11C-methionine PET/CT after inconclusive 99mTc-MIBI-SPECT/CT for localisation of parathyroid adenomas in primary hyperparathyroidism

Aim: To investigate the efficacy of PET/CT with C-11-methionine for localizing parathyroid adenomas in patients with suspected primary hyperparathyroidism and inconclusive results of cervical ultrasonography and Tc-99m-MIBI-SPECT/CT. Patients, method: Retrospective analysis of imaging data of 18 patients and correlation with clinical outcome, in particular intraoperative findings and histopathology of excised tissue. Results: 12 of 18 patients received surgery. In 10 patients single parathyroid adenomas were found (diameter: 5-20 mm), 2 patients presented parathyroid hyperplasia (5 excised hyperplastic glands (diameter: 2-12 mm). PET/CT correctly localized all adenomas and 1 of 5 hyperplastic glands. The sensitivity per patient was 91.7% (11 of 12), the sensitivity per lesion 73.3% (11 of 15). All lesions missed by; PET/CT had a size smaller than 9 mm and a volume of less than 0.2 ml. In 6 patients no surgery was performed. Five of them had a negative or atypical PET/CT. Further follow-up indicated familial hypocalciuric hypercalcemia in 3 of them (thus, PET/CT true negative), in the remaining 2 patients no validation is available. One patient with 2 highly suggestive lesions rejected surgery so far. Conclusion: PET/CT with C-11-methionine is a very sensitive method for the detection of parathyroid adenomas, even if they are too small to be visualized by Tc-99m-MIBI-SPECT/CT.