Endocrine Abstracts

Purpose: Persistence of well-differentiated thyroid carcinoma most commonly involves cervical lymph nodes. The purposes of the study were to evaluate the ability of FDG-PET/CT imaging to localize residual disease in initial stage M0 thyroid carcinoma thyroid cancer patients and to compare FDG-PET/CT to neck US.

Methods: FDG-PET/CT and neck US results of 93 patients were retrospectively analysed. All FDG-PET/CT were performed during thyrotropin stimulation (34 patients after THW and 59 patients after rhTSH).

Results: About 37/93 patients had a FDG uptake and 29/37 of the FDG avid lesions underwent re-operation. FDG-PET/CT findings were true-positive in 22 patients: cervical disease only (n=17), cervico-mediastinal disease (n=3), pulmonary metastases (n=2). The sensitivity, PPV, specificity, NPV and accuracy of FDG-PET/CT were 35, 59.5, 50, 26.8 and 39.7%, respectively. All patients with persistent Tg and aggressive papillary thyroid carcinoma (PTC) variants had FDG foci. Moreover, FDG-PET uptake provided more frequently complementary information compared to neck US in aggressive PTC variants than in other PTC histotypes (P<0.0001). FDG-PET/CT was also more useful in patients with rhTSH-Tg>5 or hypo-Tg>10 ng/ml than those with lower TSH-stimulated Tg values (P<0.049). In this group, FDG-PET provided additional value to neck US in 83.3% of reoperated patients.

Conclusion: Because FDG-PET has a low sensitivity in initial stage M0 thyroid carcinoma, it should not been performed in all patients with residual Tg. However, if only patients with high TSH-stimulated Tg or aggressive PTC variants are considered, FDG-PET provides additional information to neck US in most patients with positive FDG-PET.