The use of dual-phase 18F-FDG PET in characterizing thyroid incidentalomas

Thyroid tuberculosis diagnosed as papillary thyroid carcinoma with fever of unknown origin

Thyroid tuberculosis is a rare disease, very few cases have been reported. It is difficult to diagnose because of no typical characteristics. We report on a patient who underwent surgery for suspected thyroid carcinoma, but who was then diagnosed with thyroid tuberculosis. The patient was a woman in her 70s. She had been diagnosed with chronic renal failure and had been on peritoneal dialysis. She complained of fever and a painful left anterior neck swelling. Computed tomography showed thyroid tumor with cervical lymph node swelling, ultrasound-guided fine needle aspiration cytology was suspected for papillary thyroid carcinoma. We performed surgery to confirm the diagnosis and determine treatment. Procedures for thyroid carcinoma were followed, including left lobectomy of the thyroid gland, central lymph node dissection and right cervical lymph node resection. Pathological examination found no malignant findings in the thyroid tissue but did find a granulation layer even in the right cervical lymph node. Tuberculosis-specific IFN-γ assay was positive, we diagnosed thyroid and cervical lymph node tuberculosis. Postoperatively, the neck pain and fever improved, she was treated as an outpatient with antituberculosis drugs therapy. Thyroid tuberculosis must be considered in patients with immunocompromised, such as this patient, who was on peritoneal dialysis.

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

Objectives

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

Methods

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

Results

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

Conclusion

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

Focal Thyroid Incidentalomas on 18F-FDG PET/CT: A Systematic Review and Meta-Analysis on Prevalence, Risk of Malignancy and Inconclusive Fine Needle Aspiration

BACKGROUND

The rising demand for ¹⁸F-fluorodeoxyglucose positron emission tomography with computed tomography (¹⁸F-FDG PET/CT) has led to an increase of thyroid incidentalomas. Current guidelines are restricted in giving options to tailor diagnostics and to suit the individual patient.

OBJECTIVES

We aimed at exploring the extent of potential overdiagnostics by performing a systematic review and meta-analysis of the literature on the prevalence, the risk of malignancy (ROM) and the risk of inconclusive FNAC (ROIF) of focal thyroid incidentalomas (FTI) on ¹⁸F-FDG PET/CT.

DATA SOURCES

A literature search in MEDLINE, Embase and Web of Science was performed to identify relevant studies.

STUDY SELECTION

Studies providing information on the prevalence and/or ROM of FTI on ¹⁸F-FDG PET/CT in patients with no prior history of thyroid disease were selected by two authors independently. Sixty-one studies met the inclusion criteria.

DATA ANALYSIS

A random effects meta-analysis on prevalence, ROM and ROIF with 95% confidence intervals (CIs) was performed. Heterogeneity and publication bias were tested. Risk of bias was assessed using the quality assessment of diagnostic accuracy studies (QUADAS-2) tool.

DATA SYNTHESIS

Fifty studies were suitable for prevalence analysis. In total, 12,943 FTI were identified in 640,616 patients. The pooled prevalence was 2.22% (95% CI = 1.90% - 2.54%, I² = 99%). 5151 FTI had cyto- or histopathology results available. The pooled ROM was 30.8% (95% CI = 28.1% - 33.4%, I² = 57%). 1308 (83%) of malignant nodules were papillary thyroid carcinoma (PTC). The pooled ROIF was 20.8% (95% CI = 13.7% - 27.9%, I² = 92%).

LIMITATIONS

The main limitations were the low to moderate methodological quality of the studies and the moderate to high heterogeneity of the results.

CONCLUSION

FTI are a common finding on ¹⁸F-FDG PET/CTs. Nodules are malignant in approximately one third of the cases, with the majority being PTC. Cytology results are non-diagnostic or indeterminate in one fifth of FNACs. These findings reveal the potential risk of overdiagnostics of FTI and emphasize that the workup of FTI should be performed within the context of the patient's disease and that guidelines should adopt this patient tailored approach.

PTEN regulates plasma membrane expression of glucose transporter 1 and glucose uptake in thyroid cancer cells

Glucose represents an important source of energy for the cells. Proliferating cancer cells consume elevated quantity of glucose, which is converted into lactate regardless of the presence of oxygen. This phenomenon, known as the Warburg effect, has been proven to be useful for imaging metabolically active tumours in cancer patients by (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET). Glucose is internalised in the cells by glucose transporters (GLUTs) belonging to the GLUT family. GLUT1 (SLC2A1) is the most prevalent isoform in more aggressive and less differentiated thyroid cancer histotypes. In a previous work, we found that loss of expression of PTEN was associated with increased expression of GLUT1 on the plasma membrane (PM) and probability of detecting thyroid incidentalomas by FDG-PET. Herein, we investigated the molecular pathways that govern the expression of GLUT1 on the PM and the glucose uptake in WRO (expressing WT PTEN) and FTC133 (PTEN null) follicular thyroid cancer cells cultured under glucose-depleted conditions. The membrane expression of GLUT1 was enhanced in glucose-deprived cells. Through genetic manipulations of PTEN expression, we could demonstrate that the lack of this oncosuppressor has a dominant effect on the membrane expression of GLUT1 and glucose uptake. We conclude that loss of function of PTEN increases the probability of cancer detection by FDG-PET or other glucose-based imaging diagnosis.

18F-FDG PET/CT oncologic imaging at extended injection-to-scan acquisition time intervals derived from a single-institution 18F-FDG-directed surgery experience: feasibility and quantification of 18F-FDG accumulation within 18F-FDG-avid lesions and background tissues

Background

¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is a well-established imaging modality for a wide variety of solid malignancies. Currently, only limited data exists regarding the utility of PET/CT imaging at very extended injection-to-scan acquisition times. The current retrospective data analysis assessed the feasibility and quantification of diagnostic ¹⁸F-FDG PET/CT oncologic imaging at extended injection-to-scan acquisition time intervals.

Methods

¹⁸F-FDG-avid lesions (not surgically manipulated or altered during ¹⁸F-FDG-directed surgery, and visualized both on preoperative and postoperative ¹⁸F-FDG PET/CT imaging) and corresponding background tissues were assessed for ¹⁸F-FDG accumulation on same-day preoperative and postoperative ¹⁸F-FDG PET/CT imaging. Multiple patient variables and ¹⁸F-FDG-avid lesion variables were examined.

Results

For the 32 ¹⁸F-FDG-avid lesions making up the final ¹⁸F-FDG-avid lesion data set (from among 7 patients), the mean injection-to-scan times of the preoperative and postoperative ¹⁸F-FDG PET/CT scans were 73 (±3, 70-78) and 530 (±79, 413-739) minutes, respectively (P < 0.001). The preoperative and postoperative mean ¹⁸F-FDG-avid lesion SUV_max values were 7.7 (±4.0, 3.6-19.5) and 11.3 (±6.0, 4.1-29.2), respectively (P < 0.001). The preoperative and postoperative mean background SUV_max values were 2.3 (±0.6, 1.0-3.2) and 2.1 (±0.6, 1.0-3.3), respectively (P = 0.017). The preoperative and postoperative mean lesion-to-background SUV_max ratios were 3.7 (±2.3, 1.5-9.8) and 5.8 (±3.6, 1.6-16.2), respectively, (P < 0.001).

Conclusions

¹⁸F-FDG PET/CT oncologic imaging can be successfully performed at extended injection-to-scan acquisition time intervals of up to approximately 5 half-lives for ¹⁸F-FDG while maintaining good/adequate diagnostic image quality. The resultant increase in the ¹⁸F-FDG-avid lesion SUV_max values, decreased background SUV_max values, and increased lesion-to-background SUV_max ratios seen from preoperative to postoperative ¹⁸F-FDG PET/CT imaging have great potential for allowing for the integrated, real-time use of ¹⁸F-FDG PET/CT imaging in conjunction with ¹⁸F-FDG-directed interventional radiology biopsy and ablation procedures and ¹⁸F-FDG-directed surgical procedures, as well as have far-reaching impact on potentially re-shaping future thinking regarding the “most optimal” injection-to-scan acquisition time interval for all routine diagnostic ¹⁸F-FDG PET/CT oncologic imaging.

Thyroid incidentalomas discovered on positron emission tomography CT scanning - Malignancy rate and significance of standardised uptake values

AIMS

Increasing use of 18F-Fluorodeoxy glucose (FDG) Positron Emission Tomography Computed Tomography (PET CT) has resulted in an increased frequency of incidentally discovered areas of focally increased FDG uptake within the thyroid gland - thyroid incidentalomas. We aimed to compare radiological characteristics of thyroid incidentalomas with cytology, histology and ultrasound findings.

MATERIALS AND METHODS

We examined all FDG PET CT scan reports for all patients undergoing this investigation over a 6 year period in a single tertiary cancer centre. All PET CT scans followed an agreed proforma allowing reports mentioning "thyroid" to be identified. Reports commenting on a positive finding within the thyroid gland were investigated further manually. Incidental mentions of thyroid with no underlying abnormality were discounted from analysis.

RESULTS

In the study period, 7221 patients underwent FDG PET CT scanning in our unit. Within this group 75 (1%) showed diffuse FDG uptake and 81 (1.1%) showed focal uptake (thyroid incidentalomas). Only 30 patients (37%) with incidentalomas had further investigation and malignancy rate was 23% (7/30). Median Standardised Uptake Values (SUV) in malignant lesions was 9.9 (range 3.5-17.8) whilst in benign lesions and diffuse lesions it was 5.4 (2.8-32) and 4.2 (2.1-25.6) respectively (p = 0.0013, Kruskal Wallis).

CONCLUSION

There remains a need to develop a standardised approach to the investigation and management of thyroid incidentalomas discovered on FDG PET CT scanning. Up to 1 in 4 of these patients will harbour thyroid malignancy.

Risk of malignancy in focal thyroid lesions identified by (18)F-fluorodeoxyglucose positron emission tomography or positron emission tomography/computed tomography: evidence from a large series of studies

Focal thyroid incidentaloma identified on (18)F-fluorodeoxyglucose positron emission tomography or positron emission tomography/computed tomography ((18)F-FDG PET or PET/CT) indicates a high risk of thyroid malignancy. A meta-analysis was performed to investigate whether the maximum standardized uptake value (SUVmax) could discriminate between benign and malignant tissues in focal lesions and to explore the cutoff value of SUVmax for the diagnosis of malignancy. A total of 29 studies were involved in this meta-analysis. The results indicated that there was no statistically significant difference in the size of the two benign and malignant groups when measured by ultrasonography (95 % confidence interval (CI), -0.79 to 0.03 min; p=0.07), while a significantly higher focal SUVmax was observed in the malignant group (95 % CI, 0.34 to 1.05; p=0.0001). In conclusion, the findings of this meta-analysis suggest that a higher focal (18)F-FDG SUVmax was associated with a higher risk of thyroid malignancy, especially at a threshold of 3.3 or more.

When should we recommend use of dual time-point and delayed time-point imaging techniques in FDG PET?

FDG PET and PET/CT are now widely used in oncological imaging for tumor characterization, staging, restaging, and response evaluation. However, numerous benign etiologies may cause increased FDG uptake indistinguishable from that of malignancy. Multiple studies have shown that dual time-point imaging (DTPI) of FDG PET may be helpful in differentiating malignancy from benign processes. However, exceptions exist, and some studies have demonstrated significant overlap of FDG uptake patterns between benign and malignant lesions on delayed time-point images. In this review, we summarize our experience and opinions on the value of DTPI and delayed time-point imaging in oncology, with a review of the relevant literature. We believe that the major value of DTPI and delayed time-point imaging is the increased sensitivity due to continued clearance of background activity and continued FDG accumulation in malignant lesions, if the same diagnostic criteria (as in the initial standard single time-point imaging) are used. The specificity of DTPI and delayed time-point imaging depends on multiple factors, including the prevalence of malignancies, the patient population, and the cut-off values (either SUV or retention index) used to define a malignancy. Thus, DTPI and delayed time-point imaging would be more useful if performed for evaluation of lesions in regions with significant background activity clearance over time (such as the liver, the spleen, the mediastinum), and if used in the evaluation of the extent of tumor involvement rather than in the characterization of the nature of any specific lesion. Acute infectious and non-infectious inflammatory lesions remain as the major culprit for diminished diagnostic performance of these approaches (especially in tuberculosis-endemic regions). Tumor heterogeneity may also contribute to inconsistent performance of DTPI. The authors believe that selective use of DTPI and delayed time-point imaging will improve diagnostic accuracy and interpretation confidence in FDG PET imaging.