Histological Aggressiveness of Fluorodeoxyglucose Positron-emission Tomogram (FDG-PET)-detected Incidental Thyroid Carcinomas

Background: We previously reported a high incidence of primary thyroid cancer in fluorodeoxyglucose positron-emission tomogram (FDG-PET)-detected incidental thyroid abnormalities. The aim of our study was to determine if these FDG-PET-detected thyroid malignancies represent a more-aggressive variant of primary thyroid carcinoma.

Materials And Methods: All patients that underwent operative intervention for FDG-PET-detected incidental thyroid abnormalities were identified (June 2003 to April 2006). Patients with a diagnosis of primary thyroid carcinoma on final histopathology were included in the study. The patient demographics and histopathological findings were analyzed to identify adverse prognostic features.

Results: In 11,500 patients, 17,250 FDG-PET scans were performed; 377 of these patients (3.2% of patients and 2.1% of FDG-PET scans) had findings positive for thyroid abnormality. Of the 32 patients that underwent operative intervention, 22 patients with a final diagnosis of primary thyroid malignancy were included in the study. A greater number of patients [12 patients, (54%)] were noted to harbor poor prognostic variants of primary thyroid carcinoma on final histopathology [tall-cell variant: 11 patients (50%) and poorly differentiated thyroid carcinoma: 1 patient (4%)]. Extra-thyroidal extension (ETE) was noted in the majority of patients [14 patients (63%)]. In patients with tall cell variant on final histopathology, the rate of ETE was even higher [10 patients (90%)].

Conclusion: Thyroid malignancies incidentally detected on FDG-PET scan harbor a high rate of unfavorable prognostic features and may represent a more-aggressive variant of primary thyroid carcinoma. These patients need to be subjected to further investigation with a view to possible operative intervention.