ABSTRACT
Tc99m-sestamibi dual-time imaging is a standard tool for localization of adenomas/hyperplasia in hyperparathyroidism. We investigated the degree and causes of localization failure among different types of hyperparathyroidism. Pre-operative parathyroid hormone levels and size of the gland were major determinants of Tc99m-sestamibi positivity; 123I scan may be helpful in localization failures. INTRODUCTION: Tc99m-sestamibi dual-time imaging is a standard tool for localization of adenomas/hyperplasia in hyperparathyroidism. However, parathyroid adenomas/hyperplasia has been reported to washout as fast as normal thyroid tissue ("rapid washout") which may lead to diagnostic failure. We aimed to evaluate the determinants of rapid washout and to determine the role of subtraction imaging for detection of parathyroid adenomas/hyperplasia with rapid washout. METHODS: Retrospective analysis of patients with hyperparathyroidism who have undergone Tc99m-sestamibi dual-time imaging and parathyroid surgery. Rapid washout was correlated to the type of hyperparathyroidism in surgically confirmed cases. Biochemical and pathological data were reviewed. RESULTS: A total of 135 hyperparathyroidism patients met the inclusion criteria. Ninety-six (72%), 29 (21%), and 10 (7%) had primary, secondary, and tertiary hyperparathyroidisms, respectively. Rapid washout was identified in 28/87 glands (32%), 14/53 glands (26%), and 1/16 glands (6%) with primary, secondary, and tertiary hyperparathyroidisms, respectively. Glands that were positive on late-phase Tc99m-sestamibi scans were significantly large being 1.7 (IQR 1.4-2.3) vs. 1.45 (IQR 1-2) cm (p = 0.003). High parathyroid hormone levels (PTH) were associated with early-phase Tc99m-sestamibi positivity in both primary (p = 0.01) and secondary hyperparathyroidism (p = 0.03) but not with last phase (p = 0.11, p = 0.37, respectively). Correlative imaging with subtraction scintigraphy was positive in 14/16 (87.5%) parathyroid adenomas. CONCLUSION: Pre-operative PTH levels and size of the gland were major determinants of Tc99m-sestamibi positivity on early-phase Tc99m-sestamibi scans, whereas size is an independent predictor of late-phase Tc99m-sestamibi positivity. Subtraction scintigraphy might be a useful tool in suspected cases of rapid washout adenomas/hyperplasia.
