Performance of 18F-FDG PET/CT in Selecting Thyroid Nodules with Indeterminate Fine-Needle Aspiration Cytology for Surgery. A Systematic Review and a Meta-Analysis

Molecular imaging of thyroid and parathyroid diseases

INTRODUCTION

Molecular imaging of thyroid and parathyroid diseases has changed in recent years due to the introduction of new radiopharmaceuticals and new imaging techniques. Accordingly, we provided an clinicians-oriented overview of such techniques and their indications.

AREAS COVERED

A review of the literature was performed in the PubMed, Web of Science, and Scopus without time or language restrictions through the use of one or more fitting search criteria and terms as well as through screening of references in relevant selected papers. Literature up to and including December 2023 was included. Screening of titles/abstracts and removal of duplicates was performed and the full texts of the remaining potentially relevant articles were retrieved and reviewed.

EXPERT OPINION

Thyroid and parathyroid scintigraphy remains integral in patients with thyrotoxicosis, thyroid nodules, differentiated thyroid cancer and, respectively, hyperparathyroidism. In the last years positron-emission tomography with different tracers emerged as a more accurate alternative in evaluating indeterminate thyroid nodules [18F-fluorodeoxyglucose (FDG)], differentiated thyroid cancer [124I-iodide, 18F-tetrafluoroborate, 18F-FDG] and hyperparathyroidism [18F-fluorocholine]. Other PET tracers are useful in evaluating relapsing/advanced forms of medullary thyroid cancer (18F-FDOPA) and selecting patients with advanced follicular and medullary thyroid cancers for theranostic treatments (68Ga/177Ga-somatostatin analogues).

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.

Improving the TIR3B oncological stratification: try to bridge the gap through a comprehensive presurgical algorithm

PURPOSE

Indeterminate cytology still puzzles clinicians, due to its wide range of oncological risks. According to the Italian SIAPEC-IAP classification, TIR3B cytology holds up to 30% of thyroid cancer, which justifies the surgical indication, even if more than half of cases do not result in a positive histology. The study aim is to identify potential clinical, ultrasound or cytological features able to improve the surgical indication.

METHODS

Retrospective analysis. A consecutive series of TIR3B nodules referred to the Endocrine Unit of Careggi Hospital from 1st May 2014 to 31st December 2021 was considered for the exploratory analysis (Phase 1). Thereafter, a smaller confirmatory sample of consecutive TIR3B diagnosed and referred to surgery from 1st January 2022 to 31st June 2022 was considered to verify the algorithm (Phase 2). The main clinical, ultrasound and cytological features have been collected. A comprehensive stepwise logistic regression was applied to build a prediction algorithm. The histological results represented the final outcome.

RESULTS

Of 599 TIR3B nodules referred to surgery, 451 cases were included in the exploratory analysis. A final score > 14.5 corresponded to an OR = 4.98 (95% CI 3.24-7.65, p < 0.0001) and showed a PPV and NPV of 57% and 79%, respectively. The Phase 2 analysis on a confirmatory sample of 58 TIR3B cytology confirmed that a threshold of 14.5 points has a comparable PPV and NPV of 53% and 80%, respectively.

CONCLUSIONS

A predictive algorithm which considers the main clinical, US and cytological features can significantly improve the oncological stratification of TIR3B cytology.

Assessment of the risk of malignancy in Bethesda III thyroid nodules: a comprehensive review

The increasing prevalence of thyroid cancer emphasizes the need for a thorough assessment of risk of malignancy in Bethesda III nodules. Various methods ranging commercial platforms of molecular genetic testing (including Afirma® GEC, Afirma® GSC, ThyroSeq® V3, RosettaGX®, ThyGeNEXT®/ThyraMIR®, ThyroidPRINT®) to radionuclide scans and ultrasonography have been investigated to provide a more nuanced comprehension of risk estimation. The integration of molecular studies and imaging techniques into clinical practice may provide clinicians with improved and personalized risk assessment. This integrated approach we feel may enable clinicians to carefully tailor interventions, thereby minimizing the likelihood of unnecessary thyroid surgeries and overall crafting the optimal treatment. By aligning with the evolving landscape of personalized healthcare, this comprehensive strategy ensures a patient-centric approach to thyroid nodule and thyroid cancer management.

Integrated Diagnostics of Thyroid Nodules

Thyroid nodules are common findings, particularly in iodine-deficient regions. Our paper aims to revise different diagnostic tools available in clinical thyroidology and propose their rational integration. We will elaborate on the pros and cons of thyroid ultrasound (US) and its scoring systems, thyroid scintigraphy, fine-needle aspiration cytology (FNAC), molecular imaging, and artificial intelligence (AI). Ultrasonographic scoring systems can help differentiate between benign and malignant nodules. Depending on the constellation or number of suspicious ultrasound features, a FNAC is recommended. However, hyperfunctioning thyroid nodules are presumed to exclude malignancy with a very high negative predictive value (NPV). Particularly in regions where iodine supply is low, most hyperfunctioning thyroid nodules are seen in patients with normal thyroid-stimulating hormone (TSH) levels. Thyroid scintigraphy is essential for the detection of these nodules. Among non-toxic thyroid nodules, a careful application of US risk stratification systems is pivotal to exclude inappropriate FNAC and guide the procedure on suspicious ones. However, almost one-third of cytology examinations are rendered as indeterminate, requiring "diagnostic surgery" to provide a definitive diagnosis. 99mTc-methoxy-isobutyl-isonitrile ([99mTc]Tc-MIBI) and [18F]fluoro-deoxy-glucose ([18F]FDG) molecular imaging can spare those patients from unnecessary surgeries. The clinical value of AI in the evaluation of thyroid nodules needs to be determined.

Thyroid Nodules: Emerging Trends in Detection and Visualization based on Citespace

BACKGROUND

Thyroid nodule (TN) is a highly prevalent clinical endocrine disease. Many countries have formed guidelines on the prevention and treatment of TN based on extensive research. However, there is a scarcity of TN-related literature based on bibliometrics.

OBJECTIVES

This study aimed to evaluate the scientific achievements and progress of TN research from a global perspective by investigating the literature for 20 years through bibliometrics.

METHODS

We searched the literature on TN in the core collection of the Web of Science database from 2002 to 2021 and used the Citespace software to analyze the co-authorship, co-citation, and co-occurrence of countries, institutions, authors, keywords, and co-cited literature.

RESULTS

We retrieved 12319 documents related to TN. The literature on TN has been growing since 2002. The United States has contributed the largest proportion of TN papers (20.64%), followed by China, Italy, and South Korea. The United States ranked first in terms of centrality (0.38). Haugen BR, Gharib H, and Cibas ES are the top three most cited authors. The papers published in Thyroid were cited most frequently (7952 times). The most prominent keywords were management, cancer, fine needle aspiration, diagnosis, malignant tumor, thyroid cancer, ultrasound, biopsy, benign, surgery, ablation, and cytology. All keywords could be divided into three categories: diagnosis stratification, treatment, and cancer. As far as potential hot spots are concerned, the keywords that have recently burst strongly and are still continuing are: "Association Guideline" (2018-2021), "Radiofrequency Ablation" (2017-2021), "Classification" (2019-2021), and "Data System" (2017-2021).

CONCLUSION

Based on the current trends, the number of publications on TN will continue to increase. The United States is the most active contributor to research in this field. Previous literature focused on stratification, cancer, surgery, and ablation, and there were different opinions on the stratification of diagnosis. There were relatively few studies on pathogenesis and treatment using medicine. More focus will be placed on association guidelines, radiofrequency ablation, classification, and data system, which may be the next popular topics in TN research.

Triple Assessment in Diagnosis of Thyroid Nodules and Its Comparison With Histopathology

BACKGROUND

 Thyroid nodules are more common than previously realised, and the rate of prevalence is hugely impacted by the method of detection and their easy access. No single test is sufficient to access the thyroid nodule at any given time. Hence this necessitates the need for clinicians to use an evidence-based protocol for their assessment and diagnosis.

AIMS AND OBJECTIVE

 To determine the likelihood of malignancy in individuals who have thyroid nodules of any size, by a) performing a triple assessment, including a history and physical examination, an ultrasound of the neck and fine needle aspiration and cytology (FNAC) b) predicting the percentage of correlation between findings of malignancy on FNAC and final histopathological diagnosis c) identifying and validate individual risk factors in the clinical examination and ultrasound imaging that point towards a nodule being malignant Methods: Patients presenting with thyroid nodules in a clinically euthyroid state were studied over a time period of 18 months. Seventy-five patients were included in this study. Patients having external cytology and ultrasonography reports were reassessed if they consented to the study. If the pathologists thought the smears were sufficient, slide reviews were accepted. A senior consultant conducted the clinical evaluation. Prior to doing the FNACs, the designated radiologist performed the majority of the ultrasonograms. If the physicians believed it was necessary, ultrasound-guided FNACs were performed. According to Bethesda criteria, the cytology was reported. The outcome of the histopathological analysis was used as the gold standard for diagnosis in this investigation.

RESULT

Out of 75 patients included in the study, the older age group (50-70) patients had mostly malignant lesions (92%). In the younger age group (20-39), about 77% had benign lesions. Benign lesions were more common in females than males according to the histopathology study. Seventy-three percent of fixed swellings turned out to be malignant. About 86% of patients who had extrathyroidal extension ended up being found to have malignant lesions but even 41% of patients who didn't have any extrathyroidal extension also turned out to be having malignant lesions. However, the presence of pressure symptoms didn't necessarily translate to being an indicator of malignancy. Ninety-seven percent of patients who had punctate microcalcifications turned out to have malignant lesions. Hypoechogenicity on imaging also is an important marker of malignancy, with about 87% of patients who had hypoechogenicity having malignant lesions proven on histopathology. All the patients who had solid lesions on imaging were proven to have malignant lesions. About 77% of patients who had cystic features ended up having benign lesions. Hence, it is a very significant marker. Intranodular vascularity, taller than wider lesions and positive lymph nodes on imaging were proven to have malignant lesions. FNAC is an important diagnostic tool. It is made out that the reporting of FNAC more or less matched the histopathological diagnosis in almost all categories.

CONCLUSION

 There are definite correlations in the role of triple assessment as a standard protocol in the diagnosis of thyroid nodules and guiding its management.

Personalized Diagnosis in Differentiated Thyroid Cancers by Molecular and Functional Imaging Biomarkers: Present and Future

Personalized diagnosis can save unnecessary thyroid surgeries, in cases of indeterminate thyroid nodules, when clinicians tend to aggressively treat all these patients. Personalized diagnosis benefits from a combination of imagery and molecular biomarkers, as well as artificial intelligence algorithms, which are used more and more in our timeline. Functional imaging diagnosis such as SPECT, PET, or fused images (SPECT/CT, PET/CT, PET/MRI), is exploited at maximum in thyroid nodules, with a long history in the past and a bright future with many suitable radiotracers that could properly contribute to diagnosing malignancy in thyroid nodules. In this way, patients will be spared surgery complications, and apparently more expensive diagnostic workouts will financially compensate each patient and also the healthcare system. In this review we will summarize essential available diagnostic tools for malignant and benignant thyroid nodules, beginning with functional imaging, molecular analysis, and combinations of these two and other future strategies, including AI or NIS targeted gene therapy for thyroid carcinoma diagnosis and treatment as well.

Molecular Imaging and Theragnostics of Thyroid Cancers

Molecular imaging plays an important role in the evaluation and management of different thyroid cancer histotypes. The existing risk stratification models can be refined, by incorporation of tumor-specific molecular markers that have theranostic power, to optimize patient-specific (individualized) treatment decisions. Molecular imaging with varying radioisotopes of iodine (i.e., ¹³¹I, ¹²³I, ¹²⁴I) is an indispensable component of dynamic and theragnostic risk stratification of differentiated carcinoma (DTC) while [¹⁸F]F-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) helps in addressing disease aggressiveness, detects distant metastases, and risk-stratifies patients with radioiodine-refractory DTC, poorly differentiated and anaplastic thyroid cancers. For medullary thyroid cancer (MTC), a neuroendocrine tumor derived from thyroid C-cells, [¹⁸F]F-dihydroxyphenylalanine (6-[¹⁸F]FDOPA) PET/CT and/or [¹⁸F]FDG PET/CT can be used dependent on serum markers levels and kinetics. In addition to radioiodine therapy for DTC, some theragnostic approaches are promising for metastatic MTC as well. Moreover, new redifferentiation strategies are now available to restore uptake in radioiodine-refractory DTC while new theragnostic approaches showed promising preliminary results for advanced and aggressive forms of follicular-cell derived thyroid cancers (i.e., peptide receptor radiotherapy). In order to help clinicians put the role of molecular imaging into perspective, the appropriate role and emerging opportunities for molecular imaging and theragnostics in thyroid cancer are discussed in our present review.

Radiofrequency ablation for treatment of thyroid follicular neoplasm with low SUV in PET/CT study

OBJECTIVES

To evaluate the feasibility of radiofrequency ablation (RFA) on follicular neoplasm with low standard uptake value (SUV) in a Positron emission tomography (PET/CT) study.

METHODS

From January 2018 to July 2019, 86 consecutive patients were diagnosed with follicular neoplasm. Of the patients, 28 with PET/CT scans were enrolled in this study. All patients received ultrasound, fine/core needle aspiration, and PET/CT scan prior to treatment. In accordance with previous studies, we recommended 6 patients who had follicular neoplasm with SUVmax ≥5 undergo surgical resection due to an elevated suspicion of malignancy. For 22 patients SUVmax <5, RFA was performed using the moving shot technique. Ultrasound was performed 6 to 12 months after each procedure.

RESULTS

Statistically significant volume reductions during follow-up between values prior to RFA and 12 months post RFA were demonstrated (12.6 ± 20.9 vs. 2.4 ± 3.0 cm³, p < 0.001). Volume reduction ratios at 6-12 months (mean: 10.1 months) after RFA were 73.3% ± 17.7%. One patient presented with vocal cord palsy and recovered within 3 months after RFA. No postprocedural hypothyroidism occurred in the RFA patients.

CONCLUSIONS

By using PET/CT, we can select patients with low SUV follicular neoplasm. RFA offers a safe and feasible alternative treatment option for patients unsuitable or unwilling to undergo surgery.KEY POINTSBy using positron emission tomography-computed tomography, we can distinguish low SUV follicular neoplasm for radiofrequency ablation.For low SUV follicular neoplasm, RF ablation offers a safe and effective alternative treatment option for patients unsuitable or unwilling to undergo surgery.

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.

Hürthle cell lesions of the thyroid: Progress made and challenges remaining

Hürthle cell-predominant thyroid fine needle aspirations (FNA) are encountered frequently in routine practice, yet they are often challenging to diagnose accurately and are associated with significant interobserver variability. This is largely due to the ubiquity of Hürthle cells in thyroid pathology, ranging from nonneoplastic conditions to aggressive malignancies. Although limitations in cytomorphologic diagnoses likely will remain for the foreseeable future, our knowledge of the molecular pathogenesis of Hürthle cell neoplasia and application of molecular testing to cytologic material have increased dramatically within the past decade. This review provides context behind the challenges in diagnosis of Hürthle cell lesions and summarizes the more recent advances in diagnostic tools.

Multimodal imaging of thyroid cancer

PURPOSE OF REVIEW

Thyroid cancer is the most common endocrine cancer in adults with rising incidence. Challenges in imaging thyroid cancer are twofold: distinguishing thyroid cancer from benign thyroid nodules, which occur in 50% of the population over 50 years; and correct staging of thyroid cancer to facilitate appropriate radical surgery in a single session. The clinical management of thyroid cancer patients has been covered in detail by the 2015 guidelines of the American Thyroid Association (ATA). The purpose of this review is to state the principles underlying optimal multimodal imaging of thyroid cancer and aid clinicians in avoiding important pitfalls.

RECENT FINDINGS

Recent additions to the literature include assessment of ultrasound-based scoring systems to improve selection of nodules for fine needle biopsy (FNB) and the evaluation of new radioactive tracers for imaging thyroid cancer.

SUMMARY

The mainstay of diagnosing thyroid cancer is thyroid ultrasound with ultrasound-guided FNB. Contrast-enhanced computed tomography and PET with [F]-fluorodeoxyglucose (FDG) and MRI are reserved for advanced and/or recurrent cases of differentiated thyroid cancer and anaplastic thyroid cancer, while [F]FDOPA and [Ga]DOTATOC are the preferred tracers for medullary thyroid cancer.

Comparison of 18F-FDG-PET and 18F-FDG-PET/CT for the diagnostic performance in thyroid nodules with indeterminate cytology: A meta-analysis

BACKGROUNDS

We performed a meta-analysis to compare F-FDG-PET and F-FDG-PET/CT for the diagnostic performance in thyroid nodules with indeterminate cytology by Bethesda classification.

METHODS

PubMed and Embase databases were searched for eligible studies from the earliest available date of indexing through September 2019. Only studies with clearly stated histopathology confirmation were included. Publication bias was assessed by Deeks funnel plot. The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value, negative predictive value, and diagnostic odds ratio was determined by random-effect analysis, respectively. All diagnostic estimate indexes were determined separately for PET alone and PET/CT and were compared pair-wisely using Z-test.

RESULTS

We included 214 patients from five PET alone studies and 420 patients from 8 PET/CT studies in this meta-analysis. The range of the prevalence of malignancy was 11% to 27% for PET alone studies (Median, 20%) and 4% to 50% for PET/CT studies (Median, 24%). The sensitivity (0.95 vs 0.73, P < .01), negative likelihood ratio (0.20 vs 0.53, P = .04) and negative predictive value (0.99 vs 0.91, P < .01) of PET alone are significantly better than those of PET/CT. For PET/CT, Fagan nomogram indicated that when the pre-test probability was set at 24%, the negative post-test probability could decrease to 12%.

CONCLUSION

This meta-analysis reveals that in evaluating thyroid nodules with indeterminate cytology by Bethesda classification, the rule-out performance of F-FDG-PET is significantly better than F-FDG-PET/CT, although the latter represents a more objective and accurate technique. We hypothesize that the lack of precise localization of suspicious FDG uptake in the neck region may have contributed to this overvaluation for PET alone studies, and advocate that future studies be performed with PET/CT rather than PET alone to avoid misinterpretation and overvaluation in this scenario.