68Ga-FAPI–Avid Submental Ectopic Papillary Thyroid Carcinoma and Lateral Neck Lymphadenopathy With Low 18F-FDG Uptake

Ectopic thyroid tissue is rare and generally occurs along the thyroglossal duct or in lateral cervical region. We reported 18 F-FDG and 68 Ga-FAPI findings of a 28-year-old woman with previously diagnosed BRAF -mutated lateral lymph node metastasis of unknown primary site. Low 18 F-FDG but increased 68 Ga-FAPI uptake was seen in a submental pretracheal nodular lesion. Postsurgical pathologic report verified the diagnosis of ectopic papillary thyroid carcinoma. High FAP expression in the tumor sample corresponded to its imaging manifestations.