(18)FDG WHOLE-BODY PET IN DIFFERENTIATED THYROID-CARCINOMA - FLIPFLOPIN UPTAKE PATTERNS OF (18)FDG AND I-131

In 27 examinations of 24 patients with differentiated thyroid carcinom a an alternating pattern of metastases with either I-131- or FDG-uptak e was found. In the follow-up of these patients this flipflop pattern was seen in 89% (17/19) of patients with metastases and uptake of I-13 1 or FDG as described here as uptake types 1 and 2 (type 1: FDG-positi ve and I-131-negative; type 2: FDG-negative and I-131-positive). In 4 patients a mixed type was observed (uptake type 3), i.e, a combination of metastases with uptake types 1 and 2 in the same patient. Metastas es of papillary or follicular thyroid carcinoma without uptake of iodi ne have all been found to be FDG-positive in patients with an increase of thyroglobuline and with negative diagnostic results from other ima ging modalities, and were histologically confirmed by surgery. False-n egative or false-positive cases were not observed in this study. The F DG uptake showed an inverse proportionality to iodine uptake and to tu mor differentiation. increased glucose metabolism is a sign of higher malignancy.