Incidence and Significance of Incidental Focal Thyroid Uptake on ¹⁸F-FDG PET Study in a Large Patient Cohort: Retrospective Single-Centre Experience in the United Kingdom

Abstract

Objective: To assess the prevalence and pathological nature of incidental focal thyroid uptake on ¹⁸F-FDG (2-[¹⁸F]-fluoro-2-deoxy-<smlcap>D</smlcap>-glucose) PET (positron emission tomography) and examine the role of the maximum standardised uptake value (SUV_max) to differentiate benign from malignant thyroid pathology. Material and Methods:¹⁸F-FDG PET reports were retrospectively reviewed. Incidental focal tracer uptake in the thyroid was noted in 147 patients (0.5%). Patients with known primary thyroid malignancy were excluded. The final diagnosis was made following ultrasonography of the neck, fine-needle aspiration cytology (FNAC) or histopathology of the surgically resected specimen where surgery was indicated. A Mann-Whitney U test was used to compare the SUV_max of benign and malignant thyroid pathology. Receiver operating characteristic (ROC) analysis was performed to identify an SUV_max cutoff in differentiating benign from malignant pathology. Results: A final diagnosis was achieved in 47/147 (32%) of the patients. The diagnoses included benign lesions in 36 patients and malignancy in 9 patients. In 2 patients, FNAC demonstrated indeterminate follicular lesions; however, surgical excision was not performed. There was a highly significant difference in the mean SUV_max of malignant focal thyroid uptake (15.7 ± 5.9) compared to that of benign lesions (7.1 ± 6.8) with a p value of 0.000123. An SUV_max of 9.1 achieved a sensitivity of 81.6%, specificity of 100% and area under the curve of 0.915 in the ROC analysis differentiating benign from malignant disease. Conclusion: The malignancy potential of incidental focal thyroid uptake remains high and warrants prompt and appropriate follow-up by the clinician. The SUV_max may aid in further characterisation of the lesion and its management.

Cytological evaluation by fine needle aspiration biopsy of incidental focal increased fluorodeoxyglucose uptake in thyroid on positron emission tomography scan

“…The probability of malignancy varies with different studies, ranging widely from 14 to 66%. [9][10][11][12][13][14][15][16] For most of the studies the subjects were patients with a non-thyroidal primary malignancy and the incidence of thyroid malignancy was considered higher is such population than the general population. Chen et al reported 14% malignancy in a series of 4,803 patients after biopsies of 83% of the incidentalomas.…”

“…3 PET incidentalomas are divided into diffuse and focal types. [9][10][11][12][13][14][15][16] The incidence of metastatic disease to the thyroid gland ranges from 1.25 to 24%. 4 Diffuse type generally suggests a benign lesion since most cases are autoimmune thyroiditis, 5,6 with rare exceptions.…”

“…1 However, the likelihood of malignancy in a PET-positive lesion is much higher, with a risk of 14-66% throughout the literature reported to date. [9][10][11][12][13][14][15][16] The incidence of metastatic disease to the thyroid gland ranges from 1.25 to 24%. Renal cell carcinoma is the most common malignancy that metastasize to the thyroid.…”

The Rate and Clinical Significance of Incidental Thyroid Uptake as Detected by Gallium-68 DOTATATE Positron Emission Tomography/Computed Tomography

“…The incidence of thyroid ''incidentalomas'' in the general population is increasing, and some require further clinical evaluation to exclude clinically significant thyroid disease. Thyroid incidentalomas have been detected by 18 F-fluorodeoxyglucose ( 18 F-FDG) positron emission tomography (PET) in up to 10% of patients (2). Thyroid cancer is one clinically important diagnosis to exclude in a patient found to have a thyroid incidentaloma.…”

“…Therefore, focal or diffuse thyroid activity usually corresponds to an anatomic abnormality. The recommended work-up includes a thyroid ultrasound (US), followed by a fine-needle aspiration (FNA) biopsy based on the thyroid nodule features detected by the US because of the high risk of malignancy (8-64%) associated with 18 F-FDG PET-positive thyroid nodules (2,4).…”