Thyroid Research Thyroid Research Archive Thyroid Cancer

Positron emission tomography occasionally reveals incidental thyroid nodules

(November 2003)

The background of the study. ¹⁸F-Fluorodeoxglucose (FDG) positron emission tomography is being used to detect metastases in patients with cancer, and also to screen for cancer in healthy people. Like other imaging procedures, FDG imaging may reveal unsuspected thyroid nodules (incidentalomas). In this study, the frequency of detection of thyroid nodules and the nature of those nodules were studied in patients undergoing FDG imaging for possible nonthyroid tumors.

How the study was done. The study subjects were 1330 consecutive patients who underwent imaging with FDG at a cancer center. In 999 patients the imaging test was done during an evaluation for metastatic cancer, and in 331 patients it was done as a screening test for cancer. Patients with thyroid cancer were excluded. Thyroid incidentaloma was defined as focal or diffuse uptake in the thyroid region; focal uptake was uptake in less than one thyroid lobe, and diffuse uptake was uptake throughout both thyroid lobes.

The results of the study. Thyroid incidentaloma occurred in 29 patients (2 percent), 21 of whom had focal uptake and 8 diffuse uptake. In 15 of the 21 patients who had focal thyroid uptake of FDG, the nodule was biopsied or removed surgically. Four patients proved to have a papillary thyroid carcinoma, four had a follicular adenoma, and seven had a hyperplastic nodule; the other six patients were not further studied. Among the eight patients with diffuse thyroid uptake of FDG, seven had chronic thyroiditis and one had subacute granulomatous thyroiditis.

The conclusions of the study. Positron emission tomography using ¹⁸F-fluorodeoxyglucose, like other imaging tests, may reveal incidental thyroid abnormalities, including thyroid carcinomas.

The original article. Kang KW, Kim SK, Kang HS, Lee ES, Sim JS, Lee IG, Jeong SY, Kim SW. Prevalence and risk of cancer of focal thyroid incidentaloma identified by ¹⁸F-fluorodeoxyglucose positron emission tomography for metastasis evaluation and cancer screening in healthy subjects. J Clin Endocrinol Metab 2003;88:4100-4.