Interobserver Agreement of Planar and SPECT Tc99m-MIBI Scintigraphy for the Assessment of Hypofunctioning Thyroid Nodules

Abstract

Introduction Thyroid scintigraphy with 99mTc-methoxyisobutylisonitrile (MIBI) is a helpful tool for the risk stratification of thyroid nodules (TN). Whereas a nodule with low or hypointense MIBI uptake has a low risk for malignancy, a hyperintense uptake may indicate a malignant nodule, which requires surgical resection. The appropriate diagnostic or therapeutic regimen of an isointense nodule with an uptake similar to the paranodular tissue is discussed controversially. Aim of this study was to assess the interobserver agreement (IA) for the assignment of TN to the three categories: hypo-, iso-or hyperintense. Methods Retrospective analysis of planar and SPECT images of MIBI scintigraphy was performed in 36 randomly selected patients with hypofunctioning TN and histological diagnosis. Four observers with different levels of experience in MIBI-scintigraphy analyzed MIBI uptake and assigned the nodules to the appropriate category. To assess the IA, Fleiss‘ Kappa was calculated. Results The study cohort included 11 patients with papillary thyroid carcinoma (diameter 20.3 mm) and 25 patients with benign nodules (diameter 24.8 mm). The IA for all nodules using planar images was 0.76 compared to 0.80 for SPECT images. The IA was better in the subgroup of malignant nodules for planar images as well as SPECT images (Kappa 0.91 and 0.90, respectively) compared to benign nodules (0.65 and 0.76, respectively). Using SPECT images, only one thyroid carcinoma presented with hypointense uptake, the remainder with hyper- or isointense uptake. In contrast, benign nodules were found in all categories. Conclusion MIBI scintigraphy shows a good IA for the interpretation of thyroid carcinoma. The IA is further improved if MIBI scintigraphy is performed in SPECT technique.

Interobserver Agreement of visual and semi-quantitative methods in 99mTc-Methoxy-Isobuty-Isonitrile (MIBI) imaging for risk stratification of hypofunctional thyroid nodules

“…MIBI has a high NPV and effectively rules out malignant TNs with notable accuracy, making it essential in the risk stratification of hypofunctioning TNs. However, MIBI imaging has a rather poor positive predictive value [13]. Therefore, refining the diagnostics i. e. by using a semiquantitative method but also using hybrid imaging [13], is desirable.…”

“…In Germany, MIBI is also used as an unspecific tracer for detection and staging tumors and for detecting parathyroid adenomas with a high sensitivity [12]. MIBI imaging has been employed for decades in the risk stratification of hypofunctioning TNs due to its high negative predictive value (NPV) exceeding 90 %, allowing for the exclusion of malignancy [2,9,12,13,14,15,16].…”

“…A hyperintense pattern indicates MIBI positivity (i. e., suspicious for malignancy), while hypointense uptake is rated as MIBI negative, suggesting a benign lesion. The meaning of an isointense uptake is less clear; some researchers consider it as a sign of malignancy (MIBI positive), while others consider TNs with isointense uptake as benign (MIBI negative) [13,17,18]. To enhance the diagnostic accuracy in discriminating malignancies in MIBI images, 3 D hybrid imaging using SPECT/CT can achieve a sensitivity improvement of 17-34 % [18,19].…”

“…Saggiorato et al compared visual and semi-quantitative methods with the latter and found a diagnostic accuracy of 95 % for non-oncocytic follicular neoplasm, along with better sensitivity and specificity than visual analysis [20]. The examination protocol for MIBI studies can vary based on different image evaluations (visual, semiquantitative methods), considering factors like acquisition time and assessment criteria-only a limited number of studies of interobserver agreement (IOA) are available [13,21]. The various out-comes of these studies, based on different work level experiences or varying performances, show the importance of a standardization to gain a better agreement.…”

Diagnostic Performance of 99mTc-Methoxy-Isobuty-Isonitrile (MIBI) for Risk Stratification of Hypofunctioning Thyroid Nodules: A European Multicenter Study

“…Fourthly, interobserver variability of MIBI imaging was not tested. However, Schenke et al and Baumgarten et al showed that the interobserver agreement was good for the planar imaging approach and was improved by using the SPECT technique [ 24 , 25 ]. Finally, our study did not address the cost-effectiveness of MIBI imaging in the clinical setting.…”