Visually discernible [18F]fluorodeoxyglucose uptake in papillary thyroid microcarcinoma: a potential new risk factor

A significant number of papillary thyroid microcarcinomas (PTMCs), despite excellent prognosis, show aggressive features such as extrathyroidal extension (EE) and lymph node metastasis (LNM) that may not always be detected preoperatively or intraoperatively. The relapse rate appears also substantial.

To assess the value of [(18)F]fluorodeoxyglucose (FDG) uptake in PTMC as a potential risk factor for preoperative risk stratification.

This retrospective study included 87 patients (17 males and 70 females; mean age = 51.2 yr, range 29-74 yr) with a unifocal PTMC who underwent preoperative FDG-positron emission tomography (PET)/computed tomography (CT)and total thyroidectomy and central lymph node dissection. Statistical analyses were performed to compare the gender, age, tumor size, and FDG uptake in PTMC with the presence of histopathologically proven EE and central LNM (cLNM).

Of the 87 patients, 44 (51%) had EE, and 27 (31%) had cLNM. PET/CT showed visually discernible FDG uptake in 46 PTMCs (53%). FDG positivity of PTMCs was the only significant variable correlated with both EE and cLNM; there was a significant difference in the prevalence of both EE (70 vs. 29%) and cLNM (41 vs. 19.5%) between the FDG-positive and FDG-negative groups. In contrast, other already known risk factors, i.e. gender, age, and size, showed a correlation with only one or neither of EE and cLNM.

The results indicate that visual FDG positivity in PTMCs is a potential risk factor that can be useful for preoperative risk stratification. Prospective studies would be warranted to assess the long-term benefit and cost effectiveness of preoperative FDG-PET/CT.