Prevalence and significance of thyroid uptake detected by 18F-FDG PET

Abstract

In this retrospective study, we sought to investigate the prevalence and the clinical significance of thyroid uptake discovered by FDG PET/CT within the thyroid gland during imaging investigation of non-thyroid disorders. This study included 5,877 subjects with no previous history of thyroid malignancy referred to our PET/CT center (1,596 for cancer screening and 4,281 for primary staging or restaging purposes) from June 2006 to April 2009. All of the patients had at least 12 months of follow-up or were censored on the date of the last follow-up. The disease status was analyzed for correlation with the maximum standardized uptake value (SUVmax). Receiver operating characteristics (ROC) curves were constructed to determine the optimal cutoff values for SUVmax. In the screening group (n=1,596), 55 patients (4%) had thyroid FDG uptake. Twenty-two subjects were referred for cytological or histological assessment and 4 (18%) were diagnosed with thyroid carcinoma. In the primary staging/restaging group (n=4,281), 165 patients (4%) had thyroid FDG-avid sites. Thirty-three patients were referred for cytological or histological assessment and 4 (12%) were found to have thyroid carcinoma. Of the 8 malignant lesions, 7 were papillary thyroid carcinoma, and 1 medullary thyroid carcinoma. Surgical resection was performed in seven out of eight patients. Three patients had lymph node metastasis (one case detected by preoperative PET/CT) and three bilateral malignant diseases (all false negative in PET/CT scans). Of the 47 benign lesions, 35 were nodular goiter or nodular hyperplasia, 6 multinodular goiter, and 6 autoimmune thyroid disease. The average value of SUVmax of malignant thyroid lesions was significantly higher than that of benign thyroid lesions (8.2±4.5 vs. 5.6±3.2, P=0.048). However, we were unable to identify an optimal SUVmax cutoff because the total area under the curve was small. The prevalence of thyroid uptake on FDG PET/CT in this study is 3.7%, which is consistent with previous observations. Of patients who received verification by cytology or histology, 14% (8/55) were found to have thyroid malignancies. However, we were unable to establish an optimal SUVmax cutoff value to differentiate benign from malignant lesions. FDG PET/CT scans were false negative in a significant proportion of patients with thyroid carcinoma and regional lymph node metastases or separate tumor nodule(s) in a contralateral lobe. Further diagnostic tests (thyroid ultrasound/fine needle aspiration) are recommended in presence of focal thyroid uptake detected by FDG PET/CT scans.

Incidence and Significance of Incidental Focal Thyroid Uptake on ¹⁸F-FDG PET Study in a Large Patient Cohort: Retrospective Single-Centre Experience in the United Kingdom

“…The significance of incidental focal thyroid uptake on 18 F-FDG PET study was first described in 2001 [10]. Many research studies are currently available on this topic, with different results on focal uptake of tracer on 18 F-FDG PET [3,4,5,6,8,9,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38]; however, a large UK series has yet to be reported. We report one of the largest studies on the evaluation of incidental focal 18 F-FDG uptake in the thyroid.…”

“…Literature evidenceon the SUV max in benign and malignant lesions vary with several reports showing a statistically significant difference [9,13,19,21,22,23,34,41] whilst many others have shown no significant difference [8,14,15,27,30,32,33,35,36]. Previous studies have also reported cutoff SUV values ranging from 3.5 to 5 in differentiated benign to malignant thyroid lesions [24,34,41].…”

Thyroid Incidentalomas on FDG PET/CT in Patients with Non-Thyroid Cancer - a Large Retrospective Monocentric Study

“…Moreover, a recent study conducted by Pagano et al [6] showed a positive correlation between the presence of SUV max > 5.0 and the diagnosis of malignancy. However, a number of studies are skeptical about using SUV max as an independent diagnostic tool [5,21,27,28]. Tsung-Ying et al [27] found a significantly higher average value of SUV max in malignant thyroid lesions, but the authors were unable to establish an optimal SUV max cutoff value to differentiate benign from malignant lesions.…”

“…However, a number of studies are skeptical about using SUV max as an independent diagnostic tool [5,21,27,28]. Tsung-Ying et al [27] found a significantly higher average value of SUV max in malignant thyroid lesions, but the authors were unable to establish an optimal SUV max cutoff value to differentiate benign from malignant lesions. Our study showed no significant difference in SUV max between benign and malignant nodules, in agreement with earlier studies [5,21].…”

Comparison of F-18 FDG-PET/CT and Tc-99m MIBI in the preoperative evaluation of cold thyroid nodules in the same patient group

“…In the FDG-PET imaging, SUVmax ratio is being used for quantitative analysis and if SUVmax ratio is higher than 2.5, any lesion in mediastinum and lung is accepted as positive [14]. On PET/CT scans, focal or diffuse thyroid gland FDG uptake can be seen in the nodule area [15]. In the present study, focal or diffuse uptake within the thyroid gland in the nodule area with a maximum standard uptake value (SUVmax) of greater than background in the FDG-PET scan was considered to be a positive lesion.…”