Thyroid incidentalomas on FDG PET/CT in patients with non-thyroid cancer - a large retrospective monocentric study

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.

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.

Hypermetabolic Hurthle Cell Adenoma on 18F-FDG PET/CT

Thyroid incidentalomas are frequently reported on ¹⁸F-FDG PET/CT scan. High risk of malignancy is thought to be associated with increased metabolic activity and high standardized uptake value. Likewise, thyroid nodules with focal FDG avidity have a higher potential to be malignant. However, some benign nodules such as follicular and Hurthle cell adenomas can also present with focal hypermetabolic activity. We report a case of a 59-year-old lady diagnosed with gastric carcinoma, who had a hypermetabolic thyroid nodule on FDG PET/CT scan. Despite the complex texture of the nodule and intense focal avidity, the histopathology was consistent with Hurtle cell adenoma.

Diagnostic Value of Volume-Based Fluorine-18-Fluorodeoxyglucose PET/CT Parameters for Characterizing Thyroid Incidentaloma

Objective

To assess clinical value of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) for differentiation of malignant from benign focal thyroid incidentaloma.

Materials and Methods

This retrospective study included 99 patients with focal thyroid incidentaloma of 5216 non-thyroid cancer patients that had undergone PET/CT. PET/CT semi-quantitative parameters, volume-based functional parameters, metabolic tumor volume (MTV), and total lesion glycolysis (TLG) of thyroid incidentaloma were assessed. Receiver-operating characteristic (ROC) analysis was conducted and areas under the curve (AUC) were compared by Hanley and McNeil test to evaluate usefulness of maximum standardized uptake value (SUVmax), MTV and TLG, as markers for differentiating malignant from benign thyroid incidentalomas.

Results

Of 99 thyroid incidentalomas, 64 (64.6%) were malignant and 35 (35.4%) were benign. Malignant thyroid incidentalomas were larger (1.8 cm vs. 1.3 cm, p = 0.006), and had higher SUVmax (11.3 vs. 4.8, p < 0.001), MTV (all p < 0.001) and TLG (all p < 0.001) than benign. TLG 4.0 had the highest performance for differentiation of malignant from benign thyroid incidentaloma in all semi-quantitative parameters with AUC 0.895 by ROC curve analysis. AUC (TLG 4.0) was significantly larger than AUC (SUVmean), AUC (MTV 2.5), AUC (MTV 3.0), AUC (MTV 3.5), AUC (TLG 2.5), and AUC (TLG 3.0), respectively (all, p < 0.05). There was no statistical difference between AUC (TLG 4.0) and AUC (SUVmax) (p > 0.05). A threshold TLG 4.0 of 2.475 had 81.3% sensitivity and 94.3% specificity for identifying malignant thyroid incidentalomas.

Conclusion

Volume-based PET/CT parameters could potentially have clinical value in differential diagnosis of thyroid incidentaloma along with SUVmax.

Evaluation of Incidental Thyroid Nodules in Cancer Patients

OBJECTIVE

Frequency of thyroid cancer in incidental thyroid nodules identified by imaging techniques in cancer patients is higher than that in the normal population. In the retrospective study, we have both investigated the incidence of thyroid cancer in incidentally identified nodules and compared the imaging techniques to determine whether there is any difference between them in detection of malign nodules.

METHODS

A total of 7319 patients who underwent thyroid fine-needle aspiration biopsy (FNAB) were included in the study. The data of 174 patients who had previously been diagnosed with a hematologic or solid malignancy prior to the FNAB procedure and had incidentally identified thyroid nodules were evaluated retrospectively.

RESULTS

Eighty-six (49.5%) of the incidental nodules were identified with ultrasonography (USG), 62 (35.6%) with positron emission tomography (PET) or PET/computed tomography (PET/CT), and 26 (14.9%) with CT. As a result of thyroidectomy, papillary carcinoma was identified in 8 (4.6%) patients, and metastasis to the thyroid of a primary cancer was found in 3 (1.7%) patients. While the papillary carcinoma proportion in the nodules identified by USG was 3.4%, PET/CT was 8.9%. A cut-off maximal standardized uptake value of 11.6 in PET/CT indicated malignancy achieving a sensitivity of 83.3% and a specificity of 91.1%.

CONCLUSION

Whether the nodule in the incidental thyroid nodules of cancer patients is identified using USG or PET/CT, the risk of thyroid cancer is similar. However, cancer risk is higher in the event of a higher focal uptake in the nodules identified by PET/CT.

Risk of Malignancy in Thyroid Incidentaloma is Not Increased in Overweight or Obese Patients, but in Young Patients

Thyroid incidentaloma is defined as an unsuspected, asymptomatic thyroid lesion that is discovered on an imaging study or during an operation unrelated to the thyroid gland. We aim to evaluate the relationship between overweight or obese and risk of malignancy in patients with thyroid incidentaloma detected by F18-flurodeoxyglucose positron emission tomography/computed tomography and factors to predict risk of malignancy in thyroid incidentaloma. From January 2010 to December 2013, a total of 238 patients were eligible for this study. Using the Bethesda system for reporting thyroid cytopathology, categories I-III were defined as a nonmalignancy and categories V-VI were defined as a malignancy. When patients with body mass index (BMI) of less than 23 and 23 or more were divided into two groups of normal and overweight or obese, risk of malignancy of thyroid incidentaloma was not significantly different between two groups (P = 0.1812). In logistic regression analysis, age was the only variable that showed a significant association with malignancy of thyroid incidentaloma (odds ratio 0.9608, P = 0.0021). However, none of sex, height, weight, and BMI was predictor of malignancy of thyroid incidentaloma. We demonstrated that being overweight or obese did not increase rate of malignancy in patients with thyroid incidentaloma.

The incidence of thyroid cancer in focal hypermetabolic thyroid lesions: an 18F-FDG PET/CT study in more than 6000 patients

BACKGROUND

The clinical significance of incidental thyroid abnormalities discovered in fluorine-18 fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) (FDG PET/CT) studies remains controversial. The aim of this large retrospective study was to (a) determine the prevalence of focal F-FDG thyroid uptake on whole-body F-FDG PET/CT studies carried out for nonthyroid cancers and (b) to test whether intense focal F-FDG thyroid uptake is associated with malignancy.

MATERIALS AND METHODS

A total of 11 921 F-FDG PET/CT studies in 6216 patients carried out at our institution between January 2012 and December 2014 were analyzed. We retrospectively reviewed the medical records of these patients. Eight hundred and forty-five/6216 (13.6%) patients had a thyroid incidentaloma on the basis of the clinical F-FDG PET/CT report. One hundred and sixty/845 (18.9%) of these underwent ultrasound and 98 (61.3%) of these underwent a fine-needle aspiration (FNA). Twenty-six of these 98 (26.5%) patients underwent thyroidectomy. Thyroid lesion and background standardized uptake value (SUVs) for each patient were measured upon review of the F-FDG PET/CT study. We measured maximum standardized uptake value (SUVmax), thyroid to background TL/TBG, thyroid to bloodpool TL/BP and thyroid to liver TL/L ratios in benign and malignant lesions. Receiver operating curves were calculated to determine optimal cut-off values between malignant and benign lesions.

RESULTS

Twenty-one of the 98 patients who underwent FNA biopsy or thyroidectomy had malignant disease (21.4%). Malignant lesions had significantly higher thyroid lesion SUVmax, TL/TBG, TL/BP, and TL/L than benign nodules. The receiver operating curves derived cut-off ratio TL/TBG of more than 2.0 differentiated benign from malignant lesions best with a specificity and sensitivity of 0.76 and 0.88, respectively.

CONCLUSION

The incidence of malignancy in biopsied focal hypermetabolic thyroid lesions is 21.4%. Lesions on F-FDG PET/CT studies, with a ratio TL/TBG more than 2.0, warrant further work-up with ultrasound and FNA to exclude malignancy.

THYROID MALIGNANCY RISK OF INCIDENTAL THYROID NODULES IN PATIENTS WITH NON-THYROID CANCER

Context

Thyroid incidentaloma is a common disorder in endocrinology practice. Current literature regarding the risk of thyroid cancer in incidentalomas found in patients with non-thyroid cancer is limited.

Objective

The aim of the present study was to investigate the frequency of thyroid malignancy in thyroid incidentalomas detected in patients with non-thyroid cancer.

Design

Case control study.

Subjects and Methods

The database of 287 thyroid nodules from 161 patients with a history of non-thyroid cancer followed between 2008 and 2014 were retrospectively evaluated.

Results

From 287 thyroid nodules, 69.7 % had a benign final cytology. Thyroid cancer detected in one nodule while follicular neoplasia detected in 4 nodules, atypia of unknown significance (AUS) detected in 10 nodules, Hurthle cell neoplasia detected in 5 nodules and suspicious for malignancy detected in 6 nodules according to fine needle aspiration biopsy results. Metastasis of the non-thyroid cancer to the thyroid gland was detected in 4 nodules. Twenty seven nodules from 15 patients were removed with surgery. There were 3 malignant nodules found after surgery (1 papillary, 1 follicular and 1 medullary cancer). In addition to these three thyroid cancers, two patients with benign nodules had co-incidental thyroid cancer detected after surgery. Finally, 11.1 % of thyroid nodules which underwent thyroid surgery had malignant histopathology except for co-incidental and metastatic cancers.

Conclusions

The frequency of thyroid malignancy seems not to be substantially increased in incidental thyroid nodules detected in patients with non-thyroid cancer when these patients were evaluated in nodule-based approach.

Management of a thyroid "incidentaloma" in a patient with cancer: a case report

The routine use of ¹⁸F-fluorodeoxyglucose-positron emission tomography (PET)/computed tomography scans for staging and assessment of treatment response for cancer has resulted in a large number of thyroid abnormalities being detected as incidental findings (“incidentalomas”). Since most PET/CT scans are performed in the setting of a known nonthyroid malignancy, the need for “incidentalomas” to be further investigated and managed depends on the stage, prognosis, and current treatment plan for the known malignancy. We present a case describing the management of an incidental F-fluorodeoxyglucose-avid thyroid nodule detected in a patient with known metastatic colorectal cancer. On the basis of this case, we discuss the management of incidental PET-detected thyroid nodules in patients with metastatic cancer. Thyroid “incidentalomas” must be seen in the context of the prognosis and treatment plan for the known malignancy.

Incidence and Significance of Incidental Focal Thyroid Uptake on (18)F-FDG PET Study in a Large Patient Cohort: Retrospective Single-Centre Experience in the United Kingdom

OBJECTIVE

To assess the prevalence and pathological nature of incidental focal thyroid uptake on (18)F-FDG (2-[(18)F]-fluoro-2-deoxy-D-glucose) PET (positron emission tomography) and examine the role of the maximum standardised uptake value (SUVmax) to differentiate benign from malignant thyroid pathology.

MATERIAL AND METHODS

(18)F-FDG PET reports were retrospectively reviewed. Incidental focal tracer uptake in the thyroid was noted in 147 patients (0.5%). Patients with known primary thyroid malignancy were excluded. The final diagnosis was made following ultrasonography of the neck, fine-needle aspiration cytology (FNAC) or histopathology of the surgically resected specimen where surgery was indicated. A Mann-Whitney U test was used to compare the SUVmax of benign and malignant thyroid pathology. Receiver operating characteristic (ROC) analysis was performed to identify an SUVmax cutoff in differentiating benign from malignant pathology.

RESULTS

A final diagnosis was achieved in 47/147 (32%) of the patients. The diagnoses included benign lesions in 36 patients and malignancy in 9 patients. In 2 patients, FNAC demonstrated indeterminate follicular lesions; however, surgical excision was not performed. There was a highly significant difference in the mean SUVmax of malignant focal thyroid uptake (15.7 ± 5.9) compared to that of benign lesions (7.1 ± 6.8) with a p value of 0.000123. An SUVmax of 9.1 achieved a sensitivity of 81.6%, specificity of 100% and area under the curve of 0.915 in the ROC analysis differentiating benign from malignant disease.

CONCLUSION

The malignancy potential of incidental focal thyroid uptake remains high and warrants prompt and appropriate follow-up by the clinician. The SUVmax may aid in further characterisation of the lesion and its management.

Risk of malignancy in thyroid incidentalomas identified by fluorodeoxyglucose-positron emission tomography

BACKGROUND

Thyroid incidentalomas detected by 2-deoxy-2-18F-fluoro-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) have been reported in 1% to 4% of the population, with a risk of malignancy of 27.8% to 74%. We performed a retrospective review of FDG-avid thyroid incidentalomas in cancer screening subjects and patients with nonthyroid cancer. The risk of malignancy in thyroid incidentaloma and its association with the maximal standardized uptake value (SUVmax) in 18F-FDG PET/CT were evaluated to define the predictor variables in assessing risk of malignancy.

METHODS

A total of 2,584 subjects underwent 18F-FDG PET/CT for metastatic evaluation or cancer screening from January 2005 to January 2010. Among them, 36 subjects with FDG-avid thyroid incidentalomas underwent further diagnostic evaluation (thyroid ultrasonography-guided fine needle aspiration cytology [FNAC] or surgical resection). We retrospectively reviewed the database of these subjects.

RESULTS

Of the 2,584 subjects who underwent 18F-FDG PET/CT (319 for cancer screening and 2,265 for metastatic evaluation), 52 (2.0%) were identified as having FDG-avid thyroid incidentaloma and cytologic diagnosis was obtained by FNAC in 36 subjects. Of the subjects, 15 were proven to have malignant disease: 13 by FNAC and two by surgical resection. The positive predictive value of malignancy in FDG-avid thyroid incidentaloma was 41.7%. Median SUVmax was higher in malignancy than in benign lesions (4.7 [interquartile range (IQR), 3.4 to 6.0] vs. 2.8 [IQR, 2.6 to 4.0], P=0.001).

CONCLUSION

Thyroid incidentalomas found on 18F-FDG PET/CT have a high risk of malignancy, with a positive predictive value of 41.7%. FDG-avid thyroid incidentalomas with higher SUVmax tended to be malignant.

PET/CT in the management of thyroid cancers

OBJECTIVE

Thyroid cancer is the most common endocrine cancer. This review evaluates the established use of (18)F-FDG PET/CT in papillary, follicular, Hürthle cell, anaplastic, and medullary thyroid cancers. The significance of incidental diffuse and focal thyroid FDG uptake is discussed. The evolving value of non-FDG radiotracers, including (124)I, (18)F-dihydroxyphenylalanine, and (68)Ga somatostatin analogs, is summarized.

CONCLUSION

PET/CT is a valuable imaging test, in the appropriate clinical context, for the management of thyroid cancers.

Thyroid Carcinoma Detected by 18F-Fluorodeoxyglucose Positron Emission Tomography Among Individuals Without Prior Evidence of Thyroid Disease: Relevance and Clinicopathologic Features

OBJECTIVE

The expanding use of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) has contributed to an increasing number of thyroid incidentalomas. The present study aimed to estimate the prevalence of 18F-FDG-PET thyroid incidentalomas and evaluate the clinicopathologic features of thyroid malignancies detected by 18F-FDG-PET.

METHODS

We reviewed all 18F-FDG-PET exams performed at the Portuguese Institute of Oncology, Lisbon, between 2007 and 2012 (n = 9,374). The inclusion criteria were focal thyroid uptake and absence of known thyroid disease.

RESULTS

Focal thyroid uptake was observed in 60 out of 9,374 18F-FDG-PET exams (prevalence of 0.64%). Fine-needle aspiration cytology (FNAC) was performed in 23 patients and reported as malignant in 14 cases (56.5% primary thyroid carcinoma; 4.3% secondary malignancy), as benign in 7 cases (30.5%) and as follicular lesion of undetermined significance in 2 cases (8.7%). Fourteen patients had surgery. A final histologic diagnosis of papillary thyroid carcinoma was established in 12 cases (52.2%). Three were multifocal (25.0%); 8 had extrathyroidal extension (66.7%); 5 had angioinvasion (41.7%); 3 had lymph nodes metastases (25.0%) and 2 showed lung metastases (16.7%). Overall, 91.7% were classified as intermediate or high risk. All patients had radioiodine therapy. At the last observation (mean follow-up was 29.9 months), persistent or recurrent disease was identified in 4 patients (33.3%) and none died from thyroid malignancy.

CONCLUSIONS

Thyroid carcinomas disclosed by 18F-FDG-PET are associated with aggressive histological criteria likely to carry a worse prognosis.