Diagnostic Performance of Technetium-99m Methoxy-Isobutyl-Isonitrile for Differentiation of Malignant Thyroid Nodules: A Systematic Review and Meta-Analysis

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

AIM

99mTc-Methoxy-Isobuty-Isonitrile (MIBI) imaging is used for risk stratifications of hypofunctioning thyroid nodules (TNs). MIBI uptake in the nodular tissue is compared to the uptake in the paranodular thyroid tissue. MIBI imaging may be interpreted visually and/or semi-quantitatively. This study aimed to evaluate the interobserver agreement (IOA) of different methods of interpreting MIBI imaging (visual and semi-quantitative approaches).

METHODS

MIBI imaging data from 2018 to 2020 were collected. Four readers with varying work experience prospectively evaluated MIBI images (planar, SPECT/CT) visually and semi-quantitatively (Wash-Out Index (WOI)). After identifying the nodules on 99mTc-pertechnetate scintigram, the readers evaluated MIBI imaging data by using early, late, early-to-late, and SPECT late acquisitions. Region of interests (ROIs) were defined for semi-quantitative analysis and average counts were calculated using the WOI formula (by Campenni et al.) 1 2. IOA was assessed using Fleiss Kappa, Pearson correlation and Analysis of Variance (ANOVA).

RESULTS

23 patients with hypofunctioning nodules were included. Kappa analysis revealed an IOA of 0.57 for all readers for early imaging (moderate agreement); perfect matches were found in 57%. For late imaging, the IOA was 0.48 (moderate) for all, with perfect matches in 48%. The visual pattern (early-to-late) exhibited an IOA of 0.45 for all, with perfect matches in 57%. SPECT/CT evaluation showed an overall IOA of 0.44, with perfect matches in 48%. The semi-quantitative approach WOI yielded an overall result of 0.64 (good agreement) and perfect matches in 91%.

CONCLUSION

The IOA for WOI was higher than for visual methods. The WOI is independent of the reader's experience level. Visual analysis requires a certain level of experience from the reader.

Reappraising the role of thyroid scintigraphy in the era of TIRADS: A clinically-oriented viewpoint

Thyroid nodules (TNs) are a common entity, with the majority being benign. Therefore, employing an accurate rule-out strategy in clinical practice is essential. In the thyroid field, the current era is significantly marked by the worldwide diffusion of ultrasound (US)-based malignancy risk stratification systems of TN, usually reported as Thyroid Imaging Reporting And Data System (TIRADS). With the advent of US (and later TIRADS), the role of thyroid scintigraphy (TS) in clinical practice has gradually diminished. The authors of the present paper believe that the role of TS should be reappraised, also considering its essential role in detecting autonomously functioning thyroid nodules and its limited contribution to detecting thyroid cancers. Thus, this document aims to furnish endocrinologists, radiologists, surgeons, and nuclear medicine physicians with practical information to appropriately use TS.

BRAF Detection in FNAC Combined with Semi-Quantitative 99mTc-MIBI Technique and AI Model, an Economic and Efficient Predicting Tool for Malignancy in Thyroid Nodules

BACKGROUND

Technology allows us to predict a histopathological diagnosis, but the high costs prevent the large-scale use of these possibilities. The current liberal indication for surgery in benign thyroid conditions led to a rising frequency of incidental thyroid carcinoma, especially low-risk papillary micro-carcinomas.

METHODS

We selected a cohort of 148 patients with thyroid nodules by ultrasound characteristics and investigated them by fine needle aspiration cytology (FNAC)and prospective BRAF collection for 70 patients. Also, we selected 44 patients with thyroid nodules using semi-quantitative functional imaging with an oncological, 99mTc-methoxy-isobutyl-isonitrile (99mTc-MIBI) radiotracer.

RESULTS

Following a correlation with final histopathological reports in patients who underwent thyroidectomy, we introduced the results in a machine learning program (AI) in order to obtain a pattern. For semi-quantitative functional visual pattern imaging, we found a sensitivity of 33%, a specificity of 66.67%, an accuracy of 60% and a negative predicting value (NPV) of 88.6%. For the wash-out index (WOind), we found a sensitivity of 57.14%, a specificity of 50%, an accuracy of 70% and an NPV of 90.06%.The results of BRAF in FNAC included 87.50% sensitivity, 75.00% specificity, 83.33% accuracy, 75.00% NPV and 87.50% PPV. The prevalence of malignancy in our small cohort was 11.4%.

CONCLUSIONS

We intend to continue combining preoperative investigations such as molecular detection in FNAC, 99mTc-MIBI scanning and AI training with the obtained results on a larger cohort. The combination of these investigations may generate an efficient and cost-effective diagnostic tool, but confirmation of the results on a larger scale is necessary.

Thyroid Imaging Reporting and Data Systems: Applicability of the "Taller than Wide" Criterium in Primary/Secondary Care Units and the Role of Thyroid Scintigraphy

BACKGROUND

To examine the applicability of the "taller than wide" (ttw) criterium for risk assessment of thyroid nodules (TNs) in primary/secondary care units and the role of thyroid scintigraphy therein.

METHODS

German bicenter study performed in a setting of primary/secondary care. Patient recruitment and analysis in center A was conducted in a prospective manner. In center B, patient data were retrieved from a database that was originally generated by prospective data collection. TNs were assessed by ultrasound and thyroid scans, mostly fine needle biopsy and occasionally surgery and others. In center A, only patients who presented for the first time were included. The inclusion criterion was any TN ≥ 10 mm that had at least the following two sonographic risk features: solidity and a ttw shape. In center B, consecutive patients who had at least ttw and hypofunctioning nodules ≥ 10 mm were retrieved from the above-mentioned database. The risk of malignancy was determined according to a mixed reference standard and compared with literature data.

RESULTS

In center A, 223 patients with 259 TNs were included into the study. For further analysis, 200 nodules with a reference standard were available. The overall malignancy rate was 2.5% (upper limit of the 95% CI: 5.1%). After the exclusion of scintigraphically hyperfunctioning nodules, the malignancy rate increased slightly to 2.8% (upper limit of the 95% CI: 5.7%). Malignant nodules exhibited sonographic risk features additional to solidity and ttw shape more often than benign ones. In addition to the exclusion of hyperfunctioning nodules, when considering only nodules without additional US risk features, i.e., exclusively solid and ttw-nodules, the malignancy rate decreased to 0.9% (upper limit 95% CI: 3.7%). In center B, from 58 patients, 58 ttw and hypofunctioning TNs on thyroid scans with a reference standard were available. Malignant nodules from center B were always solid and hypoechoic. The overall malignancy rate of hypofunctioning and ttw nodules was 21%, with the lower limit of the 95% CI (one-sided) being 12%.

CONCLUSIONS

In primary/secondary care units, the lowest TIRADS categories for indicating FNB, e.g., applying one out of five sonographic risk features, may not be appropriate owing to the much lower a priori malignancy risk in TNs compared to tertiary/quaternary care units. Even the combination of two sonographic risk features, "solidity" and "ttw", may only be appropriate in a limited fashion. In contrast, the preselection of TNs according to hypofunctioning findings on thyroid scans clearly warranted FNB, even when applying only one sonographic risk criterion ("ttw"). For this reason, thyroid scans in TNs may not only be indicated to rule out hyperfunctioning nodules from FNB but also to rule in hypofunctioning ones.

Could Negative Tc-99m-Methoxyisobutylisonitrile (MIBI) Scintigraphy Obviate the Need for Surgery for Bethesda III and IV Thyroid Nodules?

In about 20% of all cases, the fine needle aspiration cytology (FNAC) results are equivocal, delivering the two common categories of indeterminate cytology, Bethesda III and IV. The observed rates of malignancy vary widely among institutions, with the urgent need for a more precise risk stratification. 99mcTc methoxyisobutylisonitrile scintigraphy (MIBI) is less expensive than molecular testing and has been shown to have a high negative predictive value. For this reason, the results of MIBI scintigraphy in adult patients with indeterminate FNAC were collected, and correlated with the final pathology reports of surgical specimens. Patients receiving FNAC, MIBI scintigraphy and surgery for sonographic suspicious hypofunctional thyroid nodules between 2015 and 2019 at the University Hospital of Cologne, Germany were identified. Sensitivity, specificity, positive predictive and negative predictive value of MIBI scintigraphy were calculated. Seventy-eight patients with sonographic suspicious hypofunctional thyroid nodules underwent surgery after interdisciplinary case discussion of both FNAC and MIBI results. In 49 (62.5%) cases, FNAC consisted of Bethesda III and IV results. In 39 (79.6%) of these cases, MIBI scintigraphy resulted in mismatch and intermediary results, but in only 4 (10.2%) of these cases was a carcinoma diagnosed. The negative predictive value of MIBI scintigraphy was 90–100%, respectively. Relying on the negative predictive value of MIBI match results might have obviated the need for surgery in 20.4% cases; one papillary microcarcinoma, however, would have been missed. MIBI scintigraphy has an underused potential for improving the diagnostic precision of hypofunctional thyroid nodules.

A multicenter survey of current practices of 99mTc-methoxy-isobutyl-isonitrile (MIBI) imaging for the diagnosis of thyroid nodules: more standardization is essential

Purpose

Molecular imaging with 99mTc-methoxy-isobutyl-isonitrile (99mTc-MIBI, MIBI) has been used in the assessment of thyroid nodules (TNs) for more than two decades. Many studies showed that MIBI imaging is a suitable tool to rule-out malignancy when negative. However, relatively low specificity and accuracy have been described, thus, limiting its acceptance in clinical practice. Additionally, different technologies, protocols, and interpretation criteria are adopted accounting for heterogeneous data reported in the literature. Therefore, the present study was undertaken to assess the clinical use and methodology of MIBI imaging in patients with nodular thyroid disease in Europe.

Methods

A questionnaire was sent to 12 European centers of Nuclear Medicine. The questionnaire encompassed ultrasound (US) and fine-needle aspiration cytology (FNAC) procedures and their evaluation as well scintigraphy imaging indications, technical procedures, and interpretation criteria of MIBI imaging.

Results

The survey showed a good agreement of different centers in approaching TNs by TSH measurement, US evaluation and 99mTc-pertechnetate thyroid scintigraphy. MIBI imaging is mainly used to assess TNs with inconclusive/indeterminate cytological findings and selection of target nodule(s) for FNAC in patients with multi-nodular goiter. Technical procedures adopted in different centers are globally comparable and the recorded differences are unlikely to impact clinical results. However, as the main result of the present study, substantial differences were found in interpretation criteria adopted in different centers.

Conclusions

Our survey supports the urgent need of standardized interpretation criteria of thyroid MIBI imaging in order to improve its diagnostic performance and make results comparable in clinical practice.

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

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 lesions in indeterminate nodules using quantitative analysis methods.

METHODS

Thirty-five 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

Twelve 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). Interobserver reproducibility was excellent. The intraclass correlation coefficient was 0.86 in benign and 0.92 in malignant lesions for early uptake result (ER) and 0.94 and 0.85 respectively for late uptake result (LR). The optimal LR cut-off  to exclude a diagnosis of malignancy was set at 5.9 . The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of this cut-off were, 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 LR is below 5.9.