Preoperative evaluation of thyroid nodules with 18FDG-PET/CT

Positron Emission Tomography/Computed Tomography in Thyroid Cancer: An Updated Review

PET/computed tomography (CT) is a valuable hybrid imaging modality for the evaluation of thyroid cancer, potentially impacting management decisions. 18F-fluorodeoxyglucose (FDG) PET/CT has proven utility for recurrence evaluation in differentiated thyroid cancer (DTC) patients having thyroglobulin elevation with negative iodine scintigraphy. Aggressive histologic subtypes such as anaplastic thyroid cancer shower higher FDG uptake. 18F-FDOPA is the preferred PET tracer for medullary thyroid cancer. Fibroblast activation protein inhibitor and arginylglycylaspartic acid -based radiotracers have emerged as promising PET agents for radioiodine refractory DTC patients with the potential for theranostic application.

Comparison of 18F-FDG-PET and 18F-FDG-PET/CT for the diagnostic performance in thyroid nodules with indeterminate cytology: A meta-analysis

BACKGROUNDS

We performed a meta-analysis to compare F-FDG-PET and F-FDG-PET/CT for the diagnostic performance in thyroid nodules with indeterminate cytology by Bethesda classification.

METHODS

PubMed and Embase databases were searched for eligible studies from the earliest available date of indexing through September 2019. Only studies with clearly stated histopathology confirmation were included. Publication bias was assessed by Deeks funnel plot. The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value, negative predictive value, and diagnostic odds ratio was determined by random-effect analysis, respectively. All diagnostic estimate indexes were determined separately for PET alone and PET/CT and were compared pair-wisely using Z-test.

RESULTS

We included 214 patients from five PET alone studies and 420 patients from 8 PET/CT studies in this meta-analysis. The range of the prevalence of malignancy was 11% to 27% for PET alone studies (Median, 20%) and 4% to 50% for PET/CT studies (Median, 24%). The sensitivity (0.95 vs 0.73, P < .01), negative likelihood ratio (0.20 vs 0.53, P = .04) and negative predictive value (0.99 vs 0.91, P < .01) of PET alone are significantly better than those of PET/CT. For PET/CT, Fagan nomogram indicated that when the pre-test probability was set at 24%, the negative post-test probability could decrease to 12%.

CONCLUSION

This meta-analysis reveals that in evaluating thyroid nodules with indeterminate cytology by Bethesda classification, the rule-out performance of F-FDG-PET is significantly better than F-FDG-PET/CT, although the latter represents a more objective and accurate technique. We hypothesize that the lack of precise localization of suspicious FDG uptake in the neck region may have contributed to this overvaluation for PET alone studies, and advocate that future studies be performed with PET/CT rather than PET alone to avoid misinterpretation and overvaluation in this scenario.

Performance of 18F-FDG PET/CT in Selecting Thyroid Nodules with Indeterminate Fine-Needle Aspiration Cytology for Surgery. A Systematic Review and a Meta-Analysis

Thyroid nodules with indeterminate fine-needle aspiration cytology (FNA) represent a major challenge in clinical practice. We conducted a systematic review and meta-analysis evaluating the ability of hybrid imaging using fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) to appropriately select these nodules for surgery. PubMed, CENTRAL, Scopus, and Web of Science were searched until July 2019. Original articles reporting data on the performance of ¹⁸F-FDG PET/CT in thyroid nodules with indeterminate FNA were included. Summary operating points including 95% confidence interval values (95% CI) were estimated using a random-effects model. Out of 786 retrieved papers, eight studies evaluating 104 malignant and 327 benign thyroid nodules were included. The pooled positive and negative likelihood ratios (LR+ and LR-) and diagnostic odds ratio (DOR) of ¹⁸F-FDG PET/CT were 1.7 (95% CI: 1.4-2.0), 0.4 (95% CI: 0.2-0.7), and 3.5 (95% CI: 1.7-7.1), respectively. No heterogeneity was found for LR+ and DOR. In patients with thyroid nodules with indeterminate FNA, ¹⁸F-FDG PET/CT has a moderate ability to correctly discriminate malignant from benign lesions and could represent a reliable option to reduce unnecessary diagnostic surgeries. However, further studies using standardized criteria for interpretation are needed to confirm the reproducibility of these findings.

Comparison of Natural Course between Thyroid Cancer Nodules and Thyroid Benign Nodules

BACKGROUND

The natural course of thyroid cancer nodules and benign nodules is different. This study was to compare the changes in size between thyroid cancer nodules and thyroid benign nodules. The risk factors associated with the changes of thyroid cancer nodules were assessed.

METHODS

This study contains retrospective observational and prospective analysis. A total of 113 patients with 120 nodules were recruited in the cancer group, and 116 patients with 119 nodules were enrolled in the benign group. Thyroid ultrasonography was performed at least two times at more than 1-year interval.

RESULTS

The mean follow-up durations were 29.5±18.8 months (cancer group) and 31.9±15.8 months (benign group) (P=0.32). The maximum diameter change in length was 0.36±0.97 mm/year in the cancer group and -0.04±0.77 mm/year in the benign group (P<0.01). The volume was significantly increased in the cancer group compared with the benign group (0.06±0.18 mL/year vs. 0.004±0.05 mL/year, respectively, P<0.01; 26.9%±57.9%/year vs. 1.7%±26.0%/year, P<0.01). Initial maximum diameter (β=0.02, P<0.01) and initial volume (β=0.13, P<0.01) were significantly associated with volume change (mL)/year. Initial maximum standardized uptake value did not predict the nodule growth.

CONCLUSION

It is suggested that thyroid cancer nodules progress rapidly compared with benign nodules. Initial size and volume of nodule were independent risk factors for cancer nodule growth.

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.

Controversy regarding when clinically suspicious thyroid nodules should be subjected to surgery: Review of current guidelines

BACKGROUND

The work-up of a thyroid nodule to diagnose malignancy is not always straightforward. There are various international thyroid societies each with their own guidelines on the approach to a thyroid nodule. The aim is therefore to determine whether a clinically suspicious thyroid nodule should be subjected to surgery.

METHOD

A review of various international thyroid society guidelines on their approach to a suspicious thyroid nodule.

RESULTS

Sixty-two relevant articles were identified of which 4 current international thyroid guidelines, consisting of 6 different international societies, were reviewed. The commonalities of each of the thyroid society guidelines are imaging, with ultrasound, and cytopathology as the main diagnostic investigations. The description and the size of the nodule are the 2 most important factors on ultrasound; however, the guidelines vary in their recommendations whether to biopsy a suspicious thyroid nodule. An indeterminate group exists whereby thyroid nodules cannot be confirmed as malignant even with fine needle aspiration cytology (FNA). Although further investigations (Technetium-99m -sestamethoxyisobutylisonitryl scan, 18F-fluorodeoxyglucose positron emission tomography/computed tomography scan, and molecular testing) may assist in the diagnosis, there are limitations. There are differences in the guidelines whether suspicious nodules should be subjected to surgery.

CONCLUSION

Ultrasound and cytopathology are the 2 most appropriate investigations to diagnose whether a suspicious thyroid nodule is benign or malignant. The clinician needs to be aware of the differences between the guidelines from the various international thyroid societies, specifically concerning the indeterminate group of patients where a definitive diagnosis cannot be made. Management decisions should be discussed with a thyroid multidisciplinary team for a consensus decision whether or not to subject a patient with a suspicious thyroid nodule to surgery.

PET/CT and prediction of thyroid cancer in patients with follicular neoplasm or atypia

PURPOSE

To examine whether addition of ¹⁸F-fluoro-deoxy-glucose positron emission tomography/computed tomography (FDG-PET/CT) to fine needle aspiration biopsy (FNAB) would improve prediction of thyroid cancer in patients with FNAB-derived follicular neoplasm or atypia, classified according to focal, multifocal, diffuse, or no FDG uptake.

MATERIALS AND METHODS

Consecutive patients with FNAB-derived follicular neoplasm or atypia planned for surgery from September 2013 to March 2016 were prospectively included and considered for analysis. All patients underwent preoperative PET/CT and a clinical head and neck examination, including ultrasound of the neck and the thyroid gland. Patients with obvious signs of thyroid malignancy were excluded from the study. Histology of the surgical specimen was used as reference standard for statistical analysis.

RESULTS

Of the 108 patients included (85 women, median age 53.4 years), 31 (29%) had a thyroid nodule that was histologically verified as malignant. Sensitivity and specificity for PET/CT in detection of thyroid cancer was 79 and 32%, respectively, including a derived positive predictive value (PPV) of 31%, and a negative predictive value (NPV) of 79%. Univariate and multivariate analyses showed no significant increase in the risk of thyroid cancer among patients with focal or multifocal FDG uptake compared to patients with no FDG uptake.

CONCLUSION

Addition of PET/CT to FNAB did not improve prediction of thyroid cancer in patients with FNAB-derived follicular neoplasm or atypia.

Diagnostic Utility of Molecular and Imaging Biomarkers in Cytological Indeterminate Thyroid Nodules

Indeterminate thyroid cytology (Bethesda III and IV) corresponds to follicular-patterned benign and malignant lesions, which are particularly difficult to differentiate on cytology alone. As ~25% of these nodules harbor malignancy, diagnostic hemithyroidectomy is still custom. However, advanced preoperative diagnostics are rapidly evolving.This review provides an overview of additional molecular and imaging diagnostics for indeterminate thyroid nodules in a preoperative clinical setting, including considerations regarding cost-effectiveness, availability, and feasibility of combining techniques. Addressed diagnostics include gene mutation analysis, microRNA, immunocytochemistry, ultrasonography, elastosonography, computed tomography, sestamibi scintigraphy, [18F]-2-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET), and diffusion-weighted magnetic resonance imaging.The best rule-out tests for malignancy were the Afirma® gene expression classifier and FDG-PET. The most accurate rule-in test was sole BRAF mutation analysis. No diagnostic had both near-perfect sensitivity and specificity, and estimated cost-effectiveness. Molecular techniques are rapidly advancing. However, given the currently available techniques, a multimodality stepwise approach likely offers the most accurate diagnosis, sequentially applying one sensitive rule-out test and one specific rule-in test. Geographical variations in cytology (e.g., Hürthle cell neoplasms) and tumor genetics strongly influence local test performance and clinical utility. Multidisciplinary collaboration and implementation studies can aid the local decision for one or more eligible diagnostics.

Examining the Role of Preoperative Positron Emission Tomography/Computerized Tomography in Combination with Ultrasonography in Discriminating Benign from Malignant Cytologically Indeterminate Thyroid Nodules

BACKGROUND

Cytologically defined indeterminate thyroid nodules are a diagnostic challenge. Surgical lobectomy remains the gold standard for definitive diagnosis. However, 70-85% of nodules are ultimately benign. The primary objective of this study was to evaluate the negative predictive value (NPV) of F18-fluorodeoxyglucose (FDG) positron emission computed tomography (PET/CT) in excluding cancer among cytologically indeterminate thyroid nodules within the authors' institution using surgical pathology as the gold-standard reference. In addition, a systematic review was performed of published prospective studies on the NPV of PET/CT in evaluating indeterminate thyroid nodules.

METHODS

A retrospective review was performed of all patients aged ≥18 years seen at the Mayo Clinic between January 1, 2000, and December 31, 2014, with cytologically defined indeterminate thyroid nodules (suspicious for Hürthle cell neoplasm or follicular neoplasm; N = 858), who had a PET/CT within one year of fine-needle aspiration (n = 80) and underwent definitive diagnostic lobectomy (n = 51). Nodules were considered PET negative if they had a standardized uptake value (SUV) <5. Additionally, a systematic review was performed of published prospective studies on the NPV of PET/CT across multiple sites.

RESULTS

Fifty-one patients met the eligibility criteria. The retrospective review combined with a systematic review of eight prospective studies suggests that indeterminate nodules with a negative PET (SUV <5) have a low risk of malignancy (NPV 94%). The cancer prevalence in the institution is 14% and 27% in the combined prospective studies.

CONCLUSIONS

PET/CT represents a preoperative, non-invasive tool that when combined with sonographic features can identify indeterminate nodules at low risk for malignancy.

Multidetector computed tomography analysis of benign and malignant nodules in patients with chronic lymphocytic thyroiditis

The aim of the present study was to compare the multidetector computed tomography (MDCT) features of benign and malignant nodules in patients with chronic lymphocytic thyroiditis (CLT). MDCT findings, including the size, solid percentage, calcification, margin, capsule, anteroposterior-transverse diameter ratio as well as the mode and the degree of enhancement of 137 thyroid nodules in 127 CLT cases were retrospectively analyzed. Furthermore, the correlation between MDCT findings and pathological results combined with the CT perfusion imaging was analyzed for the differences between benign and malignant nodules. A total of 77.5% (31/40) of malignant nodules were completely solid, and 33% (32/97) of benign nodules were predominantly cystic. Compared with the benign nodules, micro-calcification and internal calcification were more frequently observed in the malignant nodules (P<0.05). MDCT features such as ill-defined margin, absence of capsule or incomplete capsule or homogeneous enhancement were more likely to be present in the malignant nodules (P<0.05). Nevertheless, no significant difference was observed in the enhancement degree at arterial or venous phase between benign and malignant nodules (P>0.05). MDCT features are useful in differentiating the benign and malignant nodules in CLT patients, and it may be essential for a radiologist to review the MDCT characteristics of nodules in the clinical practice.

Preoperative Lymph Node Staging by FDG PET/CT With Contrast Enhancement for Thyroid Cancer: A Multicenter Study and Comparison With Neck CT

Objectives

The purpose of this study was to compare lymph node (LN) staging using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) with contrast-enhancement (CE) PET/CT and contrast-enhanced neck CT (neck CT) in patients with thyroid cancer with level-by-level comparison with various factors.

Methods

This was a retrospective multicenter study. A total of 85 patients were enrolled. Patients who underwent a preoperative evaluation by CE PET/CT and neck CT for thyroid cancer were enrolled. The gold standard for LN was the combination of surgical pathology and clinical follow-up. We compared CE PET/CT with neck CT using a level-by-level method. Factors, including age, sex, camera, arm position, tumor size, extra-thyroidal extension, tumor location, number of primary tumors, primary tumor maximum standardized uptake value, and the interval from scan to operation were also analyzed.

Results

Overall accuracy was 81.2% for CE PET/CT and 68.2% for neck CT. CE PET/CT was more sensitive than neck CT (65.8% vs. 44.7%). Also, CE PET/CT showed higher negative predictive value (77.2% vs. 66.1%). CE PET/CT showed good agreement with the gold standard (weighted kappa [κ], 0.7) for differentiating N0, N1a, and N1b, whereas neck CT showed moderate agreement (weighted κ, 0.5). CE PET/CT showed better agreement for the number of levels involved with the gold standard (weighted κ, 0.7) than that of neck CT with the gold standard (weighted κ, 0.5). The accuracies for differentiating N0, N1a, and N1b were 81.2% for CE PET/CT and 68.2% for neck CT. Level-by-level analysis showed that CE PET/CT was more sensitive and has higher negative predictive value for detecting ipsilateral level IV and level VI LNs than neck CT. Other analyzed factors were not related to accuracies of both modalities.

Conclusion

CE PET/CT was more sensitive and reliable than neck CT for preoperative LN staging in patients with thyroid cancer.

Incidence of Thyroid Carcinoma in Fluorodeoxyglucose Positron Emission Tomography-Positive Thyroid Incidentalomas

OBJECTIVE: Fluorodeoxyglucose (FDG) whole body positron emission tomography (PET) scan may show clinically occult second lesions. Such lesions in the thyroid are increasingly common. There are several recent reports of a high probability of malignancy in these lesions ranging from 14% to 63%.

STUDY DESIGN AND SETTING: This is a retrospective review of 15,711 PET scans at a multi-disciplinary thyroid clinic at a tertiary care university medical center. Twenty-two patients were referred with thyroid PET “incidentalomas.” The review included 18 FDG-PET scans, ultrasound guided fine needle aspiration biopsies, and thyroid surgery pathology. Aspiration cytology or pathology were the main outcome measures.

RESULTS: Three patients had malignancy of the PET-positive thyroid lesions. Papillary thyroid micro carcinomas were detected in four of the specimens that showed a benign pathology of the dominant nodule.

CONCLUSION: Our experience shows a 14% malignancy rate for the dominant (imaged) nodule and a total malignancy rate of 32% when the incidental micro carcinomas are included. Both of these rates are significantly lower than results published previously.

Role of 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in the Evaluation of Cytologically Indeterminate Thyroid Nodules

BACKGROUND

Thyroid nodules with indeterminate fine-needle aspiration biopsy (FNAB) results remain a diagnostic dilemma, because 70 - 85% of these nodules have been found to be benign after thyroid surgery.

OBJECTIVES

The purpose of this study was to evaluate the usefulness of 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in the preoperative diagnosis of cytologically indeterminate nodules.

PATIENTS AND METHODS

Forty-six patients were included in this study. These individuals had undergone FDG PET/CTs for the preoperative evaluation of thyroid nodules with indeterminate FNAB results. The results of the preoperative PET/CT scans were compared with the postoperative pathological results and statistically analyzed.

RESULTS

Of the 46 patients included in our study, the histopathology of the surgical specimens revealed thyroid cancer in 17 individuals (37%, 17/46). The PET/CT scan showed a positive result in 27 patients. Of these, 16 patients (59.3%) were found to have thyroid carcinomas. In addition, the PET/CT scan was considered to be negative in 19 patients, 18 (94.7%) of whom had benign lesions. For the detection of malignant lesions, the values for the sensitivity and specificity, and the positive predictive and negative predictive values were 94%, 62%, 59%, and 95%, respectively.

CONCLUSION

The FDG PET/CT showed a high sensitivity and a high negative predictive value for identifying malignancies in thyroid nodules with indeterminate FNAB results. Therefore, the FDG PET/CT may be a helpful tool in the clinical management of these nodules. When an FDG positive lesion is detected, further examination is recommended.

SUVmax of 18F-FDG PET/CT in the differential diagnosis of benign and malignant thyroid nodules according to tumor volume

BACKGROUND

The aim of this study was to investigate whether the maximum standardized uptake value (SUVmax) measured on fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) could be used as the primary means of differential diagnosis of thyroid nodules when tumor volume is assessed.

METHODS

We studied 192 patients who underwent preoperative 18F-FDG PET/CT followed by thyroidectomy. We evaluated the correlation between the volume of thyroid nodules, 18F-FDG uptake on visual analysis, and the mean SUVmax measured on 18F-FDG PET/CT.

RESULTS

When stratified by tumor volume, the mean SUVmax was higher in malignant than in benign nodules in nodules≥1 cm3 (p<0.001). However, it did not differ between benign and malignant nodules smaller than 1 cm3. At a cut-off value of SUVmax of 6, the respective sensitivities of 18F-FDG PET/CT, ultrasonography, and fine needle aspiration cytology were 60.8, 96.4, and 99.1%, and the respective specificities were 95.9, 98.2, and 96.8%.

CONCLUSIONS

18F-FDG PET/CT is limited as a primary modality in the differential diagnosis of benign and malignant thyroid nodules because of its low sensitivity.

Molecular Analysis by Gene Expression of Mitochondrial ATPase Subunits in Papillary Thyroid Cancer: Is ATP5E Transcript a Possible Early Tumor Marker?

BACKGROUND

Cancer development involves an "injury" to the respiratory machinery (Warburg effect) due to decreased or impaired mitochondrial function. This circumstance results in a down regulation of some of the ATPase subunits of the malignant tissue. The objective of this work was to assess and compare the relative expression of mRNA of mitochondrial ATPase subunits between samples of thyroid cancer and benign nodules.

MATERIAL AND METHODS

Samples from 31 patients who had an operation for PTC at the General Hospital of Mexico were snap-frozen and stored at -70°C. Thirty-five patients who had an operation for benign tumors were also included in the study. mRNA expression levels of alpha, beta, gamma, and epsilon subunits of F1 and "c12" of subunit Fo were determined by real-time RT-PCR (by duplicate), in order to determine if abnormal expression of these genes could partially explain the Warburg effect in papillary thyroid cancer (PTC).

RESULTS

ATP5E transcript alteration (down-expression) was highly associated to PTC diagnosis OR=11.76 (95% confidence interval, 1.245-237.98; p=0.04).

CONCLUSIONS

Relative down-expression of ATP5E transcript was highly associated with PTC diagnosis. This transcript alteration may be used as a tumoral marker in papillary thyroid cancer.

The usefulness of standardized uptake value in differentiation between benign and malignant thyroid lesions detected incidentally in 18F-FDG PET/CT examination

Introduction

In the last decade, (18)F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET and PET/CT) has become one of the major diagnostic tools used in oncology. A significant number of patients who undergo this procedure, due to non-thyroidal reasons, present incidental uptake of (¹⁸F-FDG) in the thyroid. The aim of the study was to compare the SUV_max (standardized uptake value) of thyroid focal lesions, which were incidentally found on PET/CT, in relation to the results of thyroid fine-needle aspiration biopsy (FNAB) and/or histopathological evaluation.

Materials and Methods

Patients referred for PET/CT examination, due to non-thyroidal illness, presented focal ¹⁸F-FDG uptake in the thyroid and were advised to undergo ultrasonography (US), hormonal evaluation, FNAB and/or total thyroidectomy at our institution.

Results

6614 PET/CT examinations performed in 5520 patients were analyzed. Of the 122 patients with focal thyroid ¹⁸F-FDG activity, 82 patients (67.2%) underwent further thyroid evaluation using FNAB. Benign lesions were diagnosed in 46 patients, malignant - in 19 patients (confirmed by post-surgical histopathology), while 17 patients had inconclusive results of cytological assessment. Mean SUV_max of benign lesions was 3.2±2.8 (median = 2.4), while the mean SUV_max value for malignant lesions was 7.1±8.2 (median = 3.5). The risk of malignancy was 16.7% for lesions with a SUV_max under 3, 43.8% for lesions with a SUV_max between 3 and 6, and 54.6% for lesions with a SUV_max over 6. In the group of malignant lesions, a positive correlation between the lesion’s diameter and SUV_max was observed (p = 0.03, r = 0.57).

Conclusions

Subjects with incidental focal uptake of ¹⁸F-FDG in thyroid are at a high risk of thyroid malignancy. A high value of SUV_max further increases the risk of malignancy, indicating the necessity for further cytological or histological evaluation. However, as SUV_max correlated with the diameter of malignant lesions, small lesions with focal uptake of ¹⁸F-FDG should be interpreted cautiously.

Clinical value of visually identifiable 18F-fluorodeoxyglucose uptake in primary papillary thyroid microcarcinoma

OBJECTIVE

This study evaluates the relationship between visually identifiable (18)F-fluorodeoxyglucose (FDG) uptake in primary papillary thyroid microcarcinoma (PTMC) and tumor aggressiveness.

STUDY DESIGN

Historical cohort study.

SETTING

Tertiary care center.

METHODS

Clinicopathological factors and PET/CT findings of 219 PTMC surgical patients who underwent preoperative (18)F-FDG positron emission tomography/computed tomography (PET/CT) were retrospectively reviewed.

RESULTS

(18)F-FDG uptake was observed in the tumors of 124 (56.6%) patients. Tumor size (odds ratio [OR] = 1.774; 95% confidence interval [CI], 1.416-2.223; P < .0001) and Hashimoto thyroiditis (OR = 2.815; CI, 1.237-6.404; P = .014) independently predicted (18)F-FDG uptake. Tumor size (OR = 1.495; CI, 1.217-1.835; P < .0001) and BRAF(V600E) mutation (OR = 3.320; CI, 1.056-10.432; P = .040) independently predicted extrathyroidal invasion. Multiplicity (OR = 2.375; CI, 1.278-4.415; P = .006) independently predicted central lymph node metastasis.

CONCLUSION

(18)F-FDG uptake in PTMC depends on tumor size and Hashimoto thyroiditis. Therefore, preoperative PET/CT for PTMC may not help in evaluating tumor aggressiveness.

Non-FDG-avid primary papillary thyroid carcinoma may not differ from FDG-avid papillary thyroid carcinoma

BACKGROUND

FDG (2-[(18)F]Fluoro-2-D-deoxyglucose-positron emission tomography (PET)/computed tomography (CT), which can detect a change in glucose metabolism in cancer cells, has been introduced as a diagnostic and prognostic tool in papillary thyroid carcinoma (PTC). However, differences in the clinicopathological and biological characteristics between primary PTCs with FDG uptake and those without FDG uptake are not well established.

METHODS

A total of 188 patients with PTC who had preoperative PET/CT scans were enrolled to compare the differences of clinicopathological parameters between FDG-avid (F-PTC; n = 150) and non-FDG-avid tumors (FN-PTC; n = 38). Immunohistochemical staining for glucose transporter (GLUT)-1 and hypoxia-inducible factor-1 alpha (HIF-1α) was performed.

RESULTS

FN-PTCs were smaller; had a lower incidence of lymphatic invasion, vascular invasion, multifocality, and central lymph node metastasis; and had a lower maximum standardized uptake value than F-PTCs. After exclusion of high-risk patients for recurrence, FN-PTCs remained smaller (p < 0.001) and had less lymphatic invasion (p = 0.061). Among tumors larger than the spatial resolution of the PET/CT scan, macrocalcification was more frequent in FN-PTC than in F-PTC (p = 0.043). While FN-PTC and F-PTC showed no difference in GLUT-1 expression (50% vs. 75%, p = 0.363), FN-PTC showed lower HIF-1α immunoreactivity than F-PTC (25.0% vs. 75.0%, p = 0.032).

CONCLUSION

Tumor size and macrocalcification are clinicopathological differences between FN-PTC and F-PTC. Biologically, HIF-1α may be responsible for increased FDG uptake in PTC.

Is fluorine-18 fluorodeoxyglucose positron emission tomography useful for the thyroid nodules with indeterminate fine needle aspiration biopsy? A meta-analysis of the literature

Background

The indeterminate fine needle aspiration biopsy (FNAB) results present a clinical dilemma for physicians. The aim of this study was to evaluate the diagnostic accuracy of fluorine-18 fluorodeoxyglucose positron emission tomography (¹⁸ F-FDG PET) in the detection of these indeterminate lesions.

Methods

Seven studies (involving a total of 267 patients) published before November 2012 were reviewed. Systematic methods were used to identify, select, and evaluate the methodological quality of the studies as well as to summarize the overall findings of sensitivity and specificity.

Results

A total number of 70 patients were confirmed to have malignant lesions, with a cancer prevalence of 26.2% (70/267; ranging from 19.6% to 40.0% in these studies). The pooled sensitivity and specificity of PET or PET/CT for the detection of cancer was 89.0% (95% CI: 79.0% ~ 95.0%) and 55.0% (95% CI: 48.0% ~ 62.0%), respectively. There was no evidence of threshold effects or publication bias. The area [±standard error (±SE)] under the symmetrical sROC curve was 0.7207 ± 0.1041. Although SUVmax was higher in malignant lesions (P < 0.01), there was still a great overlap. The best cut-off value of SUVmax for differentiation was 2.05; but with a high sensitivity of 89.8% and low specificity of 42.0%.

Conclusion

F-FDG PET or PET/CT showed a high sensitivity in detecting thyroid cancers in patients with indeterminate FNAB results. Further examination was strongly recommended when an FDG-avid lesion was detected.

F18-FDG-PET/CT thyroid incidentalomas: a wide retrospective analysis in three Italian centres on the significance of focal uptake and SUV value

Thyroid incidental uptake is defined as a thyroid uptake incidentally and newly detected by imaging techniques performed for an unrelated purpose and especially for non-thyroid diseases. Aim of the study was to establish the prevalence and pathological nature of focal thyroid incidentalomas detected at F18-FDG-PET/CT in patients studied for oncological purposes and not for thyroid disease. Secondary end point was to establish a possible maximum standardised uptake value cut-off over which a malignant lesion should be suspected. We have retrospectively evaluated 49519 patients who underwent F18-FDG-PET/CT for oncologic purposes in three Nuclear Medicine Centres (N.1 = 11278, N.2 = 31076, N.3 = 7165). A focal incidental thyroid uptake was diagnosed in 729 (1.5 %) patients (287-39.4 % male and 442-60.6 % female; average age: 65.26). Of 729 thyroid incidentalomas 211 (28.9 %) underwent further investigation to determine the nature of the nodule; 124/211 (58.8 %) incidentalomas were benign, 72/211 (34.1 %) malignant, 4/211 (1.9 %) non-diagnostic at cytological examination in the absence of surgery and histological evaluation and 11/211 (5.2 %) were indeterminate at cytological examination. A centre-based receiver operating curve (ROC) analysis of the patients with a definitive diagnosis was performed to identify a SUVmax cut-off useful in differentiating benign from malignant incidentalomas. In the centre N.1 it was 4.8 (sensitivity = 95.7 %, specificity = 46.4 %, area under the curve = 0.758); 5.3 in the centre N.2 (sensitivity = 76.3 %, specificity = 72.5 %, area under the curve = 0.815); 7 in the centre N.3 (sensitivity = 57.1 %, specificity = 79.3 %, area under the curve = 0.627). F18-FDG-PET/CT thyroid incidentalomas are a relevant diagnostic reality which requires further investigations and clinical management especially considering that, despite mainly benign, approximately one third of focal thyroid uptakes are malignant.

Pitfalls in the staging of cancer of thyroid

Thyroid cancer includes several neoplasms originating from the thyroid gland-from indolent and curable histologies of differentiated thyroid carcinoma to aggressive anaplastic thyroid carcinoma. Differentiation of thyroid nodules is problematic on CT and MR imaging unless there is evidence of extrathyroidal extension. Evaluation of regional lymph nodes is often performed clinically or with ultrasound. The retropharyngeal and mediastinal lymph nodes are better evaluated by CT and MR imaging. Nuclear scintigraphy is useful for staging and treatment of distant metastasis in differentiated thyroid carcinoma. PET may have a role in aggressive cancers. Accurate staging affects surgical management and subsequent therapy.

Thyroid Incidentalomas on Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography: Incidence, Malignancy Risk, and Comparison of Standardized Uptake Values

Introduction

To determine the incidence of fluorine-18-fluorodeoxyglucose (FDG) avid thyroid incidentalomas detected on positron emission tomography (PET) with integrated computed tomography (CT), and correlate the FDG–PET-CT findings to cytology.

Methods

A total of 942 FDG–PET-CT reports were retrospectively reviewed. Patients with FDG-avid thyroid incidentalomas were further reviewed for correlative cytology.

Results

The incidence of FDG-avid thyroid incidentalomas is 2.2%. Thyroid malignancies were identified in 3 of 6 patients who underwent cytologic correlation, with a positive predictive value of 50% (95% confidence interval, 14%-86%). The mean maximum standardized uptake values of benign and malignant FDG-avid thyroid incidentalomas were 5.6 and 6.6, respectively.

Conclusion

A FDG-avid thyroid incidentaloma may predict underlying malignancy. Cytologic assessment should be considered for FDG-avid thyroid incidentalomas.

Thyroid incidentaloma

Because of emerging investigation modalities many of the thyroid lesions are picked up and that poses a big dilemma about management of such lesions. Majority of these lesions especially in iodine-deficient regions, are not significant and may be only followed up without any active treatment but, sometimes the small lesions may be microcarcinoma. This article discusses about the reliability of clinical examination of neck for detection of such lesions, the controversy of such lesion being benign or malignant, and how to evaluate these lesions and the recommendation as per American Thyroid Association guidelines.

Risk of malignancy in thyroid incidentalomas detected by 18F-fluorodeoxyglucose positron emission tomography: a systematic review

BACKGROUND

The expanding use of (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) has led to the identification of increasing numbers of patients with an incidentaloma in the thyroid gland. We aimed to review the proportion of incidental thyroid cancers found by (18)F-FDG PET or PET/computed tomography imaging.

METHODS

Studies evaluating thyroid carcinomas discovered incidentally in patients or healthy volunteers by (18)F-FDG PET were systematically searched in the PubMed database from 2000 to 2011. The main exclusion criteria were known thyroid disease, lack of assigned diagnoses, investigation of diffuse uptake only, or investigation of patients with head and neck cancer, or cancer in the upper part of the thorax.

RESULTS

Twenty-two studies met our criteria comprising a total of 125,754 subjects. Of these, 1994 (1.6%) had unexpected focal hypermetabolic activity, while 999 of 48,644 individuals (2.1%) had an unexpected diffuse hypermetabolic activity in the thyroid gland. A diagnosis was assigned in 1051 of the 1994 patients with a focal uptake, 366 of whom (34.8%) had thyroid malignancy. Likewise, a diagnosis was assigned in 168 of 999 patients with a diffuse uptake, 7 of whom (4.4%) had thyroid malignancy. In the eight studies reporting individual maximum standardized uptake values (SUV(max)), the mean SUV(max) was 4.8 (standard deviation [SD] 3.1) and 6.9 (SD 4.7) in benign and malignant lesions, respectively (p<0.001).

CONCLUSIONS

Incidentally found thyroid nodules, using (18)F-FDG PET, are at high risk of harboring malignancy if uptake is focal. SUV are significantly higher in malignant than in benign nodules. The pronounced inhomogeneity and other shortcomings of the studies are discussed.

Surgical management of primary intrathoracic goiters

Intrathoracic goiters account for 3.1%-5.8% of all mediastinal masses. Primary intrathoracic goiters, which receive their blood supply from mediastinal vessels and disconnect at the cervical thyroid, are even rarer. This report presents two cases of surgical resection of benign and malignant primary intrathoracic goiters. Usefulness of a whole-body (18)F-fluorine-2-fluoro-D: -glucose positron emission tomography/computed tomography study and intraoperative fine-needle aspiration cytology in the management of primary intrathoracic goiters is discussed.

Can the pathology of a thyroid nodule be determined by positron emission tomography uptake?

OBJECTIVES

To determine if standardized uptake values (SUV) on positron emission tomography (PET) are predictive of thyroid pathology and the significance of serial SUV measurements of thyroid nodules over time.

STUDY DESIGN

Case series with chart review.

SETTING

Academic health center.

SUBJECTS

In total, 23,384 PET and PET/computed tomography (CT) scans were performed between December 2001 and April 2011.

METHODS

Patients with incidental thyroid uptake were identified. SUV(max), age, sex, size of thyroid lesion, indication for PET scan, and cytology/pathology were collected.

RESULTS

Incidental thyroid uptake was noted in 1309 PET scans (5.60%), focal uptake in 690 (2.95%), and diffuse uptake in 619 (2.65%). Complete data were available for 359 PET scans from 103 patients. Malignancy was identified in 28 patients (27%). Twenty-five of the 28 lesions (89%) were primary thyroid malignancies. A significant difference between malignant SUV(max) and benign SUV(max) was found (mean ± SD, 7.04 ± 7.88 for malignancies vs 3.85 ± 3.06 for benign tumors, P = .0292). Receiver operating characteristics curves were constructed on patients with PET data within 3 months of diagnosis and indicated that a SUV(max) of 4.2 differentiated maximally between benign and malignant lesions. Serial SUV uptake had no significant change over time.

CONCLUSION

All thyroid nodules with focal uptake on (18)F-fluorodeoxyglucose-PET/CT should be considered at higher risk of malignancy than those discovered incidentally by other imaging modalities. Higher SUV(max) values are more indicative of malignant lesions. All lesions should be evaluated with ultrasonography ± fine-needle aspiration if no clinical contraindications exist. Size of the primary nodule does not influence SUV(max) uptake.

Is (18)F-fluorodeoxyglucose-PET/CT useful for the presurgical characterization of thyroid nodules with indeterminate fine needle aspiration cytology?

BACKGROUND

Thyroid nodules found incidentally on (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET) have been shown to be malignant in 30%-50% of cases. The American Thyroid Association recommends performing fine needle aspiration cytology (FNAC) for thyroid nodules showing FDG uptake. On the other hand, the role of FDG-PET in characterizing thyroid nodules with indeterminate cytology before surgery is not clear. The goal of this study was to evaluate the role of FDG-PET/computed tomography (CT) in predicting malignancy of thyroid nodules with indeterminate FNAC and to correlate FDG uptake with pathological and ultrasonographic (US) features.

METHODS

Between November 2006 and October 2009, 55 patients (42 women, mean age: 50 years) planned for surgery for 56 thyroid nodules with indeterminate FNAC were prospectively included and considered for analysis. All patients underwent presurgical FDG-PET/CT (Siemens Biograph, mean FDG injected activity: 165 MBq) and neck US. Pathology of the corresponding surgical specimen was the gold standard for statistical analysis.

RESULTS

At pathology 34 nodules were benign, 10 were malignant (7 papillary and 3 follicular carcinomas), and 12 were tumors of uncertain malignant potential (TUMP). The median size of the thyroid nodules was 21 mm (range: 10-57). Sensitivity, specificity, positive (PPV), and negative predictive (NPV) values of FDG-PET in detecting cancer/TUMP were 77%, 62%, 57%, and 81%, respectively. In multivariate analysis, cellular atypia was the only factor predictive of FDG uptake (p<0.001). Hurthle cells and poorly differentiated components were independent predictive factors of high (≥5) SUV Max (p=0.02 and p=0.02). Sensitivity, specificity, PPV, and NPV of US in detecting cancer/TUMP were 82%, 47%, 50%, and 80%, respectively. In multivariate analysis, hypervascularization was correlated with malignancy/TUMP (p=0.007) and cystic features were correlated with benignity (p=0.03).

CONCLUSION

Adding FDG-PET findings to neck US provided no diagnostic benefit. The sensitivity and specificity of FDG-PET in the presurgical evaluation of indeterminate thyroid nodules are too low to recommend FDG-PET routinely.

The Role of 18F-Fluorodeoxyglucose Positron Emission Tomography in the Prognostication, Diagnosis, and Management of Thyroid Carcinoma

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) plays an increasingly important role in the prognostication, diagnosis, and management of thyroid carcinoma. For patients diagnosed with primary or persistent/recurrent thyroid carcinoma, a finding of FDG-PET positivity implies a more aggressive tumor biology and a distinct mutational profile, both of which carry prognostic significance. Therefore, FDG-PET positivity may be a useful potential risk factor for preoperative risk stratification in primary thyroid carcinoma. This information may help in the planning of subsequent treatment strategy such as the extent of thyroidectomy, prophylactic central neck dissection, and radioiodine ablation. FDG-PET scan has also been found to be a useful adjunct in characterizing indeterminate thyroid nodules on fine needle aspiration cytology. However, larger-sized prospective studies are required to validate this finding. FDG-PET or FDG-PET/CT scan has become the imaging of choice in patients with a negative whole-body radioiodine scan, but with an abnormally raised thyroglobulin level after total thyroidectomy and radioiodine ablation.

18FDG-positron emission tomography/computed tomography (PET/CT) scanning in thyroid nodules with nondiagnostic cytology

OBJECTIVE

To assess the role of positron emission tomography/computed tomography (PET/CT) scans with (18) FDG ((18)FDG-PET/CT) in the evaluation of thyroid nodules with nondiagnostic cytology.

SUBJECTS AND METHODS

Eighty-eight patients with a single euthyroid nodule and repeatedly nondiagnostic ultrasound-guided fine-needle cytology (US-FNC) were enrolled in the present study. Nodules concentrating (18)FDG were considered positive (i.e. suspicious for malignancy). Histological findings were obtained after surgery in all patients.

RESULTS

None of 41 patients with negative (18)FDG-PET/CT scan had a final histological diagnosis of malignancy (i.e. no false-negative results). Twenty-nine patients with final histological diagnosis of thyroid cancer had positive (18)FDG-PET/CT scan. Eighteen patients with final histological diagnosis of benign lesions (including four with follicular adenomas) also had positive (18)FDG-PET/CT scans. The sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) were 100%, 69%, 79%, 62% and 100%, respectively.

CONCLUSIONS

A negative (18)FDG-PET/CT scan accurately excludes malignancy in thyroid nodules with non-diagnostic US-FNC procedures. Histology is still necessary to distinguish benign from malignant disease in (18)FDG-PET/CT-positive nodules, but unnecessary surgery could have been reduced from 88 to 41 cases (46%) in our series.

Utility of ¹¹C-choline imaging as a supplement to F-18 FDG PET imaging for detection of thyroid carcinoma

PURPOSE

We present 4 patients with thyroid carcinoma who underwent ¹¹C-choline PET/CT for the detection of their primary tumor and its metastases. Previous F-18 FDG PET had shown no abnormal tracer uptake in the lesions in 3 patients and only mild uptake in 1 patient.

MATERIALS AND METHODS

Four patients aged between 24 and 59 years (2 newly diagnosed and 2 with recurrence) underwent whole-body F-18 FDG PET/CT. The patients then underwent regional ¹¹C-choline PET/CT imaging on a separate day.

RESULTS

All of the lesions in 4 patients were ¹¹C-choline avid except for a few small lung metastases. The SUVmax of the lesions was 7.94 ± 4.93. ¹¹C-choline imaging detected 3 primary tumors in 4 patients, 1 tumor in the tracheal wall in 1 patient, 7 cervical lymph nodes metastases in 3 patients, and several lung metastases in 1 patient.

CONCLUSIONS

¹¹C-choline PET/CT may be a promising supplement to F-18 FDG PET/CT in the detection of thyroid carcinoma and its metastases.

Incidental thyroid "PETomas": clinical significance and novel description of the self-resolving variant of focal FDG-PET thyroid uptake

BACKGROUND

Recent series of incidental thyroid activity on fluorodeoxyglucose positron emission tomography (FDG-PET) in patients evaluated for nonthyroidal malignancy, which we refer to as a "PEToma," have suggested that such lesions are associated with a significant incidence of primary thyroid cancer.

METHODS

We retrospectively reviewed 6457 FDG-PET scans performed on 4726 patients from May 2004 to March 2007. We reviewed the cases of patients whose PET or computed tomography (CT) radiology reports described PET uptake within the thyroid to identify incidence and malignant potential of PETomas and evaluate their clinical and histopathologic features.

RESULTS

We found that 160 patients (3.4%) had incidental, abnormal FDG uptake in the thyroid gland, 103 of whom had focal uptake (the PEToma group). Of these patients, 50 (48%) underwent further investigations, including ultrasonography in 48, fine-needle aspiration cytology in 38 and computed tomography in 3. Ten patients underwent surgery, and papillary thyroid cancer was identified in 9. The remaining 53 patients with PETomas underwent no further investigation. Interestingly, 5 patients who had focal uptake within the thyroid showed either spontaneous resolution on repeat FDG-PET (self-resolving) or no focal lesion on subsequent ultrasonography (false-positive).

CONCLUSION

The incidence of papillary thyroid cancer in the present series is similar to that in the literature. Although some patients will show self-resolving or false-positive focal thyroid uptake on FDG-PET, we believe that, if the patient's clinical status permits, the evaluation of patients with incidental thyroid PEToma should include ultrasonographic confirmation and fine-needle aspiration cytology.

The role of 18F-fluorodeoxyglucose positron emission tomography in thyroid neoplasms

(18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has established itself as an important imaging modality in many oncological and nononcological specialties and, as a consequence, it is increasingly being used in clinical practice. Since the first report of FDG being taken up by metastatic differentiated thyroid carcinoma (DTC) cells >20 years ago, various groups of investigators have explored the potential role of FDG-PET scanning in patients with benign and malignant thyroid neoplasms. With the increasing demand for FDG-PET scanning, clinicians are faced with the challenge of managing an increasing number of FDG-PET-detected thyroid incidentalomas because their significance remains unclear. The aims of this review are to address some of these issues, specifically, the clinical significance of FDG-PET-detected thyroid incidentalomas, the ability of FDG-PET to characterize thyroid nodules, especially those with indeterminate fine needle aspiration cytology results, and the role of FDG-PET in patients with confirmed primary DTC and with suspected recurrent DTC, by reviewing the current literature.

Incidental thyroid carcinoma by FDG-PET/CT: a study of clinicopathological characteristics

BACKGROUND

The rising incidence of incidental thyroid carcinoma (ITC) detected during fluoro-2-deoxy-D: -glucose (FDG)-positron emission tomography (PET)/computed tomography (CT) scanning poses a challenge to clinicians. The present study aims to critically evaluate the clinicopathological characteristics of ITC detected by FDG-PET/CT.

METHODS

Among the 557 patients managed at our institution, 40 (7.2%) patients were identified as having ITC. Of these, 22 patients had their tumor detected by FDG-PET/CT (PET group) and 11 by ultrasonography (USG group). Additional bedside ultrasonography ± fine-needle aspiration (FNA) was done in all patients at their clinic visit. The clinicopathological characteristics were compared between the PET and USG groups.

RESULTS

The PET group had significantly more patients with history of nonthyroidal malignancy (P < 0.001). Papillary carcinoma was the most common histological type in both groups. Despite having similar histological and prognostic features including tumor size, tumor multifocality, capsular invasion, extrathyroidal extension, and lymph node metastases, tumor bilaterality (or presence of contralateral tumor focus) was significantly more frequent in the PET than the USG group (P = 0.04). The tumors were also more advanced by the tumor-node-metastasis (TNM) staging system in the PET group (P = 0.021). None of the contralateral tumor foci were evident preoperatively. One patient in the USG group developed metastatic thyroid carcinoma in neck lymph nodes 28 months after thyroid resection.

CONCLUSION

ITC by FDG-PET/CT had higher incidence of tumor bilaterality than those detected by ultrasonography. Total thyroidectomy should be considered for ITC detected by FDG-PET/CT even for tumor size <10 mm.

Prospective evaluation of solitary thyroid nodule on 18F-FDG PET/CT and high-resolution ultrasonography

PURPOSE

The utility of 18F-FDG PET/CT in the assessment of thyroid nodules is unclear as there are several conflicting reports on the usefulness of SUV as an indicator to distinguish benign from malignant thyroid lesions. This study incorporated an additional parameter, namely dual time point imaging, to determine the diagnostic accuracy of PET/CT imaging. The performance of 18F-FDG PET/CT was compared to that of high-resolution ultrasound which is routinely used for the evaluation of thyroid nodules.

METHODS

Two hundred patients with incidentally detected solitary thyroid nodules were included in the study. Each patient underwent ultrasound and PET/CT evaluation within 7 days of each other, reported by an experienced radiologist and nuclear medicine specialist, respectively, in a blinded manner. The PET/CT criteria employed were maximum SUV (SUV(max)) at 60 min and change in SUV(max) at delayed (120 min) imaging. Final diagnosis was based on pathological evaluation and follow-up.

RESULTS

Of the 200 patients, 26 had malignant and 174 had benign nodules. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of ultrasound were 80.8, 81.6, 39.6, 96.6 and 81.5%, respectively. Using SUV(max) at 60 min as the diagnostic criterion, the above indices were 80.8, 84.5, 43.8, 96.7 and 84%, respectively, for PET/CT. The SUV(max) of malignant thyroid lesions was significantly higher than benign lesions (16.2 +/- 10.6 vs. 4.5 +/- 3.1, respectively; p = 0.0001). Incorporation of percentage change in SUV(max) at delayed imaging as the diagnostic criterion yielded a slightly improved sensitivity, specificity, PPV, NPV and accuracy of 84.6, 85.6, 46.8, 97.4 and 85.5%, respectively. There was a significant difference in percentage change in SUV(max) between malignant and benign thyroid lesions (14.9 +/- 11.4 vs. -1.6 +/- 13.7, respectively; p = 0.0001). However, there was no statistically significant difference (95% confidence interval) between the diagnostic performance of PET/CT and ultrasound.

CONCLUSIONS

Routine use of 18F-FDG PET/CT with SUV(max) at 60 min as the sole diagnostic criterion does not appear to have a significant advantage over high-resolution ultrasound in the evaluation of thyroid nodules. Incorporation of dual time point imaging enhances image interpretation, and yields a higher diagnostic performance, yet it is not statistically significant. Bearing in mind the cost, limited availability and radiation exposure, routine use of 18F-FDG PET/CT for distinguishing benign from malignant thyroid nodules cannot be recommended.

Evaluation of a thyroid nodule

The thyroid specialist frequently evaluates thyroid nodules because they may represent malignancy. Nodules are typically found on physical examination or incidentally when other imaging studies are performed. Malignant or symptomatic nodules that compress nearby structures warrant surgical excision. Yet, the majority of thyroid nodules are asymptomatic and benign, so the thyroid surgeon must rely on diagnostic studies to determine when surgery is indicated. Ultrasound is the preferred imaging modality for thyroid nodules, and the ultrasound guided fine-needle aspiration biopsy (FNAB) is the preferred method of tissue sampling. Nodules 1 cm or larger or nodules with suspicious sonographic appearance warrant cytologic analysis to better quantify the risk for malignancy. Molecular biomarkers are a powerful adjunct to cytology. Detecting malignancy preoperatively allows total thyroidectomy in a single operation without the need for frozen section or a second operation for completion of a thyroidectomy if malignancy is found during the initial thyroid lobectomy.

High incidence of thyroid cancer in focal thyroid incidentaloma detected by 18F-fluorodeoxyglucose [corrected] positron emission tomography in relatively young healthy subjects: results of 3-year follow-up

As 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is becoming a common imaging modality, the number of thyroid incidentalomas identified by FDG-PET (PET incidentaloma) is increasing. The purpose of this study was to elucidate the risk of cancer in focal thyroid PET incidentaloma in healthy subjects of relatively younger age as well as the usefulness of repeated FDG-PET. The study was conducted with an observation period of three years. A total of 1,501 healthy volunteers (mean age, 43.5+/-9.7 years) underwent the first FDG-PET from August 2003 to July 2004. When focal thyroid PET incidentaloma was found, further diagnostic examination was conducted. When thyroid cancer was suspected, surgical resection was performed with the patient' s agreement. Patients with PET incidentaloma without surgery were offered annual US and FDG-PET and finally FNAB was performed in the fourth year. Focal thyroid PET incidentaloma was observed in 20 subjects. The final diagnoses in 20 subjects were malignant in 11 (ten papillary thyroid carcinoma (PTC) and one thyroid carcinoma showing thymus-like differentiation), indeterminate in one, and benign in eight subjects. Seven patients not treated surgically at the first examination had annual FDG-PET. One patient with PTC showed increasing SUVmax, but another with a benign nodule exhibited a similar increase. Others (one with PTC, one with an indeterminate nodule, and three with benign nodules) exhibited negligible SUVmax changes. When closely examined, focal thyroid PET incidentaloma in relatively young healthy adults has a high probability of malignancy. Repeated FDG-PET to follow up patients with thyroid nodules is ineffective.

Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer

BACKGROUND

Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent. Since the publication of the American Thyroid Association's guidelines for the management of these disorders was published in 2006, a large amount of new information has become available, prompting a revision of the guidelines.

METHODS

Relevant articles through December 2008 were reviewed by the task force and categorized by topic and level of evidence according to a modified schema used by the United States Preventative Services Task Force.

RESULTS

The revised guidelines for the management of thyroid nodules include recommendations regarding initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, and management of benign thyroid nodules. Recommendations regarding the initial management of thyroid cancer include those relating to optimal surgical management, radioiodine remnant ablation, and suppression therapy using levothyroxine. Recommendations related to long-term management of differentiated thyroid cancer include those related to surveillance for recurrent disease using ultrasound and serum thyroglobulin as well as those related to management of recurrent and metastatic disease.

CONCLUSIONS

We created evidence-based recommendations in response to our appointment as an independent task force by the American Thyroid Association to assist in the clinical management of patients with thyroid nodules and differentiated thyroid cancer. They represent, in our opinion, contemporary optimal care for patients with these disorders.

Incidental thyroid lesions detected by FDG-PET/CT: prevalence and risk of thyroid cancer

BACKGROUND

Incidentally found thyroid lesions are frequently detected in patients undergoing FDG-PET/CT. The aim of this study was to investigate the prevalence of incidentally found thyroid lesions in patients undergoing FDG-PET/CT and determine the risk for thyroid cancer.

METHODS

FDG-PET/CT was performed on 3,379 patients for evaluation of suspected or known cancer or cancer screening without any history of thyroid cancer between November 2003 and December 2005. Medical records related to the FDG-PET/CT findings including maximum SUV(SUVmax) and pattern of FDG uptake, US findings, FNA, histopathology received by operation were reviewed retrospectively.

RESULTS

Two hundred eighty five patients (8.4%) were identified to have FDG uptake on FDG-PET/CT. 99 patients with focal or diffuse FDG uptake underwent further evaluation. The cancer risk of incidentally found thyroid lesions on FDG-PET/CT was 23.2% (22/99) and the cancer risks associated with focal and diffuse FDG uptake were 30.9% and 6.4%. There was a significant difference in the SUVmax between the benign and malignant nodules (3.35 +/- 1.69 vs. 6.64 +/- 4.12; P < 0.001). There was a significant correlation between the SUVmax and the size of the cancer.

CONCLUSION

The results of this study suggest that incidentally found thyroid lesions by FDG-PET/CT, especially a focal FDG uptake and a high SUV, have a high risk of thyroid malignancy. Further diagnostic work-up is needed in these cases.

Recent developments in predicting thyroid malignancy

PURPOSE OF REVIEW

To provide an update on potential predictors of thyroid malignancy and how their use may alter clinical management.

RECENT FINDINGS

As thyroid nodules become more prevalent clinicians are increasingly impelled to identify the optimal predictor(s) of thyroid malignancy, with the goal of guiding management based on assessed risk. The gold standard evaluation for thyroid nodules is ultrasound-guided fine-needle aspiration biopsy. Fine-needle aspiration biopsy is not perfect and adjuncts which complement its predictive value are being investigated from several innovative perspectives. These include large tumor size (> or =4 cm), which appears to be an independent predictor of thyroid malignancy; 18F-fluorodeoxyglucose positron emission tomography, which appears to facilitate exclusion of malignancy in cytologically indeterminate thyroid nodules; and peripheral blood and fine-needle aspiration biopsy analysis of molecular markers, which may help to identify malignant thyroid nodules with greater specificity.

SUMMARY

Fine-needle aspiration biopsy of large thyroid nodules has a high false-negative rate and should be considered for diagnostic lobectomy. Nodule size appears to be an independent factor predicting malignancy and indeterminate lesions at least 4 cm should be considered for initial total thyroidectomy. Nuclear imaging may aid exclusion of malignancy in thyroid nodules and molecular markers have great promise in predicting thyroid malignancy with higher specificity.