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Utility Of SPECT-CECT In Localization Of Normocalcemic Primary Hyperparathyroidism
*Alexa J Loncharich, *Elizabeth M Huffman, *Rodica I Muraru, *Mark Tann, *Hadley E Ritter, Alexandria D McDow
Indiana University School of Medicine, Indianapolis, IN

Objectives: Normocalcemic primary hyperparathyroidism (nPHPT) is characterized by normal calcium levels with elevated parathyroid hormone (PTH), unattributable to secondary causes. Prior studies have examined localization accuracy using ultrasonography, scintigraphy, and four-dimensional computed tomography (4DCT). Little is known about the utility of single-photon emission computed tomography hybridized with contrast enhanced CT imaging (SPECT-CECT) in nPHPT patients.
Methods: We performed a retrospective analysis of nPHPT patients receiving preoperative parathyroid localization at a single institution between 2015-2018. Exclusion criteria included patients with renal failure, vitamin D deficiency, malabsorptive disorders, liver disease, hypercalciuria, and certain medications. Patients underwent pre-operative localization with SPECT-CECT, which entailed early and late planar images of neck and mediastinum following administration of Tc-99m sestamibi, SPECT, and CT with and without contrast. Parathyroidectomy was performed with intraoperative PTH monitoring and pathologic confirmation of disease. SPECT-CECT location (left vs. right, superior vs. inferior) was compared to the surgically confirmed pathologic location using percent agreement and Kappa score (k). Sensitivity of SPECT-CECT localization from ROC analysis using pathologically confirmed location as gold standard was calculated.
Results: Thirty-nine patients met inclusion criteria and were analyzed. The mean age of the cohort was 63.6+/-11 years and 87.2% were female. The mean preoperative calcium, PTH, and Vitamin D were 10.3+/-0.2 mg/dL (normal 8.5-10.5 mg/dL), 102.6+/-45.7 pg/mL (normal 10-65 pg/mL), and 48.5+/-13.7 ng/mL (normal 30-100 ng/mL), respectively. SPECT-CECT revealed a single gland in 69.2%, multiglandular disease (MGD) in 7.7%, and was non-localizing in 23.1% of patients. Pathology revealed 61.5% had a single adenoma and 38.5% had MGD. SPECT-CECT accurately localized single adenomas with a sensitivity of 90.0% and 71.4% for left and right laterality, respectively (agreement=85.2%, k=0.61, p<0.001). SPECT-CECT accurately localized superior and inferior adenomas with a sensitivity of 50% and 81.8%, respectively (agreement=63.0%, k=0.29, p=0.05). SPECT-CECT accurately localized one of the parathyroid glands in 66.7% and all parathyroid glands in 33.3% of patients with MGD.
Conclusion: SPECT-CECT accurately localized 85.2% parathyroid adenomas in nPHPT patients with single adenomas but may be less useful in localizing MGD. Compared to prior studies examining ultrasonography, scintigraphy, and 4DCT, SPECT-CECT is a superior method of parathyroid localization in nPHPT patients.


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