From May 2017 to November 2019, a total of 60 patients who underwent parathyroidectomy in the Sixth Affiliated Hospital of Sun Yat-sen University were included in this study. All patients received US, dual-phase 99mTc-MIBI scintigraphy, early SPECT/CT and delayed SPECT/CT, and SHPT were confirmed by pathological results. Patient demographics (gender, age, dialysis vintage), imaging, laboratory values, operative and pathological results were collected. Laboratory values conclude serum calcium, phosphorus, creatinine, alkaline phosphatase (AKP), preoperative parathyroid hormone (PTH) and postoperative PTH within the first week.
All patients with SHPT received an intravenous injection of 555 MBq of 99mTc-MIBI. Dual-phase 99mTc-MIBI scintigraphy was obtained at 15 min and 120 min after injection. SPECT/CT integrated imaging was performed immediately after the early and delayed planar imaging. The imaging acquisition was using Symbia Intevo 6, Siemens Healthcare. The acquisition was set at energy peak of 140 keV, window width of 20%, matrix of 128×128, magnification of 1-fold, and counts of 600 k per frame with low-energy high resolution collimation. The CT scanning parameter was set at FOV of 40 cm, CT tube current of 200 mA, CT tube voltage of 130 kV, slice thickness of 2.5 mm, reconstruction matrix of 128×128, and reconstruction thickness of 2.5 mm. Imaging data were reconstructed using flash 3D. Ultrasonography was performed using the equipment (LOGIQ E9; GE Healthcare, USA), equipped with a linear probe 9L (8.4-9 MHz) and ML6-15 (10-15MHz).
Dual-phase 99mTc-MIBI scintigraphy
The images were diagnosed by 2 experienced nuclear medicine doctors who were blinded to the laboratory, surgical, and pathological results. The image was considered positive on visual analysis when it met one of the following criteria: (1) Abnormal 99mTc-MIBI uptake was observed on both the early and the delayed image. (2) Evident abnormal 99mTc-MIBI uptake was observed on the early image even if not on the delayed image. It was considered negative when abnormal 99mTc-MIBI uptake was observed on neither early nor delayed image.
Early SPECT/CT and delayed SPECT/CT
SHPT was diagnosed positive on the early or delayed SPECT/CT if CT indicated parenchyma space occupying lesion at the parathyroid region, while SPECT image showed abnormal 99mTc-MIBI accumulation compared to neck muscles and blood vessels. It was considered negative if abnormal 99mTc-MIBI uptake was observed on neither early nor delayed SPECT when CT indicated parenchyma space occupying lesion at the parathyroid region, and if abnormal 99mTc-MIBI uptake was observed on both early and delay phase but no parenchyma space occupying lesion at the parathyroid region on CT image.
The images were assessed by experienced ultrasound doctors blind to the laboratory, surgical, and pathological results. Typical ultrasound image was demonstrated as an oval or asymmetrical hypoechoic mass at the upper and lower pole of the thyroid back, having variable dimensions, separated by the thyroid gland. It may rarely present with
calcifications or cystic degeneration. Color doppler examination showed parathyroid vascular pedicle and a vascular arch located at the periphery of the gland.
Definition of ectopic parathyroid glands
It was considered parathyroid glands position normal when the lower glands were related to the lower pole of the thyroid gland, and when the upper glands were found near the upper pole of the thyroid. Hyperplastic parathyroid gland located inside the superior mediastinum regions and thyroid gland was regarded as ectopic parathyroid gland.
Parathyroidectomy and final diagnosis
All patients were submitted to surgery by the same surgical team. The surgical technique consisted of bilateral parathyroidectomy, bilateral recurrent laryngeal nerve exploration and forearm parathyroid gland transplantation. Hyperplastic parathyroid glands resected in operation were confirmed by pathological examination regarded as the golden standard for final diagnosis. The US, dual-phase 99mTc-MIBI scintigraphy, early SPECT/CT and delayed SPECT/CT findings for each gland were defined as true positive, false positive, true negative, or false negative on the basis of the pathology results. Comparisons of sensitivity, specificity and accuracy rate between different groups were made according to the parathyroid pathology results.
Metric data are expressed as mean ± SD. Categorical variables were analyzed using the χ2 or Fisher’s exact test. Spearman correlation was used for statistical analysis. A P value less than 0.05 was considered to indicate statistical significance. Statistical analysis was performed using the IBM SPSS version 20.0 statistical software.