Ultrasound stratification of the FDG-avid thyroid nodule.

AIM

To determine whether the malignancy risk in an 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG)-avid thyroid nodule can be stratified according to the presence or absence of suspicious ultrasound features and thereby identify which nodules require further cytological assessment.

MATERIALS AND METHODS

A retrospective review of FDG-positron-emission tomography (PET) combined with computed tomography (CT) studies with FDG-avid thyroid nodules (defined as FDG uptake greater than blood pool) that were further assessed with ultrasound and fine-needle aspiration cytology or surgery was performed. FDG-avid thyroid nodules were classified as having either suspicious ultrasound features (marked hypo-echogenicity, irregular margins, microcalcifications, marked hypervascularity, or nodules that were taller than they were wide) or no suspicious ultrasound features and these findings were correlated with the subsequent cytological results.

RESULTS

Forty-eight FDG-avid thyroid nodules were assessed. On cytological assessment five nodules were malignant (10.4%), nine were indeterminate (18.75%), and 34 were benign (70.8%). On ultrasound, 24 (50%) had no suspicious features and 24 (50%) had one or more suspicious features. Of the nodules with no suspicious features, 22 (91.6%) were benign, two (8.3%) were indeterminate, and none were malignant. Of the nodules with suspicious features, five (20.8%) were malignant, seven (29.1%) were indeterminate, and 12 (50%) were benign. The absence of suspicious ultrasound features demonstrated a strong association with benign cytology (p=0.009). Out of the suspicious sonographic features, marked hypoechoic appearance (p=0.02), irregular margins (p=0.009), and taller than wide morphology (p=0.04) were statistically most significantly associated with malignancy.

CONCLUSION

The rate of malignancy in FDG-avid thyroid nodules is low in the absence of specific suspicious ultrasound features. The SUV values are non-discriminatory to differentiate between benign and malignant cytology. This suggests that ultrasound can be used to further stratify an FDG-avid thyroid nodule and invasive procedures to investigate the FDG-avid thyroid nodule may not be necessary in the absence of suspicious ultrasound features.