Background: Our aim was to design a practical algorithm for management of an increasing number of incidental findings of thyroid lesions identified by (18)F-fluorodeoxyglucose positron emission tomography with computed tomography (FDG-PET/CT).
Methods: The reports of 3641 patients examined by FDG-PET/CT for evaluation of nonthyroid cancer were reviewed. The anatomic locations and standardized uptake values (SUV) of any focally increased thyroid FDG uptake were reanalyzed and related to surrounding normal thyroid ((T)SUV(max)/(thy)SUV(mean) ratio) and liver ((T)SUV(max)/(liver)SUV(mean)).
Results: Focal FDG uptakes in the thyroid were reported in 37 cases (1%; 26 women). Neoplastic thyroid lesions were diagnosed in 16 patients: papillary thyroid cancer in 9, follicular neoplasia in 5, and metastatic lesions (lung cancer and squamous cell carcinoma) in 2. Benign lesions were diagnosed in 11 patients. Ten patients with malignancy elsewhere did not undergo thyroid examination. In all, 11 patients underwent thyroid surgery (8 with papillary cancer, 3 with follicular adenoma); the median tumor size was 12 mm (8-40 mm). The (T)SUV(max)/(thy)SUV(mean) ratio was higher for the malignant lesions [median 5.53 (2.75-30.81) vs. 3.70 (1.82-31.70); P < 0.05], albeit with a considerable overlap between individual patients. The (T)SUV(max) and (T)SUV(max)/(liver)SUV(mean) did not differ between groups. The (T)SUV(max)/(thy)SUV(mean) and / (thy)SUV(mean) ratios correlated with the tumor size (r = 0.64 and r = 0.66; P < 0.05).
Conclusions: An incidental finding of focal uptake of FDG in the thyroid is associated with a significant risk of thyroid cancer. If the patient would benefit from thyroidectomy if a malignancy were identified, further diagnostic workup with ultrasonography-guided fine-needle aspiration and cytology is recommended.