PURPOSE: Preoperative localization of the diseased parathyroid gland(s) in primary hyperparathyroidism allows for minimally invasive surgery. This study was designed to establish the optimal first-line preoperative imaging modality.

PATIENTS AND METHODS: Ninety-one patients were studied consecutively in a prospective head-to-head comparison of dual isotope (Tc-MIBI vs I) subtraction parathyroid scintigraphy (PS), dual-phase PS, 4-dimensional (4D) CT, and ultrasonography (US). Surgery, histological confirmation, and postoperative normalization of Ca and parathyroid hormone were the reference standard.

RESULTS: Ninety-seven hyperfunctioning parathyroid glands (HPGs) were identified by the reference standard. Sensitivity and specificity for subtraction PS, dual-phase PS, 4D-CT, and US were 93%, 65%, 58%, and 57% as well as 99%, 99.6%, 86%, and 95%, respectively. Interrater agreement was excellent for subtraction PS (κ = 0.96) while only fair for 4D-CT (κ = 0.34). Pinhole imaging and subtraction of delayed images (the latter especially in case of a nodular thyroid gland) increased the sensitivity of subtraction PS. SPECT/low-dose CT did not increase sensitivity but aided in the exact localization of the HPGs. Of 7 negative subtraction PS studies, 4D-CT and US were able to locate 3 and 1 additional HPGs, respectively.

CONCLUSIONS: Dual isotope pinhole subtraction PS has higher diagnostic accuracy compared with dual-phase PS, 4D-CT, and US as a first-line imaging study in primary hyperparathyroidism. In case of a negative scintigraphy or suspicion of multiglandular disease, 4D-CT and/or US is recommended as a second-line modality. However, diagnostic algorithms should be adapted in accordance with local availability and expertise.