Differentiating pathologic parathyroid glands from thyroid nodules on neck ultrasound: the PARATH-US cross-sectional study.

Background: Neck ultrasound (US) is a widely used and accessible operator-dependent technique that helps characterize thyroid nodules and pathologic parathyroid glands (PPGs). However, thyroid nodules may sometimes be confused with PPGs. PARATH-US study aims at identifying US characteristics to differentiate PPGs from thyroid nodules, as there is no study, at present, which directly compares the US features of these two common neoplasms. Methods: PARATH-US is a single-center study that was conducted at a tertiary referral center, including consecutive lesions from patients undergoing neck US examination from 2016 to 2022. Findings: 176 PPGs (158 patients: serum calcium levels 2.91 [IQR 2.74-3.05] mmol/L, PTH levels 173 [112-296] ng/L) were compared to 232 size- and volume-matched thyroid nodules (204 age- and sex-matched patients). The morphologic patterns, echoic content and vascular status were all different between PPGs and thyroid neoplasms (p < 0.01 for all comparisons). The combined parameters maximally discriminated PPGs from thyroid nodules (OR, 7.6; 95% CI: 3.4, 17.1, p < 0.0001). When applying risk stratification systems developed for thyroid malignancies, 58-63% of PPGs were classified as high-risk lesions. Parathyroid adenomas had larger sizes and volumes than hyperplasias (p = 0.013 and p = 0.029). Serum calcium and PTH levels were significantly correlated with PPG size and volume (p < 0.0001 for all comparisons). Interpretation: We demonstrate the presence of distinct US characteristics in PPGs, which help differentiate them from thyroid nodules. When mistaken for thyroid nodules, PPGs bear high-risk US features. When dealing with high-risk cervical lesions detected on US, a PPG should be suspected, and an assessment of calcium levels recommended to avoid unnecessary invasive procedures. Funding: CYTO-TRAIN, C2022DOSRH053, funded by the French Regional Health Agency.