Lung nodule detected by F-18 fluorodeoxyglucose positron emission tomography-computed tomography in patients with papillary thyroid cancer, negative (131)I whole body scan, and undetectable serum-stimulated thyroglobulin levels: two case reports

INTRODUCTION: When a pulmonary nodular lesion is detected by F-18 fluorodeoxyglucose positron emission tomography-computed tomography in a patient with post-surgical papillary thyroid carcinoma with undetectable serum-stimulated thyroglobulin levels and negative (131)I whole body scan, diagnosis and management of the nodule may be confusing. CASE PRESENTATION: We describe two post-surgical patients with papillary thyroid carcinoma who showed pulmonary nodular lesions detected by F-18 fluorodeoxyglucose positron emission tomography-computed tomography. In both cases serum-stimulated thyroglobulin levels were undetectable and nodular lesions were not detected by (131)I whole body scan. In the first case, a 64-year-old Asian woman showed one focal increased fluorodeoxyglucose uptake lesion in the right lower lobe of one of her lungs. Based on the histologic study, the pulmonary nodular lesion was diagnosed as a solitary pulmonary metastasis from papillary thyroid carcinoma. In the second case, a 59-year-old Asian woman showed a new pulmonary nodule in the right lower lobe. The computed tomography scan of her chest revealed a 9mm nodule in the anterior basal segment and another tiny nodule in the posterior basal segment of the right lower lobe. Six months later, both nodules had increased in size and miliary disseminated nodules were also seen in both lungs. Based on their histology, the pulmonary nodular lesions were considered to be primary lung adenocarcinoma. CONCLUSIONS: The present cases emphasize that physicians should be cautious and make efforts for an accurate diagnosis of pulmonary nodules detected on F-18 fluorodeoxyglucose positron emission tomography-computed tomography in patients with papillary thyroid carcinoma with no evidence of metastasis such as negative (131)I whole body scan and undetectable stimulated serum thyroglobulin levels.