Thyroid Incidentalomas on 18F-FDG PET/CT: Clinical Significance and Controversies

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.

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.

MANAGEMENT PRINCIPLES OF INCIDENTAL THYROID 18F-FDG UPTAKE IDENTIFIED ON 18F-FDG PET/CT IMAGING

PURPOSE

The purpose of this study is to determine the clinical significance of incidental thyroid 18F-FDG PET/CT uptake in oncology patients with the focus achieving the most appropriate management of this challenging situation.

MATERIALS AND METHOD

Two thousand five hundred and eighty 18F-FDG PET/CT studies performed at our institute in the past 4 years were retrospectively reviewed. Patients with incidental FDG uptake in the thyroid gland were further analysed.

RESULTS

The prevalence of incidental FDG uptake in thyroid gland was 7.6% (129 patients). 26 patients (20.1%) had diffuse 18F-FDG PET/CT uptake, 103 patients (79.1%) had nodular uptake in thyroid gland. All diffuse uptake patients who were further examined diagnosed to be a benign condition. 53 patients in the nodular uptake group were further examined and the final histopathology examinations revealed an 18.8% malignancy rate. SUV max values ranged from 2 to 21.8 with a significant highness in malignant lesions.

CONCLUSION

18F-FDG PET/CT uptake in the thyroid gland may be diffuse or nodular. Diffuse uptake needs no further examination as it usually accompanied by benign thyroid disorders. Patients with nodular uptake whose general condition is good should be further examined due to high rates of malignancy.

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.

The Role of Metabolic Volumetric Parameters in Predicting Malignancy in Incidental Thyroid Nodules Detected in 18F-FDG PET/CT Scans

Objectives

The metabolic activities of tumors can be calculated volumetrically during positron emission tomography/computed tomography (PET/CT) imaging using metabolic tumor volume (MTV) and total lesion glycolysis (TLG). This study aimed to evaluate the roles of MTV and TLG in predicting the malignancy risk of incidental thyroid nodules detected by PET/CT imaging.

Methods

Active metabolic areas of each section were manually drawn by region of interest to calculate the MTV of nodules, and all obtained values were then summed. TLG, the product of mean standardized uptake value and MTV, was calculated by multiplying two values. All participants underwent thyroid ultrasonography imaging. All nodules were divided into risk classes according to the European Thyroid Image Reporting and Data System (EU-TIRADS) that was developed by the European Thyroid Association. The American Thyroid Association Guidelines were used to determine which thyroid nodules would undergo thyroid fine-needle biopsy (FNAB). Results were classified according to the Bethesda scoring system.

Results

TLG levels were significantly higher in malignant or malignant-suspicious nodules than in benign nodules (p=0.013). Although MTV levels were high in malignant or malignant-suspicious nodules than in benign and non-diagnostic nodules, it was statistically insignificant at limit values (p=0.079). Areas under curve (AUC) were 0.726 (p=0.005) and AUC: 0.668 (p=0.039) for TLG and MTV, respectively. The 2.3 g cut-off value of TLG has a sensitivity of 85.7% and specificity of 59.0%. The 1.7 mL cut-off value of MTV has a sensitivity of 78.6% and specificity of 60.4%.

Conclusion

We believe that TLG evaluation will be useful in predicting high-risk malignancy or malignancy suspicion based on EU-TIRADS risk classification of incidental thyroid nodules detected in PET/CT images. We believe that unnecessary thyroid FNABs can be avoided for thyroid incidental nodules if such relation and cut-off values are determined and that it will be useful in hastening the operation of the necessary patients.

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.

Thyroid Cancer Identified After Positron Emission Tomography (PET) Shows Aggressive Histopathology

BACKGROUND

Incidental thyroid nodules with focal uptake on positron emission tomography (PET) have an increased risk for malignancy, with the majority being differentiated thyroid cancer (DTC). It is unclear whether these cancers have more aggressive histopathology compared with DTC diagnosed via other means.

METHOD

Electronic medical record of two medical centers was queried for the period of 2001-2016 to identify patients who underwent PET imaging for nonthyroid-related indications and who were found to have focal thyroid uptake. Patients who underwent thyroid nodule fine needle aspiration biopsy (FNAB) and subsequent thyroidectomy with a final diagnosis of DTC were further reviewed. A comparison group, matched for age, tumor type, and tumor size, was selected from consecutive patients who underwent surgery for DTC.

RESULTS

Among 35,124 PET scans reviewed, 227 (0.6%) patients were found to have focal thyroid uptake and underwent FNAB: Fourty-seven (21%) were found to have cancer (36 papillary thyroid cancer (PTC), 9 metastases, and 2 lymphoma). Sixty-seven patients proceeded to surgery: Thirty-one with FNAB of PTC and the rest with indeterminate FNAB necessitating diagnostic thyroidectomy. Compared with the control group, the PET PTC patients involved more men (54% versus 26%, P = 0.003), had more advanced tumor stage (P = 0.03), and had increased BRAF mutation on final pathology (78% versus 42%, P = 0.05).

CONCLUSIONS

This study demonstrates that DTC detected on PET is most commonly of the papillary type. Despite the small sample size, the results suggest that these PTC may be more aggressive than PTC detected through other means and more frequently harbor BRAF mutations.

Small cell lung cancer with thyroid gland oligometastasis: A case report

Extensive disease small cell lung cancer (ED-SCLC) is a systemic disease characterized by diffuse metastases and a poor prognosis. Oligometastatic cases in ED-SCLC are rare. This study reports the case of a 72-year-old Japanese male. A mass lesion was identified on chest computed tomography (CT). Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) revealed a solitary thyroid gland lesion with high FDG uptake as an extrapulmonary finding, suggesting thyroid cancer or a goiter. Upon confirmation of diagnosis, treatment of SCLC was prioritized, and chemoradiotherapy for limited disease SCLC was initiated without further examination of the thyroid gland. The thyroid nodule disappeared after treatment. Two years later, the disease recurred, and a thyroid nodule was found to have reappeared. Upon fine needle aspiration cytology of the thyroid, small cell carcinoma was detected. Therefore, in cases of SCLC, it is necessary to carefully investigate the thyroid for solitary lesions to consider the possibility of oligometastasis. KEY POINTS: SIGNIFICANT FINDINGS OF THE STUDY: Manifesting as a solitary lesion, oligometastasis, particularly in the thyroid, is rare in cases of ED-SCLC. WHAT THIS STUDY ADDS: In SCLC cases, it is necessary to carefully investigate the thyroid for solitary lesions to consider the possibility of oligometastasis.

The role of histogram analysis of grayscale sonograms to differentiate thyroid nodules identified by 18F-FDG PET-CT

The role of histogram based on ultrasound (US) images for thyroid nodules found in fluorine-18 fluorodeoxyglucose (18F-FDG) Positron Emission Tomography/Computed Tomography (PET-CT) is unknown. We aimed to assess whether histogram analysis using gray scale US could differentiate thyroid nodules detected by PET-CT.In this study, 71 thyroid nodules ≥1 cm were identified in 71 patients by conducting 18F-FDG PET-CT, from January 2010 to June 2013. Subsequently, either grayscale US-guided fine needle aspirations or core needle biopsies were performed on each patient. Each grayscale US feature was categorized according to the Korean Thyroid Imaging Reporting and Data System (K-TIRADS). Histogram parameters (skewness, kurtosis, intensity, uniformity, and entropy) were extracted from the grayscale US images followed by statistical analysis using the Chi-Squared or Mann-Whitney U tests.The 71 nodules comprised 30 (42.3%) benign nodules, 30 (42.3%) primary thyroid malignancies, and 11 (15.4%) metastatic lesions. Tumor size, US findings, and histogram parameters were significantly different between the benign and malignant thyroid nodules (P = .011, P = .000, and P < .02, respectively). A comparison showed that parallel orientation and an absence of calcifications were found more frequently in metastatic thyroid nodules than in primary thyroid malignancies (P = .04, P < .000, respectively). However, histogram parameters and K-TIRADS were not significantly different between primary thyroid malignancies and metastatic lesions.There is a limit to replacing cytopathological confirmation with texture analysis for the differentiation of thyroid nodules detected by PET-CT. Therefore, cytopathological confirmation of nodules appearing malignant on US images cannot be avoided for an ultimate diagnosis of metastasis.

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).

Thyroid Ultrasound: Diffuse and Nodular Disease

Thyroid ultrasound with gray-scale and color Doppler is the most helpful imaging modality to differentiate normal thyroid parenchyma from diffuse or nodular thyroid disease by evaluating glandular size, echogenicity, echotexture, margins, and vascularity. The various causes of diffuse thyroid disease often have overlapping sonographic imaging features. Thyroid nodules may be hyperplastic or neoplastic, with most due to benign hyperplastic changes in architecture and benign follicular adenomas; only a small percentage are malignant. A systematic approach to nodule morphology that includes evaluation of composition, echogenicity, margin, shape, and any echogenic foci can guide decision to biopsy or follow nodules.

Evaluation of Malignancy Risk in 18F-FDG PET/CT Thyroid Incidentalomas

Thyroid incidentalomas detected by 18 fluoro-2-deoxy-d-glucose (FDG)-positron emission tomography/computed tomography (PET/CT) are a real challenge for nuclear medicine physicians and clinicians. This study aimed to evaluate the risk of malignancy for patients with focal thyroid incidentalomas (TIs) diagnosed through FDG PET/CT. Data from 6900 patients, with a known primary tumor, who had an FDG PET/CT investigation performed were analyzed for the presence of incidental thyroid uptake. The focal TIs were reported, and the patients were referred for further investigation to the endocrinology department. There were 126 patients (1.82%) who presented with focal thyroid uptake, and for 87 of them, investigations were completed with ultrasonography (US), and for 29 with a fine needle aspiration biopsy (FNAB) procedure. Malignancy was detected in 7.93% (10/126) of cases. An arbitrary cutoff value of four was established for the standard uptake value lean body mass (SUVlbm Max) to differentiate the malignant nodules from the benign ones, and this value was significantly associated with malignancy (p = 0.0168). TIs are not so frequent, but they have a potential malignancy risk, and a proper evaluation is required. Even though SUVlbm Max is a predictive factor for malignancy, the FNAB remains the main diagnostic method for the therapeutic management of these patients.

Usefulness of both PET/CT with F18-FDG and whole-body diffusion-weighted imaging in cancer screening: a preliminary report

OBJECTIVE

Positron emission tomography/computed tomography (PET/CT) with fluorodeoxyglucose (F18-FDG) is useful for the detection of malignant lesions, including metastatic lesions, and this technique is widely used in cancer screening. However, this approach may occasionally yield false-positive and false-negative findings. At our PET center, to increase the accuracy of PET/CT, we use PET/CT and whole-body diffusion-weighted imaging (WB-DWI) together. This study aimed to assess the usefulness of this combination.

METHODS

We examined 29 subjects with confirmed diagnosis. All of them had undergone PET/CT and WB-DWI on the same day. Twenty-seven of them also underwent ultrasonography, blood testing, and upper gastrointestinal series on the same day and two fecal occult blood tests on another day. WB-DWI was performed on a 1.5-T MRI unit with a b value of 0 and 800 or 1000 s/mm². For all 29 cases, PET/CT and WB-DWI were classified to be positive or negative, and the diagnostic ability was calculated for each modality.

RESULTS

Among the 29 subjects, 17 had malignant tumors and 12 had benign tumors or no abnormalities. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of PET/CT were 65%, 25%, 55%, 33%, and 48%, respectively; while the corresponding values for WB-DWI were 59%, 100%, 100%, 63%, and 76%, respectively. By considering the result to be negative when PET/CT findings were positive but WB-DWI findings were negative, specificity increased from 25 to 100%, and accuracy increased from 48 to 76%. On the other hand, by considering the result to be positive when the findings of either PET/CT or WB-DWI were positive, sensitivity increased from 65 to 76%, and accuracy increased from 48 to 55%.

CONCLUSIONS

Our results suggest that using both PET/CT and WB-DWI together can increase accuracy in cancer screening. However, this approach was not able to detect malignant lesions in some cases, indicating that there were limitations with imaging certain organs. Therefore, it is important to further understand the features of PET/CT and WB-DWI and use them appropriately for each organ. Additionally, given that the study sample was relatively small, further research is needed to validate these findings.

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.