18F-FDG–Avid Thyroid Incidentalomas: The Importance of Contextual Interpretation

FDG-avid thyroid nodules are at a significantly increased risk of malignancy

BACKGROUND

FDG-avid thyroid incidentalomas pose a diagnostic challenge due to their potential for malignancy. This study evaluated the malignancy rates in FDG-avid thyroid nodules, stratified by fine needle aspiration (FNA) cytology results.

METHODS

A retrospective cohort study was conducted on patients with FDG-avid thyroid incidentalomas who underwent surgical resection between 2012 and 2023. The primary outcome was malignancy rates stratified by pre-operative cytology results. Logistic regression was used to assess the utility of patient age, gender and nodule size for predicting malignancy in FDG-avid thyroid incidentaloma.

RESULTS

Of 258 patients included, malignancy rates stratified by cytology were: Bethesda I (15.4 ​%), Bethesda II(11.1 ​%), Bethesda III(29.1 ​%), Bethesda IV(34 ​%), Bethesda V (83.3 ​%), and Bethesda VI (98.3 ​%). The overall malignancy rate was 48.1 ​%, predominantly papillary thyroid carcinoma. No significant differences in malignancy were observed concerning age, gender, or nodule size.

CONCLUSION

FDG-avid thyroid nodules exhibit a significantly higher risk of malignancy, particularly in Bethesda categories III to VI.

The Role of Positron Emission Tomography/Computed Tomography in the Management of Differentiated Thyroid Cancer: Current Applications and Future Perspectives

Differentiated thyroid cancer (DTC), comprising papillary and follicular thyroid carcinoma, is the most common thyroid malignancy and typically has a favourable prognosis when detected early. Positron emission tomography/computed tomography (PET/CT) has emerged as a valuable imaging modality, integrating metabolic and anatomical data. Although PET/CT is not usually part of the initial diagnostic process due to DTC's indolent nature and low metabolic activity, it plays an essential role in selected clinical scenarios. This includes identifying recurrence in patients with elevated thyroglobulin (Tg) levels and negative radioactive iodine (RAI) scans, evaluating metastatic disease, and guiding treatment in advanced cases. As the use of PET/CT evolves in oncology, this review explores its application in regard to staging, detection of recurrence, and follow-up in terms of managing DTC while also evaluating potential challenges that may occur in the future. The review also considers emerging radiotracers and the theragnostic potential of PET/CT.

Consensus statement on the management of incidentally discovered FDG avid thyroid nodules in patients being investigated for other cancers

With the widespread use of 18F-fluorodeoxyglucose positron emission tomography (FDG PET/CT) in the investigation and staging of cancers, incidental discovery of FDG-avid thyroid nodules is becoming increasingly common, with a reported incidence in the range 1%-4% of FDG PET/CT scans. The risk of malignancy in an incidentally discovered FDG avid thyroid nodule is not clear due to selection bias in reported retrospective series but is likely to be less than 15%. Even in cases where the nodule is found to be malignant, the majority will be differentiated thyroid cancers with an excellent prognosis even without treatment. If, due to index cancer diagnosis, age and co-morbidities, it is unlikely that the patient will survive 5 years, further investigation of an incidental FDG avid thyroid nodule is unlikely to be warranted. We provide a consensus statement on the circumstances in which further investigation of FDG avid thyroid nodules with ultrasound and fine needle aspiration might be appropriate.

Role of [18F]FDG PET/CT in the management of follicular cell-derived thyroid carcinoma

Follicular cell-derived thyroid carcinomas constitute the majority of thyroid malignancies. This heterogeneous group of tumours includes well differentiated, poorly differentiated, and undifferentiated forms, which have distinct pathological features, clinical behaviour, and prognosis. Positron emission tomography with 2-[18F]fluoro-2-deoxy-D-glucose combined with computed tomography ([18F]FDG PET/CT) is an imaging modality used in routine clinical practice for oncological patients. [18F]FDG PET/CT has emerged as a valuable tool for identifying patients at high risk of poor clinical outcomes and for facilitating individualized clinical decision-making. The aim of this comprehensive review is to summarize current knowledge regarding the role of [18F]FDG PET/CT in primary diagnosis, treatment, and follow-up of follicular cell-derived thyroid carcinomas considering the degree of differentiation. Controversial issues, including significance of accidentally detected [18F]FDG uptake in the thyroid, the role of [18F]FDG PET/CT in the early assessment of response to molecular targeted therapies, and its prognostic value are discussed in detail.

Exceptionally Rare Isolated Thyroidal Metastasis of Pulmonary Carcinosarcoma: A Tale of 18F-FDG-positive Thyroid Nodule

Pulmonary carcinosarcomas (PCS) are uncommon and aggressive malignant tumors with epithelial and mesenchymal components and have a worse prognosis than other non-small-cell lung cancers. Metastases of non-thyroidal malignancies to the thyroid are rare. We reported a unique case of isolated thyroidal metastasis of PCS and discussed 18F-fluorodeoxyglucose (18F-FDG) positivity in incidentally found thyroid nodules on 18F-FDG positron emission tomography scan.

Incidentally detected 18 F-FDG PET-CT-avid thyroid nodules in patients with advanced malignancy: long-term oncological outcomes from a single-centre retrospective cohort

OBJECTIVES

In this retrospective study, we assessed the clinical outcomes of patients with a primary malignancy who had incidentally detected thyroid avidity on their staging 18 F-fluorodeoxyglucose PET-computed tomography ( 18 F-FDG PET-CT) examinations.

METHODS

A focused retrospective search was made using a Radiology Information System to identify only patients with positive thyroid nodules on their 18 F-FDG PET-CT imaging between January 2012 and December 2017. Patient demographics, principal oncological diagnosis, and stage were recorded. The sonographic appearances of thyroid nodules, number of fine needle aspiration (FNA) attempts, final cytology, management plan, and clinical outcome were recorded. Follow-up records were available for between 2 and 7 years.

RESULTS

Following exclusions, 136 patients were found to have incidental thyroid avidity on their 18 F-FDG PET-CT. A total of 50 of these patients proceeded to thyroid ultrasound assessment. Of these, 37 patients underwent FNA (average 1.3 FNA attempts) with 17 having atypical cytology and 6 diagnosed with an incidental thyroid cancer either by FNA or thyroidectomy. Four patients who underwent surgery had benign pathology. All thyroid cancers identified were indolent papillary cancers without any impact on the treatment plan or survival.

CONCLUSION

The clinical outcomes of patients with an established primary malignancy are determined by their primary cancer and not by incidentally detected thyroid cancer. It may therefore be reasonable not to formally investigate a proportion of incidental 18 F-FDG PET-CT positive thyroid nodules where added benefit is unlikely. In such cases, a 'watch-and-wait' approach to the thyroid might be considered more appropriate.

Prediction of Malignant Thyroid Nodules Using 18 F-FDG PET/CT-Based Radiomics Features in Thyroid Incidentalomas

OBJECTIVE

The purpose of the current study was to evaluate the diagnostic performances of 18 F-FDG PET/CT-based radiomics features for prediction of malignant thyroid nodules (TNs) in thyroid incidentaloma (TI).

METHODS

PubMed, Cochrane database, and EMBASE database, from the earliest available date of indexing through December 31, 2022, were searched for studies evaluating diagnostic performance of 18 F-FDG PET/CT-based radiomics features for prediction of malignant TNs in TI. We determined the sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LRs; positive and negative LRs), and estimated pooled area under the curve.

RESULTS

Across 5 studies (518 patients), the pooled sensitivity of 18 F-FDG PET/CT was 0.77 (95% confidence interval [CI], 0.67-0.84), and a pooled specificity was 0.67. Likelihood ratio syntheses gave an overall positive LR of 2.3 (95% CI, 1.5-3.6) and negative LR of 0.35 (95% CI, 0.26-0.47). The pooled diagnostic odds ratio was 7 (95% CI, 4-12). The pooled area under the curve of fixed effects was 0.763 (95% CI, 0.736-0.791), and that of random effects was 0.763 (95% CI, 0.721-0.805).

CONCLUSION

18 F-FDG PET/CT-based radiomics features showed a good diagnostic performance for prediction of malignant TNs in TI.

Clinical Characteristics, Diagnostic Approach and Outcome of Thyroid Incidental Findings vs. Clinically Overt Thyroid Nodules: An Observational Single-Centre Study

Context: Thyroid nodules are common and can present as clinically overt nodules (visible, palpable or symptomatic nodules) and so-called incidentalomas (coincidental findings on imaging techniques). The majority are benign but recognizing clinically relevant nodules remains a challenge. Current Dutch guidelines recommend to refrain from additional diagnostic testing in incidentalomas other than FDG-PET-incidentalomas, unless there are suspicious clinical and/or sonographic features. However, there is no consensus on the further approach and no "real-life" data on the outcome of such an approach. Objective: To compare clinical characteristics, diagnostic approaches and clinical outcome between patients referred with thyroid incidentalomas and non-incidentalomas at one academic referral thyroid clinic. Methods: Clinical and demographical characteristics, diagnostic and therapeutic approaches and outcome were retrospectively obtained from the files of all patients newly referred because of thyroid incidentalomas or non-incidentalomas to our institution (between March 2011 and January 2017). Subsequently, the data were compared between both groups. Results: In total, 351 patients (64.3%) were referred because of non-incidentalomas and 195 (35.7%) because of incidentalomas. Incidentalomas were smaller (48.7% <2 cm) than non-incidentalomas (23.4% <2 cm). Furthermore, incidentalomas were less often symptomatic (15.9 vs. 42.7% p < 0.001). Fine-needle aspiration was performed in a similar percentage of the patients in the two groups (62.6% of incidentalomas vs. 69.8% in non-incidentaloma, p = 0.08). Significantly less malignancies were found among incidentalomas compared to non-incidentalomas (5.1% vs. 11.1%, p = 0.019). Moreover, significantly more malignancies occurred in PET-incidentalomas than non-PET-incidentalomas (11.8% vs. 2.8%, p = 0.023). In fact, the proportion of malignancies in PET-incidentalomas and non-incidentalomas was similar (11.8% vs. 11.1%, p = 0.895). Stability or decrease in size was observed in 96.5% of nodules receiving ultrasound follow-up. Conclusions: Patients with small asymptomatic thyroid incidentalomas represent an important proportion of the patients referred for additional diagnostic evaluation. The risk of malignancy in these patients is lower than in those with symptomatic palpable lesions, particularly in the patients with incidentalomas discovered on CT, MRI or US. Our findings support the current recommendations from the Dutch guidelines to not indiscriminately perform additional analysis and treatment on all incidentalomas, but prioritize this to FDG-PET-incidentalomas and clinically relevant non-PET-incidentalomas. Moreover, US features can further refine the selection of the patients who require immediate FNAC and/or surgery.

Incidentalomas in the head & neck

Incidental findings (IFs) in the head & neck are a frequent challenge to the reporting radiologist. A combination of complex anatomy, widely varied imaging techniques and the high prevalence of benign pathology, makes safe and appropriate management of head & neck IFs problematic. The non-head & neck radiologist is unlikely to have prior personal experience of the relevant specialties or current involvement with the pertinent multidisciplinary teams, creating unfamiliarity with both the clinical aspects of head & neck disease and the value of examination techniques. This triumvirate of complex anatomy, pathology and imaging creates the perfect environment for excessive investigation and overdiagnosis. In this article, the most frequently encountered and clinically relevant head & neck IFs are summarised. To reflect daily clinical practice, we will firstly consider anatomic abnormalities identified on cross-sectional imaging and ultrasound, followed by a review of PET-CT incidental findings.

The FDG Pattern of Autonomously Functioning Thyroid Nodules Correlates With Thyroid-Stimulating Hormone and Histopathology

PURPOSE OF THE REPORT

Whereas the 18 F-FDG PET/CT pattern of malignant thyroid neoplasia is known, the glucose uptake of autonomously functioning thyroid nodules (AFTNs) has not been fully investigated. We aimed to analyze the FDG uptake of AFTNs and its correlation with clinical, laboratory, ultrasonography, and histological features.

METHODS

We retrospectively analyzed the records of all AFTN patients from 2 centers, in which an 18 F-FDG PET/CT, thyroid function tests, and neck ultrasound were available within a 3-month window from the thyroid scintigraphy. Forty-five patients (35 female patients; median age, 65 years) were retrospectively included. The presence of FDG uptake was compared with the laboratory data and, whenever available, the histology.

RESULTS

Over a 36-month follow-up, 20 patients underwent surgery; 4 cancers, 10 follicular adenomas, and 6 follicular hyperplasias were found. Twenty-two AFTNs (48.9%) were FDG-positive, whereas the remaining 23 (51.1%) were not. Thyroid-stimulating hormone (TSH) was significantly lower in FDG-positive AFTNs than in negative ones (0.055 [0.02-0.42] vs 0.65 [0.2-0.96] mIU/L, P = 0.0018). On multivariate analysis, only TSH was independently associated with FDG uptake ( P = 0.008). On receiver operating characteristic curve analysis, TSH <0.08 mIU/L indicated FDG-positive AFTNs, with 64% sensitivity, 87% specificity, 4.88 positive likelihood ratio, and 0.42 negative likelihood ratio. In histologically proven benign lesions, TSH was significantly lower in follicular adenomas than in follicular hyperplasias ( P < 0.001). Patients with cancer had TSH in the low-normal range.

CONCLUSIONS

Autonomously functioning thyroid nodules show heterogeneous uptake FDG pattern, which depends on histopathology and thyroid function. Particularly, follicular adenomas tend to display increased glucose uptake and suppressed TSH.

Radiomics Analysis of [18F]FDG PET/CT Thyroid Incidentalomas: How Can It Improve Patients’ Clinical Management? A Systematic Review from the Literature

Background: We performed a systematic review of the literature to provide an overview of the application of PET-based radiomics of [18F]FDG-avid thyroid incidentalomas and to discuss the additional value of PET volumetric parameters and radiomic features over clinical data. Methods: The most relevant databases were explored using an algorithm constructed based on a combination of terms related to our subject and English-language articles published until October 2021 were considered. Among the 247 identified articles, 19 studies were screened for eligibility and 11 met the criteria, with 4 studies including radiomics analyses. Results: We summarized the available literature based on a study of PET volumetric parameters and radiomics. Ten articles provided accurate details about volumetric parameters and their prospective value in tumour assessment. We included the data provided by these articles in a sub-analysis, but could not obtain statistically relevant results. Four publications analyzed the diagnostic potential of radiomics and the possibility of creating precise predictive models, their corresponding quality score being assessed. Conclusions: The use of PET volumetric parameters and radiomics analysis in patients with [18F]FDG-avid thyroid incidentalomas outlines a great prospect in diagnosis and stratification of patients with malignant nodules and may represent a way of limiting the need for unnecessary invasive procedures; however, further studies need to be performed for a standardization of the method.

Retrospective Analyses of 18FDG-PET/CT Thyroid Incidentaloma in Adults: Incidence, Treatment, and Outcome in a Tertiary Cancer Referral Center

Background: A thyroid incidentaloma (TI) is an unexpected, asymptomatic thyroid lesion discovered during the investigation of an unrelated condition. The aim of the present study is to examine the incidence of ¹⁸Fluorodeoxyglucose (FDG)-positron emission tomography (PET) TI, the associated management strategies and the outcomes in a tertiary cancer referral center. Methods: This study involves a retrospective cohort study of 1003 patients with TI found on ¹⁸FDG-PET/CT scans performed between January 2010 and January 2020 for a nonthyroidal malignancy. The Kaplan-Meier method was used for survival analyses in patients concerning an underlying malignancy, with a prevalence of 5% or higher in this cohort. Logistic- and cox regression analyses were performed to analyze predictors of thyroid malignancy and mortality. A propensity score weighted method was used to control for baseline differences between the intervention (additional TI diagnostics) and control (no TI diagnostics) group. Results: FDG-positive TI occurred in 1.9% (1003/52,693) of the oncologic ¹⁸FDG-PET/CT scans performed in our center. Thyroid surgery was performed in 47 patients (6%) and a thyroid malignancy was detected in 31 of them, which is 66% of those who had an operation and 4% of all patients. During the follow-up (median 6 years), 334 deaths (42%) related to different types of cancer (38%) or other causes (4%) were observed. One patient died from medullary thyroid cancer. In multivariate analysis adjusted for age, gender and the type- and stage of nonthyroidal malignancy, were independent predictors of survival (P < .05). Conclusions: The incidence of TI in this tertiary cancer referral center was comparable to current literature. Further thyroid workup was performed in less than half of the patients, and only a minority of patients underwent thyroid surgery. Since only one patient died from thyroid cancer, the strategy to withhold from thyroid diagnostics and treatment seems valid for most TI. Active thyroid treatment might benefit a subgroup of patients in whom the primary nonthyroidal malignancy is successfully treated or presumably stable. A wait-and-see policy with ultrasound follow-up could be an alternative strategy. These considerations should be part of the shared decision making in cancer patients with a TI.

The dilemma of 18F-FDG PET/CT thyroid incidentaloma: what we should expect from FNA. A systematic review and meta-analysis

PURPOSE

¹⁸F-FDG thyroid incidentaloma (TI) occurs in ~2% of PET/CT examinations with a cancer prevalence of up to 35-40%. Guidelines recommend fine-needle aspiration cytology (FNA) if a focal ¹⁸F-FDG TI corresponds to a sonographic nodule >1 cm. The aim of this systematic review and meta-analysis was to provide evidence-based data on the diagnostic distribution of ¹⁸F-FDG TIs in the six Bethesda systems for reporting thyroid cytopathology (BETHESDA) subcategories.

METHODS

Original studies reporting ¹⁸F-FDG TIs and cytologically classified according to BETHESDA were included. Six separate meta-analyses were performed to obtain the pooled prevalence (95% confidence interval, 95% CI) of ¹⁸F-FDG TIs in the six BETHESDA subcategories.

RESULTS

Fifteen studies were finally included. Nine studies were from Asian/Eastern and six from Western countries. FNA data according to BETHESDA was available in 2304 cases. The pooled prevalence of ¹⁸F-FDG TIs according to BETHESDA was BETHESDA I 10% (6-14), BETHESDA II 45% (37-53), BETHESDA III 8% (3-13), BETHESDA IV 8% (5-12), BETHESDA V 6% (4-9), BETHESDA VI 19% (13-25). A significantly different prevalence was found in the BETHESDA IV between Asian/Eastern (2%) and Western (19%) studies.

CONCLUSION

Two-thirds of focal ¹⁸F-FDG TIs undergoing FNA have either malignant (BETHESDA VI) or benign (BETHESDA II) cytology while a minority will have indeterminate (BETHESDA III or IV) FNA results. Significant differences between Asian/Eastern and Western studies are also present in the prevalence of indeterminate FNA results.

Characteristics of malignant thyroid lesions on [18F] fluorodeoxyglucose (FDG)-Positron emission tomography (PET)/Computed tomography (CT)

Objectives

To determine the imaging variables that can best differentiate malignant from benign thyroid lesions incidentally found on F-18 FDG PET/CT scans.

Methods

All F-18 FDG PET/CT studies starting from 2011 to end of 2016 were reviewed for incidental thyroid lesions or metabolic abnormalities. Only patients who were found to have FNAB or histopathology were included. Patients with known thyroid malignancy were excluded. Patients were analyzed for age, sex, SUVmax, non-enhanced CT tissue density in mean Hounsfield units (HU), uptake pattern (focal or diffuse) and gland morphology (MNG or diffuse). A control group of 15 patients with normal thyroid glands were used to assess the tissue density in HU for normal thyroid tissue. Sensitivity, specificity, PPV, NPV and accuracy to detect malignancy were calculated. Pearson Chi-square test was used to compare categorical variables while unpaired T-test and one way ANOVA test were used to compare means of continuous variables. ROC analysis was used to assess the best cut off points for SUVmax and HU. Regression analysis was used to detect the independent predictors for malignant lesions.

Results

Biopsy was unsatisfactory or indeterminate in 4/48 patients (8%). Only 44 patients (mean age 55.2 ± 14.7; 30 females (68 %)) with unequivocal FNAB or histopathology were included for further analysis. MNG was noted in 17/44 patients (38.6 %). Thyroid malignancy was found in 16/44 (36.4 %), benign thyroid lesions in 28/44 (63.6 %). Thyroid malignancies were 12 papillary, 1 follicular, 1 Hurthle cell neoplasm and 2 lymphoma. Benign lesions were 23 benign follicular or colloid nodules and 5 autoimmune thyroiditis. Focal FDG uptake pattern was more frequently associated with malignant lesions compared to benign lesions (75 % vs. 43 %; p = 0.039). The mean SUVmax and tissue density (HU) were both higher in malignant than benign lesions (8.8 ± 8.3 vs. 3.6 ± 1.9, p = 0.024) and (48.9 ± 12.7 vs. 32.9 ± 17.5, p = 0.003) respectively. The mean HU in the control group with normal thyroid tissue was 90 ± 7.4 significantly higher than in both the benign and malignant lesions (p < 0.001). ROC analysis revealed SUVmax cutoff of >4.7 and HU cutoff of >42 to best differentiate malignant from benign lesions. The sensitivity, specificity, PPV, NPV and accuracy to detect malignancy for SUVmax>4.7 were 68.8 %, 78.6 %, 64.8 %, 81.5 & 75.0 % (p = 0.002), for HU > 42 were 81.3.0 %, 75.0 %, 65.0 %, 87.5 & 77.3 % (p = 0.0003) and for both parameters combined were 87.5 %, 60.7 %, 56.0 %, 89.5 % and accuracy of 70.5 % (p = 0.002) respectively. Only HU > 42 and SUVmax>4.7 were independent predictors for malignancy with odd ratios 8.98 and 4.93 respectively.

Conclusion

A higher tissue density (HU > 42) and SUVmax>4.7 as well as tendency for focal uptake pattern are the most significant characteristics associated with malignant thyroid lesions occasionally detected on PET/CT.

Update on the Evaluation of Thyroid Nodules

Thyroid nodules (TN) are prevalent in the general population and represent a common complaint in clinical practice. Most are asymptomatic and are associated with a 7%-15% risk of malignancy (1). Methods: PubMed and Medline were searched for articles with a focus on the epidemiology, diagnosis, and management of TN over the past 5 y. Results: The increase in frequency of imaging has led to a rise in the incidence of incidentally diagnosed TN. The initial evaluation of a TN includes assessing thyroid function, clinical risk factors, and neck imaging. Ultrasound remains the gold standard for assessing TN morphology, and biopsy is the standard method for determining whether a TN is benign. Recently published risk stratification systems using morphologic characteristics on ultrasonography have been effective in reducing the number of unnecessary biopsies. Advances in molecular testing have reduced the number of surgical procedures performed for diagnostic purposes on asymptomatic TN with indeterminate cytology. Scintigraphy is the first-line study for assessing a hyperfunctioning nodule. Many TN can be followed clinically or with serial ultrasound after the initial diagnosis. Surgical intervention is warranted when local symptoms are present, in patients with clinical risk factors, as well as in most situations with malignant cytology. Active surveillance is an option in cases of micropapillary thyroid cancer. Emerging nonsurgical approaches for treating TN include ethanol ablation for TN; sclerotherapy for thyroid cysts; and thermal techniques, such as radiofrequency ablation, laser ablation, microwaves, and high-intensity focused ultrasound. Conclusion: Most TN are benign and can be safely monitored. The indications for biopsy and frequency of imaging should be tailored on the basis of risk stratification. Treatment options should be individualized for each patient's particular situation. Active surveillance should be considered in certain cases of papillary microcarcinoma.

Is sonographic intra-nodular vascularity a reliable predictor of thyroid malignancy? A UK tertiary centre study

OBJECTIVE

British Thyroid Association 2014 guidelines emphasised ultrasound assessment of nodules. One ultrasonographic differentiator of debatable relevance is intra-nodular vascularity. This is the first UK study conducted to address this question.

METHODS

Ultrasound reports for thyroid surgery patients over 10 years were retrospectively reviewed. Reports documenting 'intra-nodular vascularity or flow' were analysed. Reports identifying peripheral vascularity only or no intra-nodular flow formed the control group. Concordance with final histology was used to determine the odds ratio for malignancy.

RESULTS

A total of 306 patients were included, and 119 (38.9 per cent) nodules demonstrated intra-nodular vascularity. Of these, 60 (50.4 per cent) were malignant compared with 42 per cent in the control group. Intra-nodular vascularity was not a statistically significant predictor of malignancy with an odds ratio of 1.39 (p = 0.18, 95 per cent confidence interval, 0.86-2.23).

CONCLUSION

Intra-nodular vascularity in isolation was not a reliable predictor of malignancy. This supports other world literature studies. Although intra-nodular flow should not be relied upon in isolation, interpretation in conjunction with other suspicious findings enhances the predictive value.

Long-Term Follow-Up of Thyroid Incidentalomas Visualized with 18F-Fluorodeoxyglucose Positron Emission Tomography-Impact of Thyroid Scintigraphy in the Diagnostic Work-Up

Our objective was to evaluate the frequency of malignancy in incidental thyroidal uptake on 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in a cohort of Danish patients, and furthermore to evaluate the impact of thyroid scinti-graphy in the diagnostic work-up. All whole-body PET/CT reports from 1 January 2010 to 31 December 2013 were retrospectively reviewed and further analyzed if visually increased thyroidal FDG uptake was reported. Patient electronic files were searched for further thyroid evaluation. Of 13,195 18F-FDG-PET/CT scans in 9114 patients, 312 PET/CT reports mentioned incidental thyroid FDG-uptake, and 279 patients were included in the study (3.1%). The thyroid was further investigated in 137 patients (49%), and 75 patients underwent thyroid scintigraphy. A total of 57 patients had a thyroid biopsy and 21 proceeded to surgery. Surgical specimens displayed malignancy in 10 cases, and one thyroid malignancy was found by autopsy. Hence, 11 patients were diagnosed with thyroid malignancies among 279 patients with incidental thyroid 18F-FDG uptake (3.9%). In 34 patients, a biopsy was avoided due to the results of the thyroid scintigraphy. We conclude that patients with thyroid incidentalomas can benefit from further diagnostic work-up including a thyroid scintigraphy.

Focal Thyroid Incidentalomas on 18F-FDG PET/CT: A Systematic Review and Meta-Analysis on Prevalence, Risk of Malignancy and Inconclusive Fine Needle Aspiration

BACKGROUND

The rising demand for ¹⁸F-fluorodeoxyglucose positron emission tomography with computed tomography (¹⁸F-FDG PET/CT) has led to an increase of thyroid incidentalomas. Current guidelines are restricted in giving options to tailor diagnostics and to suit the individual patient.

OBJECTIVES

We aimed at exploring the extent of potential overdiagnostics by performing a systematic review and meta-analysis of the literature on the prevalence, the risk of malignancy (ROM) and the risk of inconclusive FNAC (ROIF) of focal thyroid incidentalomas (FTI) on ¹⁸F-FDG PET/CT.

DATA SOURCES

A literature search in MEDLINE, Embase and Web of Science was performed to identify relevant studies.

STUDY SELECTION

Studies providing information on the prevalence and/or ROM of FTI on ¹⁸F-FDG PET/CT in patients with no prior history of thyroid disease were selected by two authors independently. Sixty-one studies met the inclusion criteria.

DATA ANALYSIS

A random effects meta-analysis on prevalence, ROM and ROIF with 95% confidence intervals (CIs) was performed. Heterogeneity and publication bias were tested. Risk of bias was assessed using the quality assessment of diagnostic accuracy studies (QUADAS-2) tool.

DATA SYNTHESIS

Fifty studies were suitable for prevalence analysis. In total, 12,943 FTI were identified in 640,616 patients. The pooled prevalence was 2.22% (95% CI = 1.90% - 2.54%, I² = 99%). 5151 FTI had cyto- or histopathology results available. The pooled ROM was 30.8% (95% CI = 28.1% - 33.4%, I² = 57%). 1308 (83%) of malignant nodules were papillary thyroid carcinoma (PTC). The pooled ROIF was 20.8% (95% CI = 13.7% - 27.9%, I² = 92%).

LIMITATIONS

The main limitations were the low to moderate methodological quality of the studies and the moderate to high heterogeneity of the results.

CONCLUSION

FTI are a common finding on ¹⁸F-FDG PET/CTs. Nodules are malignant in approximately one third of the cases, with the majority being PTC. Cytology results are non-diagnostic or indeterminate in one fifth of FNACs. These findings reveal the potential risk of overdiagnostics of FTI and emphasize that the workup of FTI should be performed within the context of the patient's disease and that guidelines should adopt this patient tailored approach.

Radiomics Analysis of [18F]-Fluorodeoxyglucose-Avid Thyroid Incidentalomas Improves Risk Stratification and Selection for Clinical Assessment

Background: [¹⁸F]-Fluorodeoxyglucose (FDG)-avid thyroid lesions incidentally detected on positron emission tomography/computed tomography (PET/CT) scans represent a tumor lesion in about 30% of cases. The present study evaluated the ability of PET metrics and radiomics features to predict final diagnosis of [¹⁸F]FDG thyroid incidentalomas (TIs). Methods: A total of 104 patients with 107 TIs were retrospectively studied; 30 nodules (28%) were diagnosed as malignant. After volumetric segmentation of each thyroid lesion, metabolic tumor volume (MTV), total lesion glycolysis (TLG), standardized uptake values (SUVs), and metabolic heterogeneity were estimated, and 107 radiomics features were extracted following a standard protocol. Results: MTV, TLG, SUVmax, SUVmean, and SUVpeak among functional PET parameters, and gray-level co-occurrence matrix (GLCM)_InverseDifferenceMoment, shape_Sphericity, GLCM_SumSquares, firstorder_Maximum2DDiameterSlice, firstorder_Energy, and GLCM_Contrast among nonredundant radiomics features, showed significantly different values between malignant and benign TIs (Mann-Whitney U-test, p < 0.01 for all). Univariate logistic regression revealed that these parameters demonstrated good ability to predict final diagnosis of TIs (p < 0.02 for all). Shape_Sphericity was the best predictor classifying 82% of TIs correctly (p < 0.0001). Only TLG, SUVmax, and shape_Sphericity retained significance (p < 0.0001) by multivariate analysis. Malignant lesion prevalence increased from 7% to 100% in accordance with the number (score, 0-3) of the three positive parameters present (χ² trend, p < 0.0001). A score of 0 excludes malignant TIs with a negative predictive value of 93%, while a score of 3 predicted malignancy with a positive predictive value of 100%. Conclusions: PET metrics and radiomics analysis can improve identification of [¹⁸F]FDG-avid TIs at high risk of malignancy. A model based on TLG, SUVmax, and shape_Sphericity may allow prediction of a final diagnosis, providing useful information for the management of TIs.

Updated Review of Nuclear Molecular Imaging of Thyroid Cancers

OBJECTIVES

We initiate this comprehensive review to update the advances in this field by objectively elucidating the efficacies of promising radiopharmaceuticals.

METHODS

We performed a comprehensive PUBMED search using the combined terms of "thyroid cancer" and "radiopharmaceuticals" or "nuclear medicine", yielding 3273 and 11026 articles prior to December 31, 2020, respectively.

RESULTS

Based on the mechanism of molecular metabolism, the evaluation of differentiated thyroid cancer and dedifferentiated thyroid cancer is largely centered around radioiodine and fluorine 18 (¹⁸F)-fludeoxyglucose, respectively. Further, ¹⁸F-L-dihydroxyphenylalanine and gallium 68 DOTATATE are the preferred tracers for medullary thyroid cancer. In dedifferentiated medullary thyroid cancer and anaplastic thyroid cancer, ¹⁸F-fludeoxyglucose is superior.

CONCLUSIONS

The future lies in advances in molecular biology, novel radiopharmaceuticals and imaging devices, paving ways to the development of personalized medication for thyroid cancer patients.

Risk Stratification of 18F-Fluorodeoxyglucose-Avid Thyroid Nodules Based on ACR Thyroid Imaging Reporting and Data System

OBJECTIVE

Fine needle aspiration (FNA) of thyroid nodules is often requested based on ¹⁸F-fluorodeoxyglucose (FDG) uptake regardless of sonographic features. The purpose of this study is to determine the risk of malignancy in FDG-avid thyroid nodules when stratified according to the ACR Thyroid Imaging Reporting and Data System (TI-RADS).

METHODS

This retrospective study included patients who underwent ultrasound-guided FNA between January 1, 2010, and November 19, 2018, and PET/CT within 1 year before the FNA. In all, 170 nodules in 166 patients (65 men, 101 women, age 60.2 ± 14.3 years) were eligible for inclusion, of which 151 had a clearly benign or malignant histology. PET images were reviewed for maximum standardized uptake value and nodule location. Sonographic features and TI-RADS category were determined by three radiologists. Patient charts were reviewed for histology. Statistical analyses included risk of malignancy in FDG-avid nodules within each TI-RADS category.

RESULTS

Of the 151 nodules, 52 were malignant (34.4%). Malignancy risk was 0% in 1 TR1 nodule (compared with 0.3% in the published TI-RADS study), 16.7% in 6 TR2 nodules (compared with 1.5%), 13.2% in 38 TR3 nodules (compared with 4.8%), 23.7% in 59 TR4 nodules (compared with 9.1%), and 68.1% in 47 TR5 nodules (compared with 35.0%).

DISCUSSION

The majority (71%, 121 of 170) of FDG-avid thyroid nodules are TR4 and TR5, with rates of malignancy greater than those in the general TI-RADS population. ACR TI-RADS is helpful in stratification of FDG-avid nodules; the risk of malignancy in sonographically low-suspicion nodules (13.3%, 6 of 45) is significantly lower than high-suspicion nodules (43.4%, 46 of 106, P < .001).

FNA indication according to ACR-TIRADS, EU-TIRADS and K-TIRADS in thyroid incidentalomas at 18F-FDG PET/CT

OBJECTIVE

Focal thyroid incidentaloma (TI) occurs in a 2% of ¹⁸F-FDG PET/CT and about one-third of TIs is cancer. Due to the lack of evidence on the optimal management of TI, current guidelines suggest performing fine-needle aspiration cytology (FNA). The study aim was to evaluate the reliability of ACR-TIRADS, EU-TIRADS, and K-TIRADS in indicating FNA in TIs.

DESIGN

We retrospectively reviewed ¹⁸F-FDG PET/CT TIs recorded during the period 2016-2019. Enrolled were TIs with histologic outcome and autonomous nodules. Cases with uncertain matching between ¹⁸F-FDG PET/CT, US/scintiscan and histology were excluded.

RESULTS

Eighty TIs at ¹⁸F-FDG PET/CT (median size 17 mm, median SUVmax 7.85) were included; a 26.2% was cancer. The percentage of nodules classified as high risk according to ACR-TIRADS, EU-TIRADS, and K-TIRADS was 20%, 30%, and 29.8%, respectively. The cancer prevalence in high-risk class was 56.2%, 66.7%, and 65.2% in ACR-TIRADS, EU-TIRADS, and K-TIRADS, respectively. ACR-TIRADS had the lowest number of cases with FNA indication (48%) and the K-TIRADS, the highest one (75%). Evaluating the reliability of the three systems in indicating FNA, we found a 100% sensitivity and NPV for EU-TIRADS and K-TIRADS; while all the three systems showed poor specificity and PPV.

CONCLUSION

All TIRADSs were reliable to stratify the risk of cancer in focal TI. Comparing their reliability in indicating FNA, we found a good performance of EU-TIRADS and K-TIRADS. Considering the high cancer percentage expected in this setting of patients, those TIRADS with higher propensity to indicate FNA should be preferred.

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.

Evidence-Based Data About Prevalence and Risk of Malignancy of Thyroid Incidentalomas Detected by Different PET Radiopharmaceuticals

Background:

To date, several meta-analyses and systematic reviews have reported data about the prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals.

Objective:

This article aims to summarize the published evidence-based data about the prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals.

Methods:

A comprehensive computer literature search of systematic reviews and meta-analyses published up to July 2019 in PubMed/MEDLINE and Cochrane library databases regarding the prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals was carried out.

Results:

We have summarized the data about prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals (fluorine-18 fluorodeoxyglucose, radiolabelled choline and prostate-specific membrane antigen) taking into account 8 evidence-based articles.

Conclusion:

Evidence-based data demonstrated that thyroid incidentalomas detected by different PET radiopharmaceuticals are not infrequent and their risk of malignancy is not negligible, in particular if focal pattern is evident at PET, thus requiring further clinical and instrumental evaluation.

Positron emission tomography-computed tomography-associated incidental neoplasms of the thyroid gland

With the increasing use of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET-CT) scans in oncology, the finding of thyroid incidentalomas, also popularly described as PET-associated incidental neoplasms (PAINs) of the thyroid gland is not unusual. The ¹⁸F-FDG PET-CT scans of all patients who underwent imaging for indications other than thyroid malignancy at our tertiary care center between January 1 and December 31, 2017, were retrospectively reviewed for PAINs of the thyroid. A total of 1737 ¹⁸F-FDG PET-CT scans were done at our center in the year 2017. 288 thyroid incidentalomas were detected in the said period; the rate of PET-CT-detected thyroid incidentalomas being 16.58%, focal incidentalomas among them being 11.7%. Only 29 out of 204 patients (14.21%) with focal thyroid incidentalomas in our cohort underwent an aspiration cytology and/or ultrasound. The rate of malignancy among the PET detected focal thyroid incidentalomas in the cohort of patients with a proven diagnosis was 10.34%. Our study highlights the challenges in the evaluation and management of PAIN in a tertiary care oncology setting. None of the factors studied including nodule size and standardized uptake value predicted the risk of malignancy. Clinicians specializing in the management of thyroid nodules need to understand the clinical significance of the PAIN, and we hope that our unique experience adds to the limited clinical information available in this regard.

Factors influencing incidental 18F-FDG uptake in the gallbladder in a large cohort of patients: A retrospective study

OBJECTIVES

This study aims to assess the incidence of incidental activity in the gallbladder and the factors that may contribute to it in a large cohort of patients undergoing ¹⁸F-fluorodeoxyglucose-PET/CT for cancer evaluation.

METHODS

8096 PET/CTs were retrospectively reviewed. Data pertaining to patient demographics and PET/CT parameters were collected. Patients' records were reviewed for gallbladder disorders for up to 3 years after the exam. The presence/absence of gallbladder uptake was visually assessed. Findings were classified as focal, diffuse increased and diffuse increased wall uptake, or no uptake. Volumetric measurements of the gallbladder and SUVmax of the gallbladder, liver and blood pool were measured. Chi-square and Student's t-test were used for statistical analysis.

RESULTS

54 cases (0.67%) of incidental gallbladder uptake were detected (uptake group). 162 exams without uptake were selected as control (no uptake group). The injection-to-scan interval, SUVmax of the liver and blood pool, and the gallbladder volume did not differ significantly between both groups. Higher blood glucose levels were observed in the uptake (109.9 ± 32.5) vs. no uptake group (97.4 ± 18) (p = 0.01), with levels >150 mg/dL more common in the uptake group (p = 0.004). The incidence of gallbladder disease within 3 years after imaging was higher for the uptake group (12/36) compared to the no uptake group (15/115) (p = 0.02). Diffuse increased wall uptake was more likely in the group who later developed a pathology (4/12) (p = 0.03).

CONCLUSION

Incidental gallbladder uptake in patients is independent of the injected FDG dose, injection-to-scan interval or gallbladder volume, but may be related to blood glucose level. There's a higher incidence of gallbladder pathology three years after the exam particularly in cases of diffuse increased wall uptake.

Thyroid incidentaloma as a "PAIN" phenomenon- does it always require surgery?

A thyroid nodule discovered during imaging study performed due to unrelated thyroid disease is known as a thyroid incidentaloma, while positron emission tomography (PET) associated incidental neoplasm of thyroid is known as a "PAIN" phenomenon.To evaluate which patients with "PAIN" phenomenon should undergo surgery in regards to cytology results.Retrospective review of 4716 patients consecutively admitted and surgically treated in tertiary surgical center. 49 (1.04%) patients with "PAIN" phenomenon were identified. All of them had ultrasound-guided fine needle aspiration biopsy (UG-FNAB) performed and cytological results were evaluated according to The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). Patients were divided into 2 subgroups according to histopathological diagnosis: group 1 (n = 25) with benign tumor and group 2 (n = 24) with thyroid cancer.Cytology results were the significant predictors of cancer occurrence in patients with "PAIN" phenomenon (P < .0001). Logistic regression analysis confirmed that category III or higher of TBSRTC in patients with "PAIN" phenomenon significantly increased the risk of cancer (OR = 168.7, P < .0001).Patients with "PAIN" phenomenon and cytology assigned to category III or higher of the Bethesda system should undergo surgery due to significant risk of thyroid malignancy.