A risk-adapted approach using US features and FNA results in the management of thyroid incidentalomas identified by 18F-FDG PET

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.

Update on the Evaluation of Thyroid Nodules

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

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.

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

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

The incidental thyroid nodule

Incidental thyroid nodules that are found on an imaging study performed for reasons other than thyroid pathology represent a common scenario encountered by health care providers. The initial workup for these nodules comprises a thorough history and physical examination, thyroid function tests, a dedicated thyroid ultrasound, and fine-needle aspiration of any suspicious lesions. Management ranges from observation and reassurance to surgical resection and depends on the cytologic diagnosis. In cases of cytologically indeterminate or discordant nodules, surgical excision (lobectomy) offers a definitive diagnosis, although molecular testing or a reasonable period of observation may be useful as less invasive adjuncts. CA Cancer J Clin 2018;68:97-105. © 2018 American Cancer Society.

18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography May Exclude Malignancy in Sonographically Suspicious and Scintigraphically Hypofunctional Thyroid Nodules and Reduce Unnecessary Thyroid Surgeries

BACKGROUND

The aim of this study was to evaluate whether ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) is useful in the further characterization of sonographically suspicious and scintigraphically hypofunctional thyroid nodules.

METHODS

Sixty-five patients with sonographically suspicious thyroid nodules that were hypofunctional on 99m-Tc-pertechnetate scintigraphy (diameter >1 cm) were retrospectively analyzed. All patients underwent evaluation with FDG-PET/CT. Thyroid nodules were sonographically categorized by Thyroid Image Reporting and Data System (TIRADS) criteria. FDG uptake in the thyroid nodules was visually compared to the remainder of the thyroid tissue and categorized as pathological or non-pathological. In cases of pathologically increased uptake, maximum standardized uptake values (SUVmax) of the suspicious nodule and the perinodular thyroid tissue were determined. Depending on the results of the FDG-PET/CT, patients underwent thyroid surgery (pathological FDG uptake) or follow-up examinations (non-pathological FDG uptake). The endpoints for comparison with the FDG uptake were either histological results or sonographic follow-up examinations of at least five years.

RESULTS

In 18/65 (28%) patients, PET/CT showed visually pathological FDG uptake in the suspicious thyroid nodules (SUVmax 7.1 ± 4.6). Of these nodules, 3/18 (17%) were sonographically categorized as TIRADS 4a, 11/18 (61%) nodules as TIRADS 4b, 3/18 (17%) nodules as TIRADS 4c, and 1/18 (6%) nodule as TIRADS 5. The other nodules without pathological FDG uptake were categorized as TIRADS 4a in 24/47 (51%) patients, as TIRADS 4b in 18/47 (38%), and as TIRADS 4c in 5/47 (11%) patients. Twenty-three patients (18 FDG positive, 5 FDG negative) underwent surgery. The other patients underwent follow-up examinations with stability on observation over at least five years as a surrogate endpoint. Taking into consideration that FDG-PET/CT was rated as true negative in 42/47 patients with stability on sonographic follow-up, sensitivity, specificity, positive predictive value, and negative predictive value of FDG-PET/CT in detecting malignancy in the suspicious thyroid nodules were 100%, 87%, 61%, and 100%, respectively.

CONCLUSION

FDG-PET/CT allows stratification of patients with sonographically suspicious and scintigraphically hypofunctional thyroid nodules with a positive predictive value of 61% and negative predictive value of 100%. The absence of visually pathological FDG uptake in suspicious thyroid nodules may be useful for avoiding unnecessary thyroid surgery.

Comparison of Core-Needle Biopsy and Fine-Needle Aspiration for Evaluating Thyroid Incidentalomas Detected by 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography: A Propensity Score Analysis

BACKGROUND

This study used a propensity score analysis to assess the roles of core-needle biopsy (CNB) and fine-needle aspiration (FNA) in the evaluation of thyroid incidentalomas detected on ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT).

METHODS

The study population was obtained from a historical cohort who underwent ¹⁸F-FDG PET/CT between October 2008 and September 2015. Patients were included who underwent ultrasound-guided CNB or FNA for incidental focal uptake of ¹⁸F-FDG in the thyroid gland on PET/CT. The primary study outcomes included the inconclusive result rates in the CNB and FNA groups. The secondary outcome measures included the non-diagnostic result rate and the diagnostic performance for neoplasms. Multivariate analysis, propensity score matching, and inverse probability weighting were conducted.

RESULTS

A total of 1360 nodules from 1338 patients were included in this study: 859 nodules from 850 patients underwent FNA, and 501 nodules from 488 patients underwent CNB. Compared to FNA, CNB demonstrated a significantly lower inconclusive result rate in the pooled cohort (23.8% vs. 35.4%; p < 0.001), propensity score-matched cohorts (22.9% vs. 36.6%; p < 0.001), and with inverse probability weighting (22.4% vs. 35.2%; p < 0.001). Non-diagnostic result rates were also significantly lower in CNB than in FNA. The diagnostic performance of the two groups in the pooled and matched cohorts was similar, with no significant differences found.

CONCLUSIONS

The significantly lower inconclusive result rates in CNB than in FNA were consistent within the propensity score-matched cohorts. Therefore, CNB appears to be a promising diagnostic tool for patients with thyroid incidentalomas detected on ¹⁸F-FDG PET/CT.

18F-Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography for Other Thyroid Cancers: Medullary, Anaplastic, Lymphoma and So Forth

Positron emission tomography/computed tomography (PET/CT) with ¹⁸F-fluorodeoxyglucose (FDG) is used in staging, restaging, and evaluation of therapy response in many cancers as well as differentiated thyroid carcinomas especially in non-iodine avid variants. Its potential in less frequent thyroid tumors like medullary, anaplastic thyroid cancers, thyroid lymphoma and metastatic tumors of the thyroid however, is not well established yet. The aim of this review is to provide an overview on the recent applications and indications of ¹⁸F-FDG PET/CT in these tumors and to focus on the controversies in the clinical setting.

Prognostic Impact of Ultrasonography Features and (18)F-Fluorodeoxyglucose Uptake in Patients With Papillary Thyroid Microcarcinoma

Objectives

To evaluate the prognostic impact of ultrasonography (US) features and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake in patients with papillary thyroid microcarcinoma (PTMC).

Methods

This study included 74 patients with a single PTMC diagnosed pathologically. Patients underwent total thyroidectomy, or near-total thyroidectomy and staging thyroid US and positron emission tomography (PET) were performed prior to surgery. US features of thyroid nodules were reviewed retrospectively and the maximum standard uptake value (SUV) of nodules was semiquantitatively analyzed on ¹⁸F-FDG PET/computed tomography (CT). Patients were followed-up for recurrence, which was defined as PTC on cytology results, elevated serum thyroglobulin (Tg) or anti-Tg antibody levels, or uptake on whole-body scintigraphy. We used univariate and multivariate analyses to evaluate whether poor prognostic outcomes were associated with US features or SUV values derived from PET/CT of nodules. In addition, subjects were divided into 2 groups for subgroup analyses: one with nodules equal to or larger than 5 mm and one with nodules smaller than 5 mm.

Results

Among the 74 patients, there was no recurrence. Thus we evaluated the correlation between SUV value and US features with poor prognostic factors of PTMC which included extrathyroid extension, central and lateral lymph node (LN) metastasis. However no clinicopathologic factors were associated with extrathyroid extension, central LN metastasis, or lateral LN metastasis.

Conclusion

In patients with PTMC, US features and SUV values on FDG-PET were not related to extrathyroid extension or LN metastasis. However, future studies with a larger sample size and longer follow-up should be performed to verify the results of this study.

Monitoring of renal ischemia reperfusion injury in rabbits by ultrasonic contrast and its relationship with expression of VEGF in renal tissue

OBJECTIVE

To evaluate the renal ischemia reperfusion injury (IRI) in rabbits using the ultrasonic contrast technique and discuss the clinical value of ultrasonic contrast technique in the diagnosis of renal IRI by comparing the time-intensity curve of renal cortex and the expression of vascular endothelial growth factor (VEGF) of renal tissue.

METHODS

Twenty 3-month-old New Zealand rabbits were randomly divided into 4 groups, namely Ctrl group, IRI-12 h, IRI-24 h and IRI-48 h groups. The two dimensional gray-scale ultrasonography was employed to determine and mark the position of rabbit kidney. Rabbits were given the intraperitoneal anesthesia with 20% urethane with the dosage of 5 mL/kg. The aseptic operation was performed after the local skin disinfection in the area of both kidneys. The right kidney of animals in the control group was excised without any treatment for the left kidney. After excising the right kidney of animals in groups of IRI-12 h, IRI-24 h and IRI-48 h, the aneurysm clip was used to clip the renal pedicle vessel of left kidney, in order to simulate the ischemia. Because of the tissue ischemia, it could be seen that the color of kidney was changed from bright red to dark red, which indicated the successful modeling of ischemia. The aneurysm clip was released after one hour of maintaining the ischemia. Then the kidney turned out to be bright red from dark red, which indicated that the reperfusion was completed. Taking this moment as the time of ischemia reperfusion, the wound was stitched up. A total of 12, 24 and 36 h after the operation, the two-dimensional and color Doppler flow imaging and ultrasonic contrast were employed for the examination. The dynamic changes of ultrasonic contrast were recorded. The quantitative analysis software (QontraXt) was adopted to analyze the time-intensity curve of echo at different positions of renal cortex. After the ultrasonic contrast testing, rabbits were put to death. The renal cortex tissue was isolated and the tissue RNA and total protein were extracted respectively. Real-time PCR and western blotting were used to detect the VEGF and the Pearson product moment correlation coefficient was used to measure the linear relationship between these two variables.

RESULTS

The ultrasonic contrast could clearly reflect the process of IRI. The results of testing at mRNA and protein level indicated that the expression of VEGF in IRI groups was significantly increased (P < 0.05) and the expression of VEGF was also increased by the time of reperfusion.

CONCLUSIONS

There is the certain correlation between the expression of VEGF and process of IRI. The correlation coefficient between the ultrasonic contrast parameters of AT and TTP and the relative expression of VEGF is over 0.9, which indicates the relatively high correlation. But there is no significant difference in the change of perfusion peak intensity between groups, which has no correlation with the expression of VEGF.

Thyroid incidentalomas detected on 18F-fluorodeoxyglucose-positron emission tomography/computed tomography: Thyroid Imaging Reporting and Data System (TIRADS) in the diagnosis and management of patients

BACKGROUND

Our aim was to evaluate the role of the Thyroid Imaging Reporting and Data System (TIRADS) in the risk stratification of thyroid incidentalomas detected on (18)F-fluorodeoxyglucose-positron emission tomography/computed tomography ((18)F-FDG-PET/CT) scans.

METHODS

Eighty-seven thyroid nodules in 84 patients showing incidentally detected increased uptake on (18)F-FDG-PET/CT who also had ultrasonography (US)-guided fine needle aspiration performed were included. On review of the US images, a TIRADS category was assigned to each thyroid nodule based on the number of suspicious US features. The correlation between the TIRADS category and the standard uptake values (SUV) on (18)F-FDG-PET/CT were calculated and compared.

RESULTS

Of the 87 thyroid nodules, 47 (54%) were benign, and 40 (46%) were malignant. The malignancy rate of the TIRADS categories were as follows: 9% for category 3, 15% for category 4a, 39% for category 4b, 72% for category 4c, and 100.0% for category 5. Combining the TIRADS with the SUV showed increased specificity and positive predictive value but decreased sensitivity and negative predictive value compared with TIRADS alone (all P < .05). The area under the receiver operating characteristics curve value of TIRADS was the greatest, comparable with the combined TIRADS and SUV (0.737 to 0.724, P = .788).

CONCLUSION

TIRADS may be applied in the risk stratification of thyroid incidentalomas detected on (18)F-FDG-PET/CT. Considering the high malignancy rate of thyroid incidentalomas showing increased (18)F-FDG uptake, ultrasonography-guided fine needle aspiration is mandatory even if there are no suspicious features present on US.