Diagnostic role of 18FDG positron emission tomography (PET) in thyroid cancer (TC): a comparative analysis with conventional imaging (CI).

18FDG PET proved to be a high sensitive technique in detecting both primary tumour and metastatic spread in various types of neoplasms. In the present study we evaluated PET diagnostic role in TC. At present 8 patients (4 F, 4 M, mean age 47.3 years) were enrolled: 4 had medullary TC (MTC) and 4 differentiated TC (DTC); 4 of them (2 MTC, 2 DTC) were investigated before therapy for staging purpose and 4 (2 MCT, 2 DTC) during the follow-up after surgery (plus 131I therapy in DTC patients), because of the presence of elevated Calcitonin (Ct) or Thyroglobulin (Tg) serum levels. PET whole body scan results were compared with radiologic CI (US, CT and/or MRI) and scintigraphic CI (131I and/or 99mTc-MIBI scan). Among the patients studied before surgery, in 2 cases (1 DTC, 1 MTC) PET correctly detected the primary tumour and the loco-regional lymphnode spread and in another patient with DTC also lung and bone metastases as well as the other CI; in the other patient with MTC, both PET and CI localized the primary tumour and lymphnode spread but PET visualized an additional pulmonary neoplastic lesion. Among the patients studied during the follow-up, in the 2 cases of DTC 131I scan was negative, while PET and CI localized multiple lung metastases, but in both cases PET visualized a greater number of neoplastic foci; in 1 patient with MTC, PET was the only method capable to detect a mediastinic spread, whereas in the other case of MTC all the imaging techniques resulted negative. Conclusions: our preliminary data suggest a higher sensitivity of 18FDG PET in comparison with CI in detecting neoplastic spread. Therefore, PET could be particularly usefull in the follow-up of MTC patients with elevated Ct levels or of DTC patients with increased Tg levels and negative 131I scan.