Benign Thyroid Lesions with Positive Results in FDG PET/CT

FDG-PET/CT is used to evaluate malignancies due to its biochemical characteristics. However, there is a possibility of false-positive results. Herein, we report two cases of false-positive thyroid lesions and discussed the limitations of FDG-PET/CT. The first case was that of a 54-year-old female found to have an FDG-avid mass in the left thyroid gland on whole-body PET/CT. Seven years later, neck sonography revealed another nodule in the right lobe of the thyroid. The two nodules progressively enlarged in size. FDG-PET/CT was performed again 12 years after the left nodule was first observed. Both nodules were FDG-avid, with even higher uptake. Since the pathological report of fine-needle aspiration (FNA) of the left nodule showed greater cellularity, the patient underwent left thyroid lobectomy and right excision. The final pathological report showed bilateral nodular goiters with a Ki-67 index <1%. The second case was that of a 67-year-old female; after surgical treatment of breast cancer and mediastinal squamous cell carcinoma, she was found to have diffuse F-18 2-Fluoro-2-deoxyglucose(FDG) uptake involving the bilateral thyroid glands during PET evaluation for cancer workup. Neck ultrasonography revealed the characteristics of Hashimoto's disease. In these two cases, we reviewed the diagnostic role of FDG-PET/CT in thyroid lesions. Diffuse FDG uptake often indicates thyroiditis, while focal uptake has ahigh false-positive rate for detecting thyroid cancer. In conclusion, a multidimensional examination of thyroid lesions is important.

關鍵字

FDG uptake ； PET/CT ； Nodular goiters ； Hashimoto's disease

並列摘要

去氧葡萄糖正子電腦斷層掃描因為其生化特性，被廣泛應用於偵測惡性疾病。然而，此檢查存在著偽陽性的可能。我們將以兩個偽陽性的甲狀腺病灶來討論去氧葡萄糖正子電腦斷層掃描的限制。第一個病例是一名54歲女性，在全身正子電腦斷層掃描中，於甲狀腺左葉看見一個去氧葡萄糖聚積的結節。七年後，經由頸部超音波，在其甲狀腺右葉看見新的甲狀腺結節。這兩個結節緩慢變大。於左側結節發現的12年後再追蹤一次正子電腦斷層掃描，發現兩個結節皆顯示去氧葡萄糖聚積，且吸收量較前次更多。由於左側結節細針抽吸的病理報告顯示較高的細胞含量，病人接受了甲狀腺左葉及右側結節切除。手術病理結果為雙側結節性甲狀腺腫且Ki-67<1%。第二個病例是一位67歲女性，在用正子電腦斷層掃描追蹤乳癌及縱膈腔鱗狀細胞瘤的術後狀況時意外在甲狀腺看見雙側瀰漫性去氧葡萄糖吸收，而頸部超音波結果顯示為橋本氏甲狀腺炎的典型特徵。在這兩個病例中，我們回顧了去氧葡萄糖正子電腦斷層在甲狀腺病灶的診斷角色：瀰漫性吸收經常代表甲狀腺炎，而局部吸收在偵測甲狀腺癌上依然存在偽陽性。綜上所述，在診斷甲狀腺病灶時，多維度、多工具的檢查是重要的。

並列關鍵字

去氧葡萄糖聚積；正子電腦斷層；結節性甲狀腺腫；橋本氏甲狀腺炎

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