Endocrine Abstracts

Aim/Introduction: Contrast-enhanced ¹⁸F-FDG PET/CT is an effective diagnostic procedure enabling a precise localization of remnants or recurrences in patients with radioiodine-negative differentiated thyroid carcinomas (DTCs). The detection of this lesions allows to cure patients without detectable distant metastases using a loco-regional surgical treatment. The aim of this study was to assess the influence of ¹⁸F-FDG PET/CT on indication of this type of treatment.

Materials and methods: A total of 194 patients (pts) with suspicion of recurrent DTC and negative 131I scans in the period 2008–2019 underwent contrast-enhanced 18F-FDG PET/CT. Examination was performed in 32 patients (pts.) due to suspicious sonography or high-risk disease despite the low TSH-stimulated thyroglobulin (TSH-Tg < 2 µg/l), in 58 pts. TSH-Tg was 2 < 10 µg/l, in 92 pts TSH-Tg > 10 µg/l and in 14 pts. due to persistent elevation or increasing level of anti-Tg. Only the first 18F-FDG PET/CT examinations were evaluated, all subsequent examinations of the same patient were not included in this study.

Results: Contrast-enhanced 18F-FDG PET/CT detected remnants or recurrences – usually lymph node (LN) involvement treatable with loco-regional surgery in 38 of 194 pts. In the subgroup with TSH-Tg 0 < 2 µg/l and suspicious sonography or high-risk disease surgery was performed: 5 pts (16%) LN metastases, 2 pts. benign (parathyroid adenoma and Schwannoma) and 2 pts. malignant (spinocellular and renal carcinoma) tumors. Subgroup – TSH-Tg 2 < 10 µg/l: 8 (14%) pts. LN metastases. Subgroup – TSH-Tg > 10 µg/l: 23 (25%) pts. LN metastasesor remnants (incidentally 2 another malignancies were detected using PET– lung and colorectal carcinoma) Subgroup with anti-TG pathology: 5 (36%) LN metastases.

Conclusion: Contrast-enhanced 18F-FDG PET/CT is an efficient diagnostic tool for indicating patients with radioiodine-negative DTCs to loco-regional surgery. The detection rate of treatable recurrences or remnants significantly increases with increase of TSH-Tg. Nevertheless, it is not possible to set the lower TSH-Tg limit for 18F-FDG PET/CT indication. Surprisingly, a high portion of the pathological findings also show pts. with persistent elevation or increase of anti-Tg. Incidental detections of another types of malignancies is also appreciable.