Discordant sestamibi uptake in synchronous parathyroid carcinoma and adenoma.

Summary: The simultaneous occurrence of parathyroid carcinoma, parathyroid adenoma, and papillary thyroid carcinoma is exceptionally rare. Herein, we present an uncommon case in which the right malignant parathyroid lesion was 99mTc-MIBI-negative and the contralateral benign parathyroid lesion was 99mTc-MIBI-positive, which was confirmed by pathological examination postoperatively. In addition, we performed bilateral internal jugular venous sampling of PTH (IJ PTH), and the results showed that the IJ PTH was higher on the side of 99mTc-MIBI-negative lesion than on the other side. These findings suggest that 99mTc-MIBI-negative lesions with ipsilateral high IJ PTH should be highly suspected of parathyroid carcinoma in the setting of patients with two suspicious parathyroid lesions detected by cervical ultrasonography or computed tomography. No germline mutations associated with hereditary endocrine tumors were identified by whole-exome sequencing. Learning points: Parathyroid carcinoma can appear negative on 99mTc-sestamibi scintigraphy; therefore, comprehensive evaluation with both ultrasound and computed tomography is essential. In cases with discordant imaging and multiple lesions, bilateral internal jugular venous parathyroid hormone sampling serves as a decisive adjunct to guide en bloc resection when carcinoma is suspected. Preoperative evaluation for concurrent thyroid nodules is recommended during parathyroid surgery planning to avoid the need for secondary neck procedures.