Prevalence and risk of cancer of thyroid incidentaloma identified by fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography

Objectives The prevalence of malignancy in thyroid nodules incidentally detected by FDG PET has not been fully characterized yet and several issues remain to be clarified. We aimed to investigate the prevalence of thyroid incidentaloma in PET/CT and risk of cancer, usefulness of FDG uptake pattern, SUVmax, CT findings, and to define the predictable variables.

Methods A total of 15,948 non-thyroid disease patients who underwent FDG PET/CT study from November 2006 to September 2010 were included retrospectively (12,080 patients for metastatic evaluation, 3,868 patients for cancer screening). When thyroid PET/CT incidentaloma was found, further diagnostic examination was conducted.

Results In our institution, the prevalence of incidental thyroid 18F-FDG uptakes was approximately 2.5% (395/15948). The prevalence of incidentaloma on PET/CT in healthy subjects (118/3,868; 3.1%) was statistically higher than that in patients with suspected or known cancer (277/12,080; 2.3%) (P<0.05). Among 395 incidentalomas, 146 patients had further examinations. Histological confirmation was obtained in 53 patients and the remaining 93 lesions were clinically monitored. Finally, 43 lesions were confirmed to be malignancies. Therefore, the cancer risk of thyroid incidentaloma on PET/CT was 29.5% (43/146). After logistic regression analysis, among the various variables, age, sex, SUVmax and calcification were the potent predictors for differentiation of malignant thyroid lesions.

Conclusions The presence of focal uptake with high SUVmax, calcification detected in CT image and especially a young man patient correlates with high likelihood of thyroid malignancy. When a focal thyroid incidentaloma is detected by PET/CT, further examination should be performed