18F-Fluorodeoxyglucose Positron Emission Tomography for Primary Thyroid Cancer: Correlation with the Clinical, Pathologic and Sonographic Findings

ABSTRACT

PURPOSE: We wanted to investigate the incidence and the clinicopathologic and sonographic characteristics of thyroid cancers that exhibit positive PET scans. MATERIALS AND METHODS: From January 2007 to February 2008, 156 patients with thyroid cancer underwent both sonography and FDG-PET for the purpose of staging the cancer. We conducted a retrospective review of their clinical, radiologic and pathologic records and we evaluated the incidence of PET-positive thyroid cancer, as well as the associated clinicopathologic aggressiveness and the sonographic features. RESULTS: The incidence of PET-positive thyroid carcinoma was 78.2% (122/156). On univariate analysis, PET-positive thyroid cancer was significantly associated with tumor size, extracapsular invasion and central lymph node metastasis, but there was no association between the sonographic features of the thyroid cancer or the sonographic features of the 2 groups of tumor (1. probably benign and 2. suspicious for malignancy) and the FDG uptake. Multivariate logistic regression analysis showed a significant association between PET positivity and both extrathyroidal extension and a higher cancer stage (III/IV) (p < 0.05). CONCLUSION: The incidence of PET positive thyroid carcinoma is high (78.2%) and PET positivity is significantly associated with tumor size, extracapsular extension and a higher stage. However, there is no significant association between PET positivity and the sonographic features of thyroid carcinoma.