Evaluation of focal thyroid lesions incidentally detected in fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography images

Abstract

Background and Purpose: Increased uptake in the thyroid gland (TG) is often identified as an incidental finding on the whole body fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography ( 18 F-FDG PET/CT) in non-thyroid cancer patients. Currently, there is no consensus on the appropriate approach for the management of these cases. Thyroid ultrasound, scintigraphy and fine-needle aspiration biopsy (FNAB) are suggested to exclude malignant thyroid lesions. Our aim is to determine the importance of increased F-18-FDG uptake in the TG on positron emission tomography/computed tomography (PET/CT) scans in patients who are being screened for various forms of non-thyroid cancer. Materials and Methods: We evaluated 2000 cases undergoing whole body PET/CT scanning between April 2011 and October 2012. The age, sex, type of primary cancer, maximum standardized uptake value (SUV max ), size of the thyroid nodules and cervical lymph nodes (CLNs) on 18 F-FDG PET/CT images and if available, the biopsy results were evaluated. Results: In total, 57 patients (23 men, 34 women, mean age ± standard deviation (SD), 60.89 ± 14 years) showed an increased fluorine-18-fluorodeoxyglucose ( 18 F-FDG) uptake by the TG (average SUV max : 4.07 ± 3.7). The CLNs were detected in 19/57 patients (33%). Only 20 cases (35%) received FNAB. The final histopathological diagnosis was papillary thyroid carcinoma in seven patients (mean SUV max ± SD: 6.0 ± 5.43) and benign thyroid disease in seven patients (mean SUV max ± SD: 2.36 ± 0.63). The FNAB results were undetermined for six patients. Conclusion: Focal high 18 F-FDG uptake in the TG may be associated with an increased risk of malignancy, but the clinical significance is unclear. More data are needed to elucidate the role of the SUV in the differentiation of benign and malign thyroid lesions. If a focal increase in 18 F-FDG uptake in the TG on PET/CT is present, a prompt histopathological evaluation should be suggested to clinicians for definitive diagnosis.

Should the Prevalence of Incidental Thyroid Cancer Determine the Extent of Surgery in Multinodular Goiter?

“…In two independent papers, Brindle et al [58] and Nayan et al [59] have emphasized that up to 25% of these incidentalomas appear to be malignant. Chun et al [60] and Yaylali et al [61] have detected malignancy in thyroid incidentalomas by 18F-FDG PET/CT in 29% and 12.3% of cases, respectively, and they have confirmed that the positive predictive value of this procedure in malignancy of thyroid incidentalomas is 41.7%. They have concluded that patients with MNG and "negative" FNAB results but with high 18F-FDG uptake in the thyroid gland require a particularly careful diagnosis and radical treatment by total or near total strumectomy.…”

The incidence of 18F-FDG PET/CT thyroid incidentalomas andthe prevalence of malignancy: a prospective study

“…In contrast to our findings, which are consistent with these systematic reviews, there is great discrepancy in the literature about the prevalence of malignancy in 18 F-FDG TIs. In different studies, which were all retrospective, the reported prevalence ranged between 14.0% and 63.6% (17)(18)(19)(20)(21)(22)26,27).…”

The incidence of thyroid cancer in focal hypermetabolic thyroid lesions

“…We measured the SUVmax of thyroid lesions and defined specific ratios to test whether malignant lesions can be discriminated from benign lesions. Several studies have shown that the thyroid lesion SUVmax was higher in malignant than in benign lesions (11-15) (Table 1); however, others state the opposite (8, 16-19) (Table 1). While there was some overlap, we identified a statistically significant difference in the thyroid lesion SUVmax, as well as the various target to background ratios among benign and malignant lesions (Figure 4).…”