Differentiating Benign and Malignant Thyroglossal Duct Cysts With Ultrasonography, CT, and PET/CT

To determine if US, CT, and/or ¹⁸F-FDG PET/CT can differentiate benign and malignant thyroglossal duct cysts (TGDCs).

In this retrospective review, we identified 72 patients with cytologically proven benign TGDCs and 11 patients with cytologically proven malignant TGDCs. Patient demographics, US and CT features, and maximum standardized uptake value (SUVmax) on PET/CT were compared. On US, TGDCs were assigned a summary score with one point each for irregular margins, solid-component appearance, vascular flow on Doppler US, and calcifications. Score performance in differentiating benign and malignant TGDCs was analyzed.

Malignant TGDCs were detected at a younger age (optimal cut-off, 43.5 years) (p = 0.001) and were larger (optimal cut-off, > 1.9 cm) (p = 0.041). Malignant TGDCs more frequently had irregular margins on US (p <0.001), calcifications on US (p <0.001) and CT (p = 0.009), and higher SUVmax on PET/CT (p = 0.001). Summary scores could be calculated for 79 TGDCs. All 54 TGDCs with a score of 0 or 1 were benign, whereas both TGDCs with a score of 4 were malignant. The 23 TGDCs with a score of 2 or 3 could not be differentiated by score.

Malignant TGDCs are diagnosed at an earlier age, are larger, and have higher uptake on PET/CT than benign TGDCs. On US, cystic TGDCs or those containing only solid tissue with smooth margins may not need an FNA (fine needle aspiration) and may be followed with serial US. TGDCs with solid tissue with irregular margins, increased vascular flow, and calcifications are likely malignant; FNA before excision may be beneficial for documenting malignancy and genetic testing. All other TGDCs require FNA for differentiation. On PET/CT, TGDCs with increased uptake require FNA.