Quantitative dual isotope 123iodine/99mTc-MIBI scintigraphy: A new approach to rule out malignancy in thyroid nodules.

Abstract Background: The aim of this study was to evaluate the role of dual isotope 123Iodine/99mTc-MIBI thyroid scintigraphy (IMS) in discriminating between malignant and benign suspect nodules using quantitative analysis methods. Methods: 35 consecutive patients with thyroid nodules of indeterminate or non-diagnostic cytology and cold on 123Iodine scintigraphy (10 Bethesda I, 24 Bethesda III-IV, 1 in which cytology was impossible) underwent IMS between 2017 and 2019 with uptake quantification at two time points ahead of thyroidectomy: early and late. Images were analyzed by two blinded physicians Results: 12 nodules were malignant and 23 benign on histopathology. Mean uptake values were lower in benign than in malignant nodules at both time points: early, 8.7±4.1 versus 12.9±3.5 (p=0.005); and late, 5.3 ± 2.7 versus 7.7±1.1 (p=0.008). Inter-observer reproducibility was excellent. The intraclass correlation coefficient was 0.86 in benign and 0.92 in malignant lesions on the early readings and 0.94 and 0.85 respectively on the late readings. The optimal cut-off to exclude malignancy on late reading was 5.9, with sensitivity, specificity, positive predictive value, negative predictive value and accuracy of respectively, 100%, 65.2%, 60%, 100% and 77.1%. Conclusion: Despite some study limitations, quantitative analysis of 99mTc-MIBI thyroid scintigraphy had a good reproducibility, which could help to rule out malignancy in non-diagnostic or indeterminate thyroid nodules and thereby reducing the number of patients undergoing unnecessary surgery when late uptake is below 5.9.