Diffuse thyroid uptake incidentally found on 18F-fluorodeoxyglucose positron emission tomography in subjects without cancer history

Clinical significance of diffuse [18F] AlF-NOTA-FAPI-04 uptake in the thyroid on PET/CT imaging

BACKGROUND

Many patients undergoing [18F] AlF-NOTA-FAPI-04 (18F-FAPI) PET/CT demonstrated diffuse thyroid uptake. These findings created challenges for accurate interpretation due to the limited understanding of physiological and non-oncologic causes of diffuse 18F-FAPI uptake in the thyroid. This retrospective study examined patients who underwent 18F-FAPI PET/CT imaging with diffuse thyroid uptake. It quantitatively assessed normal thyroid uptake, compared 18F-FAPI uptake between normal and diseased thyroids, and explored potential associations with diffuse thyroid uptake. The study may improve the accuracy of 18F-FAPI PET/CT interpretation for thyroid and facilitate appropriate management of diffuse thyroid uptake on 18F-FAPI PET/CT.

RESULTS

A total of 38 patients were included in this study based on the inclusion criteria. The mean SUVmax, SUVmean, and TBR of normal thyroid were 7.09 ± 3.83, 4.24 ± 2.25 and 3.93 ± 1.73, respectively. Quantitative analysis revealed no significant asymmetry in 18F-FAPI uptake between the right and left thyroid lobes (SUVmax: right 6.69 ± 2.96 vs. left 6.54 ± 3.28, p = 0.84; SUVmean: right 4.19 ± 1.73 vs. left 4.18 ± 1.97, p = 0.98), consistent with the diffuse uptake pattern observed. There was no significant correlation between Hashimoto thyroiditis, serum TSH levels, and the degree of diffuse thyroid uptake (all p > 0.05 for SUVmax, SUVmean, and TBR). Furthermore, no association was observed between sex, age, immunotherapy, and diffuse thyroid uptake (p > 0.05).

CONCLUSIONS

Diffuse uptake of 18F-FAPI in the thyroid may not significantly relate to Hashimoto thyroiditis or abnormal serum TSH levels. Lesions on 18F-FAPI PET/CT scans might be hard to detect due to the moderate uptake in normal thyroid tissue.

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.

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.

Detection of thyroiditis on PET/CT imaging: a systematic review

PURPOSE

The incidence and clinical significance of thyroiditis detected by molecular imaging methods is a clinical challenge that is not widely investigated in the literature. The aim of this systematic review was to analyze published data about the detection of thyroiditis on PET or PET/CT using different tracers.

METHODS

A comprehensive computer literature search of the Scopus, PubMed/MEDLINE, Embase, and Cochrane library databases was conducted up to November 2019 to find relevant papers on the detection of thyroiditis by PET/CT, the metabolic appearance, and the clinical significance.

RESULTS

Twenty-six articles were selected and retrieved in full-text version. From the analyses of these studies, the following main findings have been found. Diffuse thyroid uptake of PET tracers is a relatively frequent event, ranging from 0.4 to 46.2%, and it is commonly related to benign disease. Thyroiditis is the most frequent reason for diffuse increased thyroid ¹⁸F-FDG uptake. Cases of malignant disease with a pattern of diffuse ¹⁸F-FDG thyroid uptake are less frequent. Preliminary studies show a possible role of thyroiditis detected by ¹⁸F-FDG PET/CT in evaluating treatment response and as a prognostic marker in oncological patients treated with immunotherapy. However, further studies are needed.

CONCLUSIONS

Diffuse ¹⁸F-FDG thyroid uptake is a relatively rare event commonly due to benign diseases, among which thyroiditis is the most common. The rate of neoplastic disease with diffuse ¹⁸F-FDG thyroid uptake is very low. Diffuse ¹⁸F-FDG thyroid uptake requires further investigation and clinical evaluation for the correct diagnosis. Currently, cases of diffuse thyroid uptake with non-¹⁸F-FDG radiotracer are only anecdotal.

Diffusely Increased 18F-FDG Uptake in the Thyroid Gland and Risk of Thyroid Dysfunction: A Cohort Study

The impact of incidentally identified diffuse thyroid FDG uptake on ¹⁸F-FDG PET/CT scan on the incidence of thyroid dysfunction remains unclear. We examined the association of diffuse thyroid FDG uptake with the development of thyroid dysfunction. This cohort study involved 39,098 Korean adults who were free of malignancy and thyroid disease at baseline and underwent regular health checkup examinations including an ¹⁸F-FDG whole body PET/CT scan, thyroid-stimulating hormone and free thyroxine. The participants were annually or biennially followed for up to 5 years. A parametric proportional hazard model was used to estimate the adjusted hazard ratio (HR) and 95% confidence interval (CI). Diffuse thyroid uptake was positively associated with increased risk of thyroid dysfunction in both the cross-sectional and cohort studies. During 104,261.4 person-years of follow-up, 102 incident hypothyroidism cases and 172 hyperthyroidism cases were identified. Multivariable-adjusted HR (95% CI) for incident hypothyroidism or hyperthyroidism comparing diffuse thyroid uptake to no uptake were 15.72 (9.23–26.77) and 7.38 (4.23–12.87), respectively. In this large cohort, incidentally, identified diffuse thyroid uptake on ¹⁸F-FDG PET/CT was associated with increased risk of both prevalent and incident thyroid dysfunction. Therefore, baseline and follow-up evaluations in individuals with diffuse thyroid uptake may help identify individuals with thyroid dysfunction.

Clinical significance of thyroid incidentalomas detected on fluorodeoxyglucose positron emission tomography scan (PETomas): An Indian experience

Thyroid incidentalomas (TIs) are being frequently detected on positron emission tomography (PET) scan. The risk of malignancy in these focal hot spots is substantially high as compared to incidentalomas detected on ultrasonography (USG)/magnetic resonance imaging/computed tomography (CT). Majority of the studies on the prevalence of TIs in PET and the risk of malignancy in them are retrospective and have had varied results. Very few prospective studies are available and very few Indian studies have been done on the subject. Hence, this study was undertaken to evaluate the clinical significance of TIs detected on fluorodeoxyglucose (FDG)-PET scan. The study included all patients undergoing FDG-PET scan for nonthyroid illness from October 2015 to October 2016. Twenty-three consecutive patients detected to have focal TI (FTI) were prospectively evaluated with detailed history and clinical examination, serum thyroid-stimulating hormone, total T4 and total T3 levels, USG neck, fine-needle aspiration cytology (FNAC), and surgery when indicated. The prevalence of FTI was 2.26%. Out of the 23 FTI cases, 19 patients agreed to undergo further evaluation and malignancy was detected in 5 patients (all papillary carcinomas) making a risk of malignancy of 26.3%. There was no significant correlation between CT attenuation characteristics and size of benign and malignant PETomas or between the maximum standardized uptake value (SUV_max) of benign and malignant PETomas. Hence, the risk of malignancy in thyroid PETomas is substantially high and warrants USG-guided FNAC and further work-up. Their SUV_maxvalues, size, and CT attenuation characteristics do not contribute in differentiating benign from malignant lesions.

Computer-Aided Diagnostic Technique in 2-Deoxy-2-[18F]fluoro-D-glucose-Positive Thyroid Nodule: Clinical Experience of 74 Non-thyroid Cancer Patients

This study verified the value of a computer-aided diagnosis (CAD) technique assisting in ultrasonography (US) diagnosis of 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸FDG)-avid thyroid incidentalomas on positron emission tomography. A total of 82 ¹⁸FDG-avid thyroid incidentalomas from 74 non-thyroid cancer patients were retrospectively analyzed with respect to US and CAD parameters (anechoic area, hyper-echoic foci, hypo-echogenicity, heterogeneity, margin, taller-than-wide shape, eccentric area) and were compared with 38 other non-¹⁸FDG-avid nodules found in the same patient group. Fine-needle aspiration cytology or surgical intervention pathology was performed for diagnosis. No significant differences in nodule size or CAD parameters were found in ¹⁸FDG-avid nodules reported as benign, indeterminate or malignant. Significantly more taller-than-wide nodules were thyroid originating than metastatic (0.30 vs. 0.16, p < 0.05). Nevertheless, combined CAD and positron emission tomography/computed tomography scores and a discrimination point of 4 resulted in a sensitivity of 75% and a specificity of 80% in prediction of incidentaloma benignity.

Correlation between anti-thyroid peroxidase antibody levels and diffuse thyroid uptake of 18F-fluorodeoxyglucose in Hashimoto's thyroiditis: a retrospective study

Background

On ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET), diffuse uptake in the thyroid gland is often observed in patients with Hashimoto’s thyroiditis. In this study, we evaluated the factors associated with diffuse uptake by comparing Hashimoto’s thyroiditis patients with or without diffuse uptake in the thyroid.

Methods

A retrospective study was conducted of 18 patients with Hashimoto’s thyroiditis who underwent blood tests, thyroid ultrasonography, and FDG-PET during the period from 2014 to 2015. The patients were divided into two groups: one with diffuse thyroid uptake (group 1, n = 13) and one without diffuse thyroid uptake (group 2, n = 5). Clinical and laboratory parameters, including maximum standardized uptake in the thyroid (SUVmax), which was defined as the higher value obtained in either the right or left thyroid lobe, were compared in the two groups.

Results

The frequency of abnormal findings, such as a rough or heterogeneous pattern, was significantly higher in group 1 (p <  0.01), as were anti-thyroid peroxidase (TPO) antibody titers, anti-thyroglobulin (Tg) antibody titers, and SUVmax (p <  0.01). The frequency of hypothyroidism did not differ significantly in the two groups. Anti-TPO and anti-Tg titers were positively correlated with SUVmax (r = 0.856, p <  0.01 and r = 0.821, p <  0.01, respectively); in univariate analysis, anti-TPO titer was predictive of SUVmax (p <  0.01).

Conclusions

The results of the current study suggest that Hashimoto’s thyroiditis patients with high titers of anti-thyroid antibodies are likely to exhibit intense diffuse FDG uptake in the thyroid, and that thyroid function may be clearly impaired, even in the presence of mild FDG uptake in the thyroid.

Clinical significance of patterns of increased [18F]-FDG uptake in the thyroid gland: a pictorial review

In the diagnosis and staging of oncologic patients, [¹⁸F]-fluorodeoxyglucose positron emission tomography (FDG-PET) is well recognized as an important functional imaging modality. FDG-PET also has been used for cancer screening in healthy individuals. In general, the normal thyroid gland shows absent or low uptake on FDG-PET, which is often identified as an incidental finding on PET. Today, thyroid FDG uptake can be seen in three patterns: diffuse; focal; and diffuse-plus-focal. Diffuse thyroid uptake is mainly considered an indicator of chronic thyroiditis. Focal thyroid uptake has been associated with malignancy (range 25-50%). Diffuse-plus-focal uptake is not well recognized and might also indicate a risk of malignancy. Understanding the patterns of thyroid FDG uptake is thus important for nuclear medicine physicians or radiologists when giving recommendations to the referring physician. In this pictorial review, we show the clinical significance of different patterns of thyroid uptake on FDG-PET [PET/computed tomography (CT)], including ultrasonography (US) findings.

Hypermetabolic Thyroid Incidentaloma on Positron Emission Tomography: Review of Laboratory, Radiologic, and Pathologic Characteristics

Introduction

Incidental hypermetabolic thyroid lesions on Positron Emission Tomography have significant clinical value and may harbor malignancy. In this study we evaluated laboratory, radiologic, and pathologic characteristics of incidental hypermetabolic thyroid lesions.

Materials and Methods

We evaluated 18 patients prospectively with various malignancies and hypermetabolic thyroid incidentaloma. The thyroid function tests, ultrasound assessment, and guided FNA biopsy were performed on all cases.

Results

We included 9 male and 9 female patients with mean age of 51 years. Most common malignancy was colon cancer. Metabolic activity quantification using maximum standard uptake value demonstrated range between 1.4 and 65.4 with mean value of 9.4. We found highest metabolic activity in patients with lung adenocarcinoma, B-cell lymphoma, and colon adenocarcinoma. On ultrasound exam most thyroid lesions were of solid, hypoechoic, noncalcified nature with either normal or peripheral increased vascularity. FNA biopsy report was benign in 15 cases and malignant or highly suggestive for malignancy in 3 other cases. Two of the three malignant cases demonstrated metabolic activity higher than average SUV max.

Conclusion

Most thyroid hypermetabolic incidentalomas are benign lesions, while higher values of SUV max are in favor of malignancy. This mandates further evaluation of incidentally found thyroid hypermetabolic lesions on routine PET/CT scans.

Malignancy rate of focal thyroid incidentaloma detected by FDG PET-CT: results of a prospective cohort study

OBJECTIVE

To evaluate the malignancy rate of focal thyroid incidentaloma (fTI) in a population of patients undergoing a 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) for a non-thyroid purpose.

DESIGN

We conducted a prospective cohort study from January 2013 to November 2014. All consecutive patients referred for a FDG PET-CT were prospectively screened. Patients with known neoplastic thyroid disease were excluded from the analysis. All patients presenting one or more fTI and who accepted to benefit from a complementary thyroid ultrasonography (US) were included and managed according to the French endocrine society consensus. Prevalence of fTI in our population and malignancy rate was assessed.

RESULTS

During the inclusion period, 10,171 patients were referred for a FDG PET-CT in our center. Fifty-three patients presenting a known thyroid disease were excluded. Among the remaining 10,118 patients, 127 (1.3%) with 131 fTI were individualized. US could not be performed in 37 patients. The remaining 90 patients (92 fTI) were explored by US ± fine-needle aspiration biopsy (FNAB). US results demonstrated a nodule aspect in 80 cases of which 60 benefited from FNAB. Nineteen of 92 fTI underwent surgery with 10 malignant lesions among the 60 patients performing both US and FNAB.

CONCLUSION

The prevalence of fTI discovered on FDG PET-CT in our population was 1.3% with 10 malignant lesions among the 60 patients performing both US and FNAB.

Does the intensity of diffuse thyroid gland uptake on F-18 fluorodeoxyglucose positron emission tomography/computed tomography scan predict the severity of hypothyroidism? Correlation between maximal standardized uptake value and serum thyroid stimulating hormone levels

Context:

F-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) scan and hypothyroidism.

Aims:

The aim was to determine whether the intensity of diffuse thyroid gland uptake on F-18 FDG PET/CT scans predicts the severity of hypothyroidism.

Materials and Methods:

A retrospective analysis of 3868 patients who underwent F-18 FDG PET/CT scans, between October 2012 and June 2013 in our institution for various oncological indications was done. Out of them, 106 (2.7%) patients (79 females, 27 males) presented with bilateral diffuse thyroid gland uptake as an incidental finding. These patients were investigated retrospectively and various parameters such as age, sex, primary cancer site, maximal standardized uptake value (SUVmax), results of thyroid function tests (TFTs) and fine-needle aspiration cytology results were noted. The SUVmax values were correlated with serum thyroid stimulating hormone (S. TSH) levels using Pearson's correlation analysis.

Statistical Analysis Used:

Pearson's correlation analysis.

Results:

Clinical information and TFT (serum FT3, FT4 and TSH levels) results were available for 31 of the 106 patients (27 females, 4 males; mean age 51.5 years). Twenty-six out of 31 patients (84%) were having abnormal TFTs with abnormal TSH levels in 24/31 patients (mean S. TSH: 22.35 μIU/ml, median: 7.37 μIU/ml, range: 0.074-211 μIU/ml). Among 7 patients with normal TSH levels, 2 patients demonstrated low FT3 and FT4 levels. No significant correlation was found between maximum standardized uptake value and TSH levels (r = 0.115, P > 0.05).

Conclusions:

Incidentally detected diffuse thyroid gland uptake on F-18 FDG PET/CT scan was usually associated with hypothyroidism probably caused by autoimmune thyroiditis. Patients should be investigated promptly irrespective of the intensity of FDG uptake with TFTs to initiate replacement therapy and a USG examination to look for any suspicious nodules.