Indeterminate thyroid nodules. The role of 18F-FDG PET/CT in the "era" of ultrasonography risk stratification systems and new thyroid cytology classifications

18 F-FDG PET/CT in Cystic Papillary Thyroid Carcinoma

ABSTRACT

A 52-year-old woman was evaluated for the appearance of a neck lump and dysphonia. Neck ultrasonography showed a large cystic nodule in the right thyroid lobe, confirmed by fine-needle aspiration cytology. Thyroid function and calcitonin were normal. 18 F-FDG PET/TC showed moderate tracer uptake by the outer ring of the large hypodense formation. Right hemithyroidectomy was performed; since intraoperative histology showed an intracystic and invasive papillary thyroid carcinoma, a completion thyroidectomy was done. Definitive histopathology confirmed the intraoperative findings. 18 F-FDG PET/CT may be a useful imaging procedure in evaluating patients with cystic thyroid nodules whenever clinical/ultrasonographic features are suspicious for malignancy.

Brain Nocardiosis Mimicking Intracerebral Invasion on 68Ga-Pentixafor PET/CT in a Patient With Multiple Myeloma

ABSTRACT

Brain nocardiosis is an uncommon but severe disease associated with high mortality. We present a case of brain nocardiosis with elevated tracer uptake on both 68Ga-pentixafor and 18F-FDG PET/CT, mimicking intracerebral invasion of multiple myeloma. This case demonstrates that nocardiosis should be considered in the differential diagnosis of brain lesions found on PET/CT with increased tracer accumulation in immunocompromised patients.

Detection of malignant lesions in cytologically indeterminate thyroid nodules using a dual-layer spectral detector CT-clinical nomogram

Purpose

To evaluate the capability of dual-layer detector spectral CT (DLCT) quantitative parameters in conjunction with clinical variables to detect malignant lesions in cytologically indeterminate thyroid nodules (TNs).

Materials and methods

Data from 107 patients with cytologically indeterminate TNs who underwent DLCT scans were retrospectively reviewed and randomly divided into training and validation sets (7:3 ratio). DLCT quantitative parameters (iodine concentration (IC), NICP (IC nodule/IC thyroid parenchyma), NICA (IC nodule/IC ipsilateral carotid artery), attenuation on the slope of spectral HU curve and effective atomic number), along with clinical variables, were compared between benign and malignant cohorts through univariate analysis. Multivariable logistic regression analysis was employed to identify independent predictors which were used to construct the clinical model, DLCT model, and combined model. A nomogram was formulated based on optimal performing model, and its performance was assessed using receiver operating characteristic curve, calibration curve, and decision curve analysis. The nomogram was subsequently tested in the validation set.

Results

Independent predictors associated with malignant TNs with indeterminate cytology included NICP in the arterial phase, Hashimoto's Thyroiditis (HT), and BRAF V600E (all p < 0.05). The DLCT-clinical nomogram, incorporating the aforementioned variables, exhibited superior performance than the clinical model or DLCT model in both training set (AUC: 0.875 vs 0.792 vs 0.824) and validation set (AUC: 0.874 vs 0.792 vs 0.779). The DLCT-clinical nomogram demonstrated satisfactory calibration and clinical utility in both training set and validation set.

Conclusion

The DLCT-clinical nomogram emerges as an effective tool to detect malignant lesions in cytologically indeterminate TNs.

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.

Molecular Diagnostics and [18F]FDG-PET/CT in Indeterminate Thyroid Nodules: Complementing Techniques or Waste of Valuable Resources?

Background: An accurate preoperative workup of cytologically indeterminate thyroid nodules (ITN) may rule out malignancy and avoid diagnostic surgery for benign nodules. This study assessed the performance of molecular diagnostics (MD) and 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG)-positron emission tomography/computed tomography (PET/CT) in ITN, including their combined use, and explored whether molecular alterations drive the differences in [18F]FDG uptake among benign nodules. Methods: Adult, euthyroid patients with a Bethesda III or IV thyroid nodule were prospectively included in this multicenter study. They all underwent MD and an [18F]FDG-PET/CT scan of the neck. MD was performed using custom next-generation sequencing panels for somatic mutations, gene fusions, and copy number alterations and loss of heterozygosity. Sensitivity, specificity, negative and positive predictive value (NPV, PPV), and benign call rate (BCR) were assessed for MD and [18F]FDG-PET/CT separately and for a combined approach using both techniques. Results: In 115 of the 132 (87%) included patients, MD yielded a diagnostic result on cytology. Sensitivity, specificity, NPV, PPV, and BCR were 80%, 69%, 91%, 48%, and 57% for MD, and 93%, 41%, 95%, 36%, and 32% for [18F]FDG-PET/CT, respectively. When combined, sensitivity and specificity were 95% and 44% for a double-negative test (i.e., negative MD plus negative [18F]FDG-PET/CT) and 68% and 86% for a double-positive test, respectively. Concordance was 63% (82/130) between MD and [18F]FDG-PET/CT. There were more MD-positive nodules among the [18F]FDG-positive benign nodules (25/59, 42%, including 11 (44%) isolated RAS mutations) than among the [18F]FDG-negative benign nodules (7/30, 19%, p = 0.02). In oncocytic ITN, the BCR of [18F]FDG-PET/CT was mere 3% and MD was the superior technique. Conclusions: MD and [18F]FDG-PET/CT are both accurate rule-out tests when unresected nodules that remain unchanged on ultrasound follow-up are considered benign. It may vary worldwide which test is considered most suitable, depending on local availability of diagnostics, expertise, and cost-effectiveness considerations. Although complementary, the benefits of their combined use may be confined when therapeutic consequences are considered, and should therefore not routinely be recommended. In nononcocytic ITN, sequential testing may be considered in case of a first-step MD negative test to confirm that withholding diagnostic surgery is oncologically safe. In oncocytic ITN, after further validation studies, MD might be considered. Clinical Trial Registration: This trial is registered with ClinicalTrials.gov: NCT02208544 (August 5, 2014), https://clinicaltrials.gov/ct2/show/NCT02208544.

Diagnostic performance of ultrasound risk stratification systems on thyroid nodules cytologically classified as indeterminate: a systematic review and meta-analysis

PURPOSE

Ultrasound (US) risk stratification systems (RSSs) are increasingly being utilized for the optimal management of thyroid nodules, including those with indeterminate cytology. The goal of this study was to evaluate the category-based diagnostic performance of US RSSs in identifying malignancy in indeterminate nodules.

METHODS

This systematic review and meta-analysis was registered on PROSPERO (CRD42021266195). PubMed, EMBASE, and Web of Science were searched through December 1, 2022. Original articles reporting data on the performance of US RSSs for indeterminate nodules were included. The numbers of nodules classified as true negative, true positive, false negative, and false positive were extracted.

RESULTS

Thirty-three studies evaluating 7,225 indeterminate thyroid nodules were included. The diagnostic accuracy was quantitatively synthesized using a Bayesian bivariate model based on the integrated nested Laplace approximation in R. For the intermediate- to high-risk category, the sensitivity levels of the American College of Radiology, the American Thyroid Association, the European Thyroid Association, the Korean Thyroid Association/Korean Society of Thyroid Radiology, and Kwak et al. were found to be 0.80, 0.72, 0.76, 0.96, and 0.97, respectively. The corresponding specificity measurements were 0.36, 0.50, 0.49, 0.28, and 0.17. Furthermore, for the high-risk category, the sensitivity values were 0.40, 0.46, 0.55, 0.47, and 0.10, while the specificity levels were 0.91, 0.90, 0.71, 0.91, and 0.99, respectively.

CONCLUSION

The overall diagnostic performance of the US RSSs was moderate in the differentiation of indeterminate nodules.

PET/CT May Assist in Avoiding Pointless Thyroidectomy in Indeterminate Thyroid Nodules: A Narrative Review

Indeterminate thyroid nodules (ITN) are commonly encountered among the general population, with a malignancy rate of 10 to 40%. However, many patients may be overtreated with futile surgery for benign ITN. To avoid unnecessary surgery, PET/CT scan is a possible alternative to help differentiate between benign and malignant ITN. In this narrative review, the major results and limitations of the most recent studies on PET/CT efficacy (from PET/CT visual assessment to quantitative PET parameters and recent radiomic features analysis) and on cost-effectiveness (compared to other alternatives (such as surgery)) are presented. PET/CT can reduce futile surgery with visual assessment (around 40%; if ITN ≥ 10 mm). Moreover, PET/CT conventional parameters and radiomic features extracted from PET/CT imaging can be associated together in a predictive model to rule out malignancy in ITN, with a high NPV (96%) when certain criteria are met. Even though promising results were obtained in these recent PET/CT studies, further studies are needed to enable PET/CT to become the definitive diagnostic tool once a thyroid nodule is identified as indeterminate.

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.

SFE-AFCE-SFMN 2022 Consensus on the management of thyroid nodules : What is the role of functional imaging and isotopic treatment?

The SFE-AFCE-SFMN 2022 consensus deals with the management of thyroid nodules, a condition that is a frequent reason for consultation in endocrinology. In more than 90% of cases, patients are euthyroid, with benign non-progressive nodules that do not warrant specific treatment. The clinician's objective is to detect malignant thyroid nodules at risk of recurrence and death, toxic nodules responsible for hyperthyroidism or compressive nodules warranting treatment. The diagnosis and treatment of thyroid nodules requires close collaboration between endocrinologists, nuclear medicine physicians and surgeons, but also involves other specialists. Therefore, this consensus statement was established jointly by 3 societies: the French Society of Endocrinology (SFE), French Association of Endocrine Surgery (AFCE) and French Society of Nuclear Medicine (SFMN); the various working groups included experts from other specialties (pathologists, radiologists, pediatricians, biologists, etc.). This section deals with the role of thyroid scintigraphy in the diagnosis of autonomous thyroid nodules, nuclear medicine in nodules with indeterminate cytology and iodine treatment for autonomous thyroid nodules.

Thyroid Nodules with Indeterminate FNAC According to the Italian Classification System: Prevalence, Rate of Operation, and Impact on Risk of Malignancy. An Updated Systematic Review and Meta-analysis

A thyroid nodule classified as indeterminate on fine-needle aspiration cytology (FNAC), hereafter referred to as an indeterminate thyroid nodule (ITN), represents a clinical dilemma. The Italian Consensus for the Classification and Reporting of Thyroid Cytology (ICCRTC) divides ITNs into low- and high-risk categories (i.e., TIR3A and TIR3B, respectively) to better manage patients. This study aimed to achieve high-evidence estimates of the prevalence, rate of operation, and risk of malignancy of ITNs, including TIR3A and TIR3B ITNs. This systematic review was conducted according to MOOSE to retrieve all original studies citing ICCRTC. The last search was performed in February 2022. The risk of bias of the included studies was assessed. Separate proportion meta-analyses were performed with a random-effect model using OpenMeta[Analyst]. The online search processed 271 studies, and 33 were finally considered. First, the cancer prevalence among ITNs was 32.4%. Second, the cancer prevalence among TIR3As was 12.4%, with heterogeneity (I₂ 90%) explained by a linear correlation between sample size and cancer rate (p = 0.009). Third, the cancer prevalence among TIR3Bs was 44.4%, with heterogeneity (I₂ 75%) explained by the inverse correlation between sample size and cancer rate (p = 0.031). Fourth, the prevalence of ITNs, TIR3A, and TIR3B among FNACs was 29.6%, 12.6%, and 12.9%, respectively, with sample size and TIR3B prevalence being inversely correlated (p = 0.04). Fifth, the operation rates of ITNs, TIR3A, and TIR3B were 54.3%, 48.3%, and 75.2%, respectively, and the sample size and TIR3A operation rate were inversely correlated (p = 0.010). These data strongly support the division of ITNs into low- and high-risk subcategories. Importantly for clinical practice, the cancer rate among ITNs is significantly influenced by the study sample size.

[18F]FDG Uptake and Expression of Immunohistochemical Markers Related to Glycolysis, Hypoxia, and Proliferation in Indeterminate Thyroid Nodules

PURPOSE

The current study explored the association between 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) uptake and the quantitative expression of immunohistochemical markers related to glucose metabolism, hypoxia, and cell proliferation in benign and malignant thyroid nodules of indeterminate cytology.

PROCEDURES

Using a case-control design, 24 patients were selected from participants of a randomized controlled multicenter trial (NCT02208544) in which [¹⁸F]FDG-PET/CT and thyroid surgery were performed for Bethesda III and IV nodules. Three equally sized groups of [¹⁸F]FDG-positive malignant, [¹⁸F]FDG-positive benign, and [¹⁸F]FDG-negative benign nodules were included. Immunohistochemical staining was performed for glucose transporters (GLUT) 1, 3, and 4; hexokinases (HK) 1 and 2; hypoxia-inducible factor-1 alpha (HIF1α; monocarboxylate transporter 4 (MCT4); carbonic anhydrase IX (CA-IX); vascular endothelial growth factor (VEGF); sodium-iodide symporter (NIS); and Ki-67. Marker expression was scored using an immunoreactive score. Unsupervised cluster analysis was performed. The immunoreactive score was correlated to the maximum and peak standardized uptake values (SUV_max, SUV_peak) and SUV_max ratio (SUV_max of nodule/background SUV_max of contralateral, normal thyroid) of the [¹⁸F]FDG-PET/CT using the Spearman's rank correlation coefficient and compared between the three groups using Kruskal-Wallis tests.

RESULTS

The expression of GLUT1, GLUT3, HK2, and MCT4 was strongly positively correlated with the SUV_max, SUV_peak, and SUV_max ratio. The expression of GLUT1 (p = 0.009), HK2 (p = 0.02), MCT4 (p = 0.01), and VEGF (p = 0.007) was statistically significantly different between [¹⁸F]FDG-positive benign nodules, [¹⁸F]FDG-positive thyroid carcinomas, and [¹⁸F]FDG-negative benign nodules. In both [¹⁸F]FDG-positive benign nodules and [¹⁸F]FDG-positive thyroid carcinomas, the expression of GLUT1, HK2, and MCT4 was increased as compared to [¹⁸F]FDG-negative benign nodules. VEGF expression was higher in [¹⁸F]FDG-positive thyroid carcinomas as compared to [¹⁸F]FDG-negative and [¹⁸F]FDG-positive benign nodules.

CONCLUSIONS

Our results suggest that [¹⁸F]FDG-positive benign thyroid nodules undergo changes in protein expression similar to those in thyroid carcinomas. To expand the understanding of the metabolic changes in benign and malignant thyroid nodules, further research is required, including correlation with underlying genetic alterations.

Updated clinical management guidance during the COVID-19 pandemic: thyroid nodules and cancer

Healthcare settings, including nuclear medicine (NM) departments, promptly adjusted their standard operating procedures to cope with the unprecedented crisis caused by coronavirus disease 19 (COVID-19) pandemic. Nuclear thyroidology has adopted changes and predicated on a careful risk-benefit analysis, in order to prevent a potential spread of the virus while being at the same time effective, safe and preserving their quality of essential services. Since most thyroid nodules (TNs) are benign, and malignant neoplasms are characterized by an indolent natural history, it is generally safe to delay diagnostic and therapeutic procedures. In this respect, the main adjustments that nuclear thyroidology has adopted are summarized into the following: general workplace adjustments including remote work for NM staff; postponing appointments for consultation, diagnostic and therapeutic purposes and rescheduling based on individualized risk stratification; telemedicine; preparation for possible issues on radiopharmaceuticals synthesis and delivery; preventing measures and protocols to minimize or avoid potential COVID-19 infection of patients and medical staff. This document should be considered as updated guidance on how clinical management of TNs and thyroid cancer has been altered, remodeled and adapted to the new circumstances in the COVID-19 era, based on the rapidly growing volume of scientific information regarding the new coronavirus.

Quantitative classification and radiomics of [18F]FDG-PET/CT in indeterminate thyroid nodules

PURPOSE

To evaluate whether quantitative [¹⁸F]FDG-PET/CT assessment, including radiomic analysis of [¹⁸F]FDG-positive thyroid nodules, improved the preoperative differentiation of indeterminate thyroid nodules of non-Hürthle cell and Hürthle cell cytology.

METHODS

Prospectively included patients with a Bethesda III or IV thyroid nodule underwent [¹⁸F]FDG-PET/CT imaging. Receiver operating characteristic (ROC) curve analysis was performed for standardised uptake values (SUV) and SUV-ratios, including assessment of SUV cut-offs at which a malignant/borderline neoplasm was reliably ruled out (≥ 95% sensitivity). [¹⁸F]FDG-positive scans were included in radiomic analysis. After segmentation at 50% of SUV_peak, 107 radiomic features were extracted from [¹⁸F]FDG-PET and low-dose CT images. Elastic net regression classifiers were trained in a 20-times repeated random split. Dimensionality reduction was incorporated into the splits. Predictive performance of radiomics was presented as mean area under the ROC curve (AUC) across the test sets.

RESULTS

Of 123 included patients, 84 (68%) index nodules were visually [¹⁸F]FDG-positive. The malignant/borderline rate was 27% (33/123). SUV-metrices showed AUCs ranging from 0.705 (95% CI, 0.601-0.810) to 0.729 (0.633-0.824), 0.708 (0.580-0.835) to 0.757 (0.650-0.864), and 0.533 (0.320-0.747) to 0.700 (0.502-0.898) in all (n = 123), non-Hürthle (n = 94), and Hürthle cell (n = 29) nodules, respectively. At SUV_max, SUV_peak, SUV_max-ratio, and SUV_peak-ratio cut-offs of 2.1 g/mL, 1.6 g/mL, 1.2, and 0.9, respectively, sensitivity of [¹⁸F]FDG-PET/CT was 95.8% (95% CI, 78.9-99.9%) in non-Hürthle cell nodules. In Hürthle cell nodules, cut-offs of 5.2 g/mL, 4.7 g/mL, 3.4, and 2.8, respectively, resulted in 100% sensitivity (95% CI, 66.4-100%). Radiomic analysis of 84 (68%) [¹⁸F]FDG-positive nodules showed a mean test set AUC of 0.445 (95% CI, 0.290-0.600) for the PET model.

CONCLUSION

Quantitative [¹⁸F]FDG-PET/CT assessment ruled out malignancy in indeterminate thyroid nodules. Distinctive, higher SUV cut-offs should be applied in Hürthle cell nodules to optimize rule-out ability. Radiomic analysis did not contribute to the additional differentiation of [¹⁸F]FDG-positive nodules.

TRIAL REGISTRATION NUMBER

This trial is registered with ClinicalTrials.gov: NCT02208544 (5 August 2014), https://clinicaltrials.gov/ct2/show/NCT02208544 .

[18F]FDG-PET/CT to prevent futile surgery in indeterminate thyroid nodules: a blinded, randomised controlled multicentre trial

Purpose

To assess the impact of an [¹⁸F]FDG-PET/CT-driven diagnostic workup to rule out malignancy, avoid futile diagnostic surgeries, and improve patient outcomes in thyroid nodules with indeterminate cytology.

Methods

In this double-blinded, randomised controlled multicentre trial, 132 adult euthyroid patients with scheduled diagnostic surgery for a Bethesda III or IV thyroid nodule underwent [¹⁸F]FDG-PET/CT and were randomised to an [¹⁸F]FDG-PET/CT-driven or diagnostic surgery group. In the [¹⁸F]FDG-PET/CT-driven group, management was based on the [¹⁸F]FDG-PET/CT result: when the index nodule was visually [¹⁸F]FDG-positive, diagnostic surgery was advised; when [¹⁸F]FDG-negative, active surveillance was recommended. The nodule was presumed benign when it remained unchanged on ultrasound surveillance. In the diagnostic surgery group, all patients were advised to proceed to the scheduled surgery, according to current guidelines. The primary outcome was the fraction of unbeneficial patient management in one year, i.e., diagnostic surgery for benign nodules and active surveillance for malignant/borderline nodules. Intention-to-treat analysis was performed. Subgroup analyses were performed for non-Hürthle cell and Hürthle cell nodules.

Results

Patient management was unbeneficial in 42% (38/91 [95% confidence interval [CI], 32–53%]) of patients in the [¹⁸F]FDG-PET/CT-driven group, as compared to 83% (34/41 [95% CI, 68–93%]) in the diagnostic surgery group (p < 0.001). [¹⁸F]FDG-PET/CT-driven management avoided 40% (25/63 [95% CI, 28–53%]) diagnostic surgeries for benign nodules: 48% (23/48 [95% CI, 33–63%]) in non-Hürthle cell and 13% (2/15 [95% CI, 2–40%]) in Hürthle cell nodules (p = 0.02). No malignant or borderline tumours were observed in patients under surveillance. Sensitivity, specificity, negative and positive predictive value, and benign call rate (95% CI) of [¹⁸F]FDG-PET/CT were 94.1% (80.3–99.3%), 39.8% (30.0–50.2%), 95.1% (83.5–99.4%), 35.2% (25.4–45.9%), and 31.1% (23.3–39.7%), respectively.

Conclusion

An [¹⁸F]FDG-PET/CT-driven diagnostic workup of indeterminate thyroid nodules leads to practice changing management, accurately and oncologically safely reducing futile surgeries by 40%. For optimal therapeutic yield, application should be limited to non-Hürthle cell nodules.

Trial registration number

This trial is registered with ClinicalTrials.gov: NCT02208544 (5 August 2014), https://clinicaltrials.gov/ct2/show/NCT02208544.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05627-2.

PET/Computed Tomography in Thyroid Cancer

Primary thyroid cancers demonstrate distinct biological behaviors depending on their histologic characteristics. The ability to accumulate radioiodine by differentiated thyroid cancer cells is lost in primary aggressive, poorly differentiated and dedifferentiated tumor cells. PET imaging comes into play in these challenging situations where it can provide additive information to radioiodine scintigraphy and conventional imaging. This review focuses on the current guidelines and future prospects of PET imaging in thyroid cancers.

Implications of US radiomics signature for predicting malignancy in thyroid nodules with indeterminate cytology

OBJECTIVES

The purpose of this study was to evaluate the role of the radiomics score using US images to predict malignancy in AUS/FLUS and FN/SFN nodules.

METHODS

One hundred fifty-five indeterminate thyroid nodules in 154 patients who received initial US-guided FNA for diagnostic purposes were included in this retrospective study. A representative US image of each tumor was acquired, and square ROIs covering the whole nodule were drawn using the Paint program of Windows 7. Texture features were extracted by in-house texture analysis algorithms implemented in MATLAB 2019b. The LASSO logistic regression model was used to choose the most useful predictive features, and ten-fold cross-validation was performed. Two prediction models were constructed using multivariable logistic regression analysis: one based on clinical variables, and the other based on clinical variables with the radiomics score. Predictability of the two models was assessed with the AUC of the ROC curves.

RESULTS

Clinical characteristics did not significantly differ between malignant and benign nodules, except for mean nodule size. Among 730 candidate texture features generated from a single US image, 15 features were selected. Radiomics signatures were constructed with a radiomics score, using selected features. In multivariable logistic regression analysis, higher radiomics score was associated with malignancy (OR = 10.923; p < 0.001). The AUC of the malignancy prediction model composed of clinical variables with the radiomics score was significantly higher than the model composed of clinical variables alone (0.839 vs 0.583).

CONCLUSIONS

Quantitative US radiomics features can help predict malignancy in thyroid nodules with indeterminate cytology.

Hürthle Cells on Fine-Needle Aspiration Cytology Are Important for Risk Assessment of Focally PET/CT FDG Avid Thyroid Nodules

Simple Summary

PET/CT fluorodeoxyglucose (FDG) scans are routinely used in patients to detect signs of malignant tumours or evidence of inflammation in the body. A total of 1–2% of patients show focal thyroid gland FDG uptake and 35–40% are malignant. FDG also detects metabolically active lesions containing mitochondria, known as Hürthle cells. Over 3 years, 47 patients in one hospital were found to have focal thyroid gland uptake. A total of 18 (38.2%) of the patients had malignancy, 15 (31.9%) had benign lesions that contained Hürthle cells and 14 (29.8%) had focally increased thyroid gland FDG PET/CT uptake with no cause identified. Exclusion of the Hürthle cell patients increased the risk of malignancy of the remaining PET-positive nodules from 38% to 68%. It is important to recognize Hürthle cells on FNA cytology in FDG PET/CT-positive nodules as this affects the risk of malignancy and the clinical management of focally FDG PET/CT-positive nodules.

Abstract

This study assesses the role of [¹⁸F] FDG PET/CT, fine needle aspiration (FNA) cytology and ultrasound in the 1–2% of patients with focally positive thyroid nodules on FDG PET/CT. All FDG PET/CT scans with focally increased thyroid FDG PET/CT uptake performed over 37 months in one institution were matched to patients undergoing thyroid FNA. Diffuse FDG PET/CT uptake patients were excluded. A total of 47 patients showed focally increased thyroid uptake. Consistent with previous studies, 18 (38.2%) patients had malignancy—12 primary thyroid carcinoma, 1 parathyroid carcinoma, 3 metastatic carcinoma to the thyroid and 2 lymphoma. A total of 15 (31.9%) lesions categorized as non-malignant contained Hürthle cells/oncocytes. A total of 14 lesions (29.8%) had focally increased FDG PET/CT uptake with no specific cytological or histopathological cause identified. No focally PET avid Hürthle cell/oncocytic lesions were found to be malignant. Exclusion of oncocytic lesions increased the calculated risk of malignancy (ROM) of focally PET avid nodules from 38% to 68%. It may be useful to exclude focally FDG PET/CT avid Hürthle cell/oncocytic lesions, typically reported as follicular neoplasm or suspicious for a follicular neoplasm, Hürthle cell type (Oncocytic) type, RCPath Thy 3F: Bethesda IV or sometimes Thy 3a: Bethesda III FNAs) from ROM calculations. Oncocytic focally PET/CT FDG avid lesions appear of comparatively lower risk of malignancy and require investigation or operation but these lesions should be readily identified by FNA cytology on diagnostic work up of focally PET avid thyroid nodules.

Usability of EU-TIRADS in the Diagnostics of Hürthle Cell Thyroid Nodules with Equivocal Cytology

The aim of this study was to compare the diagnostic effectiveness of EU-TIRADS in two groups of nodules with equivocal cytology (categories III-V of Bethesda system), with and without Hürthle cells (HC and non-HC). The study included 162 HC and 378 non-HC nodules with determined histopathological diagnosis (17.9% and 15.6% cancers). In both groups calculated and expected risk of malignancy (RoM) for high, intermediate and benign risk categories of EU-TIRADS were concordant. RoM for low risk category was higher than expected in both groups, but especially in HC (HC: 13.9%, non-HC: 7.0%, expected: 2-4%). The majority of cancers in HC of that category were follicular thyroid carcinomas (FTC) and Hürthle cell thyroid carcinoma (HTC) (60.0% vs. non-HC: 16.7%). The diagnostic efficacy of EU-TIRADS was lower in HC (the area under the receiver operating characteristics curve (AUC): 0.621, sensitivity (SEN): 44.8%, specificity (SPC): 78.9% for high risk threshold) than in non-HC (AUC: 0.711, SEN: 61.0%, SPC: 77.7%). AUC was the highest for category V (AUC > 0.8, both groups) and the lowest for category IV (inefficient, both group). If intermediate risk category was interpreted as an indication for surgery, 25% of cancers from category III and 21.4% from category IV would not be treated in the HC group (0.0% and 7.4% from non-HC group, respectively). EU-TIRADS does not aid making clinical decisions in patients with cytologically equivocal HC nodules, particularly those classified into category IV of Bethesda System for Reporting Thyroid Cytopathology (BSRTC).