Oncocytic adenomas of thyroid-mimicking benign or metastatic disease on 18F-FDG-PET scan

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.

Hürthle Cell Thyroid Adenoma Showing Avid Uptake on 18F-PSMA-1007 PET/CT

We report the case of a 74-year-old man with suspected recurrent prostate carcinoma who underwent F-PSMA-1007 PET/CT for restaging the disease. PET/CT imaging presented an incidentaloma with intense F-PSMA-1007 uptake in the right thyroid lobe. Biopsy and genomic sequencing test confirmed the diagnosis of Hürthle cell thyroid adenoma. Therefore, it is important to raise awareness of this benign lesion in the differential diagnosis of incidental thyroid nodules with high F-PSMA-1007 activity.

A prospective cohort study to assess the role of FDG-PET in differentiating benign and malignant follicular neoplasms

Background

Follicular and Hürthle cell neoplasms are diagnostic challenges. This prospective study was designed to evaluate the efficacy of [18F]-2-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography/computed tomography (PET/CT) in predicting the risk of malignancy in follicular/Hürthle cell neoplasms.

Materials and methods

Fifty thyroid nodules showing follicular/Hürthle cell neoplasm on prior ultrasonography guided fine needle aspiration cytology (FNAC) were recruited into this study. A FDG-PET/CT scan, performed for neck and superior mediastinum, was reported by a single observer, blinded to the surgical and pathology findings. Receiver operating characteristic (ROC) curve analysis of maximum standardized uptake value (SUVmax) and the area under the curve (AUROC) were used to assess discrimination between benign from malignant nodules. Youden index was used to identify the optimal cut-off SUVmax for diagnosing malignancy. Sensitivity, specificity, predictive values and overall accuracy were used as measures of performance.

Results

Our study group comprises of 31 benign and 19 malignant thyroid nodules. After excluding all Hürthle cell adenomas, the AUROC for discriminating benign and malignant non-Hürthle cell neoplasms was 0.79 (95% CI, 0.64–0.94; p = 0.001); with SUVmax of 3.25 as the best cut-off for the purpose. PET/CT had sensitivity of 79% (95% CI, 54–93%), specificity of 83% (95% CI, 60–94%), positive predictive value (PPV) of 79% (95% CI, 54–93%), and negative predictive value (NPV) of 83% (95% CI, 60–94%). The overall accuracy was 81%.

Conclusions

FDG-PET/CT can help in differentiating benign and malignant non-Hürthle cell neoplasms. SUVmax of 3.25 was found to be the best for identifying malignant non-Hürthle cell follicular neoplasms.

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Earlier meta-analyses have not considered Hürthle cell neoplasm separate from other follicular neoplasm.

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Hürthle cell neoplasm are known to show high FDG uptake.

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FDG-PET/CT can help in differentiating benign and malignant non-Hürthle cell thyroid nodules.

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A cut-off SUVmax of 3.25 enhances the accuracy of FDG-PET/CT in identifying cancers in thyroid nodules.

FDG-PET characteristics of Hürthle cell and follicular adenomas

OBJECTIVE

Follicular (FN) and Hürthle cell neoplasms (HCN) are considered indeterminate on thyroid fine needle aspiration cytology and are preoperative diagnostic challenges. The role of [(18)F]-2-fluoro-2-deoxy-D-glucose (FDG) in characterizing indeterminate thyroid nodules remains equivocal, because of the increased FDG uptake by some benign thyroid nodules. The objective of this study was to compare the FDG positron emission tomography/computerized tomography (PET/CT) characteristics of follicular (FA) and Hürthle cell adenomas (HCA).

METHODS

Twenty-nine patients with 31 thyroid nodules underwent FDG-PET/CT scans of the neck and superior mediastinum for indeterminate FN/HCN, and were later found to have benign adenomas on final histopathology. All scans were reported by a single observer, who was blinded to the surgical and pathology findings. Receiver operating characteristic (ROC) curve analysis of maximum standardized uptake value (SUVmax) and the area under the curve (AUROC) were used to assess discrimination between FA and HCA. Youden index was used to identify the optimal cut-off SUVmax. Sensitivity, specificity, predictive values and overall accuracy were used as measures of performance.

RESULTS

The mean age of our study cohort was 60.7 ± 12.6 years and 77 % of the patients were females. Age of the patients (p = 0.48), their gender (p = 0.52), and the size of thyroid nodules (p = 0.79) were similar for FA and HCA. Increased focal FDG uptake was observed in 100 % of HCA and 52 % of FA (p = 0.02). SUVmax of HCA was significantly higher (p < 0.001) than that of FA. SUVmax of 5 was the best cut-off for discrimination between HCA and FA, with AUROC of 0.90 (95 % CI, 0.79-1.00; p = 0.001). With this cut-off, FDG-PET/CT had sensitivity of identifying HCA of 88 % (95 % CI 47-99 %), specificity of 87 % (95 % CI 65-97 %), positive predictive value of 70 % (95 % CI 35-92 %), and negative predictive value of 95 % (95 % CI 74-99 %). The overall accuracy was 87 %.

CONCLUSIONS

HCA shows significantly higher focal FDG uptake as compared to FA and should always be considered in the differential diagnosis of FDG-PET positive thyroid nodules.