 21, Number 6 / August, 2007 (Source: Annals of Nuclear Medicine)