18F-FDG PET/CT of Squamous Cell Carcinoma in a Thyroglossal Duct Cyst.

Thyroglossal duct cyst is a common congenital cyst in the neck. The incidence of primary carcinoma of the thyroglossal duct is less than 1% in all age groups. We present the case of a 63-year-old man with rapid expansion of a known thyroglossal duct cyst with mixed solid/cystic components. F-FDG PET/CT showed a large anterior neck mass with a non-FDG-avid cystic component and a hypermetabolic heterogeneous mass on the right side confirmed by histopathology to be squamous cell carcinoma. Although rare, F-FDG PET/CT can assist with evaluating the extent of malignant involvement in thyroglossal duct cyst squamous cell carcinoma.