Incidental thyroid lesions on FDG-PET/CT: a prevalence study and proposition of management

Thyroid incidentaloma is defined as an unsuspected, asymptomatic thyroid lesion that is discovered on an imaging study. The purpose of this study is to determine incidentally identified thyroid lesions by FDG-PET/CT in cancer patients by virtue of preoperative staging and to pay attention how should be the management of these patients with thyroid lesion.

From January 2011 to January 2013, 2654 patients underwent FDG-PET/CT in our institution. Among them, 34 patients had thyroid incidentaloma. All patients underwent ultrasonographic (US) examination. If there is a nodul, fine needle aspirations (FNA) were performed to these patients. We did not perform FNA to patients who had diffuse thyroid uptake. Patients were divided into two groups; malign and non-malign patients according to FNA histo-pathologic results. Group 1 (N.=11) diagnosed malignancy in histo-pathologic evaluation, group 2 (N.=23) could not diagnosed malignancy in histo-pathologic, clinic and radiologic evaluation. These two groups were compared statistically in terms of SUV max levels that reached in PET examinations.

Incidentally thyroid lesions were found in 34 patients in the course of FDG-PET/CT examination (25 females and 9 males), mean age 57.7 years. Nodular goitre in 12 patients, hyperthyroidism in 2 patients, sub-clinic hyperthyroidism in 3 patients and hashimoto thyroiditis in 6 patients were diagnosed in non-malignancy group (Group-2). Group 1 included 11 patients with incidentally diagnosed thyroid malignancy. 11 patients malignancy diagnoses were verified by FNA and 9 of them were operated. In PET evaluation thyroid up-take was diffuse in 9 patients, at left lob in 12 patients and at right lop in 13 patients. When we compared the groups according to SUV max levels; we found that malignant thyroid lesions had a significantly higher (P<0.001) SUVmax than benign thyroid lesions. A cut off SUVmax value (>6.2) was found in the study.

The incidental finding of focal thyroid uptake on FDG-PET scanning has an elevated malignancy risk from other thyroid nodules. According to our knowledge diagnose, treatment and follow-up of these patients should be in multidiscipliner approach. Oncology, endocrinology, endocrine surgeon, interventional radiology, pathology and psychiatry should be gathered in multidiscipliner team. For these reason these patients need more careful evaluation.