18F-fluorocholine PET/CT semi-quantitative analysis in patients affected by primary hyperparathyroidism: a comparison between laboratory and functional data.

Introduction: this retrospective study aims to establish 18 F-fluorocholine (FCH) positron emission tomography / computed tomography (PET/CT) performance in finding hyperfunctioning parathyroid glands, analyse a potential role for semi-quantitative PET parameters and assess factors that may influence PET/CT outcome. Methods: : forty patients with suspect primary hyperparathyroidism (pHPT) and negative/equivocal conventional imaging underwent FCH-PET/CT in our Institution.For every lesion, visual and semi-quantitative analyses were performed on PET/CT images. In qualitative analysis, a lesion was considered positive if a clear focus of uptake, significantly higher than normal thyroid tissue, was identifiable. Ectopic focal uptake was also regarded as positive PET result. Lesion SUV Max was measured by assigning a spheric VOI to the suspect area of uptake. Thyroid SUV Mean was assessed by placing a spheric VOI inside the contralateral thyroid lobe, and SUV ratio was calculated using this background region.All patients were subsequently submitted to surgery and histopathologic workup.Sensitivity, positive predictive value (PPV) and accuracy were calculated based on histopathologic reports for every lesion.Pearson’s test was used to assess a correlation between laboratory and histopathologic features with SUVr. Results: : four out of the 40 patients who underwent surgery for pHPT had more than one histologic proven unhealthy parathyroid and three had papillary thyroid cancer (PTC). A total of 48 lesions were analysed.We found 42/48 lesions (87.5%) to have true-positive uptake, whereas three lesions (6.7%) had false-positive uptake (PTC). Three histologic proven parathyroid adenomas showed no uptake (6.7%); the sensitivity/PPV were 93.3% and accuracy was 87,8%.Pearson’s test showed a significant correlation between PTH values and parathyroid size with SUVr values (r=0.56 and 0.55 respectively, p<0.01 for both features). Discussion: as stated in recent literature, we observed excellent diagnostic sensitivity of FCH-PET/CT in patients with pHPT, providing surgeons a fine tool to optimize treatment.More studies are needed to improve the evaluability of semi-quantitative parameters towards a further improvement of diagnostic accuracy.