A. G. Ramirez1, N. Nuradin1, U. Syed1, V. Grajales2, M. A. Zeiger1, J. B. Hanks1, P. W. Smith1 1University Of Virginia,Surgery,Charlottesville, VA, USA 2University Of Pittsburg,Urology,Pittsburgh, PA, USA
Introduction:
The incidence of 18F-fluorodeoxyglocose positron emission tomography (FDG-PET) avid thyroid incidentalomas is 1-2% with an associated 35% malignancy rate. Thus it is recommended that all FDG-PET avid thyroid lesions be evaluated with ultrasound (US) and fine needle biopsy. North American studies examining prevalence are mixed and difficult to interpret due to poor rates of clinical evaluation of these incidentalomas. Socio-demographic and clinical factors associated with surgical resection of incidentalomas and malignancy are also not well-defined. This study’s objective was to assess our single-institutional malignancy rate, and characterize factors associated with further evaluation of incidentalomas, and surgical resection.
Methods:
All patients undergoing FDG-PET from February 2000-March 2015 with focal thyroid uptake were identified. Those with a history of thyroid cancer or previously evaluated thyroid lesion were excluded. Patient characteristics, US and FDG-PET findings including maximum standardized uptake value (SUVmax) pathology results were reviewed. Descriptive statistics were performed using Student’s t-test and X2-squared test as appropriate. Factors were compared using parametric statistical methods and logistic regression to control for confounders.
Results:
Of 15,399 FDG-PET scans performed, 179 thyroid incidentalomas were identified (1.2%). 59/179(33%) underwent US and 49 (27.4%) had further histological evaluation. 13/49(26.5%) were resected with 10 (16.9%) confirmed malignancies.(Figure) Resection and malignancy were associated with higher SUVmax, p=0.0002 and p =0.0003, Bethesda classification 5-6, p=0.004 and p<0.0001, respectively. After adjustment for confounders, patients with a prior non-thyroidal cancer diagnosis regardless of stage (OR 0.19 p=0.004) were less likely to pursue evaluation of a thyroid incidentaloma. Patients who did not receive adjuvant therapy within 6 months of the FDG-PET (OR 3.9 p=0.012) and lesions with higher SUVmax (OR 1.13 p=0.004) were more likely to obtain US. Nodule size, TSH, and socio-demographic factors including age, race, sex, and insurance status were not significantly different for patients undergoing further evaluation of incidentaloma, receiving surgery, or malignancy.
Conclusion:
Our malignancy rate for imaged thyroid incidentalomas, evaluated and resected, was 16.9%, which is lower than previously reported (35%). These data are suggestive of epidemiological variation and differences in patient selection and preferences. Higher SUVmax and Bethesda classification were associated with malignancy. Despite this lower rate of malignancy, US and biopsy should be pursued when appropriate in the context of the patient’s overall clinical status.
