CASE REPORT Subacute Thyroiditis Presenting as a Focal Lesion

SUMMARY: A 52-year-old man presented with subacute thyroiditis and showed an intensely hyper-metabolic thyroid lesion on 18F-FDG PET/CT. The patient also had coexisting chronic lymphocytic thyroiditis. The lesion of subacute thyroiditis revealed an SUVmax of 9.1 g/mL and was ill-defined, heterogeneous, markedly hypoechoic, and hypovascular on US. Biopsy demonstrated histologic findings of subacute thyroiditis, which should be included in the differential diagnosis of an intensely hypermetabolic thyroid lesion on 18F-FDG PET/CT. ABBREVIATIONS: 18F-FDG PET/CT [18F] fluorodeoxyglucose whole-body positron-emission to-mography and CT; FDG fluorodeoxyglucose; US sonography; PD power Doppler; PTC papillary thyroid carcinoma; SUVmax maximum standardized uptake value; US-FNAB sonogra-phy-guided fine-needle aspiration biopsy Subacute thyroiditis is an uncommon inflammatory dis-ease of the thyroid gland that occursmost often inmiddle-aged women. It is usually preceded by an upper respiratory tract infection and is presumed to be caused by a viral infec-tion. A postviral inflammatory response leads to giant cell in-filtration into the thyroid follicles, ultimately resulting in fol