Endocrine Abstracts

Aim/Introduction: [¹⁸F]fluorocholine (FCH) positron emission tomography/computed tomography (PET/CT) has gained an important role in the preoperative diagnosis of patients with primary hyperparathyroidism (pPHP). In these patients, thyroid nodules are frequently found on preoperative ultrasound. FCH PET/CT provides a high negative predictive value to reliably rule out cancer in thyroid nodules with low uptake. However, more than half of benign thyroid nodules have been reported to have high uptake of FCH. The aim of our study was to evaluate the characteristics of FCH PET/CT uptake in hyperfunctioning and hypofunctioning benign thyroid nodules.

Materials and Methods: A retrospective study was performed in patients with pPHP who were investigated by FCH PET/CT and concomitantly diagnosed with thyroid nodules larger than 1 cm on thyroid ultrasound. [^99mTc]pertechnetate scan was performed in all patients, and the benign nature of the nodules was confirmed by either high uptake or by fine-needle aspiration biopsy in patients with low uptake. Neck PET/CT acquisitions were performed 10 (early) and 60 (late) minutes after injection of 1.3 MBq/kg FCH, and the maximum standardized uptake value (SUV max) of the nodules was measured.

Results: Thirty-four patients (30/88.2% female, mean age 66.9±9.3 years) with 34 (15/44% hypofunctioning, 19/56% hyperfunctioning) thyroid nodules were included. Mean early SUVmax was 5.2±1.8; no difference in SUVmax was detected between hyperfunctioning and hypofunctioning thyroid nodules (mean, 4.9±1.8 and 5.6±1.7, respectively, P = 0.28). The mean late SUVmax was 4.3±1.8; no difference in SUVmax was found between hyperfunctioning and hypofunctioning thyroid nodules (mean, 4.3±2.1 and 4.4±1.3, respectively, P=0.42). A trend towards a positive but non-significant correlation (r = 0.3, P=0.09) of thyroglobulin level (mean 37.5±38.3 µg/l) with SUVmax in the early acquisition phase was observed, but no further statistically significant correlation of early or late SUVmax with TSH (mean 1.32±0.82 mIU/l), free T₄ (mean 15.3±2.01 pmol/l), free T₃ (mean 4.92±0.73 pmol/l), thyroid antibodies (median thyroid peroxidase antibodies level 86.53±253.52 kU/l, median thyroglobulin peroxidase level 37.9±103.9 kU/l) or nodule volume (mean 4.48±4.89 mL) was observed.

Conclusion: Hypofunctioning and hyperfunctioning thyroid nodules do not differ significantly in FCH uptake. The biochemical parameters of thyroid function and autoimmunity do not correlate with FCH uptake in benign thyroid nodules. Further studies should identify those characteristics of benign thyroid nodules that contribute to high uptake on FCH PET/CT scans to increase the specificity of FCH PET/CT in detecting malignant thyroid nodules.