F18‐Fluorodeoxyglucose Positron Emission Tomography in Detecting Metastatic Papillary Thyroid Carcinoma with Elevated Human Serum Thyroglobulin Levels But Negative I‐131 Whole Body Scan

Abstract

Papillary carcinomas are the most common thyroid malignancies. They invade the regional lymphatics and metastasize frequently to local lymph nodes in the neck. Distant metastasis, generally to the lungs, is also common. Methods. The aim of this study is to evaluate the effectiveness of F18‐fluorodeoxyglucose (FDG) positron emission tomography (PET) to detect metastatic lesions in patients with papillary thyroid carcinomas (PTC) after nearly total thyroidectomy and I‐131 treatments who present with elevated human serum thyroglobulin (hTg) levels but negative I‐131 whole body scan (WBS). Twenty patients with PTC who underwent nearly total thyroidectomy and radioiodine treatments were included in this study. Results. All of the 20 patients had negative I‐131 WBS results and elevated hTg levels (hTg ≥ 2.0 µIU/mL) under thyroid‐stimulating hormone (TSH) stimulation (TSH ≥ 30 µIU/mL). Conclusions. FDG‐PET was performed to detect metastatic lesions. F18‐fluorodeoxyglucose‐PET could detect hypermetabolic lesions in 17 patients but failed to demonstrate miliary pulmonary metastases in two patients. No definite lesion was found in FDG‐PET, x‐ray chest computed tomography (CT) and other imaging studies of the remaining one patient. This study showed that FDG‐PET is a useful tool in detecting metastatic lesions in PTC with elevated hTg but negative I‐131 WBS. However, miliary lung metastases may be missed in FDG‐PET. In this circumstance, chest CT should be included in the follow‐up protocol.