Role of 18F-FDG - PET/CT in Patients with Differentiated Thyroid Cancer Who Present with Elevated Thyroglobulin and Negative 131I Whole Body Scan

Abstract

Aim of the work: To detect the ability of 18F-FDG with PET/CT to explain the elevated Tg levels in patients with negative 131I whole body diagnostic dose scan and to correlate of 18F-FDG with PET/CT with other diagnostic methods and histopathologic diagnosis.Patients and methods: 20 patients (13 males and 7 females) with pathologicall proven differentiated cancer thyroid were included in the study. All patients were subjected to near total thyroidectomy. 8 out of the 20 patients also underwent lymph node dissection. All received 131I ablation and had a negative whole body scan during follow up. They had unexplained elevated (> 10 ng/ml or more) or rising serum Tg levels (5-10ng/ml). All patients were subjected to full history, clinical examination, Laboratory and radiological assessment as well as 18F-FDG PET/CT study.Results: Neck US detected 7 lesions in 6 patients, all of them confirmed to be positive by PET/CT and an additional 13 neck lesions were detected by PET/CT in 15 patients. CT chest detected 8 patients, 6 of them confirmed by PET/CT while 2 lung lesions were negative. Eight additional mediastinal lymph node metastases were detected by PET/CT. PET/CT showed positive findings in 19/20 patients. In the remaining no cause for the elevated Tg was found with PET/CT or other radiological methods. PET/CT directed the management in 14/20 patients either to surgery or to external radiotherapy with normalization of Tg level within weeks after treatment.Conclusion: 18F-FDG PET/CT is of undeniable clinical value in patients with negative 131I whole-body scan results who are suspected of having a metastatic thyroid disease. It is able to detect significantly additional tumor sites than US or CT procedures.