Comparative performance of 11C-methionine and 11C-choline PET/CT in primary hyperparathyroidism: Impact of adenoma weight on PET detectability

PURPOSE: To evaluate the diagnostic performance of [¹¹C]methionine (MET) PET/CT for preoperative localisation in primary hyperparathyroidism (PHPT) with negative or inconclusive first-line imaging, and to compare it with [¹¹C]choline (CHO) PET/CT in a head-to-head analysis, focusing on determinants of adenoma detectability. METHODS: Fifty-one patients with biochemically confirmed PHPT underwent MET PET/CT following inconclusive conventional imaging. In a subgroup of 25 patients, CHO PET/CT was also performed. Imaging findings were correlated with surgical and histopathological results. Detection rates and positive predictive values (PPV) were calculated, and semiquantitative parameters, including standardized uptake value (SUV) and lesion-to-background ratio (LBR), were analysed. Associations between PET findings, biochemical markers, and adenoma weight were explored. RESULTS: MET PET/CT achieved a patient-based detection rate of 76.5% with a PPV of 88.2%. In the head-to-head subgroup, CHO detected more lesions than MET (27 vs. 14; p = 0.0025) and identified all histologically confirmed adenomas, with comparable PPVs (90.0% vs. 77.8%). CHO demonstrated significantly higher SUV and LBR values. Adenoma weight was significantly associated with PET findings: MET-positive adenomas were significantly heavier than MET-negative adenomas, whereas CHO maintained high lesion detection even in adenomas weighing 0.5 g or less. Additionally, a trend towards higher uptake with increasing PTH and calcium levels was observed for CHO SUVmax. CONCLUSION: Adenoma weight appears to be a major determinant of PET detectability in PHPT. The ability of CHO PET/CT to detect adenomas weighing 0.5 g or less, which may remain occult on MET, provides a plausible explanation for its superior lesion detection, while both tracers maintain a high positive predictive value. These findings further support the use of choline-based PET imaging in patients with inconclusive first-line studies.