Endocrine Abstracts

Objectives: Detection rate of thyroid nodules is increasing with use of new imaging modalities, like 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT). To avoid unnecessary operations, differentiating between benign and malignant 18F-FDG PET/CT-positive thyroid nodules is essential. Many authorities recommend fine needle aspiration biopsy (FNAB) for exclusion of malignancy in thyroid nodules. Although FNAB is a simple, easily performed procedure, less invasive diagnostic approaches are required. Malignant thyroid nodules tend to have higher maximum standardized uptake values (SUVmax) but there is no clear information about the utility of Hounsfield Unit (HU) values for the prediction of malignancy. This study evaluated the HU values beside SUVmax for detecting malignancy risk of PET/CT-positive thyroid nodules.

Methods: We retrospectively studied 98 patients who had FNAB for thyroid nodules detected on PET/CT within the period; January 2011 to December 2015. The FNABs and surgical pathological results were recorded. On non-contrast CT scans taken during PET imaging, the HU of the nodules were calculated besides SUV max values of the nodules.

Results: The mean age of the study population was 57.6±13.8 years, and 75 (76.5%) of the patients were women. The most common primary malignancy detected in these patients was breast cancer. If more than one nodule was detected on a PET/CT scan, FNAB was performed on the nodule that had the higher SUV_max. FNABs revealed benign results in 32 patients (32.7%), malignant in 18 (18.4%), non-diagnostic in 20 (20.4%), indeterminate in 28 (28.5%). 24 patients underwent thyroidectomy due to their inconvenient general health conditions. When the FNAB and postoperative pathological results of nodules evaluated together, 38 of them were considered as benign and 25 of them were malignant. Only 24.5% of the cases were subjected to thyroidectomy, the malignancy rate was 25.5% in our cohort. Mean SUVmax was significantly higher (P< 0.001) in malignant versus benign nodules. Area under curve (AUC) was 0.824 for SUVmax; the cut-off value was over 5.55 (P<0.001), with 80% sensitivity, 84.5% specificity. But mean HU values were not significantly different (P=0.73).

Conclusions: We defined a SUVmax cut-off value of 5.5 for malignant potential of thyroid nodules detected on PET/CT. However; we did not find any merit in using HU values for discriminating between malignant and benign nodules.