Incidental focal thyroid uptake on FDG positron emission tomographic scansmay represent a second primary tumor

Purpose: This article discusses the value of incidental thyroid uptake of f luorodeoxyglucose (FDG) on whole-body positron emission tomography (PET) sc ans performed in patients with cancer. This issue has been reported diverse ly in the literature. Materials and Methods: Whole-body PET scans of four patients with cancer (t wo of them women; age, 49 to 78 years) in whom focal thyroid uptake was vis ualized and subsequently correlated with thyroid carcinoma based on cytolog ic or histopathologic data were reviewed. The clinical outcomes of these pa tients were analyzed retrospectively. Maximum and average standardized upta ke values (SUVs) of thyroid accumulation were recalculated in all patients. Results: Two of the four patients referred for FDG PET scans had lung adeno carcinomas, one had prostrate carcinoma, and one had an unknown primary tum or. Focal thyroid uptake was visualized, with maximum and average SUVs rang ing from 3.7 and 2.3 to 53 and 34, respectively. These findings were correl ated with cytologic (two patients) or histopathologic data (two patients) t hat indicated thyroid carcinoma. In two patients, their treatment was chang ed and total thyroidectomy was performed; in one of them the SUVs of the fo cal thyroid accumulation (maximum and average values of 7.9 and 4.8, respec tively) were less than the cutoff Values for thyroid cancer noted in the li terature. The clinical condition of the other two patients did not permit a dditional investigation or treatment for thyroid carcinoma. Conclusion: Increased focal thyroid uptake on whole-body FDG PET scans shou ld not be overlooked, even when it is not marked, and should prompt further investigation to rule out cancer.