Quantitative Evaluation of Parathyroid Adenoma and Hyperplasia in Reference to Thyroid using Tc-99m MIBI SPECT/CT

Objectives: The main underlying diseases of hyperparathyroidism consist of primary adenoma or secondary hyperplasia. Tc-99m MIBI single-photon emission computed tomography/computed tomography (SPECT/CT) has been used to help surgeons explore the location of the parathyroid diseases but any quantitative parameters have never been systemically investigated for this purpose. Using the quantitative SPECT/CT technique, we measured the standardized uptake value (SUV) of Tc-99m MIBI over the pathologically proven parathyroid adenoma and hyperplasia, and compared with thyroid tissue as a reference. The aim of the study was to establish objective criteria for adenoma and hyperplasia in patients with hyperparathyroidism. Methods: From Oct 2015 to Oct 2017, 53 consecutive patients with hyperparathyroidism (defined as elevated level of PTH and Ca) underwent preoperative Tc-99m MIBI quantitative SPECT/CT and surgical exploration. The time interval between the SPECT/CT and surgery was 40.89±61.08 days (range: 1-292 days). Because thyroid was considered as reference tissue, we excluded 9 subjects with thyroid abnormalities such as current thyroid cancer or previous thyroidectomy. Proven false negative Tc-99m MIBI SPECT/CT studies from 5 patients with 8 lesions (4 adenoma and 4 hyperplasia) were also excluded: the pathologically measured volume of the lesions was less than 0.5 cm³. Finally, 39 patients (male:female=17:22, age=59.25±11.38 years) with their 44 lesions (30 adenoma and 14 hyperplasia) were enrolled. All the patients experienced normalized PTH level immediately after the surgery. Quantitative SPECT/CT was performed at 10 min and 2 h post injection of Tc-99m MIBI (dose=20 mCi) and SUVs (maximum and mean) were measured over the apparent parathyroid lesions under guidance of SPECT/CT images. Normal thyroid tissue, evidenced by normal thyroid function tests (n=34) and imaging studies (ultrasonography or CT) served as reference. Results: The maximum SUVs of adenoma, hyperplasia and thyroid were 13.15±6.81 g/mL, 8.11±5.15 g/mL, and 7.01±2.61 g/mL at 10 min (early phase) and those values decreased to 7.59±5.80 g/mL, 4.89±2.96 g/mL, and 2.21±1.07 g/mL at 2 h (delayed phase). On the other hand, the mean SUVs for adenoma, hyperplasia and thyroid at the early phase were 6.74±3.05, 4.56±2.68, and 4.93±1.61 and those values also reduced to 3.89±1.98, 2.98±2.12, and 1.72±0.67 at the delayed phase. The adenoma showed significantly higher maximum (p<0.0001) and mean SUVs (p<0.0001) than thyroid at the early and delayed phases by repeated-measures ANOVA (analysis-of-variance) test, but the hyperplasia did not. Conclusion: Parathyroid adenoma had significantly higher quantitative parameter (SUV) than reference thyroid tissue in early and delayed phases of Tc-99m MIBI SPECT/CT. Quantitative Tc-99m MIBI SPECT/CT may provide the operating surgeons with objective criteria especially for parathyroid adenoma.