Endocrine Abstracts

Introduction: The first-line imaging modalities to locate adenomas preoperatively in primary hyperparathyroidism (PHPT) are ultrasonography (US) and subtraction scintigraphy (SuSc). When these contradict each other or are inconclusive an [11C]-methionine PET/CT (MET-PET/CT) or a 4-dimensional computed tomography (4D-CT) can be performed.

Objectives: The aim of this retrospective study was to evaluate the value of MET-PET/CT in the preoperative localization of adenomas in PHPT, especially when US and/or SuSc were inconclusive or negative.

Methods: All patients that underwent parathyroidectomy in the UZ Brussel in the period of 01-01-2008 until 31-12-2017 (10 years) for hyperparathyroidism were selected with exclusion of secondary and tertiary hyperparathyroidism, renal insufficiency (CKD stage 3B or worse), MEN syndrome and known malignancy. Finally, 84 patients were included. The results of US, SuSc, MET-PET/CT and 4D-CT were correlated to intraoperative decline in parathyroid hormone (PTH) levels and to the anatomopathological analysis. Sensitivity and specificity were calculated per-lesion for each imaging modality.

Results: 75 patients (89%) had a single parathyroid adenoma and nine patients (11%) had multiglandular PHPT (four patients had two adenomas, and five patients had hyperplasia). Not every patient underwent every imaging modality: 75 (90 adenomas), 62 (75 adenomas), 16 (22 adenomas) and 8 (8 adenomas) patients underwent respectively US, SuSc, MET-PET/CT and 4D-CT. The observed per-lesion sensitivity of US, SuSc, MET-PET/CT and 4D-CT is respectively 40.0%, 32.0%, 59.1% and 62.5%. The observed per-lesion specificity of US, SuSc, MET-PET/CT and 4D-CT is respectively 95.5%, 91.4%, 95.7% and 96.0%. Due to the limited sample size, especially in 4D-CT, the 95%-Clopper Pearson confidence intervals are large and therefore difficult to interpret. A sub-analysis on paired data only between two imaging modalities with a McNemar test showed a significant better per-lesion sensitivity of MET-PET/CT compared to US (P=0.039) and a significant higher per-lesion specificity of US compared to SuSc (P=0.035). The difference in per-lesion sensitivity between MET-PET/CT and SuSc showed a P-value of 0.070. In 70% of the cases where MET-PET/CT was performed after inconclusive or contradicting US and/or SuSc, MET-PET/CT had an additional value in localization of the adenoma.

Conclusion: MET-PET/CT seems a valuable imaging modality in hyperparathyroidism with a higher per-lesion sensitivity than US. Especially when US and/or SuSc are inconclusive or negative, MET-PET/CT directs the surgeon to the correct localization of the adenoma.